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

Abstract

Early-maturing maize hybrids of North American and European origin were studied at 2 locations in Ontario (Elora and Guelph) [Canada] and 2 tests at Lethbridge, Alberta (with and without irrigation) in 1979 and 1980 to evaluate whether hybrids tolerant of high densities were also relatively more resistant to drought stress, and to identify morphological or physiological traits related to density tolerance and drought resistance. Hybrids (12) were grown in 1979 and 6 in 1980. Hybrids were grown at 3 densities (30,000, 60,000 and 90,000 plants/ha) in Ontario and 4 densities (25,000, 50,000, 75,000 and 100,000/ha) at Lethbridge. Data collected in 1979 included measurements of grain yield (analyzed as ln (yield/plant)), date of mid-anthesis (MA), days from mid-anthesis to mid-silking (DAS), percent of 2nd 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 ln (yield/plant) was observed in the Ontario tests. Linear regression coefficients of ln (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 2 indices were correlated (r = 0.75, P < 0.01) in 1979, but not in 1980 (r = 0.62, P > 0.05). The 2 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.