Asian Research Thesis Index

Abstract

Salinity is among major threats to crop production and food security worldwide. World population is increasing at an alarming rate especially in the third world countries like Pakistan. So it requires more food production to ensure food security for this ever increasing world population. As the area under cultivation is limited and cannot be increased, we must resort to extensive salt affected areas worldwide to ensure food security. To utilize these salt affected areas we must devise strategies to able the crop plants to tolerate salinity and give economical yields. To accomplish this current research was planned to identify salt tolerant genotypes and alleviating the salinity stress by potassium application. In the preliminary experiment two salt-tolerant (Indent-1 and Nagina) and two salt-sensitive (Peto-86 and Red Ball) tomato genotypes were identified from fifteen genotypes based on the higher growth, lower Na + and higher K + accumulation at three NaCl levels (Control, 75 and 150 mM) in hydroponics experiment. Subsequently in the second experiment, the alleviating effects of potassium in foliar and solution form (0, 4.5 and 9 mM) on salt tolerant and sensitive genotypes were studied at same NaCl levels combined with. Results showed that response of tolerant genotypes was higher to potassium application compared to sensitive genotypes. It can also be concluded that salt tolerance of Indent-1 and Nagina might be due to higher value of antioxidant enzymes (SOD, CAT, GR), photosynthetic gas exchange, membrane stability index (MSI), Chlorophyll contents (Chl a and b), K + , K + /Na + and lower values melon dialdehyde (MDA) and Na + . Third experiment was conducted in pots under control, 7.5 and 15 dS m -1 salinity and control, 180 and 360 kg ha -1 (in soil) and 4.5 and 9 mM (foliar) potassium treatments to check the interactive effect of salinity and potassium on tomato fruit quality and yield. Potassium treatments significantly increased the fruit yield in tomato genotypes with highly significant values in tolerant genotypes than sensitive genotypes. Both salinity and potassium positively affected the fruit quality characteristics (TSS, TA, pH, DM %) in both tolerant and sensitive genotypes, however the fruit quality was higher in tolerant compared to sensitive genotypes. In the fourth experiment involvement of phytohormones (ABA, ethylene) in salt tolerance of tomato genotypes and changes in xiiistomatal morphological characteristics in response to NaCl and potassium application were studied. The experiment was conducted under controlled conditions in a climatic chamber with three NaCl (0, 75 and 150 mM) and two potassium levels (0, 4.5 mM) in hydroponics using salt-tolerant (Indent-1) and salt-sensitive (Red Ball) genotypes. The results revealed that salt-tolerant genotype had higher values of ABA and ethylene and correspondingly higher growth, chlorophyll content index (CCI), stomatal conductance (gs), lower Na + and higher K + as compares salt-sensitive genotype. Stomatal density (SD) and stomatal aperture size (SA) were significantly decreased by NaCl, with non-significant differences between the salt tolerant and sensitive genotypes suggesting these characteristics were not genetically controlled rather influenced by the environment. Based on the results of this research it was concluded that application of potassium increases yield and quality of tomato fruits under soil salinity and it could be used as an effective practice to produce even a salt sensitive species like tomato under saline conditions.

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