Hybrid Rice Outperforms Inbred Rice in Resistance to Sheath Blight and Narrow Brown Leaf Spot

Sheath blight (ShB, caused by Rhizoctonia solani AG1-1A) and narrow brown leaf spot (NBLS, Cercospora janseana) are among the most important diseases affecting rice production in Texas and other southern United States. Because of high yielding potential, hybrid rice acreage has continually increased. Understanding the relative levels of resistance to ShB and NBLS in hybrids over inbreds is important to effective disease management but remain largely unknown. Comparative performance of hybrid rice and inbred rice was evaluated with 173 hybrid and 155 inbred genotypes (cultivars and elite breeding lines) over five crop seasons (2016 to 2020) and two locations in Texas. The results show that genotype, cultivar type (hybrid or inbred), location, and their interactions had a significant effect on the severity of ShB and NBLS. ShB severities in hybrid genotypes were significantly lower than in inbred genotypes, with an average of 27% reduction in disease severity over the 5 year x 2 location evaluation. Most (53%) of the hybrid genotypes were rated moderately resistant (MR), whereas almost all (97%) of the inbred genotypes ranged from very susceptible (VS) to moderately susceptible (MS). Similarly, NBLS severities in hybrid genotypes are significantly lower than those in inbred genotypes. All but four hybrid genotypes exhibit immune reaction to NBLS. In contrast, 77% of the inbred genotypes exhibit the NBLS symptoms, with disease resistance reactions ranging from susceptible (S) to resistant (R). The results demonstrate that hybrid rice is generally less susceptible to sheath blight and has a higher level of resistance against NBLS compared to inbred rice.