Diversity analysis of mutants from gamma-irradiated seeds of anther culture-derived line from traditional rice variety Pokkali

Pokkali is a salt-tolerant traditional rice variety with poor agronomic traits such as tall, photo-period sensitive, late maturing, with low grain yield. Seeds of an anther culture-derived line from Pokkali were irradiated with 250 Gy of gamma rays from 60Lo. From the resulting mutant populations, 10 promising mutant lines were identified, characterized phenotypically with 42 agro-morphological traits, and genotyped with 169 Simple Sequence Repeat (SSR) markers mapped across 12 rice chromosomes. Phenotypic variation was observed in 16 (38%) morphological, 11 (26%) agronomic and 4 (10%) grain quality traits. The lines were separated from the wild type by 13.9%. Euclidean distance, computed from agro-morphological traits. Principal Component Analysis identified plant height, culm length, filled and unfilled grains, and spikelets per panicle as contributing traits to the observed variation. At molecular level, 95 of 169 (60%) SSR markers were polymorphic, and were used for analysis. A total of 279 alleles were amplified, ranging from two to eight, with an average of three alleles per locus. Genetic Diversity Index ranged from 0.1653 to 0.8430, averaging 0.4826. Polymorphism Information Content (PIC) of the markers, ranged from 0.1515 to 0.8254, with an average of 0.4017. A total of 32 highly polymorphic markers were identified, with PIC values of 0.5124 to 0.8254. Cluster analysis by Simple Matching Coefficient (SMC) using NTSYS 2.0 (Rohlf, 1998) separated the 10 mutant lines from the wildtype, with 40% similarity. A similarity of 49% within the lines was observed. Seven SSR markers amplifying the SalTol QTL region conferring salt tolerance at seedling stage generated amplicons in 4 (40%) lines, which were phenotyped as salt tolerant. This study confirmed that phenotypic and genetic variability exist among the lines and between the lines and wildtype, supporting the effectiveness and potential use of mutation in variety improvement.