Agro-morphological characterization of early flowering rice mutants induced by gamma irradiation

Early flowering (EF) rice mutants were developed from Talang Sirah, a local rice variety originating from Solok, Indonesia, which is locally favored, but its availability remains limited due to late flowering and low yields. The study focuses on characterizing these EF mutants and assessing agro-morphological and yield traits in field trials.

Seeds of the Talang Sirah genotype were exposed to a 300 Gy dose of gamma rays from cobalt-60 as a radiation source. The EF trait was confirmed in the M₃ generation, and the screening and selection processes for the eight mutant lines were extended until the M₈ generation. Agro-morphological traits were evaluated in the field, while the data were analyzed using correlation, principal component analysis (PCA), and cluster methods, including dendrogram, partitioning around medoids (PAM), and parallel coordinates plot (PCP) analyses.

Talang Sirah flowered at approx. 126 days, whereas all mutants exhibited flowering times at 26 to 34 days earlier. Four mutants (TSG132, TSG134, TSG139, and TSG140) showed a grain yield (>8.2 t ha^-1), which was higher than the WT and the national variety (Ciherang), i.e. 5.2 and 6.47 t ha^-1, respectively. Based on PCA analysis (87.32% of the total variation), a very close and a moderate association was observed between the number of tillers, 1000-grain weight (g), and grain yield (g). All analyses separated genotypes into three clusters (average silhouette at 0.45) for all genotypes, confirming that Talang Sirah and Ciherang were completely distinct. Meanwhile, all mutants formed a large cluster with subtle differences (early vs. high-yielding mutants). In further analysis, two clusters were identified among mutants, where all mutants showed early flowering and harvesting, except for TSG136.

These findings confirmed that gamma-ray irradiation improves genetic variation associated with EF, agronomic traits, and yield improvement in local rice germplasm.