Screening Common Bean (Phaseolus vulgaris) for Resistance to Tomato yellow leaf curl virus

Commercial cultivars of common bean (Phaseolus vulgaris) were screened for resistance to Tomato yellow leaf curl virus (TYLCV). Fourteen-day-old bean plants were inoculated with TYLCV by means of the whitefly vector (Bemisia tabaci). Following inoculation, plants were sprayed with an insecticide, kept in an insect-proof greenhouse for 4 weeks, and monitored for disease symptom development. The presence of viral DNA in the inoculated plants was assayed by dot blot hybridization and by polymerase chain reaction. Out of the 42 cultivars that were tested, 24 were found to be susceptible: the plants exhibited severe symptoms and accumulated high levels of viral DNA. In all, 18 cultivars were found to be resistant to the virus: 1 cultivar showed mild symptoms while the other 17 showed no symptoms following inoculation. From the 17 symptomless cultivars, plants of 3 cultivars contained viral DNA while no viral DNA was detected in the plants of the other 14 cultivars. When the effect of bean plant age on viral inoculation by whiteflies was assayed, it was found that the success rate of TYLCV infection was highly dependent on bean plant age. When 14-day-old susceptible bean plants were inoculated, nearly 100% infection was achieved but, when 26- or 12-day-old plants of the same cultivar were inoculated, the infection rates were only 34 and 40%, respectively.