Reaction of Maize Hybrids and Inbreds to Southern Corn Leaf Blight1

Abstract

AbstractThe southern corn leaf blight (SCLB) epidemic of 1970, caused by Bipolaris maydis (Nisikado) Shoemaker, race T, decreased yield of maize (Zea mays L.) 15% nationwide. Use of Texas male‐sterile cytoplasm (T) in the production of hybrids was an important factor in the severity and spread of SCLB. Some information, however, indicated that some T‐cytoplasm lines showed more tolerance to SCLB infection than others in 1970. Our primary objective was to determine the effects of SCLB infection on inbred lines that had shown a differential reaction to SCLB in T cytoplasm. Inbred lines and hybrids produced among the inbred lines were evaluated.Nine inbred lines and 144 reciprocal single crosses produced on normal (N) and T cytoplasm were artificially infected and compared in greenhouse seedling and field tests for reaction to SCLB. Data also were obtained in the field tests for yield and five other agronomic traits.Correlations of the greenhouse tests with the field tests for SCLB infection were 0.56* (* significant at the 1% level) for the inbred lines and 0.65* for the single crosses. On the average, the inbred T‐cytoplasm lines averaged 8.4% less than those on N cytoplasm; B67TRfRf, however, was 55.3% lower yielding than its N counterpart. The effects of SCLB infection on yield for the T‐cytoplasm single crosses were greater than for the inbred lines. The 72 T‐cytoplasm single crosses averaged 19.9% less yield than the 72 N‐cytoplasm single crosses. Yield losses using hybrids produced on T cytoplasm ranged from 13.4% for B68 × Mol7 to 37.2% for B67 × W64A; B68 and Mol7 were classified as relatively resistant and B67 and W64A as being susceptible to SCLB in T cytoplasm. Our results show that inbred lines express different levels of reaction to SCLB infection in T cytoplasm.