Identification of the CesA7 Gene Encodes Brittleness Mutation Derived from IR64 Variety and Breeding for Ruminant Feeding

Rice straw presents challenges as livestock feed due to its low digestibility and the presence of chemical residues. One potential solution is to focus on breeding brittle varieties that possess disease-resistance traits. In this study, AZ1803, a brittle mutant line isolated from the IR64 mutant pool, was chosen for gene identification and breeding. The AZ1803 mutant was crossed to the TNG67 variety to generate a mapping population and to the CS11 variety for fine mapping and breeding. The gene was mapped on chr. 10 between RM467 and RM171 SSR markers and was narrowed down to RM271 and RM5392 with 600 kb proximately interval. The AZ1803 and IR64 sequencing results revealed a substitution mutant in the Exon 9th of the OsCesA7 gene, resulting in an amino acid mutation at the end of the transmembrane domain 5th of the CESA7, responsible for cellulose synthesis for the secondary cell wall. The cellulose content of AZ1803 was reduced by 25% compared with the IR64. A new brittle and disease-resistant variety was bred by using developed markers in marker-assisted selection. In addition, bending tests and bacterial blight inoculation were applied. The bacterial lesion length of the bred variety is 64% lower than that of AZ1803. The rice straw of the new variety can be used for livestock feeding, which increases farmer income and reduces pesticide residues and air pollution from straw burning.