RESISTANCE TO 2-SPOTTED SPIDER-MITE TETRANYCHUS-URTICAE IN STRAWBERRYCULTIVARS AND WILD-SPECIES OF FRAGARIA AND POTENTILLA

Cultivars of strawberry and wild species of Fragaria and Potentilla we re tested for resistance to two-spotted spider mite, Tetranychus urtic ae, mainly by recording the numbers of eggs laid over a standard perio d. On some clones of F. chiloensis significantly fewer eggs were laid than on the standard, cv. Elsanta, in no-choice tests, and fewer eggs were laid on clone DL-40 than 'Elsanta' in a choice test. Differences were detected in the numbers of eggs laid on individual strawberry cul tivars tested, but, as with the F. chiloensis clones, the results of t he experiments showed inconsistencies. The number of eggs laid and the time for development from egg to adult were similar overall on newly- propagated plants and one year old plants that had experienced dormanc y and chilling. However, some cultivars, and clone DL-40, gave results significantly different from 'Elsanta' for these parameters. Results from experiments with the progeny of crosses using cultivars/clones sh owing reduced fecundity did not suggest the involvement of major genes , since there was no clear segregation between resistant and susceptib le categories in either the F1 or F2 generations. No reductions in the numbers of eggs laid were found in the species of Potentilla tested.