'Taggart' Rice Variety Has Enhanced Blast Field Resistance

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'Taggart' Rice Variety Has Enhanced Blast Field Resistance

PEST MANAGEMENT: DISEASESThe ‘Taggart’ Rice Variety HasEnhanced Blast Field ResistanceF.N. Lee, K.A.K. Moldenhauer, and S.B. BelmarABSTRACTEnvironmental conditions highly favorable for the rice blast [Magnaportha grisea(T.T. Hebert) M.E. Barr] disease during 2009 better defined rice blast field resistancefor the newly released variety ‘Taggart’. Average panicle blast severity ratings for theTaggart variety were 7.4 in tests at the University of Arkansas Pine Tree Research Station(PTRS) and 5.7 in tests at the University of Arkansas Rice Research and ExtensionCenter (RREC) with an average severity rating of 6.6 over the two upland nurseries.These ratings were substantially lower than the corresponding severity ratings of 8.7and 8.6 for the ‘Wells’ variety and ratings of 8.9 and 9.0 for the ‘Francis’ variety in thePTRS and RREC nursery plots, respectively. Average ratings over both nurseries were8.6 for Wells and 8.9 for Francis.Taggart is a new high yield variety with increased blast field resistance for Arkansasrice growers. Taggart apparently does not contain known partial resistance genesand could prove to be a valuable research tool to comprehend interactions between theblast fungus and the rice plant.INTRODUCTIONArkansas rice growers have long relied upon field resistance, often unintentionally,as their primary blast control strategy. Historically, new ‘blast resistant’ varieties withmajor resistance genes are typically overcome by the disease within 1 to 3 years dueto pathogen adaptations which result in new races or an unexpected rapid increase ofpreviously identified races. Once major gene resistance fails, Arkansas rice growers mustrely upon inherent field resistance and cultural practices to control the rice blast disease.65


AAES Research Series 581In addition, many blast-susceptible varieties produce very high yields in the absence ofrice blast disease and are preferred by knowledgeable rice growers who utilize culturalpractices to achieve efficacious rice blast control. Since 2000, Arkansas growers haveproduced record per-acre rough rice yields while growing high yield blast susceptiblevarieties such as Wells and Francis. Blast control was achieved by growers manipulatingcultural practices until the blast resistance expressed in Wells, Francis, and othersusceptible varieties became comparable to that of major resistant gene varieties.Unfortunately, most field resistant varieties are subject to substantial yield reductionwhen overwhelmed by rice blast during adverse environmental conditions includingan extended drought or unexpected loss of flood water. Research data collected todate indicates the newly released Taggart variety (Moldenhauer et al., 2009) exhibitsenhanced field resistance during environmental conditions that favor blast disease inthe less resistant Wells and Francis. This research is part of our ongoing effort to betterdefine and utilize field resistance as a blast control strategy.PROCEDURESRice blast severity was evaluated on test entries growing in inoculated upland blastnurseries using the standard visual 0 to 9 scale where a 0 rating indicates complete diseaseimmunity and the 9 rating indicates complete disease susceptibility usually endingwith total yield loss and/or plant death. Ratings are often summarized as visual ratingsof 0 to 3 = R (resistant), 3 to 4 = MR (moderately resistant), 5 to 6 = MS (moderatelysusceptible to susceptible), 7 = S (susceptible), and 8 to 9 = VS (very susceptible). Plantswere bulk inoculated with multiple blast races including IB-1, IB-49, IC-17, IE-1, IH-1,and IG-1 growing on ryegrass seed-corn mixture. Panicle blast ratings were made at R7to R8 growth stages when grain is filled but before grain begins to mature.Four replications of selected breeding lines were included in the nursery testslocated at the University of Arkansas Pine Tree Research Station (PTRS) near Colt,Ark., and the University of Arkansas Rice Research and Extension Center (RREC) nearStuttgart, Ark. Additional plots of Taggart, Wells, and Francis were included within thestandard inoculated blast nursery tests and visually rated to generate additional fielddata.RESULTS AND DISCUSSIONPanicle symptoms on plants growing in the near perfect environmental conditionsfor the rice blast disease during 2009 clearly defined the newly released rice varietyTaggart as having increased rice blast field resistance (Table 1). Average panicle blastseverity ratings for the Taggart variety were 7.4 in PTRS tests and 5.7 in RREC testswith an average rating of 6.6 for both locations. These ratings were substantially lowerthan the corresponding ratings of 8.7 and 8.6 for the Wells variety and ratings of 8.9 and9.0 for the Francis variety in the PTRS and RREC nursery plots, respectively. Averageratings over both locations were 8.6 for Wells and 8.9 for Francis. The 2009 data agree66


B.R. Wells Rice Research Studies 2009with data from PTRS nurseries conducted during 2005 thru 2008 where Taggart panicleblast ratings averaged 4.0 compared to 6.1 and 7.5 for Wells and Francis, respectively(Lee et al., 2009).In terms of applied rice production ratings, disease reactions are assigned basedupon observed disease severity during conditions favoring severe disease developmentin historical and recent test plots and grower fields across Arkansas. Wells, which has asusceptible (S) blast reaction rating, is generally considered to represent the minimumacceptable level of blast field resistance for use in Arkansas rice production fields. Incomparison, Francis has a very susceptible (VS) blast reaction rating but is often grownby Arkansas producers willing to assume the economic risk because Francis has a highyield potential. Rice pathologists with the University of Arkansas Division of Agriculturestrongly recommend that rice cultivars with a VS blast reaction rating be plantedonly in wide open fields with excellent water management (deeper consistent flood)and no strong history of neck blast disease, and then only by growers experienced inthe management of blast.Due to the limited production history, the blast reaction for Taggart is currentlyplaced as being S but the rating may change with additional grower use. AlthoughTaggart is obviously more resistant than Wells, the exact ranking of Taggart relativeto maximum achievable field resistance in rice varieties requires additional research.Regardless, Taggart should serve Arkansas growers well when standard blast culturalcontrol recommendations are followed.SIGNIFICANCE OF FINDINGSTaggart provides Arkansas rice growers a new high yield variety with increasedblast field resistance relative to Wells, Francis, and other blast susceptible varieties.Taggart represents progress in the search for increased blast field resistance.Taggart apparently does not contain known partial resistance genes and could prove tobe a valuable research tool in efforts to understand basic interactions between the blastfungus and the rice plant.ACKNOWLEDGMENTSRice grower check-off funds distributed by the Arkansas Rice Research andPromotion Board were utilized to support this research.LITERATURE CITEDK.A.K. Moldenhauer, J.W. Gibbons, F.N. Lee, J.L. Bernhardt, E.E. Wilson, Jr., R.K.Cartwright, R.J. Norman, M.M. Blocker, D.K. Ahrent, V.A. Boyett, J.M. Bullock,and E. Castaneda. 2009. Taggart, A high yielding large kernel long-grain rice variety.In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds). B.R. WellsRice Research Studies, 2008. University of Arkansas Agricultural ExperimentStation research Series 571:68-73. Fayetteville, Ark.67


AAES Research Series 581F.N. Lee, R.D. Cartwright, K.A.K. Moldenhauer, and S.M. Belmar. 2009. Rice blastcontrol strategies for new rice cultivars ‘Taggart’ and ‘Templeton’. In: R.J. Norman,J.-F. Meullenet, and K.A.K. Moldenhauer (eds). B.R. Wells Rice ResearchStudies, 2008. University of Arkansas Agricultural Experiment Station researchSeries 571:80-86. Fayetteville, Ark.Table 1. Summary of panicle blast severity rating data from varietiesin inoculated upland blast field nurseries located on the University of ArkansasPine Tree Research Station, Colt Ark., 2005 to 2008, and 2009; and on theUniversity of Arkansas Rice Research and Extension Center, Stuttgart, Ark., 2009.Panicle blast rating zResistance PTRS RREC PTRS/RRECVariety source 2005-2008 2009 2009 2009Taggart Field 4.0 7.4 5.7 6.6Wells Field 6.1 8.7 8.6 8.6Francis Field 7.5 8.9 9.0 8.9Templeton Pi-ta 2.0 3.3 3.1 3.2Cybonnet Pi-ta 2.7 4.8 2.7 3.7Banks Pi-ta 3.7 5.3 2.5 3.9zStandard visual rating scale 0 to 9 where 0 = resistant (R) and 9 = very susceptible (VS).Panicle blast ratings were made at R7 to R8 growth stages when grain is filled but before grainbegins to mature.yUpland nursery plants were artificially inoculated in 4- to 6-leaf growth stage with multiple blastraces including IB-1, IB-49, IC-17, IE-1, IH-1, and IG-1. Upland plots were flooded as necessarywith plants being intermittently drought stressed during the growing season.68

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