Use of a detached leaf screening method for segregating Colorado potato beetle (Leptinotarsa decemlineata Say) resistant Solanum hybrid lines

A diploid segregating population for resistance to Colorado potato beetle (CPB) was developed by crossing the resistant Mexican species Solanum pinnatisectum (S. pnt., 2n = 2.v = 24) with the Susceptible S. cardiophyllum (S. (cph., 2n = 2x = 24). A resistant hybrid plant from this cross was selected and backcrossed as a female to S. cph ill order to generate a backcross family. A beetle feeding preference test bioassay was developed to examine segregation for CPB resistance ill 345 backcross progeny. A screening method that optimized the length of the feeding period allowed the quantification of CPB resistance in the backcross progeny. Percent resistance of the test lines over the Susceptible control was determined using the formula R = 100 x [C/(C + L)] where C and L indicated the amount of damage to the control and test line, respectively, in each Petri dish. All backcross progeny showed ail acceptable normal distribution only after 4 and 8 h of feeding. The expression of resistance in the backcross population for this study varied not only among the progeny, but also was influenced by duration of exposure to CPB. A chi(2) test of 1 R:3S ratio of the 8-h data indicated that CPB resistance was controlled by two genes. Of he five feeding time exposures (4, 8, 12, 20 and 24 h) used in this Study, the 8-h exposure was shown to be the optimal time for evaluating resistance to CPB in our potato hybrids.