Studies on drought and heat tolerance at seedling stage in varieties and hybrids of pomegranate (Punica granatum L.)

Abstract

In the recent times pomegranate has become a commercially important fruit crop due to wide consumer preference, and has attracted many growers especially for its wider adaptability, relatively low cultivation cost, good yields, excellent shelf life and export potential of fruits, apart from its in built drought and heat tolerance. To understand genetic variation for drought and heat tolerance a study was undertaken. Hybridization was done from August to February employing 80 genotypes grown in Indian Institute of Horticultural Research. The varieties/hybrids involved in crossing and selfing were Ganesh, Ruby, Ornamental, Daru, Double flower, Amblidana, Kabul yellow, (Ganesh x Ornamental), (Ganesh x Daru). A total of 6 selfing, 25 single cross hybrids and 14 three ways cross hybrids were made. More number of fruit set was observed in selfing followed by in single cross and three way cross hybrids. Crosses involving Ganesh, Ruby and Daru produced more number of fruits, whereas crosses using Kabul yellow produced less number of fruits. Seeds of Yercaud, Kandhari, P-26, Jodhpur red, G-137, Jodhpur collection, Muscut, Dholka, P-23, H4, Jaloore seedless, P5/02 were used to raise seedlings and observations like Seedling height, primary root length, number of secondary roots, specific leaf area, cell membrane stability and chlorophyll content were measured after 105 days of sowing. Analysis of variance revealed significant differences for all the 8 characters studied among the 25 genotypes, which included 15 hybrids and 10 varieties. Phenotypic coefficient of variation values was higher than genotypic coefficient of variation values but difference between phenotypic coefficient of variation and genotypic coefficient of variation was not high. Heritability values in broad sense were high for all characters studied except for primary root length. High genetic advance as percentage of mean was observed for all 8 characters studied. Yercaud was found to have high heat and drought tolerance as measured by CMS (27.5%) and chlorophyll after stress. The 2 popular varieties Ruby and Ganesh showed no significant difference for plant height, number of secondary roots, specific leaf area, chlorophyll before and after stress. Hybrid double flower x Daru was found to be heat tolerant due to its low solute leakage while hybrid (Ganesh x Kabul yellow) x Ganesh showed high drought tolerance among the hybrids studied due to high chlorophyll content. The field studies at Hiriyur involving 10 multiple cross hybrids and 2 varieties indicated that there was a positive association of chlorophyll and fruit yield. Further, high chlorophyll content was also associated with drought tolerance at seedling stage. Correlation studies revealed that heat tolerance was positively associated with plant height, primary root length and negatively associated with number of secondary roots, root to shoot ratio, specific leaf area and chlorophyll before and after stress. This indicated that, genotypes with higher plant height and primary root length possessed better heat tolerance. Chlorophyll after stress is positively correlated with all the 7 characters indicating decrease in temperature tolerance and leaf thickness will improve the drought tolerant hybrids.