Novel cotton germplasm with host plant resistance to twospotted spider mite

Host plant resistance to twospotted spider mite (Tetranychus urticae Koch) in cotton is desirable to reduce crop damage, as well as to reduce or eliminate pesticide use targeted at this pest. A range of Gossypium genotypes were evaluated over two crop seasons and their resistance identified in terms of spider mite population development, leaf damage and effect on cotton yield and fibre quality. There were low to moderate numbers of spider mites on Gossypium hirsutum L. race lines and a Gossypium barbadense L. cultivar and extremely low numbers in accessions of Gossypium arboreum L., Gossypium thurberi Tod. and Gossypium trilobum (DC.) Skovst. compared with commercial cultivars. Mites reduced lint yield of the three G. hirsutum genotypes (Sicot 71, Siokra 24 and 81024-15) but had no significant effect on yield of the two G. arboreum genotypes, BM13H and Roseum A256 in either season. Yield loss was related to leaf area damaged by mites. BM13H, Roseum A256 and Sipima 280 were classified as mite-resistant, in terms of low mite numbers, low amount of leaf damage per mite and low yield loss per mite. In addition, the genotypes of G. thurberi (GOS5310), G. trilobum (GOS5332) and G. hirsutum race line (TX111) were also defined as mite-resistant, in terms of low mite numbers, low amount of leaf damage per mite, although there are no yield data because these genotypes are photoperiod sensitive and did not flower during the experiments. These mite-resistant genotypes can be candidates for the development of mite-resistant upland cotton cultivars.