Germination of common bean under constant and alternating cool temperatures

Abstract

In western Canada, common bean is often sown in cool soils, which causes poor germination and uneven stand establishment. A major goal in bean breeding is to find and assess cold-tolerant parental material. Seed germination and emergence of 12 diverse common bean genotypes, which included adapted Prairie cultivars, were evaluated in petri dishes under 15 alternating and five constant temperature regimes. Cumulative heat hours to maximum germination were calculated for all 12 genotypes using a base temperature of 9°C. Six genotypes were tested for emergence in soil in growth chambers at two temperature and three soil moisture regimes. In petri tests, optimal temperatures for bean germination were 16/16°C (day/night temperature) or higher. G8823, G9345 and AC Polaris germinated below 10°C, and all genotypes germinated at 12°C or higher. Rapid germinating genotypes with >0.09 cumulative heat hours per percentage germination were G8823, G9345 and AC Polaris, which took the least number of cumulative heat hours to germinate (<1100 heat hours). CDC Pinnacle was the highest representative of the medium germination rate group, having 1170 heat hours to germination. Emergence and plant development in soil were decreased by low moisture availability or cooler temperatures. Genotypes with >80% emergence in soil were CDC Crocus, CDC Nighthawk, CDC Pinnacle and CDC Polar Bear. Differing genotype rankings in soil versus petri dishes demonstrated that germination in controlled cool conditions may still be complicated by dormancy, moisture availability, seed coat thickness, imbibition rate and differing viabilities of seed lots. G8823, G9345 and AC Polaris are promising genotypes for developing cultivars that can germinate under cool temperatures (<10°C) at the highest rate. Key words: Phaseolus vulgaris, common bean, germination, temperature