Rice Genetics IV - IRRI books - International Rice Research Institute

Table 1. Frequencies of mutations observed in IR64 populations treated with three mutagens.TreatmentMutant phenotype Gamma ray Diepoxybutane Fast neutronObserved (no.) % Observed (no.) % Observed (no.) %Zebra 1/482 0.21 1/500 0.07 2/531 0.38Spotted leaf (spl1) 2/1,000 0.20 2/3,000 0.07 1/2,000 0.05Elongated upper internode 1/100 0.10 1/1,500 0.07 1/531 0.18White stripe 1/482 0.21 2/1,500 0.13 1/336 0.30Extra glume 2/425 0.47 0/1,500 0 1/531 0.18Gold hull 1/1,000 0.10 1/1,500 0.07 2/531 0.38Table 2. Categories of IR64 disease-response mutants against blast and bacterial blight.Number of mutants resistant to bMagnaporthe Xanthomonas oryzaeMutation Morphology a grisea races pv. orzyae races BothdiseasesSingle Multiple Single MultipleLoss in resistance Normal 0 2 2 1 –Gain in resistance Normal 2 3 2 – 3Abnormal 2 – 2 – 2Lesion mimics Normal – – – – –Abnormal 0 – 16 – 3aAbnormal morphology includes dwarfing, stunting, and reduced tillering. b Numbers refer to mutantsgenetically confirmed by M 3 segregation data. Four M. grisea isolates representing diverse genetic groupswere used to screen for susceptibility to blast. Xoo isolate PXO61 was used to screen for a change fromresistance to susceptibility to bacterial blight. PXO99 was used to screen for a change from susceptibilityto resistance. – = mutant class has not been found.tion, such as flowering time, number of tillers, and degree of sterility. More carefulobservation in quantitative variation is expected to yield additional mutants.Biotic stressesTo identify genes involved in broad-spectrum resistance, we have searched for mutantswith a gain or loss in resistance to multiple races of a pathogen and to multiplepathogens. We have screened about 10,000 lines for altered response to the blastfungus Magnaporthe grisea and the bacterial blight pathogen Xanthomonas oryzaepv. oryzae (Xoo). About 0.3% of the mutants showed altered response to the pathogens.The observed mutation frequencies are similar to those found in other plantspecies mutagenized by chemicals or irradiation (Okubara et al 1994). Single-geneinheritance has been confirmed in approximately 30 mutants with altered response toone or two pathogens (Table 2). Of special interest are those mutants with a loss orgain in resistance to multiple races of one or more pathogens. For example, a gammaray-inducedmutant GR-740-12-8 shows a loss in resistance to five of six races ofXoo to which IR64 is resistant and enhanced susceptibility to four races. SegregationDeletion mutants for functional genomics: . . . 243