Screening and Identification of Disease-tolerant Genotypes of Parental Bt G. hirsutum, G. barbadense and H×B Hybrid Cotton with Enhanced Yields

Host plant resistance is a durable, permanent solution for effective disease management in cotton. It reduces agrochemical use, is eco-friendly and is durable. Field evaluation is a practical method to identify cotton genotypes with natural resistance to diseases, including H×B hybrids with higher yields.

Parental Bt G. hirsutum, G. barbadense and H×B cotton hybrids were screened under field conditions for Alternaria leaf spot (ALS), Tobacco Streak Virus (TSV), grey mildew, external boll rot and rust diseases. Pathological data were recorded at monthly intervals and PDI was calculated. Yield levels were compared with disease-tolerant H×B hybrids for selection.

Of sixty-six G. barbadense male parents, 19 entries, namely B1, B3, B8, B12, CCB26, ICB53, ICB58, ICB40(B), ICB183(B), CCB141, CB99, ICB284, CCB143(B), CCB25(B), CCB29(B), CCB11A(B), SM14, ICB86 and CCB64, were free from all diseases. Another 14 entries were disease-free, except for ALS. Five entries were free from all diseases except rust. Five entries were susceptible to most diseases. All four female G. hirsutum parents were infected with ALS and rust. Among 18 BG II G. hirsutum parents, V3 was free of all diseases. Ten entries were free from TSV and grey mildew but infected with ALS and rust. Seven entries were infected with ALS, TSV and rust. Among 50 H×B hybrids of BG I, six crosses, namely GJHV 374 Bt × ICB 28, GJHV 374 Bt × ICB 174, GJHV 374 Bt × ICB 194, Rajat Bt × CCB 141, Rajat Bt × ICB 75 and PKV 081 Bt × ICB 258, were free from all diseases. Four crosses were free of diseases except rust. ALS, TSV and rust were recorded in 14 crosses. Of the 14 BG entries, one entry, 211-437, was found free of all diseases. The entries 211-445 and GJHV 374 Bt were found disease-free, except for rust. Four entries, including 211-431, PKV 081 Bt, Rajat Bt and Suraj Bt, were infected with ALS, TSV and rust. All seven commercial BG II hybrids were infected with ALS and rust. Hybrids Ankur Anish, RCH659 and US7067 were also infected with TSV. The six H×B-F₁ BG I cotton hybrids that remained free of all the diseases studied and recorded higher seed cotton yields with improved fibre parameters. Hybrids, such as GJHV 374 Bt × ICB 264 and Rajat Bt × CCB 141, were free from ALS and TSV but showed rust incidence, yet maintained reasonably good yields and fibre quality.