Drought stress intensifies early blight and compromises potato yield

This study investigated the effects of water stress on early blight disease, Alternaria alternata (EB)-severity and yield performance in 44 potato genotypes, including two control cultivars 'Agria' (susceptible) and 'Marfona' (moderately resistant) to EB, under field conditions in Esfahan, Iran over two years (2021-2022). A strip-plot design within a randomized complete-block design with three replications was used to compare conventional irrigation with water stress (30% reduction in irrigation). The disease-severity percentage (DSP) and yield components (total, marketable and nonmarketable yields) were evaluated.

ANOVA results showed no significant differences between years for DSP or total yield, but water stress significantly increased DSP (from 28 to 36 ton ha^-1 and reduced total yield) (from 39 to 29 ton ha^-1, a decrease of ≈26%). Significant genotype effects and interactions (stress × genotype, year × genotype) were observed. Water stress significantly increased DSP in susceptible genotypes such as 10/24-R3 (from 57 to 67) and 'Marfona' (from 47 to 53), whereas resistant genotypes such as 7/27-R1 (12 to 13) and 6/27-R2 (15 to 24) showed minimal changes. The highest total yields under nonstress conditions were observed in genotypes such as 25/34-R3 (56 ton ha^-1) and 5/27-R3 (55 ton ha^-1), with significant reductions under stress. Moreover, there was no significant correlation between disease severity and total yield (r = -0.080^ns), whereas it was significant between water stress and total yield (r = 0.668**), but not significant between nonwater stress and total yield (r = -0.236^ns). Moreover, there was a significant correlation between water stress and disease severity (0.927**); but a nonsignificant association between nonwater stress and disease severity (r = -0.183^ns). Phylogenetic analysis of A. alternata isolates using the gpd gene revealed genetic diversity, grouping into two main clades.

The study highlights the importance of selecting drought- and disease-resistant genotypes to mitigate the combined effects of abiotic and biotic stresses. In addition to genotype selection, appropriate irrigation timing, especially during tuber formation and bulking stages, can reduce drought's adverse effects. Overall, the combined assessment of water-stress responses, genotype-specific resistance patterns and phylogenetic relationships of A. alternata isolates provides practical guidance for selecting resilient potato genotypes and optimizing irrigation management, thereby supporting breeding and integrated disease control strategies under increasing drought and climate variability. © 2026 Society of Chemical Industry.