Effects of Drought Stress on Almond Cultivars Responses Grafted on Different Rootstocks

In this study, the response of selected almond cultivars on different rootstocks under drought stress base on Morpho-physiological traits using a factorial experiment in a randomized complete block design with three replications was investigated. The experimental was carried out at the Temperate Fruit Research Center of Horticultural Sciences Research Institute (HSRI) in 2016. The factors included cultivars in five levels (Supernova, Texas, Marcona, Shokoufeh and K13-40), rootstocks in three levels: GF-677, GN-22) (Peach × almond hybrids) and seedlings of bitter almond No.32 (Somewhat resistant to drought stress) and drought stress in four levels: irrigation intervals of 3 (control), 5, 10 and 15 days. The factors such as leaf abscission, leaf area (LA), cell membrane stability index (MSI), chlorophyll fluorescence (CF) and chlorophyll content index (CCI), minimal fluorescence (F0), maximal fluorescence (Fm), variable fluorescence (Fv) and maximum quantum yield of photosystem II (Fv/Fm) were measured. The results showed that the interaction between the cultivar and the rootstock for F0 and for CCI was significant at 1% level. Interactions of cultivar and drought stress were significant for Fm and Fv at the 5% level and for CCI, F0, Fv/Fm at the 1% level. Interactions of rootstock × drought were significant for CCI, F0, Fv/Fm at the 1% level. Drought decreased Fv with increasing F0 and decreasing Fm, in the evaluated cultivars and reduced the Fv/Fm in sensitive cultivars on seedling rootstock and GN-22 from 0.82 to 0.66 but in resistance cultivar Shokoufeh on GF-677 was from 0.818 to 0.789. As a general result, all of the cultivars on the GF-677 rootstock showed greater resistance to drought stress, and Shokoufeh and Marcona cultivars, especially on the GF-677 rootstock, tolerated drought stress better, and these combinations of rootstock - scion were superior to present experiment.