NYS804? Manipulating growth in bedding plants Peter Goodwin University of Sydney

Transcription

1 NYS804? Manipulating growth in bedding plants Peter Goodwin University of Sydney

2 NY99047 This report is published by the Horticultural Research and Development Corporation to pass on information concerning horticultural research and development undertaken for the nursery industry. The research contained in this report was funded by the Horticultural Research and Development Corporation with thefinancialsupport of the Newports Nursery. All expressions of opinion are not to be regarded as expressing the opinion of the Horticultural Research and Development Corporation or any authority of the Australian Government. The Corporation and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this report and readers should rely upon their own enquiries in making decisions concerning their own interests. Cover price: $22.00 (GST Inclusive) HRDC ISBN Published and distributed by: Horticultural Research & Development Corporation Level 1 50 Carrington Street Sydney NSW 2000 Telephone: Fax: (02) (02) horticulture@horticulture.com.au Copyright 2001 ^ s ^ '' HORTICULTURAL V RESEARCH & DEVELOPMENT CORPORATION HRD\C Partnership in horticulture

3 HORTICULTURAL RESEARCH AND DEVELOPMENT CORPORATION & OASIS HORTICULTURE PTY LTD HRD\C FINAL REPORT NY99047 (31 November 2000) Manipulating growth in bedding plants Peter Goodwin The University of Sydney

4 HRDC Project Number: NY99047 Principal Investigator's Name and Contact Details: Dr Peter Goodwin Reader in Horticulture, University of Sydney Department of Crop Sciences John Wool ley Building A20 University of Sydney, NSW 2006 Phone: Fax: It is difficult to manipulate plant growth so that it is at the stage desired by the consumer at the time of purchase. A number of chemicals are currently used to advance or retard the growth of nursery stock to aid the programming of production to suit consumer demand. This project aimed to provide greater understanding of how one of these chemicals ethephon, achieved its effects, with the general aim of enabling more effective use of the chemical by the nursery industry. This research was sponsored by the Horticultural Research and Development Corporation (HRDC), and was made possible by contributions from Oasis Horticulture Pty Ltd. A special thanks goes to the nursery operators and staff of Oasis Horticulture for their generous assistance in providing the necessary plants. Peter Goodwin, Scott Lee 29 November 2000 Any recommendations contained in this publication do not necessarily represent current HRDC policy. No person should act on the basis of the contents of this publication, where as to matters of fact or opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication.

5 CONTENTS 1. MEDIA SUMMARY 2 2. TECHNICAL SUMMARY 3 3. INTRODUCTION 4 4. AIMS OF THE PROJECT 5 5. MATERIALS AND METHODS PLUG PRODUCTION APPLICATION OF ETHEPHON MEASUREMENT OF ETHYLENE PRODUCTION 6 6. RESULTS 8 7. DISCUSSION 9 8. TECHNOLOGY TRANSFER RECOMMENDATIONS AND AREAS FOR FUTURE RESEARCH REFERENCES 10

6 1 Media Summary It is difficult to manipulate plant growth so that plants are at the stage desired by the consumer at the time of purchase. A number of chemicals are currently used to advance or retard the growth of nursery stock to aid the programming of production to suit consumer demand. This project aimed to provide greater understanding of how one of these chemicals ethephon, achieved its effects, with the general aim of enabling more effective use of the chemical by the nursery industry. The results indicate that ethephon acts by releasing ethylene. Further research is needed to explore in more detail its mode of action in regulating the growth of ornamental plants Ornamental plant producers should test ethephon as a possible alternative agent to chlormequat and daminozide for manipulating plant growth. -2-

7 2. Technical Summary The aim of this project was to conduct a preliminary examination of the mode of action of ethephon in modifying plant growth. The work was conducted on petunias (Petunia x'hybrida 'Lady Jessie Bradman') plugs and punnets. The results show that there is a substantial production of ethylene within a few hours of applying ethephon. It is recommended that ornamental plant producers explore the possible use of this chemical as an alternative agent to chlormequat and daminozide for manipulating plant growth. There are a number of other areas that need to be included in future research on this problem, including: What species show a useful response to ethephon What are the nature of the responses What are the most useful stages for it to be applied How long term are the responses, and do they carry over to benefit the consumer. -3-

8 3. Introduction Potted colour, and high quality seedling transplants are in great demand. Time and space limited gardeners are demanding plants that have had a head start, and will quickly establish and flower in the garden. The trend towards smaller residential lot sizes means smaller gardens. In response, the nursery industry has to offer plants that fit into smaller spaces, and perform in a relatively short time frame. Flowering annuals meet this demand. Consumer satisfaction is gauged by how the plants perform. Primarily, performance is dependent on the genetics of the plant variety. In addition, performance and quality of plants produced is also directly influenced by cultural practices implemented at the production stage. The production of annuals occurs in two steps at the nursery, giving rise to the punnets which the customer plants in the garden. The first stage is the germination of the seed to give plugs, and the second the growing on of the plugs to punnets of a saleable size. A plug is a containerised transplant. Seed is mechanically sown into individual cells in a plug tray. Plug trays commonly used in Australia and the US hold 512 plugs. After germination the seedling grows in its own miniature container until ready to transplant (Styer and Koranski 1997). Advantages plugs offer relate to less time and labour to transplant, faster and more uniform growth after transplanting, earlier and more uniform flowering, increased production per square meter, and plants can be held for delayed transplanting. Transplanted plugs keep more root hairs, which quickly absorb water and nutrients. This active root system allows more uniform and faster plant growth with little or no transplant shock (Styer and Koranski 1997). With increased emphasis being placed on quality in the nursery industry, plug and punnet growers have faced many quality related issues. Growers would agree that quality refers to a well-formed root system, good branching, controlled height, good colour, timely flowering, and absence of pests and disease (Styer and Koranski 1997). Temperature, moisture, nutrition, and light predominantly govern plant height and flowering (Dole and Wilkins 1999). In addition to these non chemical growth control measures, chemical growth regulators are also in wide use for height control. Daminozide (Alar, also -4-

9 known as B-Nine) and chlormequat ( Cycocel ) are synthetic growth regulating chemicals that prevent a plants natural production of gibberellins, at different parts of the pathway. Their primary use is to achieve a shorter plant through reduction of internodal elongation (Styer and Koranski 1997). Unfortunately, these chemical growth regulators have variable effects, and short term benefits. In the major plug production months during spring and summer. Alar / Cycocel applications may need to be as frequent as three applications each week. This highlights the short lasting effects of such chemical growth regulators. Costs of production greatly increase with such a high frequency of applications due to labour, and the cost of Alar / Cycocel. 4. Aims of the Project Alternatives or supplements to the existing growth regulators would be of considerable interest to the nursery industry, especially to bedding plant producers. One chemical which is available, but not commonly used is 2-chlorethyl-phosphonic acid, ethephon. This project was a preliminary examination of the mode of action of ethephon on bedding plants, focusing on its ability to promote ethylene production. 5. Materials and Methods 5.1. Plug production Seed of Petunia x hybrida Grandiflora 'Lady Jessie Bradman' was sown into 512 plug trays. The plug medium was 1:1 peat and sand, with the incorporation of nitrogenous fertiliser. All seeded trays were covered with vermiculite. At the germination stage, plug trays were placed in a glasshouse for two to three weeks. After this period the plants were large enough to be moved into a shadehouse, until they were ready to be transplanted. In the shadehouse area, plants received fertiliser via the irrigation system on alternate days. The composition of the liquid fertiliser was as follows: Calcium nitrate: 190g/1000L Mono ammonium phosphate: 30 g/1000 L -5-

10 Potassium nitrate: 76 g/1000 L. Clear water is used on other days to promote root growth. In general, plants were watered twice each day, depending on the weather conditions Application of ethephon A very important piece of equipment used for the application of ethephon was a pressurised sprayer. A hand held one litre 'Hills pressurised mist sprayer' was utilised due to its ability to maintain uniform pressure, presence of a spray release stop button, high quality plastic components, and a manageable one litre volume. The nozzle was adjusted to a level that gave a fine droplet size that evenly covered the leaf surface. Varying concentrations were accurately prepared using a Pippetteman to measure the volume of ethephon needed to make the desired dilution. 5.3 Measurement of ethylene production Ethylene evolution from ethephon treated plants was determined with the use of a Shimadzu 8A gas chromatograph (GC), with a flame ionisation detector. Nitrogen and air were the carrier gases. The GC column packing material was Poropak Q, and is recommended to separate moderately volatile compounds from ethylene. The injection temperature was set at 140 C, while the column temperature was 120 C. The GC was turned on for two hours prior to injecting samples to ensure all impurities were removed from the machine. Three ethephon concentrations were applied: 0 ppm, 400 ppm and 1000 ppm. Immediately after applying ethephon to the plugs, three samples were randomly taken, and placed in 30 ml reaction vials. Vials were stoppered with a rubber serum cap. The first series of readings were taken half an hour after ethephon application. An ethylene standard was prepared by diluting pure ethylene gas. A 110 ml glass vial was filled with ethylene gas. From this vial, 1.0 ml was extracted using a syringe, and injected into a second vial. Finally, 1.0 ml was taken from the second vial, and injected into a rubber sealed -6-

11 third vial. One millilitre of the third dilution vial was injected into the gas chromatograph to obtain a peak of known concentration. Samples were maintained at 25 C between readings. After half an hour, a hypodermic syringe and needle was used to draw out a 1.0 ml sample of the atmosphere above the plant in the vi al. This sample was injected into the gas chromatograph in order to determine the concentration of ethylene that had been released from the leaf surface. Three replicates were used for each of the three treatments. Measurements were taken every hour after the initial measurement, until ethylene production levels slowed down and began to level out. A reading was also taken 27 hours after ethephon application. In order to determine the levels of ethylene being released 24 hours after ethephon application, samples of each of the three treatments were placed into vials as outlined, 24 hours after ethephon was applied. These plants remained at 25 C for two hours prior to ethylene levels being measured. 6. Results Measurement of ethylene evolution from petunias treated with ethephon. The measurement of ethylene was important as it is a plant hormone responsible for many plant growth and development processes. After having applied ethephon to Petunia x hybrida 'Lady Jessie Bradman' plugs, ethylene production was measured half an hour later. Both 400 ppm and 1000 ppm ethephon treated plants were releasing similar amounts of ethylene at half an hour (Figure). One hour after the first measurement, petunias treated with 1000 ppm began to produce ethylene at a considerably higher rate than those treated with 400 ppm. Two and a half hours after ethephon was applied, plants treated with 400 ppm ethephon reached a peak ethylene production rate. It was not until three and a half hours after ethephon was applied that -7-

12 petunias treated with 1000 ppm ethephon recorded their maximum ethylene evolution rate (Figure). Ethylene production rates of both treatments dropped slightly at some stage before slightly increasing again. The drop reached a low at three and a half hours after ethephon application for 400 ppm, and four and a half hours for 1000 ppm ethephon treated petunia plugs. Sampling vials that remained sealed for 22.5 hours after the last measurement was taken (27 hours after ethephon was applied), recorded very low ethylene production rates. Production rates were near to half the rate recorded half an hour after ethephon was applied, and are represented as the last reading on the Figure. New petunia samples were taken twenty four hours after ethephon was applied. Plant samples were placed in sealed vials for two hours to determine an accurate rate of ethylene production. Petunias treated with 400 ppm produced nmoles ethylene/gram fresh weight/hour. Petunias treated with 1000 ppm ethephon produced nmoles ethylene/gram fresh weight/hour. Therefore, ethylene was still being released in very small amounts, one day after ethephon was applied. -8-

13 Hours after ethedhon application Figure 15: Evolution of ethylene from ethephon treated Petunia x hybrida plugs. Discussion A starting point of the research was to determine the qualities of ethephon that evoke physiological responses in plants. Warner and Leopold (1969) provided evidence that ethephon degrades to ethylene. They showed that production of ethylene occurs not only in the presence of plant tissue, but also in the presence of added base. Thus, it is the basic nature of plant tissues that promotes the degradation of ethephon into ethylene (Warner and Leopold 1969). Chromatographic analysis of petunias treated with varying concentrations of ethephon in the current study supported Warner and Leopold's research as it revealed that ethephon degrades to produce ethylene. In addition, the current study on petunias demonstrates that ethylene production increases with increasing ethephon concentration. -9-

14 Chromatographic analysis of the petunias treated with ethephon uncovered a peak in ethylene production within one hour of applying ethephon at 400 ppm and within three and a half hours at 1000 ppm ethephon. Ethylene was still being released at very low rates one day after ethephon application. This result contrasts with research by Yamaguchi et al (1971) which found that 200 ppm ethephon applied to tomato leaves gave a maximum ethylene production rate two days later. A number of factors could explain this contrast in the timing of peak ethylene production rates. The tomato plants used by Yamaguchi et al (1971) were mature and fruiting. Petunias used in the current study were only four weeks old. The tomato would have much thicker epidermal and fibrous tissue. Thus the slow rise to the maximum ethylene production rate for the tomato when compared to the petunia seedlings may be a reflection of the time required for the ethephon to penetrate the thick epidermis of the tomato, into cells where the ph was favourable for ethephon degradation. 8. Technology Transfer All aspects of this work have been carried out in close consultation with Oasis Horticulture, who provided part of the funds for the work. Release of information to industry will be mainly by the final report on the project. 9. Recommendations and Areas for Future Research There are a number of areas that need to be included in future research on ethephon, including: What species show a useful response to ethephon What are the nature of the responses What are the most useful stages for it to be applied How long term are the responses, and do they carry over to benefit the consumer References Dole, J.M and Wilkins, H.F (1999). Floriculture. Principles and Species. Prentice-Hall, Inc. Styer, R.C and Koranski, D.S. (1997). Plug and Transplant production. A Grower's Guide. Ball Publishing, Batavia, Illinois USA

15 Warner, H. L, and Leopold, A.C. (1969). Ethylene evolution from 2-chloroethylphosphonic acid. Plant Physiology 44: Yamaguchi, M, Wang Chu, C, and Yang, S.F. (1971). The fate of 14C(2- chloroethyophosphonic acid in summer squash, cucumber, and tomato. Journal of the American Society of Horticultural Science 96(5):