BREEDING, GENETICS, AND PHYSIOLOGY Phenotypic Analysis of the 2006 MY2 Mapping Population in Arkansas E.J. Boza, K.A.K. Moldenhauer, R.D. Cartwright, S. Linscombe, J.H. Oard, and M.M. Blocker ABSTRACT The RiceCAP MY2 Cypress / LaGrue mapping population was evaluated in 2006 for phenotypic characteristics in Arkansas and Louisiana, as part of a coordinated effort to determine markers for milling. The population will be milled by researchers in Beaumont, Texas, at a later date. Three hundred twenty-five F 5 rice lines, parents, and six controls were planted at the Rice Research and Extension Center (RREC), Stuttgart, Ark. At germination, uniform stand was observed throughout the test. Date of first heading (HVS = Heading Variability Score) ranged from 2 to 3 (2 = all plants in rows within 2 to 5 days and 3 = all plants in rows within 6 to 10 days). A range of 22 days was observed in maturity among the progeny evaluated, ranging from 72 to 94 days. The parents were different in days to heading by only one day. Plant height ranged from 70 to 141 cm. The vast majority of the lines were harvested between 18 and 22% moisture content with a few exceptions below 18% and some that were harvested at 23 to 24% due to initial lodging. In general, a relatively later planting date in Arkansas might help to differentiate the recombinant inbreeding lines for milling quality. INTRODUCTION Rice (Oryza sativa) is one of the most important crops for the growing human population. By 2020, the world will need to produce 350 million tons more rice per year to feed an anticipated 3 billion more people than in 1992 (Rice Almanac, 2002). In addition to its economic importance, rice plays a major role as a model for cereal genomics because of its relative small genome of 440 Mbp and close relatedness to 60
B.R. Wells Rice Research Studies 2006 major cereals (Izawa and Shimamoto, 1996; Gale et al., 1998; Moore et al., 1995). The quest for high quality rice has been a major component in the development of improved germplasm in the U.S. Milling quality is part of a complex trait for which the genetic basis of inheritance is still under investigation (Dong et al., 2004). The advent of DNA technology is providing new opportunities to develop elite rice germplasm with improved grain quality including milling performance, appearance, cooking, milling characteristics, and the recovery of milled head rice. Identification and mapping of genomic regions associated with controlling milling yield in rice will facilitate breeding of new rice varieties with high milling quality and therefore a better market price. The objectives of this study were to a) evaluate the MY2 mapping population in Arkansas for phenotypic characteristics and milling quality, and b) evaluate a relatively late planting that would help to differentiate the Recombinant Inbreeding Lines (RIL s) for milling quality. MATERIALS AND METHODS Parents and Population Development Three hundred twenty-five F 4 lines of the MY2 Cypress/LaGrue mapping population were generated and provided to RiceCAP by Dr. Linscombe (Crowley, La.). The F 5 lines were grown in Crawley in 2005 to produce enough seed for replicated field trials at multiple locations (AR and LA) in 2006. Replicated controls that included original parents (Cypress and LaGrue), and six controls ( Trenasse, Madison, RT0134, Spring, Cocodrie, and MCR01277) were included in the field planting (Table 1). Field Evaluations During 2006, 325 F 6 rice lines, parents, and controls were planted at the Rice Research and Extension Center (RREC), Stuttgart, Ark., in a Crowley silt loam soil (fine, montmorillonitic, thermic Typic Albaqualfs) using a randomized complete block (RCB) design with two replications. Each rice line was planted in two-row plots approximately 2.5 feet long (12-in. row spacing). Quilt fungicide at 21 oz/acre + Quadris at 6 oz/acre, and Karate insecticide at 2.5 oz/acre were applied at early booting and again 10 days later to prevent disease and stem borers, respectively. A third application of Karate was needed to control stem boders. Frequency distributions, plots figures, and correlation analysis of family means were conducted using SAS 9.1 PROC FREQ, PROC PLOT, and PROC CORR (SAS Institute, N.C.). RESULTS AND DISCUSSION A uniform and consistent stand was observed throughout the trial at germination. The great majority (approximately 95%) of the rows had at least 1 plant every 2 in. of row length and about 5% had somewhat less (intermediate) than 1 plant every 2 in. 61
AAES Research Series 550 Parents (Cypress and LaGrue) had a normal and intermediate stand, respectively (Fig 1). Date of first heading (HVS = Heading Variability Score) ranged from 2 to 3 in a 1 to 5 scale (2 = all plants in rows start heading within 2 to 5 days and 3 = all plants in rows within 6 to 10 days) where 1 = all plants in rows start heading on the same day and 5 = all plants in rows >14 days. The first HVS was recorded 65 days after emergence (DAE) and last one 89 DAE (Fig 2). Variability in maturity was not observed between parents. The parents were different in days to heading by only one day, but a range of 22 days was observed in maturity among the progeny evaluated ranging from 72 to 94 days, suggesting a very uniform and compact population for maturity (Fig 3). Overall, about 85% of the population was observed to head within 2 to 5 days and 15% within 6 to 10 days. No families were observed to head within 11 to 14 days or >15 days. Plant height ranged from 30 to 56 in. The parents were different in plant height by only 1 in., but a range of 26 in. was observed among the progeny evaluated, suggesting transgressive segregation for plant height (Fig 4). At harvesting, 2.99% of the lines were harvested between 110 to 114 DAE, 56.4% at 116 to 119, 26.8% at 120 to 124, 10.4% at 125 to129, 3.0% at 130 to134, and <1% at 136. The parents (Cypress and LaGrue) were harvested at 117 and 124 DAE, respectively (Fig 5). A significant achievement was to harvest about 94.0% of the families between 18 and 22% moisture content (Fig. 6). A few exceptions ertr below 18% and some that were taken out of the field at 23 to 24% moisture content due to initial lodging. SIGNIFICANCE OF FINDINGS Milling quality in rice is a very difficult trait to improve; however, it is of much economic importance to the rice industry. Phenotypic evaluations together with genotyping studies on the MY2 Cypress/LaGrue mapping population are very important efforts to generate an association between molecular markers and quantitative trait loci (QTLs) that control milling quality of rice. A coordinated effort with Louisiana, Texas, and Mississippi as part of the RiceCAP project is underway to conduct a full study on this population. ACKNOWLEDGMENTS The project was supported by the USDA Cooperative State Research, Education and Extension Service National Research Initiative Coordinated Agricultural Program on rice (RiceCAP) - Grant No. 2004-35317-14867. LITERATURE CITED Dong, Y., E. Tsuzuki, D. Lin, H. Kamiunten, H. Terao, M. Matsuo, and S. Cheng. 2004. Molecular genetic mapping of quantitative trait loci for milling quality in rice (Oryza sativa L.). J. Cereal Sci. 40:109-114. 62
B.R. Wells Rice Research Studies 2006 Gale, M.D. and K.M. Devos. 1998. Comparative genetics in the grasses. Proc. Natl. Acad. Sci. USA 95:1971-1974. Izawa, T. and K. Shimamoto. 1996. Becoming a model plant: The importance of rice to plant science. Trends Plant Sci. 1:95-99. Moore, G., K.M. Devos, Z. Wang, and M.D. Gale. 1995. Cereal genome evolution: Grasses, line up and form a circle. Curr. Biol. 5:737-739. Rice Almanac. IRRI. 2002. Source book for the most important economic activity on earth. Edited by J.L. Maclean, D.C. Dawe, B. Hardy, and G.P. Hettel. Table 1. Phenotypic characteristics between parents and checks in the MY2 population grown in Arkansas. Phenotypic Parent Variety check characteristic CPRS z LGRU TRNS MDSN RT0134 SPRG CCDR MCR01277 Stand 9.0 8.0 9.0 9.0 9.0 9.0 9.0 9.0 First heading 76.0 79.0 71.0 79.0 72.0 64.0 71.0 76.0 50% heading 78.0 83.0 74.0 82.0 76.0 66.0 73.0 80.0 Plant height 104.0 107.0 101.0 90.0 117.0 109.0 97.0 100.0 Days to harvest 117.0 124.0 116.0 121.0 116.0 111.0 116.0 119.0 Weight at 478.0 506.0 827.0 424.0 781.0 587.0 780.0 626.0 harvest (g) Moisture content 19.6 20.2 21.4 18.4 20.3 17.8 19.2 24.1 at harvest (%) z CPRS= Cypress; LGRU= LaGrue; TRNS= Trenasse; MDSN= Madison; RT0134= RiceTec line; SPRG= Spring; CCDR= Cocodrie; and MCR01277= LA line. 63
AAES Research Series 550 Fig. 1. Frequency distribution of rice stand using family means in the MY2 population grown in Arkansas. Fig. 2. Frequency distribution of days to first heading using family means in the MY2 population grown in Arkansas. 64
B.R. Wells Rice Research Studies 2006 Fig. 3. Frequency distribution of days to 50% heading using family means in the MY2 population grown in Arkansas. Fig. 4. Frequency distribution of plant height using family means in the MY2 population grown in Arkansas. 65
AAES Research Series 550 Fig. 5. Frequency distribution of days to harvesting using family means in the MY2 population grown in Arkansas. Fig. 6. Frequency distribution of percentage of moisture content at harvest using family means in the MY2 population grown in Arkansas. 66