Occurrence of the exotic mite Schizotetranychus krungthepensis (Acarina: Tetranychidae) in sugarcane germplasm in India

Abstract The exotic leaf mite Schizotetranychus krungthepensis Naing & Auger (Acarina: Tetranychidae), recorded on sugarcane in Thailand in 2014, began appearing on sugarcane in different states of India recently. Its occurrence in a severe form was noticed in sugarcane germplasm being maintained at the ICAR-Sugarcane Breeding Institute Research Centre, Kannur, Kerala State, during April – December in 2016 and 2017. The incidence of the mite was assessed in the International Society of Sugar Cane Technologists (ISSCT) collection of Saccharum spontaneum L. accessions (79) and Indian hybrids (260). In S. spontaneum, infestation rate (cane basis) was the lowest (66.67%) in IS 76-151. Intensity of attack (leaf basis) was the lowest (42.48%) in IS 76-164 and highest (99.28%) in SH 61-4-1 with infestation index ranging from 42.48 to 99.28. On the basis of infestation index, 76 out of 79 accessions (96.2%) were highly susceptible, three (3.8%) moderately susceptible and none least susceptible. In Indian hybrids, mite infestation ranged 1.8-100.0%; more than 60.0% accessions showed >50.0% infestation rate. Recently developed Indian hybrids showed a maximum of 20 web rows/leaf and more than 1000 webs/leaf which, however, did not differ significantly among the hybrids. Infestation parameters in the germplasm examined were not influenced by quantitative and qualitative morphological characters. A method developed to assess leaf damage from web density and mean web area indicated an approximate 11.79% leaf area loss due to the mite. Resistant sources thus identified from both S. spontaneum and Indian hybrids would be useful for introgression to evolve hybrids with mite resistance.