Genetic enhancement of in vitro-culture derived tungro resistance rice breeding lines

Three rice tungro disease (RTD) resistant doubled haploid breeding lines (DHL), viz PR29264-AC10, PH29264-AC47, PR29264-AC31, were generated from anthers of the cross R2-8 x IR65 cultured in vitro. The DHL were genetically differentiated from the parent, IR65, using microsatellite markers. The resistance to RTD is controlled by single recessive gene. This study aimed to improve the RTD resistant DHL for agronomic and grain quality traits through single seed descent (SSD), characterize the SSD-derived advanced population, and determine the efficiency of SSD. With SSD all plants in the present generation are selfed, and single seed from each plant is used to obtain the next generation. PR29264-AC 10 and PR29264-AC 47 were crossed with RTD susceptible IR64. A total of 415 F2 plants were advanced through SSD. At F8 generation 198 (48 percent) lines were uniform, while 217 (52 percent) segregates for height and flowering. Among uniform lines, 142 (78 percent) had erect, while 40 (22 percent) had droopy leaves. Field evaluations were conducted for the F9 and F10 populations. Heading, maturity, plant height, culm length, productive tillers and yield were determined. Broad-sense heritability, h square, as indicator of performance repeatability, was computed for each trait from the analysis of variance. Heading, maturity, plant height and culm length are highly heritable (h square greater than 0.5), thus, may be used for selection at early generation. Genotype main effect account, for 21 percent to 42 percent of the total variation. Productive tillers and grain yield had low h square (h square less than 0.2), where 22 percent and 82 percent of the variation, respectively, was attributed to season main effect. Productive tillers and grain yield need to be evaluated for several seasons to make selection more effective. Of the uniform F8 lines evaluated for RTD, 13 (7.6 percent) were resistant (R), while 23 (13.5 percent) had intermediate (I) resistance. Nine lines with resistance to RTD were selected for their improved field performance and yield, and evaluated for grain physico-chemical qualities, with IR64 as the standard. Four lines have improved amylose content and reduced chalky grains. With improved genetic backgrounds, the RTD resistant SSD lines, serve as better parents, for use in the introgression of resistance into the new recipient genotypes. Moreover, the SSD advanced lines may be used as mapping populations to further study genetically the resistance conferred by the DHL, for molecular marker development, and ultimately, for cloning the gene.