No abstract

Bush type snap beans (Phaseolus vulgaris L.) with resistance to the root-knot nematode, Meloidogyne incognita (cotton strain) are being developed by using PI-165426 as the resistant parent. PI-165426 (resistant), ‘Black Valentine’ (susceptible) and F5 breeding line B3864 (resistant) were inoculated with second-stage larvae. There were no significant differences in larval penetration of roots. Root tips showed slight swellings at infection loci of resistant and susceptible plants. Necrosis was evident in the resistant lines 4 days after inoculation. Histological studies of early infections showed that resistance was due to absence of adequate giant cell development and to hypersensitive reaction within the infected portion of the root. When soil temperature was changed from 16 to 28°C, galling, female development, and egg mass production in the resistant plants were increased.

Field tests involving 47 pairs of snap bean breeding lines, near-isogenic except for differences in seed color, demonstrated that colored-seeded sub-lines were superior to their white-seeded counterparts in emergence and seedling vigor. In 11 yield comparisons between colored- and white-seeded isogenic sub-lines, the colored-seeded sub-lines outyielded their white-seeded counterparts by an average of 67%. Covariance techniques were used to adjust yields to remove stand effects. The results suggested that differences in stand based on seed color was a major factor affecting yield.