Influence of time of planting and genotypes on leaf reddening, seed-cotton yield and productivity efficiency in Bt cotton (Gossypium hirsutum)

A field experiment was conducted during 2014–15 and 2015–16 at College of Agriculture, University of Agricultural Sciences, Raichur, Karnataka, India, to study the interaction between cultivars (‘Bindas’, ‘Bunny-Bt’, ‘ATM’ and ‘Dr. Brent’) and planting time (II fortnight of June, and I and II first fortnights of July and August) on leaf reddening, seed-cotton yield and productivity efficiency, and a new measure to assess reddening tolerance in Bt cotton (Gossypium hirsutum L.). Early sowing during June II fortnight particularly with cv. ‘Bindas’ showed lower leaf-reddening indices [0, 0, 0.62 and 0.86 at 90, 105, 120 and 135 days after sowing (DAS), respectively], higher seed-cotton yield (4.17 t/ha) and consequently higher productivity efficiency (0.48). However, higher leaf reddening (1.55, 1.99, 2.00 and 2.60, 1.67, 1.97, 1.99 and 2.56 at 90, 105, 120 and 135 DAS respectively) and lower seed-cotton yield (0.86 and 0.84 t/ha respectively) resulting in lower productivity efficiency (0.13 and 0.13 respectively) were registered with delayed sowing during II fortnight of August, particularly with reddening susceptible cultivars ‘Bunny-Bt’ and ‘Dr Brent’. In all, productivity efficiency emerged as effective inclusive tool in assessing leaf-reddening tolerance over leaf-reddening index alone in Bt cotton cultivars.