چكيده انگليسي :
The tolerance of plants to drought stress is a complex phenomenonin which diverse morphological, physiological, and biochemical mechanisms are involved. In forage grasses, the selection of genotypes that perform better in these conditions and, in addition to high performance, have the ability to survive, recover, and grow vigorously during both summer and cold seasons, is of high importance. In breeding programs focused on forage grasses, understanding the genetic diversity and relationships between genotypes is crucial for selecting parents for effective crossings and adopting suitable breeding methods.
Stress memory is one of the mechanisms that plants have evolved to adapt to environmental fluctuations. Unfortunately, few researches have been carried out in the field of genetics of drought tolerance in connection with stress memory and developing tolerant cultivars in Dactylis glomerata as a valuable forage and turfgrass. This research was conducted in three separate studies to investigate 24 half-sib families from four polycross groups with different levels of phenotypic (low and high) and molecular (low and high) diversity to investigate forage, seed, root system, stress memory, and germination and seedling growth. In the first study, the effect of different levels of phenotypic and molecular diversity of parents on forage, seed, summer dormancy, persistence and recovery characteristics of polycross progeny was investigated. In both water conditions, considerable genetic variation was observed among progenies indicating that the progeny performance depends on the type and level of diversity among the parental genotypes. Crosses between parents with wide molecular and phenotypic diversity led to simultaneous increase of forage and seed yield, increase of recovery percentage, recovery forage yield, winter growth score, persistence, and summer dormancy index of progeny.
In the second study, the effect of drought stress on the physiological characteristics and root system of polycross groups and the relationship with the phenomenon of stress memory were investigated. Results delineated direct effects of drought stress on plant performance, physiological traits, and root system characteristics. One of the interesting results about the effect of drought stress is the ability of plants to mitigate the adverse effects of drought stress through the induction of stress memory. In facts, the plants that were subjected to two instances of drought stress (D1D2) exhibited enhanced resilience to future stresses compared to those exposed only once (D2). The role of pre-treatment with drought stress was underscored in augmenting relative leaf water content, proline content, chlorophyll a and b content, total chlorophyll content, total chlorophyll/carotenoid ratio, ascorbate peroxidase activity, dry matter yield, root volume, wet and dry root weight across both soil rozospher depths (0-30 cm and 30-60 cm) and in both Syn1 and Syn2 generations.
Results indicated that the polycross groups with high molecular diversity displayed clear responses to stress memory. Induction of stress memory in these groups, particularly in Syn1 and Syn2 generations, indicates the positive effect of genetic diversity on drought tolerance. The presence of high molecular and phenotypic diversity among parents resulted in a notable increase in germination and seedling growth percentages, yield enhancements, and increased drought tolerance in the polycross progeny. The rate inbreeding depression of various traits was depended on the moisture environmental conditions and the type and level of genetic diversity among parents. The increase in parental diversity was effective in reducing the rate of inbreeding depression for dry weight of roots, biomass, and seedling. Overall, the results of this research emphasize the necessity of using molecular markers in the selection of polycross parents to achieve high yield and more tolerance to stress in the next generations.
