Pak. J. Agri. Sci., Vol. 44(1),2007 COMPARATIVE GROWTH AND LEAF IONIC COMPOSITION OF FOUR COTTON (Gossypium hirsutum L.) GENOTYPES IN RESPONSE TO SALINITY Shahid Pervaiz, M. Saqib, Javaid Akhtar, M. Atif Riaz, M. Anwar-ul-Haq and M. Nasim Saline Agriculture Research Centre, University of Agriculture, Faisalabad, Pakistan Corresponding Author's e-mail: shahidsarc@gmail.com Salinity is a major limiting factor for crop production around the globe. Besides many reclamation strategies, selection of crop cultivars tolerant to salinity can also improve crop production on salt affected lands. The present experiment was planned to study growth and ionic composition of four cotton genotypes as affected by salinity. Genotypes were grown either under salinity (150 mol m,3 NaCI) or under normal conditions and were compared for growth and leaf ionic composition. NaCI salinity significantly decreased shoot as well as root growth of all the cotton genotypes. The concentration of Na" and cr were significantly increased in the leave of plants grown under salinity whereas the K+: Na+ ratio was decreased. Cultivars differed significantly for both growth and ionic composition. Genotype CIM-446 performed better under salinity and was categorized as a relatively salt-tolerant genotype. The order of the salinity tolerance of the cotton genotypes is CIM-446 > NIAB-98 > NIAB-999 > Krishma. The tolerant genotype CIM-446 accumulated lower Na+ and cr in its leaves and maintained higher K+: Na' ratio. Keywords: Cotton, genotypes, growth, ion imbalance, K+: Na+ ratio and salinity. INTRODUCTION The excessive accumulation of salts in soils of arid and semi-arid regions is a potential factor for limiting crop production from irrigated agriculture. Low precipitation accompanied by high evapotranspiration results in salt accumulation in the root zone which hinders plant growth. Salinity affects seed germination, growth and reproduction with induced changes in anatomy and morphology of plants. A decline in total leaf area is often first detectable response to salt stress in crop plants (Bradford and Hsiao, 1983). Increase in leaf area has been found to be more sensitive to salinity than either leaf emergence rate or dry matter accumulation (Curtis and Lauchli, 1985). Different plant species differ in their salinity tolerance. Some plant species are tolerant e.g., barley, cotton and sugar-beet, some are moderately tolerant, e.g. rye, sunflower, sorghum and soybean where as some are salt-sensitive, e.g., carrot, okra, onion and peas (Maas, 1986). Genetic variability has also been found among the genotypes of different crops including cotton (Qadir and Shams, 1997 and Akhtar and Azhar 2001). In Pakistan about 2.79 mha area was under cotton crop during 2002-2003 (Anonymous, 2004). Cotton genotypes differ in their response to salinity and among the various important varieties tested in past, NIAB-78 and MNH-93 are the most salt tolerant (Qureshi and Barrett-Lennard, 1998). Although cotton is considered as fairly tolerant to salinity (Maas, 1986), yet a decrease of 41 % in seed yield in slightly salt affected soils has been reported (Qayyum and Malik, 1988). Cotton is quite sensitive to salinity at germination and seedling stages but comparatively tolerant thereafter (Bhatti and Rashid, 1980). Therefore, the spotty pattern in crop stand at maturity under saline soil conditions is actually initiated at the time of germination and vegetative growth phase. In saline soils, Na+ and CI- are the dominant ions affecting plant growth (Khan, 1987. and Maas, 1993). Under these conditions, the activities of some essential nutrients may also be reduced (Gratten and Grieve, 1992) and plants may experience nutritional disorders. The situation can be improved by selecting salt tolerant cotton genotypes for moderately salt affected soils. The selection and development of new genotypes of a particular crop is a continuous need due to natural segregation of parental characters. This situation necessitates a regular selection/screening of genotypes against salinity. The present study was, therefore, conducted to evaluate salinity tolerance of different cotton genotypes under controlled conditions. MATERIALS AND METHODS The seeds of four cotton genotypes (Krishma, NIAB- 999, NIAB-98 and CIM-446) were obtained from NIAB and Ayub Agricultural Research Institute, Faisalabad. The experiment was carried out in the wire house having glass covered roof and sides with iron wire screen but there was no control on humidity, temperature and light. Delinted seeds of all the genotypes were sown in pre- washed sand in the polyethylene lined iron trays. The seeds were irrigated regularly with water. At two leaf 79