Evaluation of response to drought stress in some of promising Iranian and foreign olive cultivars using using yield-based indices

The evergreen tree olive (Olea europaea L.) is considered as one of the oldest plants cultivated in the Mediterranean basin. Drought is one of the most abiotic stresses that reduces olive yield in tropical and subtropical climates. Hence, identification of tolerant cultivars for cultivation in drought-prone areas is considered as one of important strategies in increasing cultivated areas for this plant. This study was aimed to investigate some of commercial cultivars and promising genotypes of olive using several yield-based drought tolerance and susceptibility indices.

To investigate the effect of drought stress on fruit yield and oil percentage in the 20 commercial cultivars and promising genotypes of olive, an factorial experiment based on randomized complete block with three replications was performed in Taroum Olive Research Station located in Zanjan province, during 2015-2017 cropping seasons. During the endocarp hardening period, drought treatments were applied based on cut of irrigation to the appearance of stress symptoms in the tree. Calculation of nine drought tolerance and susceptibility indices based on fruit yield and oil percentage under drought and normal irrigated conditions, correlations among indices and yields and principle component analysis based on correlation coefficient matric were followed.

Based on results, drought reduced fruit yield in all cultivars and genotypes, while it increased oil percentage in some of genotypes. Correlation coefficient analysis showed that all indices except TOL and SSI had significant positive relation with fruit yield and oil percentage under non-stress and drought stress conditions. The results of principal component analysis (PCA) showed that the first two components justified 98.78 and 99.59% of the total variation of fruit yield and oil percentage, respectively. The angles between indices in biplots rendered by PC1 and PC2 confirmed the results of correlation analysis. With respect to all three-dimensional graphs rendered by yields and STI index, promising genotype T7 placed in A group and it was selected as the most tolerant genotypes than others. Furthermore, this result was supported by the results of principal component analysis.

In general, our results revealed that the genotype T7 was identified as the most drought tolerant than other cultivars and genotypes. Thus, use of this genotype in breeding programs for improving tolerant of olive and also for cultivation in drought-prone environments is recommended. According to this results there was significant genetic diversity between studding genotypes that can be used in any improvement perspectives in the breeding projects.