Soil Environ. 33(2): 133-141, 2014 www.se.org.pk Online ISSN: 2075-1141 Print ISSN: 2074-9546 *Email: agronomistryk@gmail.com © 2014, Soil Science Society of Pakistan (http://www.sss-pakistan.org) Morpho-physiological characterization of chilli genotypes under NaCl salinity Zaid Mustafa 1 , Muhammad Aslam Pervez 1 , Chaudhary Muhammad Ayyub 1 , Amar Matloob 2* , Abdul Khaliq 2 , Saddam Hussain 2,3 , Muhammad Zahid Ihsan 4 and Madiha Butt 1 1 Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan 2 Department of Agronomy, University of Agriculture, Faisalabad, Pakistan 3 College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, China 4 Department of Arid Land Agriculture, Meteorology and Environ. Sci., King Abdul Aziz University, Jaddah, Saudi Arabia Abstract Salinity is a stringent abiotic stress that limits plant growth and development. Present study was undertaken to explore morpho-physiological responses of different chilli (Capsicum annum L.) genotypes to NaCl-induced salinity. Seedlings of six chilli genotypes (Loralai, Sanam, Desi, Kundri, Asia Bok and Magnum) were subjected to five NaCl salinity levels (0, 25, 50, 75 and 100 mM). A separate control for each genotype was maintained for comparison. Increasing salinity levels significantly reduced shoot and root elongation as well biomass accumulation. Transpiration rate, stomatal conductance, photosynthetic activity and chlorophyll contents were a lso reduced although genotype-specific responses were evident for these attributes with the exception of photosynthetic rate. At upper limits of salinity (100 mM), Desi and Loralai genotypes produced more shoot and root length and higher fresh and dry biomass than rest of the chilli genotypes. Moreover, comparatively higher stomatal conductance and transpiration rate were also observed for these genotypes at all salinity levels. Desi and Loralai genotypes accumulated less Na + and higher Ca 2+ and K + ions than other chilli genotypes. Based on various parameters studied, Desi and Loralai genotypes appeared to be promising salt-tolerant chilli genotypes. Keywords: Na + ion, photosynthetic activity, salt stress, seedling growth, stomatal conductance Introduction Salinity is one of the most important abiotic constraints limiting crop productivity; 10 percent of world’s arable land area is estimated to be salt-stressed (Zhani et al., 2012). Salinity has deleterious effects on growth and development of plants by inducing various biochemical and physiological changes (Munns and Tester, 2008). In Pakistan, nearly 10 million ha area is badly affected by salinity, i.e., 12.9 percent of country’s land (FAO, 2008). The arid and semi-arid conditions in Pakistan have aggravated the saline conditions, typically in irrigated areas where availability of fresh water is inadequate. Hot pepper (Capsicum annuum L.) commonly known as chilli is one of the most important vegetable and spice crops of Solanaceae family. It is a crop of much economic significance, as it occupies largest area among vegetable crops in the country, followed by potato and onion. It is mainly grown in Sindh and southern Punjab provinces as a summer crop. During 2011-12, it was grown on an area of 21.8 thousand ha, with an annual production of 37.2 thousand tons (Govt. of Pakistan, 2012). Like other crops, growth and yield of chilli are also adversely affected by salinity (Zhani et al., 2012). Rhoades et al. (1992) reported a 14% reduction in chilli yield with each increasing unit of salinity. The harmful implications of salinity arise presumably because of induction of osmotic stress, ionic imbalance and subsequent oxidative stress (Tester and Davenport, 2003). Furthermore, higher concentration of salts under saline conditions causes severe ion toxicity by depositing high concentration of Na + , which inhibits cell division and expansion, lowers calcium and potassium contents, and causes membrane instability and increased respiration rate (Shahid et al., 2011). Salt stress is also responsible for decreased biosynthesis of chlorophyll and photosynthetic efficiency (Munns, 2002). Under stressful environments, photosynthetic rate declines in response to lower than normal stomatal conductance, depression in carbon uptake and metabolism, inhibition of photochemical capacity (Mundree et al., 2002). Soil salinity affects the growth of plants by altering water relations as a result of salt accumulation in the intercellular spaces (Zhang et al., 2006), injurious effects of toxic ions (Saboora and Kiarostami, 2006), osmotic stress (Almodares et al., 2007) and reduced water-use efficiency (Grewal, 2010). With dwindling land resources and little scope for horizontal expansion, crop production on saline soils is inevitable and a challenging task. Hence, effective