RESISTANCE TO DROUGHT AND DENSITY STRESS IN CANADIAN AND EUROPEAN MAIZE (Zea mays L.) HYBRIDS

Early-maturing maize hybrids of North American and European origin were studied at two locations in Ontario (Elora and Guelph) and two tests at Lethbridge, Alberta (with and without irrigation) in 1979 and 1980 to (1) evaluate whether hybrids tolerant of high densities were also relatively more resistant to drought stress, and (2) identify morphological or physiological traits related to density tolerance and drought resistance. Twelve hybrids were grown in 1979 and six in 1980. Hybrids were grown at three densities 30 000, 60 000 and 90 000 plants/ha) in Ontario and four densities (25 000, 50 000, 75 000 and 100 000/ha) at Lethbridge. Data collected in 1979 included measurements of grain yield (analyzed as In (yield/plant)), date of mid-anthesis (MA), days from mid-anthesis to mid-silking (DAS), percent of second ear silking, tassel dry weight, leaf water potential, leaf stomatal conductance, and leaf area index (LAI). Grain yield, MA, DAS, and LAI were monitored in 1980. A significant hybrid-by-density interaction for In (yield/plant) was observed in the Ontario tests. Linear regression coefficients of In (yield/plant) vs. density for the individual hybrids served as indices of relative density tolerance. A significant test-by-hybrid interaction at Lethbridge was used as a basis for computing indices of drought resistance. The two indices were correlated (r = 0.75, P < 0.01) in 1979, but not in 1980 (r = 0.62, P > 0.05). The two measures of stress tolerance or resistance were correlated negatively with MA, DAS, and LAI, but not with other plant traits measured. Screening for density tolerance and for early date of silking relative to anthesis could be beneficial in breeding for drought resistance.Key words: Maize, drought, hybrids, plant-density, resistance