muhammad iqbal*, Sami Ul-Allah
Department of Plant Breeding and Genetics, UCA&ES, The Islamia University of Bahawalpur-PAKISTAN
Cotton (G. hirsutum) is a crop of tropical and subtropical regions but despite of this, it is highly sensitive to heat stress. Heat stress during flowering and boll growth period cause shedding of flowers and bolls which cause a significant loss in yield. There is only a little information is available which describes the effect of high temperature on development of fruiting parts in cotton. Therefore an experiment was conducted to assess the effect of heat stress on development of reproductive parts. A two year experiment was laid out in randomized complete block design with four replications and three factors during 2013-15. The factors included four sowing dates (1 April, 1 May, 30 May and 30 June) and three cotton cultivars (IUB-222, IUB-13 and IUB-63). Flowering in early sowing (1 April and 1 May) initiated during high temperatures of June and July and these are taken as heat stressed whereas flowering in late sown (30 May and 30 June) initiated during optimum temperatures of august and September and these were taken as non-stressed. Data was collected for daily mean temperature, days taken to initiation of square development, days taken from square to flower, days taken from flower to boll open, boll retention, boll size, seed weight, seed volume, seed density and seed surface area. The analysis of variance revealed that significant (P≥0.05) genotypic and sowing date diﬀerences existed for all studied traits and genotype × sowing date interaction was also significant (P≥0.05). The results revealed that heat stress decreased the days taken for initiation of square development, days taken from square to flower and flower to boll open, boll retention, and boll size. Due to reduction in boll retention and boll size there was reduction in the yield. All seed traits seed weight, seed volume, seed density and seed surface area reduced with heat Correlation analysis revealed that mean daily temperature had significant (P≥0.05) negative correlation with all the traits studied. The genotype IUB-63 performed best and was least affected by the heat stress, so proved as heat tolerant genotype. It is conclude from the results that fruit development traits and seed physical traits can be an effective selection criteria for heat stress breeding.