PEST MANAGEMENT: DISEASES. Historical Use Of Field Resistance to Control Rice Blast Disease in Arkansas

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1 PEST MANAGEMENT: DISEASES Historical Use Of Field Resistance to Control Rice Blast Disease in Arkansas F.N. Lee, R.D. Cartwright, C.E. Wilson Jr., and K.A.K. Moldenhauer ABSTRACT Rice diseases can drastically reduce rice yield and quality and limit growers variety options. Effective control of rice blast is critical to successful rice production in Arkansas. Rice varieties grown in Arkansas since 1968 are susceptible to multiple blast races found in Arkansas. Although susceptible to most U.S. blast races in greenhouse tests, the varieties Starbonnet (1968 to 1984) and Cypress (1994 to 2002) had good field resistance and were usually grown without requiring special cultural management to control blast. Varieties such as Labelle (1975 to 1984), Lemont (1985 to 1995), Lebonnet (1976 to 1984), and Tebonnet (1986 to 1991) had some field resistance but were at times severely damaged by blast. Although rice blast severely reduced Newbonnet (1985 to 1995) yields, many growers adapted cultural practices to induce field resistance in this high-yielding variety. Since 2000, numerous growers have changed to very-high-yielding varieties such as Wells and Francis, which can suffer complete yield losses from rice blast when drought-stressed. These varieties require deep flood management to induce levels of field resistance necessary to control rice blast. The Pi-ta blast-resistance gene found in Katy provided complete blast control from 1989 until A new race of the blast fungus called IE-1k that could damage the resistant Pi-ta rice varieties was detected in grower fields during 1994, but this new race did not cause significant damage until 2004 in the new Pi-ta-based variety Banks. Research indicates adequate levels of field resistance are critical to rice blast control. 133

2 AAES Research Series 540 INTRODUCTION The state average yield of 6910 lb/acre (154 bu/acre) produced during 2004 was a record high for Arkansas (Wilson and Branson, 2005). The average yield of 6650 lb/acre in 2005 is the sixth consecutive year that state average yields exceeded 6100 lb/acre. Increased yields are attributed to use of very-high-yield-potential varieties accompanied by improved management including more intense but efficient herbicide, fertilizer, fungicide, insecticide, and water management. Yield loss to diseases including rice blast, sheath blight, and kernel smut was limited by control strategies that integrated variety resistance, cultural practices, and fungicides. Frequent rainfall in May and June created environmental conditions during 2004 that were the most conducive for rice blast in several years. Although lower yielding blast-resistant Pi-ta gene varieties were available, growers planted over 75% of the state rice acreage in blast-susceptible varieties during Due to this large acreage of blast-susceptible varieties, early-season blast incidence was higher than observed in previous years with up to 300,000 acres estimated to have had leaf blast. However, losses to rice blast were limited by proper cultural disease-control practices, primarily flood management (Wilson et al., 2005). The rapid grower shift to higher yielding but blast-susceptible varieties highlighted the need to better understand the role of field resistance in rice blast control. PROCEDURES Acreage information was obtained from the USDA National Agricultural Statistics Service and from rice variety distribution summaries generated from the University of Arkansas Rice DD50 program enrollment. Data examined were limited to long-grain varieties. Varieties were grouped according to percent of total acres planted over long periods of time with major long-grain varieties. Rice variety blast-susceptibility ratings were determined using data from greenhouse and inoculated field nurseries. RESULTS AND DISCUSSION Production records show Arkansas growers quickly change to new higher-yielding rice varieties, often within one or two years of release. Released in 1967, Starbonnet was planted on 68% of state acres during 1971 and on an average of 49.64% of state acres from 1969 thru Starbonnet, Labelle, and Lebonnet varieties were planted on a combined 80% of total state acres from 1975 thru In an incredibly rapid shift, growers planted 76.2% and 90.7% of total state acres during 1985 and 1986, respectively, to Newbonnet, Lemont, and Tebonnet varieties. Due to widespread rice blast epidemics from 1985 to 1987, Newbonnet acres declined to about 30% or 40% of state acres from 1988 thru The varieties Cypress, Alan, and LaGrue predominated during 1994 and 1995 at 62% and 68%, respectively, of planted acres and then declined to less than 40% of state acres by 1999 as acres planted to the Pi-ta-R gene varieties Katy, Kaybonnet, and Drew increased. Released in 1989, Katy peaked 134

3 B.R. Wells Rice Research Studies 2005 at 21% of state acres in 1992 then declined. Peak use of the Pi-ta-R gene-resistance occurred during 1998 when Drew and Kaybonnet were planted to 37% and 8.4%, respectively, of total state acres. The very high yielding Wells and Cocodrie varieties quickly became established after Although Cocodrie plantings have declined, Wells remains popular and, with the addition of Francis and CL 161, blast-susceptible varieties were grown on over 78% of total acres planted during Continued grower preference for rice varieties appears to be due to a complicated interaction between desirable agronomic characteristics and general management requirements of the many variables adversely impacting rough rice and milling yields. All rice varieties utilized from 1968 thru 2005 were susceptible to one or more of the blast races capable of causing unexpected yield reduction when conditions were favorable for disease. The degree of blast field-resistance in these varieties determined losses to rice blast. Although very susceptible in greenhouse tests to most U.S. blast races, Starbonnet and Cypress were seldom observed to develop blast in production fields. Labelle, Lemont, and Lebonnet also exhibited some field resistance but were subject to severe damage by rice blast under special circumstances. Although very susceptible to blast, Newbonnet had substantial field resistance when grown in deep-flooded heavy soils. The high-yielding varieties utilized since 2000 are very susceptible to common blast races in greenhouse tests and are subject to complete grain blanking when growing in drought-stressed field nurseries (Table 1). When flooded, however, blast resistance of these varieties increases dramatically. Field observations and research data indicate flood-induced blast field-resistance is cumulative and, in select varieties, can approach the immunity levels expressed by major R-gene resistance. Wells likely represents the least acceptable level of field resistance for grower use, but remains the most widely grown variety. LaGrue and Francis require very careful management due to sub-standard levels of field resistance. The Pi-ta-R gene conferred immunity to known U.S. blast races when first used in Katy in Soon new Pi-ta virulent blast races IE-1k and IB-33 were detected in greenhouse tests. Although detected in grower fields during 1994, field plantings of Pi-ta varieties were not damaged by race IE-1k until significant blast developed in drought-stressed Banks during 2004 and 2005 (Lee et al., 2005a). Greenhouse tests show race IE-1k damage in Pi-ta gene varieties is mediated by flood-induced field resistance (Lee et al., 2005b). SIGNIFICANCE OF FINDINGS The historical and current blast vulnerability of Arkansas rice varieties demonstrates the value of field resistance in rice blast control. Flood-induced blast fieldresistance has been observed in all rice varieties tested to date including compromised R gene varieties. Although major resistance genes provide blast-free varieties, they are frequently overcome by new races of the blast pathogen and must possess field resistance to control the disease in the long term. 135

4 AAES Research Series 540 LITERATURE CITED Lee, F.N., R.D. Cartwright, Y. Jia, J.C. Correll, K.A.K. Moldenhauer, J.W. Gibbons, V. Boyett, E. Zhou, E. Boza, and E. Seyran A preliminary characterization of the rice blast fungus on Banks rice. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 529: Fayetteville, Ark. Lee, F.N., M.P. Singh, and P.A. Counce Flood-induced field resistance in Drew and related Pi-ta gene varieties compromised by new blast races. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 529: Fayetteville, Ark. Wilson Jr., C.E. and J.W. Branson Trends in Arkansas rice production. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 529: Fayetteville, Ark. Wilson Jr., C.E., R.D. Cartwright, J.W. Gibbons, A.L. Richards, D.L. Frizzell, J.W. Branson, S. Runsich, and C.E. Parsons Evaluation of rice varieties for performance and disease reaction on farms. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 529: Table 1. Annual blast-susceptibility rating for cultivars grown under drought-stressed conditions in the rice-blast field nursery conducted on the Pine Tree Branch Experiment Station near Colt, Ark. Year of evaluation Six-year Cultivar average Cocodrie 5.0 z Cypress Wells LaGrue Francis z Visual susceptibility rating using the 0= none to 9 = panicle completely blanked by rice blast. 136

5 B.R. Wells Rice Research Studies 2005 Fig. 1. Percent of total rice acres planted to long-grain rice varieties in Arkansas during 1968 through