Cultivar - Specific Biostimulant Application Enhances Heat Stress Tolerance and Pest Resistance in Potato (Solanum tuberosum) under Semi - Arid Conditions

Heat stress caused by climate change makes it hard to grow potatoes in semi-arid areas, and it also makes pests more of a problem. This study examined the cultivar-specific responses of two Solanum tuberosum cultivars to a foliar VIGORIZER biostimulant (25% Ascophyllum nodosum, 0.5% glycine betaine, 0.05% Fe-EDDHA) under field circumstances in Nineveh, Iraq, where temperatures above 28 °C during tuberization. A split-plot randomized complete block design examined a heat-sensitive cultivar ('Riviera') and a heat-tolerant cultivar ('Arizona') with and without the management of a biostimulant. There were big differences between genotypes. Using biostimulants made 'Riviera' plants perform much better. The tuber weight increased from 192 to 385 g plant⁻¹, the total yield was from 0.49 to 0.82 kg plant⁻¹, the SPAD chlorophyll index went up by 4.4 units, and the tuber crude protein went up by 46%. The Colorado potato beetle (Leptinotarsa decemlineata) caused 57% less damage to the leaves of treated "Riviera" plants. "Arizona" showed slight but important gains in yield and nutritional levels. Physiological and nutrient analyses connected the improvements in "Riviera" to better nitrogen uptake (leaf N went from 2.94% to 3.48%) and more stable photosystem II. A notable cultivar × treatment interaction (η² = 0.74) demonstrates that biostimulant efficacy is contingent upon genotype. These results show that applying foliar biostimulants to certain areas can help plants deal with heat stress and make them stronger and more resistant to pests in potato varieties that are prone to them.