EFFECT OF UGHT AND TEMPERANRE APPLIED T0 ONEON SULBS 1N STORAGE 0N THEE SUBSEQUENT VEGETATEVE AND REPRODUCTWE'DEVELOPMENT

Transcription

1 EFFECT OF UGHT AND TEMPERANRE APPLED T0 ONEON SULBS 1N STORAGE 0N THEE SUBSEQUENT VEGETATEVE AND REPRODUCTWE'DEVELOPMENT finesis for the Degree of M. 5. meme: STATE UNVERSTY. PHELDON BRENT 999:1.qu 1974

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3 ABSTRACT EFFECT OF LGHT AND TEMPERATURE APPLED TO ONON BULBS N STORAGE ON THER SUBSEQUENT VEGETATVE AND REPRODUCTVE DEVELOPMENT By Phildon Brent DeMille EXperiments were conducted to ascertain the vegetative and reproductive development of onion bulbs (Allium 2223 L.) after receiving light and temperature treatments while in storage. The Open pollinated onion variety 'Trapp's Downing Yellow Globe' was used. Bulbs were exposed simultaneously to fluorescent and incandescent light in three different storage temperature regimes (7 C. 7 and 2 C, and 2 and 7 C). Each temperature regime included the following light treatments: continuous light, a 12-hour photoperiod, and continuous dark. n addition, at one temperature regime some bulbs were transferred after half the storage period from continuous light to continuous dark and vice versa. Bulbs were planted in the spring and the following data were recorded at the time each bulb flowered: days to flowering from planting, number of leaves. number of seed-stalks, and seed-stalk height. At maturity the seed was harvested and the seed yield was determined. Light was shown to be effective in reducing the number of days to flowering in all treatments where bulbs were

4 exposed to some light during the storage period. n general, continuous light was more effective in reducing days to flowering than a 12-hour photoperiod. Light applied to onion bulbs during the first half of the storage period tended to reduce the number of days to flowering to a greater extent than light applied only during the second half of the storage period. Subjecting the bulbs to a temperature of 2 C during the first half of the storage period delayed flowering and reduced the number of leaves more than did the 2 C temperature during the last half of storage or a continuous temperature of 7 C. Exposing onion bulbs to light in storage had no effect on the number of leaves, the number of seed-stalks, or seed yield. Storage temperature did influence seed yield and the highest seed yields occured when bulbs were stored at 7 C for the first half of the storage period. ncreases in yields were the result of more and larger seed being produced per bulb.

5 EFFECT OF LGHT AND TEMPERATURE APPLED TO ONON BULBS N STORAGE ON THER SUBSEQUENT VEGETATVE AND REPRODUCTVE DEVELOPMENT BY Phildon Brent DeMille Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCENCE Department of Horticulture l97h

6 :3 <9. ". hi..- " f..i dc ACKNOWLEDGMENTS The author expresses appreciation to Dr. H. Grant Vest for the suggestion of the problem, and his guidance during the course of this study. Appreciation is due also to Drs. M. L. Lacy and R. C. Herner who served as guidance committee and assisted in the preparation of the manuscript.

7 TABLE OF CONTENTS Page LST OF TABLES... iv LST OF FGURES... NTRODUCTON... LTERATURE REVEW... MATERALS AND MTHODSOOOOOOOOOOOOOOOOOO RESULTSOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Days to Flowering... Continuous Storage 7 C... First Half 7 C - 2nd Half 2 C (Dark)... lst Half 2 C (Dark)-2nd Half 7 C... Storage Temperatures... Number of Leaves... Number of Seed-stalks... Seed-stalk Height... Seed Yield... Weight per Seed... Number of Seed per Bulb... Number of Seed per Umbel b 2a DEECUSSOFJOOO OOOOOOOOOOOOOOOOOOOOOO 28 BBJ~3GRAPHY OOOOOOOOOOOOOOOOOOOO iii

8 LST OF TABLES TABLE Page 1. Light and temperature treatments used on onion bu1bs in stomgeoooooooocoooooocoooooooooo Summary of days to flowering as affected by different light treatments and storage temperaturesoooooooooooooooooo ooooooooooo l7 3. Summary of the number of leaves for bulbs exposed to light treatments in three storage tempemturesoooooooooo Summary of the number of seed-stalks for bulbs exposed to light treatments in three storage tempemturesooooooooooooooooooocccooooooooo Summary of seed-stalk height (in centimeters) for bulbs exposed to light treatments in three storage temperatures Summary of the seed yield (in grams) per bulb for bulbs exposed to light treatments in three storage temperatures Summary of the weight (in milligrams) of each seed from bulbs exposed to light treatments in three storage temperatures Summary of the number of seed per bulb for bulbs exposed to light treatments in three storage temperatures Summary of the number of seed per umbel for bulbs exposed to light treatments in three storage temperatures iv

9 LST OF FGURES FGURE 1. Number of days to flowering for bulbs exposed to light treatments while stored at a...OOOOOOOOOOOOOOOOOOOOOO Number of days to flowering of bulbs stored at 7 C during lst half and at 2 C during 2nd half of the storage period... Number of days to flowering of bulbs stored at 2 C during lst half and at 7 C during 2nd half of the storage period... Page

10 NTRODUCTON Temperature and light are among the environmental factors that have a pronounced influence on the growth and development of the onion plant. Temperature and light (4, 5, 13, l#, l6, 17, 18 both influence bulb development, and temperature at which the bulbs are stored has been reported (3, 5, 8, 9, 17) to influence bolting. The demand for high quality and productivity of onions has increased in recent years. Research efforts are being made to develop superior high yielding and disease resistant varieties of onions, and to ascertain environmental effects on seed production. nformation that can be gathered from this research will be useful for the grower and seedsman. Onion bulbs are commonly stored for various lengths of time during the winter before being planted in the spring for seed production. 'Low onion seed yields have caused concern for continued supply, and research is underway to investigate the factors responsible. There is no information available to date on the effect light on onion bulbs in storage may have on seed production of these bulbs when they are planted. The object of this research was to determine what influence light and storage temperature have not only on seed yields, but on time to flowering, on the number of leaves and seed-stalks produced, and on seed-stalk height. 1

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12 LTERATURE REVEW The onion plant is sensitive to its environmental surroundings and responds in a number of ways to external stimuli such as temperature and light. Early work on the response of onion plants to light was reported by Gardner and Allard (h). Onion sets of the 'Silverskin' variety grown under different.day-lengths showed that plants exposed to a 10-hour day-length failed to form bulbs and remained vegetative while normal bulb formation occured under longer day-lengths. t was concluded that with this variety bulb formation was a result of the long days of summer while short days favored vegetative growth. McClelland (1h) reported onions to be not only sensitive to varied light exposures, but that varieties also differed in their sensitivity, and what was a sufficient exposure for one variety may be inadequate for another. Magruder and Allard (13) studied the effects of different day-lengths on bulb formation in eighteen varieties commonly grown in the United States and eight other varieties commonly grown in Europe. Controlled day-lengths ranged from 10 to 18 hours while the check treatment (normal day-length) varied from 12.h to 14.9 hours. t was found that the variety Yellow Bermuda' was the only one to bulb in the lo-hour daylength. Most of the other American varieties bulbed in daylengths from 12 to 14 hours, while the varieties from EurOpe 2

13 3 required a day-length of about 16 hours. The combined effects of light and temperature were studied by Thompson and Smith (17), and Heath and Holdsworth (5). Thompson and Smith planted sets in the greenhouse on October 29 and kept them at two different temperature ranges. n December the bulbs were placed into either long-day or normal-day length at one of three temperature ranges: 10.0 to 15.6 C, 15.6 to 21.1 C, and 21.1 to 26.7 C. Plants given a long-day and kept at 21.1 to 26.7 C formed bulbs and matured. At 15.6 to 21.1 c bulbs were formed and the tops had fallen over, but were still green, but plants in the 10.0 to 15.6 C range were still green and showed no signs of bulbing. Plants in the normal day-length showed almost no bulbing at any of the three temperature ranges. Heath and Holdsworth (5) also used onion sets to determine day-length and temperature effects on bulb formation. The plants were grown throughout the summer at an 11 1/2 hour daily illumination at two different temperature ranges (means 18 and 26 C respectively). n October half of the bulbs from each temperature range were transferred to a 16 1/2 hour day of supplemental light while the other half remained in the short day illumination. They found that bulbing began after five weeks at the high temperature range (mean 24 C) and there was no bolting. At the low temperature range (mean 14 C) only 7% of the plants produced bulbs after 10 weeks, and at 16 weeks only 40% had formed bulbs. Of the plants remaining in the short-day length in the high or low temperature, only 3% formed bulbs.

14 a When fluorescent lighting began to replace incandescent lighting in greenhouses, other responses of plants were noted. Borthwick and Parker (2) reported that with sugar beets grown for seed 2? of a total of 29 plants developed seed-stalks when they received incandescent light while only 2 of 31 plants had seed-stalks under the white fluorescent, and no seed-stalks had developed in the daylight fluorescent. The bulbing response in onions was also reported (18) to be affected differently by fluorescent and incandescent lights. Three onion varieties were grown in the greenhouse under 16 hours incandescent or fluorescent light, and under 15 hours of incandescent or fluorescent light followed by one hour of the opposite light. The greatest bulb diameter occured in bulbs grown under 16 hours of incandescent light, the second largest occured under 15 hours of incandescent followed by 1 hour of fluorescent. Plants grown under fluorescent light for 16 hours or 15 hours followed by one hour of incandescent showed little or no bulbing. A later study (16) was done to determine the influence of a B (blue), R (red), and FR (far-red) light on bulbing in onion plants. Onion plants in the 3 to 4 leaf stage received 8 hours of sunlight followed by 16 hours of mixed R + FR, B + FR, and R + B. t was found that mixed light of R + FR caused an increase in bulb diameter with an increase of FR intensity, and decreased with greater R intensity, but R light promoted bulb formation when its intensity was less than that of FR. Bulb diameter increased in a B + R where there was an increase of B but decreased with an increase of intensity of R light.

15 5 When bulbs were irradiated with B + FR the bulb diameter increased with the intensities of B and FR light. No reference has been made in any of the above citations as to the effect light has on stored onion bulbs. However, the effect of temperature on stored onion bulbs and sets has been studied by many investigators (3, 8, 9, 17). Boswell (3) studied the effect of storage temperature on bulbs in storage and their subsequent vegetative and reproductive development. He reported that when bulbs were stored at 0, 4.4, and 10.0 C the flower primordial formation was almost totally inhibited at 0 C, and that an exposure to 0 C for six months inhibited floral development less than an exposure of eight months. Thompson and Smith (17) stored sets of 'Ebenezer,'Yellow Globe Danvers', 'Southport Yellow Globe', and 'Red ethershield' in temperatures of -l.l, 0, 4.4, 10.0, and 10.0 to 15.6, and 15.6 to 21.1 C. The storage period ran from October to April. The highest percent of seed-stalk development came from sets stored at 4.4 and 10.0 C. The lowest percent of seed-stalk development came from sets stored at 15.6 to 21.1 C. The percentage of seed-stalks increased when sets were transferred the last month of storage from -l.l, and O C to 4.4 or 10.0 C. Jones (8) studied temperature and its effect on seed production in the 'Ebenezer' onion. Mother bulbs were stored in California from August 4 until they were planted on December 6. The storage temperatures were 3.5, to 12, 16 to 22(cellar storage), 30 C, and common storage which was about the same as the outside temperature. Bulbs stored at 7.5 and 11 to 12 C produced their seed-stalks earliest and were the first to

16 flower. There was also a greater number of seed-stalks and higher seed yield at these temperatures. Jones and Emsweller (9) stored bulbs at temperatures of 3.3, 7.8, 11.7, 30.0 C, and in a cellar storage at 16.1 to 21.7 C from late July or early August before planting them in the field in early December. The earliest flowering occured from bulbs stored at 7.8 and 11.7 C. The greatest number of seed-stalks occured at 11.7 and the least at 30.0 C.

17 MATERALS AND METHODS During 1971 and 1972 bulbs of Allium cepa L., variety 'Trapp's Downing Yellow Globe', were grown at the Michigan State University Muck Farm, harvested after each growing season, and cured for approximately four weeks following harvest. Bulbs were then selected for uniform size and randomly assigned to light treatments before being placed into controlled storage chambers. The storage period ran throughout the winter both years. n the first year, the storage period began October 25, 1971 and ended April 21, The total storage time was 179 days. Midway through the storage some bulbs were changed from one light treatment to another. The midway point was a predetermined date set to equal approximately half the storage period. The predetermined midway point the first year occured after 88 days of storage or on January 21, The storage period the second year began October 27, 1972 and continued to April 19, 1973 for a total of 174 days. The predetermined midway point occured on January 24, 1973 or 89 days. One cold storage chamber was used for the 1971 experiment, and two chambers were used for the 1972 experiment. These chambers were kept at 7 C {45 F). Each storage chamber was partitioned into three light proof sectidns in order to accommodate each of the following light treatments: 1) Continuous light; 7

18 8 2) 12-hour photoperiod: 3) Continuous dark. The three sections in each chamber were constructed so that air could circulate freely from section to section throughout the entire chamber in order to maintain a constant temperature. Light in all treatments was provided by two 40 watt cool white fluorescent tubes and one 40 watt incandescent lamp suspended at approximately 50 cm above the bulbs. The light intensity was measured to be approximately 150 foot candles of light. Bulbs in each treatment were arranged upright one layer high on a flat surface to assure maximum exposure to the light source. Thermometers were kept in each section and temperatures were checked regularly and recorded on a recording thermograph. Maximum and minimum thermometers were used when the thermograph broke down during the storage period. There were no detectable differences in the temperatures of the different compartments at bulb level or at approximately 30 cm just below the level of the lights. At the midway point in the storage period, a previously selected random sample of bulbs was removed from the continuous light and continuous dark treatments and interchanged. n addition, random samples of bulbs from each light treatment were removed and placed in a dark cold storage at approximately 2 C (35 F). Other bulbs already in this storage were then placed in each of the three light treatments for the remainder of the storage period (Table 1). At the completion of the storage period the bulbs from each treatment were randomly planted and enclosed within two

19 9 Table 1. Light and temperature treatments used on onion bulbs in storage. TEMPERATURE C 1. Continuous Light hour Photoperiod 3. Continuous Dark 4. lst Half Light - 2nd Half Dark 5. lst Half Dark - 2nd Half Light TEMPERATURE lst HALF Z,C - 2nd HALF 2 C (Dark) 6. Continuous Light - Dark hour Photoperiod - Dark 8.. Continuous Dark - Dark TEMPERATURE lst RALF 2 Cg(Dark) - 2nd HALF Z C 9. Dark - Continuous Light 10. Dark - lz-hour Photoperiod 11. Dark - Continuous Dark

20 x 7.3 m lumite mesh cages. Prior to flowering, bees were placed into the cages to provide for pollination as the flowers opened. n 1971, each treatment consisted of 20 bulbs and was replicated two times (40 bulbs). n 1972 forty bulbs per treatment were used, but the bulbs were divided into two subsamples of five bulbs in each of four replications. Several bulbs per treatment were used in order to minimize the variation found in the open pollinated onion variety used. The number of days until flowering was determined from the date of planting to the date the first floret opened on the primary seed-stalk. The number of leaves (1972 only), the number of seed-stalks, and seed-stalk height were recorded for each bulb at the time the first floret opened on the primary seed-stalk. Mature umbels were harvested and dryed at 35 C. The seed was threshed by hand and cleaned by removing trash and light, non-viable seeds. Seed yield was expressed as the average weight of seed per bulb. Seed of each treatment was combined and five samples of 1000 seeds each were taken from each treatment to find the weight per seed. An analysis of variance of seed per bulb and seed pmm~umbel was performed from only first year data because the second year the weight of seed of the individual bulbs was not obtained.

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22 RESULTS DAYS TO FLOWERNG Continuous Storage 7 C Data obtained in the two experiments ( and ) showed that light was effective in reducing the number of days to flowering when bulbs were exposed to light while stored at 7 C (Figure 1). n the first experiment.bulbs kept in continuous light flowered earlier than bulbs from all other treatments. n the second experiment.bulbs kept in continuous light flowered later than bulbs from the other light treatments, but this was attributed to extreme genetic differ ences in dormancy noted for 3 individual bulbs inthe continuous light treatment. A The bulbs that flowered last in both experiments were those that received no light during the storage period. n the first experiment,bulbs kept in continuous dark flowered 2.8 days later than bulbs kept in continuous light. Likewise, the data obtained in the second experiment showed that there was a difference of 1.7 days between the number of days to flowering for bulbs kept in continuous light and bulbs kept in con tinuous dark. n order to expose bulbs to one half the light received by the bulbs in continuous light a 12-hour photoperiod was used, as well as interchanging bulbs half way through the 11

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24 12 Number of days to flowering for bulbs ex-, posed to light treatments while stored at 7C. lst Year 74 2nd Year lst Year 2nd Year lst Year Figure 1. 2nd Year a: 2 2,w.5. g - a g * H m E; 72 a O P 2, 3 7O a " 5 :3 it: ' Light l2-hr Dark Light Dark l Dark Light l/'bulbs were transferred after half the storage period from continuous light to continuous dark and vice versa. 2/'Continuous light treatment used as standard for determining differences in days to flowering.

25 13 storage period from light to dark and vice versa. Results from these treatments showed that bulbs receiving a 12-hour photoperiod flowered later than those bulbs receiving continuous light, but interchanged from light to dark and dark to light half way through the storage period. Bulbs kept in the 12-hour photoperiod always flowered earlier than bulbs kept in continuous dark. Bulbs exposed to light during the first half of the storage flowered before those that were exposed to light during the last half of the storage period. lst Half 7 C - 2nd Half 2 C (Dark) Results also showed that light was effective in reducing the number of days to flowering when bulbs were exposed to light treatments at 7 C and then placed in dark storage at 2 C for the last half of the storage period (Figure 2.). n both experiments bulbs exposed to continuous light flowered before those bulbs receiving the 12-hour photoperiod and those kept in continuous dark. These data are similar to those already reported for the continuous 7 C storage temperature. However, there were significant differences in the second experiment between the number of days to flowering for bulbs stored in continuous light and those in the continuous dark. The light effect which the bulbs received at this particular temperature regime was retained by the bulbs even after they were removed from the light and placed into the dark at a colder temperature. This result was the same as that obtained when bulbs were kept at 7 C and interchanged after half the storage time from light to dark_and vice versa»

26 it: Figure 2. Number of days to flowering of bulbs stored at 7 C during lst half and at 2 C during 2nd half of the storage period.. Days to Flowering, 43-: g, \ a e m a «4 >: >4 m o >: >4 :1 + '6 +3 'u.a m c m c u r-on' HN g 83 let Year,3 = b 3 "3 2nd Year A 3 + m a = : g 7 8' ab :1-1 a: 1 az/ o Light 12-hr Dark l/'continuous light treatment used as standard for determining differences in days to flowering. ;/ Means followed by the same letter are not significantly different at the 5% level (Duncan's new multiple range test.

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28 15 let Half 2 0 (Dirk) - 2nd Half 7 C When bulbs were removed from dark storage at 2 C and placed in the light treatments at 7 C for the second half of their storage period, results again showed the effect that light had on reducing the number of days to flowering (Figure 3). Bulbs placed into continuous light flowered earlier than bulbs placed into either the lz-hour photoperiod, or those kept in continuous dark. These data were similar to the results reported in the previous two storage regimes. Data obtained in the second experiment showed that bulbs placed in continuous light and in the lz-hour photoperiod flowered significantly earlier than bulbs placed in continuous dark. Differences in the number of days to flowering between bulbs in continuous light and continuous dark treatments were greater in this storage regime than in the other two regimes. n the first experiment, there were 3.2 days difference in flowering between bulbs kept in continuous light and bulbs kept in continuous dark. n the second experiment, there were 4.4 days difference in the number of days to flowering between these same two light treatments. Storage Tempgratureg The results from the three storage temperatures are summarized in Table 2. The mean of each storage temperature showed that temperature also had an effect on the number of days to flowering. Bulbs stored at 7 C flowered significantly earlier than bulbs stored the first half at 2 C and the second half of the storage time at 7 C. Significant differences were not

29 is Figure 3. Number of days to flowering of bulbs stored at 2 C during lst half and at 7 C during 2nd half of the storage period. lst Year 2nd Year lst Year 2nd Year 5 8 b - 4 h lst Year «a 3 g - 2nd Year 3.0 fi~ g m a o. = 2 2i: '2 g g S l 3 a - a 7..-: - o a o 72 8: Light 12-hr Dark 1/ Continuous light treatment used as standard for determining differences in days to flowering. ;/ Means followed by the same letter are not significantly different at the 5% level (Duncan' 8 new multiple range test

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31 17 Table 2. Summary of days to flowering as affected by different light treatments and storage temperatures. l9zl-22 Light lst Half 7C lst Half 2C Treatment 70 2nd Half 20 2nd Half 70 Mean Contlnuous. Light a.1./ Continuous Dark b Mean Light lst Half 7C lst Half 2C Treatment 70 2nd Half 20 2nd Half 7C Mean Continuous Light a 80.5a 79.9a 12-Hour Photoperiod ab 81.0a 80.4a Continuous Dark b 84.9b 82.9b Mean 80.la 80.9ab 82.1b 1/ Means followed by the same letter in each year are not significantly different at the 5% level (Duncan's new multiple range test).

32 obtained in the first year, but the trends were the same as those of the second year. 18 Cold temperature (2 C) during the first half of the storage period had a greater effect in delaying the flower dates than did cold during the last half of storage or a continuous temperature of 7 C. Significant differences in the days to flowering were found when averaged across the three storage temperatures. Data showed that bulbs in continuous light flowered significantly earlier than bulbs in continuous dark. The largest differences in the flowering dates for both experiments occured between bulbs stored in continuous light at 7 C and bulbs kept in continuous dark at the storage temperature of 2 C the first half and 7 C the second half of the storage time. This difference was about 5 days. NUMBER OF LEAVES The light treatments did not influence the number of leaves that were produced by bulbs stored in any of the three storage temperature regimes. However, storage temperatures had a marked effect on the number of leaves that were produced (Table 3). Bulbs that were kept at 2 C the first half of the storage time and 7 C the second half produced significantly fewer leaves than bulbs kept in the other two storage temperatures. NUMBER OF SEED-STALKS There were no appreciable differences in the number of seed-stalks for bulbs receiving the three light treatments. Storage temperature effects were evident only from bulbs in

33 19 Table 3. Summary of the number of leaves for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 lst Half 20 Treatment 70 2nd Half 20 2nd Half 70 Mean Continuous Light v24.l 12-hour Photoperiod Continuous Dark Mean 24.7al/fl 24.8a 21.0b 1/ Means followed by the same letter are not significantly different at the 5% level (Duncan's new multiple range test.

34 20 the second experiment (Table 4). Bulbs stored at 7 C produced significantly more seedstalks than bulbs stored at 2 C the first half and at 7 C the second half of the storage period. These results are similar to those obtained from the effects of storage temperature on the number of leaves. Correlation studies indicated that the number of leaves increased with the increase in the number of seed-stalks. SEED-STALK HEGHT There were no significant differences in seed-stalk height associated with light treatments: however, storage temperatures produced significant differences in seed-stalk height in both experiments (Table 5). Bulbs stored at 7 C had significantly shorter seed-stalks than those kept in the other temperature treatments. The highest seed-stalks were produced from bulbs stored in 7 C the first half and 2 C the second half of the storage time. SEED YELD The light treatments did not cause appreciable differences in seed yield: however, analysis of the data from storage temperatures showed significant differences for seed yield associated with temperature (Table 6). The highest seed yields were obtained from bulbs stored at 7 C the first half and 2 C the second half of the storage time. n the first experiment, the lowest yields were obtained from bulbs stored in the 7 C storage temperature. n the second experiment the lowest seed yields were obtained from

35 21 Table 4. Summary of the number of seed-stalks for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 lst Half 2C Treatment 70 2nd Half 20 2nd Half 70 Mean Continuous Light lz-hour Photoperiod Continuous Dark Mean Light lst Half 70 lst Half 20 Treatment 70 2nd Half 2C 2nd Half 7C Mean Continuous Light hour Photoperiod Continuous Dark Mean 4.2al/fii 3.8ab 3.3b 1/ Means followed by the same letter are not significantly different at the 5% level (Duncan's new multiple range test.

36 Table 5. Summary of seed stalk height (in centimeters) for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 let Half 2C Treatment 70 2nd Half 2C 2nd Half 7C Mean Continuous Light lz-hour Photoperiod ,1' Continuous Dark Mean 89.2ai/1 98.5b 97.3b Light lst Half 70 lst Half 20 Treatment 7C 2nd Half 2C 2nd Half 70 Mean Continuous Light hour Photoperiod Continuous Dark 97, Mean 96.3a 103.0b 97.9b 1/ Means followed by the same letter in both years are not significantly different at the 5% level (Duncan's new multiple range test).

37 23 Table 6. Summary of the seed yield (in grams) per bulb for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 lst Half 2C Treatment 7C 2nd Half 2C 2nd Half 70 Mean Continuous Light hour Photoperiod Continuous Dark Mean 10.3al/8 13.1c 12.1b Light lst Half 7C lst Half 2C Treatment 70 2nd Half ZC 2nd Half 70 Mean Continuous Light hour Photoperiod Continuous Dark Mean ll.la 12.1a 10.1b 1/ Means followed by the same letter in both years are not significantly different at the 5% level (Duncan's new multiple range test).

38 24 bulbs stored in the storage temperature of 2 C the first half and 7 C the second half of the storage period. Weight per Seed Analysis of variance showed that there were significant differences among weights of onion seed associated with the storage treatment means (Table 7). However, there were no appreciable differences in the weights of individual seeds as affected by the light treatments. The smallest seeds in both experiments were produced from bulbs in the continuous 7 C storage temperature. Number of Seedgper Bulb Analysis showed that light had no effect on the number of seeds produced per bulb (Table 8). However, in both experiments bulbs stored at 7 C the first half of the storage period and 2 C the second half produced more seed than bulbs receiving the other two temperature treatments. Number of Seed per Umbel The highest number of seeds produced per umbel in both experiments was from bulbs stored at 7 C the first half and 2 C the second half of the storage period. The smallest amount of seed produced per umbel in both experiments was from bulbs stored in the continuous 7 C storage temperature (Table 9).

39 Table 7. Summary of the weight (in milligrams) of each seed from bulbs exposed to light treatments in three storage temperatures Light lst Half 76 lst Half ZC Treatment 70 2nd Half 20 2nd Half 7C Mean. 1/ Continuous Light 3.84g 4.03 cd 4.15a hour Photoperiod 3.97ef 4.08 b 4.18a 4.08 Continuous Dark 4.00de 4.17a 4.07bc 4.08 Mean Light Qt Half 7c 1:1: Half 20 8 Treatment 70 2nd Half 20 2nd Half 7C Mean Continuous Light 3.83f 4.06a 3.93bc hour Photoperiod 3.87cdef 3.9lbcde 4.02a 3.93 Continuous Dark 3.859f 3.94b 3.92bcd 3.90 Mean / Means followed by the same letter in each year are not significantly different at the 5% level (Duncan's new multiple range test).

40 26 Table 8. Summary of the number of seed per bulb for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 lst Half 2c Treatment 7C 2nd Half 20 2nd Half 70 Mean Continuous Light l2-hour Photoperiod Continuous Dark Mean a / f1 8V3006.4<b Light lst Half 70 lst Half 2C Treatment 70 2nd Half 20 2nd Half 7C Mean Continuous Light hour Photoperiod Continuous Dark Mean / Means followed by the same letter are not significantly different at the 5% level (Duncan's new multiple range test.

41 27 Table 9. Summary of the number of seed per umbel for bulbs exposed to light treatments in three storage temperatures Light lst Half 70 lst Half 20 Treatment 70 2nd Half 2C 2nd Half 70 Mean Continuous Light hour Photoperiod Continuous Dark Mean Light lst Half 7C lst Half 2C Treatment 7C 2nd Half 20 2nd Half 70 Mean Continuous Light 660, hour Photoperiod Continuous Dark Mean

42 5..1. col. 'l (( a - a)._.

43 DSCUSSQNMM.- t is well known that storage temperatures influence many subsequent vegetative and reproductive developments in onion bulbs (3, 8, 9). Some results of this study might seem to indicate that the reduction in the number of days to flowering was a temperature response rather than a light response. Although differences in temperature between light and dark chambers could not be detected,it.was possible that bulbs did accumulate heat from the lights and flower earlier in response to a heat rather than a light stimulus. However, this cannot account for all the differences because bulbs that were exposed to continuous light and received a cold treatment of 2c,'either the first or second half of the storage, flowered before bulbs kept in the continuous dark treatment at 7 C. f it were a heat and not a light response, those bulbs in the colder temperature would have been expected to flower after the bulbs in the warm temperature of 7 C, which is optimum for flower initiation. This did not occur: therefore, some of the response has to be associated with exposure to light. The most noticeable effect that light had on stored onion bulbs was the subsequent alteration of their flowering dates. The reason for this earlier flowering was difficult to explain, but there are several factors which should be considered. 28

44 c r,. 'V'

45 Some of the results tended to support the presence of 29 of a phytochrome system in the bulbs. Light may have served as the stimulus in activating this system: bringing about physiological and/or morphological developments which lead to earlier flowering. Wave lengths in the red and far-red regions of the light spectrum are known to activate phytochrome. The incandescent and fluorescent lights used in this experiment provided wave lengths in the far-red and red regions, respectively, of the light spectrum. Phytochrome has been detected in at least one species of the genus Allium, Allium neapolitanum (11). Although it was reported (7) that phytochrome was not detectable with spectrophotometry in Allium ggpg_l., this is not convincing proof of the absence of phytochrome. The results from this study would tend to support the presence of phytochrome in onion bulbs, at least in the variety employed in this experiment. Land et. al. (12) reported the effect of incandescent light, rich in the far-red spectrum, in promoting flowering in several plants, and presented a model of how phytochrome participates in the flowering. n addition, phytochrome was theorized (18) to be involved in the bulbing response in onions because incandescent and fluorescent light differed in their induction of the bulbing process. With one exception in this study, bulbs flowered earlier when exposed to continuous light than when exposed to either a 12-hour photoperiod or continuous dark. Therefore, it would appear that the variety of onion used acted as a long-day

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47 30 plant in regard to the flowering response through the possible activation of the PFR form of phytochrome. The activation of P may have initiated the morphological development that lead PR to earlier flowering. Since exposing bulbs to continuous light for either the first half or the second half of the storage period resulted in earlier flowering than the bulbs in 12-hour photoperiods, it would appear that there was a greater accumulation of PFR induced activities and a greater development in floral initiation in continuous rather than in the alternating light. The 12-hour photoperiod resulted in the conversion of PFR to the red absorbing form during each 24-hour period. Thus the floral development in these bulbs was not as rapid as in continuous light. When bulbs in the 7 C temperature regime were interchanged after half the storage time, the days required for flowering were less for bulbs that received light during the first half of the storage. t appears that as the bulbs responded to light, whether the first or second half of the storage, the response to light during the first half must have resulted in earlier floral initiation. f early floral initiation did occur, the development, whether morphological or physiological, was retained when bulbs were placed in the dark. This was also evident for bulbs that received a temperature change to 2 C after the light treatments, and development was not reversed in the dark or colder temperature. Results from this experiment have shown that light duration was a major factor in reducing the number of days

48 31 to flowering; continuous light being more effective than the 12-hour photoperiod. These same results were reported by Pertuit (15) who exposed lily bulbs to incandescent light during cold storage. He found that light intensity and duration during 6 weeks cold storage increased the flowering percentages. However, increased light duration was more effective in increasing flower percentages and forcing time than increased light intensity. Light could not be determined to be a factor in the development of any plant characteristic that was measured other than the days to flowering. This fact in itself may be indicative of the presence of a phytochrome system acting only on the process of floral development. Significant differences in flowering dates were not obtained for some treatments in either experiment. n addition, two or three days difference in the days to flowering does not seem to be a great difference, but some facts must be taken into consideration when considering the small differences. t appears that the differences in days to flowering would have been greater if less than the optimum temperature (7 C) for floral initiation had been used (Table 2). The optimum temperature for flowering was used to insure flowering to its greatest potential. There was a wide variation of genetic makeup represented by plants from an open pollinated source. t is likely that plants of the same genetic makeup would tend to be more uniform in a particular response and possibly this response would vary from variety to variety. The Open pollinated variety was used to

49 32 insure that the bulbs possess the genetic potential of responding to the light stimulus. Also, many hybrid varieties are sterile, and it was desired to obtain data from seed yield. As was mentioned, two or three days difference in the days to flowering may not seem to be a great difference, but noticeable differences in seed yield may result because of the short time pollen remains viable. Two or three days difference in "nicking" between two inbred parents may result in a loss of considerable seed, especially in the production of large quantities of hybrid seed. ' The direct effect of temperature on the flowering dates of onion bulbs was evident by data obtained from bulbs stored in the dark treatment, since these bulbs received no light while in storage. The continuous temperature of 7 C and this temperature for the first half of the storage induced earlier flowering in the bulbs than bulbs stored in the dark at 2 C then 7 C. The colder temperature (2 C) during the first half of the storage time had more effect in delaying flowering than did the cold temperature during the second half of the storage. The fact that bulbs kept at 2 C during the first part of the storage had fewer leaves than those bulbs which were at 7 C during the first half of storage was probably due to the inhibitory effect of this temperature at the time leaf initiation was taking place. Because there was no difference in the number of leaves between bulbs kept continuously at 7 C and those bulbs kept at 7 C the first half of storage, it is likely that leaf initiation proceeds to its genetic potential

50 33 during the first part of the storage. Abdalla and Mann () noted that leaf initiation was much slower at temperatures of 0 and 30 C than at 15 C. Heath and Mathur (6) reported that only one or two leaf initials were produced in ordinary storage (temperature not specified), and these were formed mainly during the latter part of the winter. Data obtained from leaf numbers in 1973 were positively correlated to the number of seed-stalks produced. t was noted in this study from visual observation that leaves were always attached around the seed-stalk. Jones and Mann (10) have said that when favorable conditions exist for flowering the apex ceases to produce leaf primordia and begins to form the inflorescence. t is understandable then to obtain the positive correlation. t is assumed that the cold temperature also had an inhibitory effect on the initiation of seedstalk primordia and thus the seed-stalk number. Seed stalk height was determined at the time the first floret opened, and it was assumed that further growth of the seed-stalk was halted. From correlation studies, the earlier flowering dates in the first experiment were associated with shorter seed-stalk height. Due to the possible biased data obtained in the results of flowering dates for a few bulbs stored in continuous light at 7 C, there was no correlation in the second experiment of flowering dates with seed-stalk height. The effect of the three storage temperatures observed on the seed-stalk height may only have been the result of flowering date, rather than a direct effect on the actual height of the seed-stalk.

51 34 t was difficult to determine if storage temperature had a direct effect on seed yield even though significant differ ences were obtained. Several factors may have influenced the actual seed yield more than storage temperature. Hot temperatures during the flowering period in 1973 may have decreased bee activity to give less seed yields for particular plots. Wet and cold conditions in 1972, on the other hand, may have caused decreased bee activity to the point of influencing seed yields opposite to those of The bees that were used in 1972 may have been more active than the ones used in 1973 or vice versa. n spite of these apparent adverse factors, some interesting comparisons can be made. The highest seed yields were obtained in both years from bulbs kept at 7 C the first half and 2 C the second half of the storage period. These results are the same as seed-stalk height. Correlation studies indicated taller seed-stalks were associated with higher seed yields. Jones (8) reported higher seed yields from 'Ebenezer' onions at 7.5 C and at 11 to 12 C, there were also more seed-stalks. and at these temperatures Results similar to Jones" was obtained in the second experiment. Correlation studies showed that the seed yield was associated with an increase of seed-stalk number. The highest seed yield per bulb occured in the first experiment as a result of more seeds rather than heavier seeds being produced per bulb. However, high seed yield in the second experiment was attributed to more seeds per bulb and

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53 35 to larger seed size. t is not known if the higher number of seeds resulted from more seeds being produced per floret or more florets being produced on each umbel. Further research is needed to ascertain the effect of light on flowering. The response that was noted on days to flowering in this experiment remained the same over two years of experimental work, and has shown that bulbs do respond to light. This response likely alters or induces physiological activity not normally active when bulbs are kept in dark storage. 3 Though this study has shown that bulbs are capable of responding to light, it is not known what wave lengths were responsible, nor is it known what effect light intensity may have on the bulb's response to light. Further research on the interaction of light and temperature may be useful in establishing correct "nicking" times for inbred lines used in the production of hybrid seed, and thus assure maximum seed production. Further research may also positively establish the presence of phytochrome in onion bulbs.

54 BBLOGRAPHY Abdalla, A. A., and L. K. Mann Bulb development in the onion and the effect of storage temperature on bulb rest. Hilgardia 35: Borthwick, H.A., and M.w. Parker Light in relation to flowering and vegetative development. 13th ntern. Hort. Congress 1-9. Boswell, V.R nfluence of the time of maturity of onions on the behavior during'storage, and the effect of storage temperature on subsequent vegetative and reproductive development. Proc. Amer. Soc. Hort. Sci. 20:23h-239. Gardner, w.w., and H.A. Allard Further studies in photoperiodism, the response of the plant to relative length of day and night. J. Agr. Res. 23: Heath, 0. V. S., and M. Holdsworth Bulb formation and flower production in onion plants grown from sets. Nature Heath, 0. V. S., and P. B. Mathur. l9u4. Studies in the physiology of the onion plant.. nflorescence initiation and development, and other changes in the internal morphology of onion sets, as influenced by temperature and day length. Ann. Appl. Biol. 31: Hillman, w. S Phytochrome levels detectable by in vivo spectrophotometry in plant parts grown or stored 1n the light. Amer. J. Bot. 51: Jones, H. A The influence of storage temperature on seed production in the Ebenezer onion. Proc. Amer. Soc. Hort. SCio 2u Jones, H. A., and S. L. Emsweller Effects of storage, bulb size, spacing, and time of planting on production of onion seed. Calif. Agr. Exp. Sta. Bull. 628: 1 pp. 10. Jones, H. A., and L. K. Mann. Onions and Their Allies. Leonard Hill Ltd. London pp. 36

55 lh Koukkari, W. L., and w. S. Hillman Phytochrome levels assayed by in vivo spectrophotometry in modified underground stems and storage roots. Physiol. Plant. 19: Land, H. C., H. M. Cathey, and L. T. Evans The dependence of flowering in several long-day plants on the spectral composition of light extending the photoperiod. Amer. J. Bot. 52: Magruder, R., and H. A. Allard Bulb formation in some American and European varieties of onions as affected by length of day. J. Agr. Res McClelland, T. B Studies of photoperiodism of some economic plants. J. Agr. Res. 37: Pertuit, Jr., A. J Effects of lighting easter lily bulbs during cold treatment on plant growth and flowering. J. Amer. Soc. Hort. Sci. 98: Terabun, M Studies on bulb formation in onion plants. V. Effect on bulb formation of mixed blue, red and far-red light. J. Japan. Soc. Hort. Sci. 39: Thompson, H. C., and O. Smith Seed-stalk and bulb development in the onion (Allium cepa L.). Cornell Univ. Agr. Exp. Sta. Bull Woodbury, G. w., and J. R. Ridley The influence of incandescent and fluorescent light on the bulbing response of three onion varieties. J. Amer. Soc. Hort '3660

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