Date of this Version
Cantu, H. 2014. An evaluation of watermelon (Citrullus spp.) germplasm for additional sources of resistance to the twospotted spider mite (Tetranychus urticae Koch). M.S. Thesis. University of Nebraska-Lincoln. U.S.
Fourteen U.S plant introduction (PI) accessions of C. lanatus var. lanatus (4), C. lanatus var. citroides (5) C. colocynthis (5) and a known susceptible commercial cultivar ‘Sugar Baby’ were evaluated for resistance to the twospotted spider mite, Tetranychus urticae Koch, in a limited free-choice and free-choice bioassay under laboratory conditions. The limited free choice bioassay, involved nine Petri dish cages that held five randomly assigned leaves individually inoculated with two adult females and one adult male. Eggs, larva, and adults were counted over a nine day period. The free choice bioassay involved the even distribution of three mite infested pinto bean pots among the 15 accessions per tier under evaluation. Four tiers (syn. replications) consisting of fifteen randomized accessions were evaluated over a three week period. In both bioassays the two-spotted spider mite strongly preferred feeding and completing its life cycle on C. lanatus var. lanatus and C. lanatus var. citroides compared to C. colocynthis. Among the C. colocynthis accessions evaluated, PI 388770, PI 525080, and PI 537300 had consistently lower injury ratings and total mite populations (eggs, adults, larva) when compared to the other PIs and the susceptible cultivar ‘Sugar Baby’. Preliminary research indicated that feeding tolerance was also found to be significantly different by changing the way we did mite counts (i.e., uncut mite counts; excised leaf counts), but a more thorough study is needed. Ultimately, this study has identified two more possible sources of two-spotted spider mite resistance in PI 525080, and PI 537300 and adds further support for the already identified resistant PI 388770.
Advisors: Tom Hoegemeyer and P. Stephen Baenziger