Root Traits Play a Role in Integrated Management of Fusarium Root Rot in Snap Beans

Fusarium root rot is a major limiting factor in snap bean (Phaseolus vulgaris L.) production. The level of genetic resistance in commercial bean cultivars is minimal and disease is frequently exacerbated by environmental factors. We investigated the contribution of vigorous, adventitious roots to enhancing root rot tolerance in snap bean. Seedling root system architecture was evaluated in 17 recombinant inbred lines (RILs) from a cross of a resistant snap bean line (FR266) and a susceptible dry bean cultivar (Montcalm). The RILs varied in tolerance to Fusarium root rot. Although overall length and branching density (as measured by fractal dimension and meristem numbers) of root systems were not related to root rot resistance, the lateral root number at the root: shoot interface was positively correlated with genotype tolerance (R 2 = 0.6*). Root diameter was also positively correlated with tolerance; this is consistent with the hypothesis that larger adventitious and basal roots are beneficial under disease stress. A field-based study of commercial snap bean cultivars compared raised and flat-bed systems of production, in a soil inoculated with Fusarium solani f. sp. phaseoli. Substantially greater yields (40% to 90%) were observed in raised beds. Root vigor was relatively high (root length density >0.2 cm.cm -3 ) and root rot scores were lower with raised than with flat-beds, in 2001, but not in 2000. Overall, this is suggestive that integrated crop management practices can improve lateral root vigor and reduce root rot severity.