RESPONSE OF A MAIZE SYNTHETIC TO S1 RECURRENT SELECTION FOR GRAIN-YIELD IN A DISEASE-STRESS ENVIRONMENT

The objective of our study was to evaluate the efficacy of selection for grain yield in a maize synthetic subjected to a disease-stress environment as a means of improving the population for grain yield and disease resistance simultaneously. The maize (Zea mays L.) synthetic BS19 was subjected to two cycles of S1 recurrent selection for each of three selection criteria: grain yield in the absence of significant disease stress; grain yield in the presence of both northern leaf blight (NLB, caused by Exserohilum turcicum (Pass.) Leonard and Suggs) and Diplodia stalk rot (DSR, caused by Stenocarpella maydis [Berk.] Sutton) induced stress; and resistance to NLB and DSR based upon a rank summation index. The original population (C0) and two advanced cycles (C1 and C2) for each of the three selection schemes were evaluated over two years in field trials for grain in the absence of disease stress, grain yield under NLB and DSR stress, and for NIB and DSR resistance per se. Grain yield in the absence of disease stress was increased an average of 6% per cycle by both selection for yield under NLB and DSR stress and selection for grain yield in the absence of disease stress, and an average of 3% per cycle with selection for disease resistance per se. Only selection for NLB and DSR resistance per se resulted in a significant gain (7% per cycle) in grain yield under NLB and DSR stress. Significant improvement in NLB resistance was observed with all three selection schemes. Resistance to DSR was significantly improved only with selection for disease resistance per se. The results of this study are in agreement with previously published theory. Selection for yield in the presence of disease stress appears, to be a viable, easy-to-use method for the simultaneous improvement of maize for grain yield and disease resistance.