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 f or grain yield in a maize synthetic subjected to a disease-stress envi ronment as a means of improving the population for grain yield and dis ease resistance simultaneously. The maize (Zea mays L.) synthetic BS19 was subjected to two cycles of S1 recurrent selection for each of thr ee selection criteria: grain yield in the absence of significant disea se stress; grain yield in the presence of both northern leaf blight (N LB, caused by Exserohilum turcicum (Pass.) Leonard and Suggs) and Dipl odia stalk rot (DSR, caused by Stenocarpella maydis [Berk.] Sutton) in duced stress; and resistance to NLB and DSR based upon a rank summatio n index. The original population (C0) and two advanced cycles (C1 and C2) for each of the three selection schemes were evaluated over two ye ars 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 signif icant gain (7% per cycle) in grain yield under NLB and DSR stress. Sig nificant improvement in NLB resistance was observed with all three sel ection schemes. Resistance to DSR was significantly improved only with selection for disease resistance per se. The results of this study ar e in agreement with previously published theory. Selection for yield i n the presence of disease stress appears, to be a viable, easy-to-use method for the simultaneous improvement of maize for grain yield and d isease resistance.