Selection for chilling and freezing resistance in common bean
Balasubramanian, Parthiba Murugaraja
Suboptimal seedbed temperatures (<15°C) in early spring, and risk of late spring- and early fall-frosts are detrimental to dry bean (Phaseolus vulgaris L.) production on the northern prairies. This study: i) determined the effects of suboptimal seedbed temperatures on dry bean seedling emergence and yield; ii) evaluated diverse accessions of cultivated and wild bean for emergence at suboptimal temperatures; iii) investigated freezing resistance in Phaseolus species; and iv) obtained interspecific hybrids between frost sensitive P. vulgaris and frost resistant P. angustissimus. The mid May planting of dry bean cultivars in 1999 and 2000 resulted in lower emergence (74 to 89%) compared to the late May planting (93 to 95%). However, highest yield was obtained in 1999 with the mid May planting, partly because two indeterminate cultivars, failed to mature prior to the first fall frost, when planted in late May. When common bean accessions were planted on May 3, 2000, G8823 had the highest emergence at 20 days after planting. The check cultivar CDC Nighthawk was comparable to G8823 at 30 days after planting. A similar trend was observed in 2001 except emergence was higher in later sampling times due to a warmer seedbed. Accessions with low cumulative thermal units to anthesis, however, were not necessarily early in maturity. G8823 was the only accession with consistent early emergence, early anthesis and early maturity in both years. Leaflets of wild relatives of common bean showed extensive supercooling and their LT50 in the presence of external nucleators was 0.5 to 1°C lower compared to the cultivated species. Exposure to cold acclimating temperatures had no effect in enhancing freezing tolerance of Phaseolus species. Phaseolus angustissimus had the highest seedling survival (55 to 85%) in response to both the fall frost of 2000 and the spring frost of 2001 when the minimum air temperatures were below -5°C. Frost sensitive common bean was crossed as the female parent with the frost resistant P. angustissimus to obtain F1 interspecific hybrids. In reciprocal crosses, flowers aborted at three days after pollination. Interspecific hybrid plants grew to produce flowers, but failed to set seed. The mid May planting of dry bean cultivars will result in higher seed yield compared to the late May planting in years with a mid September or earlier frosts. Successful introgression of both resistance to suboptimal seedbed temperatures during emergence (accession G8823) and frost resistance (P. angustissimus) into common bean may expand the gographic distribution of bean crop to higher altitudes and latitudes.