Effects of restricted irrigation and arbuscular mycorrizal fungus (AMF) applications on grafted sultana seedless grape saplings growed under high altitude conditions

The increase in water issues and drought risk due to climate change necessitates the adoption of alternative measures in agricultural production worldwide. In this context, research on viticulture, an economically significant agricultural activity, has gained even more importance. This study investigates the effects of different irrigation applications and Arbuscular Mycorrhizal Fungus (AMF) applications on grafted Sultani Çekirdeksiz grape vines under high altitude conditions. The study was conducted in 2022 and 2023 at the vineyard practice area of the Faculty of Agriculture, Van Yüzüncü Yıl University, situated at 1669 meters elevation. Grafted Sultani Çekirdeksiz (clone 7) vines were used, inoculated on drought-tolerant 1103 P and drought-sensitive 5BB rootstocks. Three different irrigation levels were applied: K0 (100% optimal irrigation), K1 (25% restricted irrigation), and K2 (50% restricted irrigation), with the ERS (Endo Roots Soluble) commercial AMF isolate included to assess its effectiveness under restricted irrigation conditions. This thesis involved measurements, weighing, observations, and analyses to determine plant growth parameters and some biochemical properties in soil and plants. The overall survival rate of the vines was 92.06%. AMF application had a significant positive impact on the general characteristics of vines grafted on 1103 Poulsen rootstock, as indicated by a 0-5 scale. Parameters such as leaf count, leaf temperature, shoot diameter, canopy width, shoot length, root fresh and dry weights, root width, root count, AMF root mycorrhizal density, and MDA concentration were statistically significant on a yearly average basis. Shoot fresh and dry weights were notably significant for both rootstocks, with the second growing season being statistically significant for vines grafted on 1103 P. In terms of shoot fresh and dry weights, AMF had a negative impact under the optimal irrigation level K0 but showed positive effects under restricted irrigation conditions. Root fresh weight (g) was significant for the average years and the second year for plants grafted on 1103 P without AMF, with K1 reaching the highest value (1102.38 g) and K2 the lowest (53.65 g). The root count parameter was significant for both rootstocks in the second year for the mycorrhizal group, with the highest values obtained with K2 + AMF (21.50 and 18.25). Root length was statistically significant in the first year for AMF present and in the second year for AMF absent in vines grafted on 1103 P, with the highest root length values recorded as K0 + AMF present (26.00 cm) in the first year and K1 + AMF absent (49.33 cm) in the second year. Regarding biochemical properties, pre-planting and AMF application revealed a rhizosphere spore density of 486.66 (spores/g soil). The rhizosphere spore density was statistically significant for both rootstocks at the end of the first and second growing seasons, with the highest counts for 1103 P rootstocks being K0 + AMF present (720.00) in the first year and K2 + AMF present (1875.00) in the second year; for 5BB rootstocks, the highest counts were K1 + AMF present (585.00) and K0 + AMF present (1815.00). Total phenolic content (mg GAE/g) was significant for 1103 P in the first year without mycorrhiza and for 5BB with mycorrhiza in both years. Total antioxidant capacity (µM/100 g) was significant for 1103 P without mycorrhiza in the first year and for 5BB with mycorrhiza in both years. Antioxidant enzyme activities showed statistical significance for APX enzyme activity (mM.gFW/min), with the highest values for 1103 P as K0+AMF absent (0.66) in the first year and K1+AMF present (0.86) in the second year; and for 5BB as K0 + AMF present (0.57) and K0+AMF absent (0.14). CAT enzyme activity values (mM.gFW/min) were significant for both rootstocks in the first year with AMF present and in the second year with AMF absent and present. The highest values for 1103 P were K1 + AMF present (0.05) in the first year and K0+AMF present (0.02) in the second year; for 5BB, K0+AMF absent (0.04) in the first year and K0+AMF absent and K2+AMF present (0.01) in the second year. SOD enzyme activity was significant for both rootstocks on a yearly average basis and for 1103 P in the second year with AMF present, with the highest activity recorded for K0+AMF absent (95.29). MDA concentration (nmol/ml) was significant for both years and AMF applications for 5BB rootstocks, with the highest values for K1+AMF absent (31.44) and K0+AMF absent (73.81). Mineral content in leaves was significant for Calcium (Ca) for 5BB rootstocks in both years with AMF present; Phosphorus (P) for 1103 P in both years and 5BB in the second year; Potassium (K) in both varieties in the second year; Magnesium (Mg) for 1103 P in the first year and 5BB in both years; Sodium (Na) for 1103 P rootstocks in both years. Additionally, levels of Iron (Fe), Copper (Cu), Manganese (Mn) for both years and rootstocks; Zinc (Zn) for 5BB rootstocks in both years were statistically significant. Although mineral content changes varied by rootstock, year, and application, AMF applications generally positively impacted mineral uptake, with irrigation levels amplifying this effect. The findings suggest that AMF applications can enhance nutrient uptake and promote plant growth in drought-prone and high-altitude areas with limited rainfall and irrigation opportunities, making them a viable alternative to chemical fertilizers. Expanding the use of mycorrhizal applications and promoting these methods to growers is essential for sustainable agriculture.