Drought resistance assessment of olive cultivars and hybrids

Background.Olive (O. europaeaL.) is one of the main fruit crops in the world. It is most widespread in the Mediterranean region. In recent years, due to global warming and aridization of the earth, most olive-producing countries have suffered significant losses and are forced to transfer olive plantings from the traditional southern regions to the more humid northern ones. Insufficient precipitation and lack of irrigation water are currently some limiting factors in this crop's spread. Producers are increasingly focusing on planting drought-resistant cultivars that could produce high and regular yields in conditions of insufficient water supply. In this regard, this study aimedto identify genotypes of O. europaeawith high adaptive ability to the arid conditions of southern Russia and to determine the most informative indicators of drought resistance for collection screening. Materials and methods.Studies of water regime indicators (water-holding capacity, water deficiency, water content) and relative electrolyte yield, when the cell membrane is damaged under conditions of dehydration of leaf tissues, were carried out on 60 intraspecific hybrids of European olive. Corregiolo and Ascolano cultivars served as the control. The experiments were performed in laboratory conditions under controlled temperature of 30°C and relative air humidity of 30%. After leaf tissues' saturation with water (control), as well as after they were dehydrated for 24, 48 and 72 hours, drought resistance indicators were assessed. Results.Based on a cluster analysis, the main indicators of drought resistance, four groups of olive genotypes with different resistance to drought were identified. The greatest interest is for hybrids in the group with very high drought resistance. This cluster consists of 14 of the most promising hybrids that are superior in drought resistance to the control olive variety Ascolano. Water loss for these accession varied from 20.81 to 33.63%, and the relative yield of electrolyte varied from 0.27 to 0.36 RU, which allows us to conclude that their drought resistance is very high. Based on the analysis of principal components between various criteria of the water regime of olive plants, the relationship and influence on the integral assessment of drought resistance was shown. It is noted that the most informative indicator, which has a negative correlation with water loss and the relative yield of electrolytes when the cell membrane is damaged, is water-holding capacity. Indicators of drought resistance such as water content in leaves, water deficit, and relative water content in leaves are not sufficiently informative for the selection breeding of drought-resistant cultivars and forms of olive.