Tolerance to sub-zero temperatures in Phaseolus acutifolius and interspecies hybrids between Phaseolus vulgaris and P. acutifolius

Abstract

Dry bean (Phaseolus vulgaris) is a sub-tropical crop severely affected by exposure to low temperatures during all of its growing stages. Cool spring temperatures and the risk of frost are major limiting factors for the early sowing of dry bean in Saskatchewan. Due to its economic importance; however, it has been introduced to Saskatchewan, but it needs to be made more cold tolerant to further expand acreage. The genes that can contribute some tolerance to low temperature stress in bean are not found within the primary gene pool, which limits the capability of breeders to generate a cultivar with such characteristics. Consequently studies have being done in order to find a possible source of genes that can induce tolerance to low temperature exposure. Phaseolus acutifolius is a relative of the domesticated dry bean and previous hybridizations with it have been successful. It is also known to be tolerant to abiotic stresses such as drought. For this reason the decision was taken to explore the level of resistance to low temperature stress exposure in several P. acutifolius accessions. Using whole plant freezing tests in controlled environment chambers, P. acutifolius W6 15578 was found to be more tolerant to exposure to sub-zero temperatures than were P. vulgaris genotypes. Interspecies hybrids were produced between P. vulgaris NY5-161 and W6 15578 and BC2 plants were produced using embryo rescue. The whole plant freezing test is a destructive method that cannot be used with unique F1 and BC2 genotypes, so an alternative methodology to evaluate the hybrids was explored. An electrolyte leakage test was used and showed similar results to the whole plant freezing test with the parent plant controls. The F1 hybrids had an intermediate tolerance to low temperature stress and the further generations (BC1 and BC2) had a better level of tolerance to this kind of stress than the cultivated parent (NY5-161). This suggests that the genes that confer tolerance to low temperature exposure are being maintained through several generations of backcrossing and that these interspecies hybrids may offer a chance for the development of improved dry bean cultivars for the Saskatchewan environment.