Rice grain quality as affected by blast-causing agent (Pyricularia oryzae) along with a molecular analysis of blast resistance at Pi5 and Pi-ta loci

摘要

Blast disease is the most devastating disease of rice worldwide, which reduces both quantity and quality of rice production. To assess the effect of fungal agent of blast, Pyricularia oryzae, on some aspects of grain quality of rice, 31 rice cultivars (including 20 local landraces) were evaluated at seedling and post-harvest stages. The cultivars were grown in three replicates in a field surrounded by blast spreader cultivars and at appropriate times blast infection type, grain infection, 100-grain weight and grain quality traits (percentage of broken rice and number of chalky seeds per panicle) were evaluated. For tracking alleles of two major blast resistance genes (including Pi5 and Pi-ta) the respective primer pairs were applied in a polymerase chain reaction (PCR) on DNA of the studied cultivars. Evaluation of blast infection type at seedling stage showed that four cultivars were completely resistant, 4 cultivars moderately resistant and 23 cultivars mainly consisted of local landraces were susceptible. Fungal treatment had significant effects on percentages of grain infection and broken rice and not on number of chalky seeds or 100-grain weight. Rice genotypes had significant differences in grain infection and also in 100-grain weight and in two quality traits including percentage of broken rice and number of chalky seeds. Most local landraces showed highest grain infection (14.4-17.6%) compared to improved modern varieties with lowest grain infection (1.3-2.7%). Results also showed that genotype by fungal treatment interaction were only significant for grain infection and broken rice. All susceptible cultivars had higher broken rice relative to resistant cultivars (10.5-13.3% vs. 2.1-4.6%) after blast infection. Molecular survey showed that most susceptible local landraces carry Pi5 dominant allele, while high-yielding modern cultivars don't carry the allele, indicating that Pi5 does not play a significant role in blast resistance at this time. Furthermore, molecular survey showed that only three cultivars including a local cultivar (Tetep) and two modern ones (IR56, IR24) harbored Pi-ta allele, and Pi-ta explained a high part of variation of blast resistance (R~2 =53.7%). These results indicate the importance of Pi-ta gene for improving rice blast-resistance and grain quality at blast infection conditions.