In hot summer of July 2011, cotton bolls were sampled from the cotton crop in research area of Plant Pathology, University of Agriculture, Faisalabad. which look apparently healthy and full sized. Bolls were looking good and asymptomatic outside. Inside story was much different because when bolls were opened transversely, seed rottening with discolored lint (Fig.1) was seen. Fiber looked immature and hard locked. Diseased bolls were compact and failed to open properly. In early stages, bolls remained asymptomatic. Dark pink spots appeared on the outer boll surface laterly. Rotted seeds exhibit hollow and dark discoloration (Fig. 2).
As boll remains compact and does not open properly, pickers can’t pull out cotton easily. If lint is pulled out and mixed with normal, it lowers the cotton quality and earning.
Faisalabad and its nearby cotton fields (University of Agriculture, Faisalabad; Ayub Agriculture Research Institute, Faisalabad and Prokka village) were visited and diseased samples were observed. Problem was seen regardless to germplasm grown either Bt or conventional.
Problem was addressed in a number of ways. Isolation process was done to identify the suspected pathogen by using dilution plate technique. Creamy whitish bacterial colonies appeared and were purified. Pathogenicity tests were conducted on Bt-121 and FH-114 grown in green house conditions. At bolls maturity stage, 20μL bacterial suspension was injected breaching the endocarp of boll wall. In control, only sterile water was injected. Treated bolls were harvested after 15 days of treatment and opened cross-sectionally. Extensive seed rottening and lint discoloration was seen in bacterial treated bolls (Fig. 3).
Considering stink bugs as a possible disease vector, trials were conducted on red cotton bug (Dysdercus cingulatus). Diseased bolls were taken and bugs (taken from field) were fed for 2 days. After two days of acquisition feeding periods, bugs were shifted on healthy bolls (taken from green house grown plants). Bugs were killed by insecticides (Acetameprid @ 0.125%) and bolls were incubated at 25 °C for 15 days. Bolls were opened and diseased symptoms were observed (Fig.4).
Further studies (disease epidemiology, impact of boll age on disease severity, plant age effect on disease severity, role of foliar nitrogen application on disease severity and in vitro and in vivo management of disease through antibiotics, plant extracts and homeopathic products) were made and will be published soon.
Fig.1:-Effected bolls with seed and boll rot disease showing discolored lint.
Fig.2:- Rotted Seed
Fig.3:- Seed rottening and lint discoloration results after pathogensity test.