Incidence of bacterial blight and Alternaria leaf spot in Bt cotton.

摘要

A field experiment was conducted during 2002-03 in Meerut, Uttar Pradesh, India, to investigate the disease incidence in some released Bacillus thuringiensis (Bt) cotton cultivars (MECH-915 and MECH-162), their non Bt counter parts along with some popular hirsutum hybrids (Om Shankar and LHH 144) and local hirsutum cultivars (H-1098 and Vikas). The incidence of bacterial blight (Xanthomonas axonopodis pv. malvacearum [X. citri subsp. malvacearum]) and Alternaria leaf spot (Alternaria spp.) was recorded at 86 and 106 days after sowing (DAS). The bacterial blight was noticed in the last week of July and thereafter its severity increased gradually reaching the peak by the end of August. The highest disease severity was recorded in MECH-915 (Bt) with percentage disease index (PDI) of 17.62 at 86 DAS and 56.39% at 106 DAS, whereas in its non-Bt counter part the PDI was as low as 3.22 and 18.62%, respectively. MECH-162 (Bt) also recorded considerable disease severity (PDI=25.95%) at 106 DAS, whereas its non-Bt counterpart showed the lowest incidence of blight (PDI=15.84%) among all the genotypes. The Alternaria leaf spot appeared after the bacterial blight. It was first noticed in the 1st week of August. Its severity was low compared to bacterial blight. The highest disease severity was recorded in MECH-915 (Bt) with PDI of 1.91% at 86 DAS and 2.95% at 106 DAS. The lowest incidence of this disease was recorded in MECH-162 (non-Bt) with PDI of 0.66% at 86 DAS and 1.09% at 106 DAS. The highest seed cotton yield (2.25 t/ha) was obtained in MECH-915 (Bt) followed by its non-Bt counterpart (2.16 t/ha). The lowest yields were recorded in Vikas and Om Shankar (1.56 and 1.58 t/ha).