SCREENING OF COTTON (GOSSYPIUM HIRSUTUM L.) GENOTYPES FOR HEAT TOLERANCE

Cotton yield is highly affected due to biotic (diseases and pests) and abiotic (heat, dought and salinity) Stresses. Among them, high temperature is the main environmental constraint which adversely reduces cotton yield and quality. High temperature above 36 degrees C affects plant growth and development especially during reproductive phase. Present studies were carried out to assess the tolerance of fifty-eight newly evolved cotton genotypes to heat stresses, based on agronomic and physiological characteristics. The genotypes were screened in field conditions under two temperature regimes. The studies were conducted at experimental farm of Nuclear Institute of Agriculture, Tando Jam, Pakistan. The results showed that March sown crop experienced high temperature (i.e. > 44 degrees C in May and June), which significantly affected crop growth and productivity. The genotypes were identified as heat-tolerant on the basis of relative cell injury percentage (RCI %), heat susceptibility index (HSI) values, boll retention and seed cotton yield (kg/ha). RCI level in cotton genotypes ranged from 39.0 to 86.0%. Out of 58, seventeen genotypes (viz. NIA-80, NIA-81, NIA-83, NIA-84, NIA-M-30, NIA-M31, NIA-HM-48, NIA-HM-327, NIA-H-32, NIA-HM-2-1, NIA-Bt1, NIA-Bt2, NIA-Perkh, CRIS-342, CRIS-134, NIAB-111 and check variety Sadori indicated high level of heat tolerance at both (heat-stressed and non-stressed) temperature regimes; as shown the lowest relative injury level and relatively heat resistant index (HSI<1) values. Such genotypes could be used as heattolerant genotypes under heat-stressed environments.