BREEDING, GENETICS, AND PHYSIOLOGY. Development of Semidwarf Long- and Medium-Grain Cultivars

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1 BREEDING, GENETICS, AND PHYSIOLOGY Development of Semidwarf Long- and Medium-Grain Cultivars J.W. Gibbons, K.A.K. Moldenhauer, F.N. Lee, J.L. Bernhardt, M.M. Anders, N.A. Slaton, R.J. Norman, J.N. Rutger, J.M. Bulloch, E. Castaneda, and M.M. Blocker ABSTRACT Semidwarf rice cultivars contribute to the continued success of Arkansas rice production. Experimental semidwarf lines are in all stages of development from segregating populations to breeder head rows. New sources of yield, disease, and stress resistance are being used as parents in the breeding program, and new techniques such as molecular-aided selection are utilized to efficiently identify disease and quality genes in segregating populations. Continued exchange and utilization of new germplasm is valuable to Arkansas rice improvement. Lines with diverse genetic origins exhibit high yields, good disease and stress tolerance, and acceptable grain quality under Arkansas growing conditions. A furrow-irrigated rice trial was planted in Results showed reduced yield and milling quality under this system, and continued breeding efforts to identify suitable cultivars are needed. INTRODUCTION Since the release of Lemont in the mid 1980 s, semidwarf rice cultivars have been grown in Arkansas. Cocodrie, and Bengal are long- and medium-grain semidwarfs that occupy a large proportion of the current rice area. These cultivars continue to be the base for semidwarf cultivar development in Arkansas. Recently, the first semidwarf long- and medium-grain cultivars Cybonnet and Medark were released by the Arkansas Experiment Station (Gibbons et al., 2006). Lee et al. (1998) have characterized several recently introduced USDA germplasm accessions as tolerant to both rice sheath blight and blast. Most of these introductions 84

2 B.R. Wells Rice Research Studies 2006 belong to the indica subtribe of cultivated rice. Indicas have been suggested as sources for yield potential and disease resistance for domestic breeding programs (Eizenga et al., 2006). Our objective is to develop genetically diverse semidwarf long- and mediumgrain cultivars that are high-yielding with excellent grain, milling, and processing quality that tolerate the common stresses and pests found in Arkansas rice fields. PROCEDURES Potential parents for the breeding program were evaluated for the desired objectives. Cross combinations were programmed that combine desired characteristics to fulfill the breeding objectives. Use of parents of diverse genetic backgrounds was emphasized. Segregating populations were planted at Stuttgart and the winter nursery at Lajas, Puerto Rico. Selection was based on grain and plant type, spikelet fertility, field and greenhouse disease reaction, and grain quality. Yield evaluations began with the preliminary yield trial, the Stuttgart Initial Test (SIT) at two locations, the Arkansas rice performance trials (ARPT) at six locations in the state, and the Uniform Regional Rice Nursery (URRN) conducted in cooperation with rice breeding programs in Texas, Louisiana, Missouri, and Mississippi. As in the past few years, the preliminary yield trial and SIT also were planted at the Pine Tree Experiment Station under high natural disease pressure using blast spreader rows. In 2006, we established three furrow-irrigated rice yield trials on two farmers fields (Locations A and B) and at the RREC (Location C), all in Arkansas County. Five cultivars, four conventional Arkansas cultivars, Wells, Cybonnet, Spring, and CL 131, and one hybrid, XP 723, were replicated 5 times in a Latin Square design. Management was performed by the farmers and with accepted practices at RREC. Planting dates were 5 May for Site A, 17 May for Site B, and 22 May for Site C. RESULTS AND DISCUSSION About 120 cross combinations were made in Emphasis was placed on triple crosses with parents selected for tolerance to straighthead disorder, blast and panicle blight disease as well as yield and grain quality. Over 500 F 1 single-plant triple crosses were selected in 2006 and will be space-planted at Stuttgart in 2007 (Table 1). Over 2000 F 2 single plants were selected during the year. Several of these crosses were made with cold-tolerant parents. Panicles from these plants were sent to the winter nursery for generation advancement. About 2000 single panicles from early flowering lines were harvested and replanted at Puerto Rico so that 2 generations will be gained from the winter nursery in The remainder of selected lines will be planted as F 4 rows at Stuttgart in Plants with known sources of the blast gene Pi-ta, and diverse cooking-quality alleles were evaluated using molecular-aided selection (MAS) allowing for a significant increase in efficiency of selection at Puerto Rico. Over 700 F 4 rows were selected in 2006 from about 3800 rows planted at Stuttgart to advance to F 5 in From over 1500 rows planted, about 150 F 5 and F 6 lines were selected based 85

3 AAES Research Series 550 on plant type, grain quality, earliness, and disease reaction to advance to preliminary yield trials in Yields of selected semidwarf lines from the preliminary yield trial are shown in Table 2. Medium-grain lines from the crosses RU /97Y228//STG02P and 97Y228/PI //STG97F showed improved blast resistance and similar yield to Medark, but had reduced milling quality. RU , STG02P , and STG97F are Arkansas medium-grain breeding lines while 97Y228 and PI are cold-tolerant introductions from California and Colombia, South America, respectively. These latter two lines are examples of newly introduced germplasm accessions that are being incorporated into the very narrow medium-grain germplasm base. Long-grain entries 1122 and 1295 yielded more than Wells and were superior in either blast reaction or milling quality. The entry 1295 is from the cross Cocodrie/ZHE733//WC 285. Cocodrie is a popular Louisiana semidwarf, japonica type while ZHE733 and WC 285 are indica introductions from China and South America, respectively. These lines will be further advanced to replicated trials for All the experimental lines are semidwarf but variation in plant height was observed. The use of blast spreader rows at Pine Tree to simultaneously evaluate for disease and agronomic traits continues to be successful. Plant growth was very good under the disease system and blast disease pressure was good enough to identify susceptible lines. In 2007 more experimental lines, including F 2 populations, will be tested under similar conditions at Pine Tree. Average grain yields from the furrow-irrigated trial (Table 3) were low. Location B produced the highest average yield across cultivars with 160 bu/acre, followed by 91 bu/acre at location A and 75 bu/acre at location C. Late planting affected yields at all locations and weed competition was intense at Location C. The hybrid XP 723 performed best at all locations ranging from 108 bu/acre at location C to 252 bu/acre at location B. The hybrids ability to produce biomass under stress conditions contributed to the high yields under furrow irrigation. Wells and Cybonnet yielded an average of 107 bu/acre across the three locations while Spring and CL 131 were 79 bu/acre and 78 bu/acre, respectively. Late harvest at location A resulted in very low total and head-rice milling yields for all entries. XP 123 had the highest head-rice yield at that location followed by CL 131 and Cybonnet. At location B, milling yields were acceptable, ranging from 55% head rice for XP 723 and Cybonnet to 52% for Spring. Average plant height varied from 32 in. at location C to 36 in. at location B. Between locations, XP 123 varied most in height while Cybonnet and CL 131 had the least difference in height between locations. Furrow-irrigated rice is being used by farmers for various reasons including reduced labor costs, ease of pesticide application, and water-use efficiency. Cultivars adapted to this modified upland rice ecosystem must have early seedling vigor, good tillering ability, and rapid leaf cover to help compete with weeds. Disease resistance especially for rice blast will be essential for successful use of the furrow-irrigated system. Breeding efforts will continue to identify cultivars adapted to furrow-irrigated rice. 86

4 B.R. Wells Rice Research Studies 2006 SIGNIFICANCE OF FINDINGS Promising semidwarf experimental lines with diverse genetic backgrounds have been identified that have good disease resistance, high yields, and good milling quality. Semidwarf long- and medium-grain rice varieties offer producers options in their choice of cultivar and management systems for Arkansas rice production. Furrow-irrigated rice requires cultivars with improved early vigor, rapid biomass production, and improved disease and pest resistance. Continued utilization of new germplasm through exchange and introduction remains important for Arkansas rice improvement. ACKNOWLEDGMENTS This research is supported by the Arkansas Rice Research and Promotion Board. Thanks to the URRN cooperators from rice growing states. LITERATURE CITED Eizenga, G.C., A.M. McClung, J.N. Rutger, C.R. Bastos, and B. Tillman Yield comparison of indica and U.S. cultivars grown in the southern United States and Brazil. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Arkansas Rice Studies University of Arkansas Agricultural Experiment Station Research Series 540: Lee, F.N., R.H. Dilday, K.A.K. Moldenhauer, J.N. Rutger, and W. Yan Sheath blight and rice blast resistance in recently introduced rice germplasm. In: R.J. Norman and T.H. Johnston (eds.). B.R. Wells Arkansas Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 468: Gibbons, J.W., K.A.K. Moldenhauer, K. Gravois, F.N. Lee, J.L. Bernhardt, J.-F. Meullent, R. Bryant, M. Anders, R. J. Norman, R. Cartwright, K. Taylor, J. M. Bulloch, and M.M. Blocker Registration of Cybonnet rice. Crop Sci. 46: Gibbons, J.W., K.A.K. Moldenhauer, K. Gravois, F.N. Lee, J.L. Bernhardt, J.-F. Meullent, R. Bryant, R. J. Norman, R. Cartwright, M. Anders, K. Taylor, J. M. Bulloch, and M.M. Blocker Registration of Medark rice. Crop Sci. 46:

5 AAES Research Series 550 Table 1. Number of early-generation lines selected in project ARK02030 during Number of lines Evaluation phase Planted Selected F 1 transplants F 2 space plants 294, F 4 panicle rows F 5 & F panicle rows Table 2. Data from the 2006 Preliminary Semidwarf Rice Yield Trial for experimental lines and check cultivars. SEREC, Rowher, Ark. Grain Disease z 50% Entry type NB ShB Vigor y Height x HD Yield Milling (in.) (bu/acre) (HR:TOT) Medark M : w M : M : L : L :68 Wells L :68 z Disease scores from field evaluation: Neck Blast (LB) at Pine Tree Experiment Station where 0 = no blast and 9 means blank panicles and Sheath Blight (ShB) at Rice Branch where 0 = no infection and 9 = plants dead. y Vigor taken preflood on scale of 1 to 4 with 1 = poor and 4 = excellent vigor. x Vigor, height, days to 50% heading, yield, and milling data are from Rohwer. w 1059 is from the cross RU /97Y228//STG02P and1056 is from the cross97y228 /PI //STG97F is from RU /Jefferson and 1295 is from Cocodrie/ZHE733/WC

6 B.R. Wells Rice Research Studies 2006 Table 3. Data from the 2006 furrow-irrigated trial at three locations for selected rice cultivars and hybrids. Cultivar Yield z Total milling Head rice Height or hybrid Loc A Loc B Loc C Loc A Loc B Loc C Loc A Loc B Loc C Loc A Loc B Loc C (bu/acre) (%) (in.) Wells Cybonnet Spring CL XP Mean (0.05) LSD z The furrow-irrigated trial was conducted at 3 locations: Loc A and B were on farmers fields and Loc C was at the RREC. Yield, total milling, head rice, and height are means of 5 replications at each location. 89