Improvement of Rice Resistance to Sheath Blight by Pyramiding QTLs Conditioning Disease Resistance and Tiller Angle

Rice resistance to sheath blight(SB) is controlled by polygenes or quantitative trait loci(QTLs) and affected by plant morphological traits. q SB-9TQ and TAC1 TQ, which control SB resistance and tiller angle(TA), respectively, were employed to test whether the combination of the two genes will further improve rice SB resistance and reduce yield loss rather than only one of them or neither. Using two pairs of near isogenic lines(NILs), TAC1 TQ was confirmed to contribute to SB resistance. However, its effect was less considerable than that of q SB-9TQ. Subsequently, the two genes were introduced into two commercial rice varieties to develop a series of NILs. The NILs carrying both TAC1 TQ and q SB-9TQshowed more resistance than the NILs containing only one of them. Comparing the grain yield per plant(GYP) under the three different SB disease conditions, namely slight, moderate and severe conditions, NILs carrying both genes apparently lost lower GYP than the NILs without the two genes and the NILs carrying only TAC1 TQ. Under slight disease condition, no significant differences were found on morphology, development and GYP associated traits except for TA between the NILs carrying both genes and either of them, indicating that the two genes have no inferior effect on rice agronomic traits. Results indicated that TAC1 TQ and q SB-9TQ have high breeding potential, and pyramiding SB resistance QTL and morphological trait QTL is a potential approach in improving rice SB resistance.