Introduction
Iran is a major center of pear (Pyrus) germplasm diversity, offering strong potential for selecting drought-tolerant genotypes. This study aimed to assess the effects of drought stress on biomass accumulation and nutrient uptake in seedlings of different Pyrus species and commercial pear rootstocks.
Materials and Methods
The collected seeds were sown in trays under greenhouse conditions. After germination, seedlings were transplanted into the growth bags filled with a suitable medium. After nine months' establishment, the uniform plants were randomly assigned to two groups: a control group with regular irrigation every 3 days, and a drought-stress group with irrigation withheld for 21 days. At the end of the drought period, shoots and roots were separated, fresh weights measured, and samples oven-dried at 50°C for two weeks to determine dry weights. Macronutrients (N, P, K) and micronutrients (Mg, Ca, S) were analyzed in roots and shoots. The experiment followed a factorial design within a completely randomized design, involving two irrigation regimes and 14 Pyrus genotypes.
Results and Discussion
Data from the interaction effects of drought stress on root fresh and dry weights revealed that the Q1 and the Dargazi had the highest root fresh weight, while the Pyrodwarf showed the lowest fresh and dry root weights. Mean comparisons indicated that in P. nivalis, P. hyrcana, P. syriaca, P. betulifolia, and the seedling genotypes LGI477 and LGI456 (derived from P. communis), the shoot dry weight under drought stress was higher than control. These genotypes may possess superior physiological, biochemical, and molecular adaptation mechanisms to drought. Moreover, P. pashia, P. betulifolia, P. amygdaliformis, Q1, the promising LGI477 genotype, and the quince rootstock BA29 exhibited higher root dry weight under drought stress than control, indicating stronger root growth under drought condition. In P. nivalis, P. syriaca, Q1, Dargazi, LGI477, and BA29 rootstock, root nitrogen did not decrease under drought, while in other genotypes, a reduction was observed. However, leaf nitrogen increased under drought in most genotypes, except for P. pashia, P. hyrcana, P. amygdaliformis, and BA29 rootstock, where it declined. Drought stress also generally increased root phosphorus content in most species and rootstocks, except for P. hyrcana, P. calleryana, and LGI477, which did not show such increases. In contrast, leaf phosphorus responses under drought were variable: increases in P. amygdaliformis and P. nivalis, decreases in Dargazi, and no significant change in P. hyrcana, P. syriaca, and LGI456. Root potassium content responded differently across genotypes, decreasing in P. nivalis, P. betulifolia, hybrid Q1, Dargazi, and Pyrodwarf rootstock, but increasing in others. Leaf potassium levels showed wide variation, with P. syriaca having the highest and Dargazi and LGI456 having the lowest values under drought stress. Dargazi showed the highest root magnesium content, while P. nivalis had the lowest; EMA and BA29 rootstocks showed no significant differences. The quince rootstock EMA had the highest root sulfur content under drought. Overall, drought stress had less pronounced effects on magnesium and sulfur than on other nutrients.
Conclusion
The findings of this study reveal clear differences among species and rootstocks in their responses to drought stress, particularly regarding their capacity to absorb and retain essential mineral nutrients under water-deficit conditions. Analysis of mean trait values revealed significant variation in how different genotypes and rootstocks cope with drought. Previous studies have reported that drought conditions typically reduce the number of lateral roots and overall root volume while promoting deeper vertical root growth. Furthermore, terminal buds tend to enter a dormancy phase, halting the plant’s longitudinal growth. As a consequence of drought stress, various growth indices decline, with the severity of reduction differing among the evaluated genotypes and rootstocks. Besides, according to the results of this study, rootstocks that demonstrated the highest dry matter accumulation in their roots during drought, along with relatively sustained growth performance, may serve as promising candidates for future breeding programs aimed at drought tolerance. Although drought stress generally led to reduced absorption of most mineral elements in both leaves and roots, the efficiency of nutrient uptake did not appear to be severely disrupted.