پژوهشنامه اصلاح گیاهان زراعی (Sep 2024)
A Study on the Genetic Diversity of Agro-Morphological Traits in Wild Populations of alfalfa (Medicago spp.) in Drought Stress Conditions
Abstract
Extended Abstract Background: Alfalfa is the most important leguminous forage that plays a key role in providing fodder needed for the production of human protein and dairy products. This plant has high nutritional value with high adaptability to different conditions. Alfalfa is recommended for sustainable agriculture because it has a deep root system and is a perennial plant, hence it can prevent soil erosion. Alfalfa is an excellent source for the biological fixation of air nitrogen. Researchers believe that 65% of the total nitrogen used in agriculture is through biological nitrogen fixation. It is very palatable and effective in the growth of livestock in terms of fodder quality and the optimal amount of energy from plants. In addition to protein, this plant is rich in vitamins, especially A, C, E, and K, as well as mineral compounds such as calcium. The distribution of the types of annual alfalfa at the global level, especially in arid and semi-arid regions, shows their resistance to water shortage and drought conditions. Alfalfa can be used as a successful plant to prevent desertification and the expansion of deserts. Among annual alfalfas, some species can adapt to 80-100 mm of winter rain for improvement and development in dry areas and desert pastures. However, most of Iran is suffering from water shortage, and one of the limitations of breeding for drought stress is the lack of resistance sources among crop genotypes. For this purpose, the evaluation of wild genotypes can be an important step in this direction. Methods: This research was conducted on perennial alfalfa genotypes (one variety) and one-year alfalfa (nine samples) in a factorial experiment (alfalfa genotypes and stress as the first and second factors, respectively) with three replications in a block design. Samples of alfalfa were evaluated in normal and severe stress conditions in the greenhouse of the Faculty of Agricultural Technology, University of Tehran (Abureihan Campus) during 2012-2013. The factorial experiment was conducted based on a randomized complete block design with three replications. The irrigation factor was water deficit stress including irrigation when soil moisture reached 30% of field capacity (severe stress), and the second irrigation level was normal conditions. Cultivation was carried out in May at a temperature of 22 °C, a photoperiod with 16 hours of light, and adequate humidity. Sixty medium plastic pots with an opening diameter of 15 cm, a height of 15 cm, and a capacity of 2 kg were filled with soil. Before planting, the seeds were broken by pulling soft sandpaper on their surfaces and performing stratification, followed by the seed germination test. Light irrigation was done one day before planting. Then, seven seeds were planted in each pot at a depth of 1 cm, and the soil surface was covered with cocopeat to protect soil moisture. The soil of the pots was watered with a sprinkler twice a day until the stress application. After reaching a height of 15 cm, 50% Hoagland's solution was used to feed the plants. After 55 days from the time of planting, the morphological traits, such as stem number, plant height, leaf number, internode number, internode length, leaf area, dry leaf weight, and dry stem weight, were evaluated at the vegetative growth stage. The weight method was used to adjust the soil moisture content. Excel software was used to draw graphs, and data were analyzed using SAS software. Means were compared using Duncan's method. Results: Drought stress negatively affected the evaluated traits. The differences between all evaluated genotypes were significant at the 1% probability level, revealing the existence of genetic diversity between genotypes that can be used for the selection of drought-tolerant genotypes in a subsequent study. The interaction effect of the genotype in stress conditions showed that the changes of different genotypes in different moisture conditions were not the same for most of the traits and genotypes. The heritability calculation results showed high general heritability for all the studied traits. The highest heritability belonged to the leaf dry weight trait (92.96 and 91.77 under full irrigation and severe stress conditions, respectively), and the lowest heritability was observed for the internode number trait (71.83 and 66.93 under full irrigation and severe stress conditions, respectively). The highest coefficient of variation belonged to the number of branches per plant trait (22.49) and the lowest value was observed for the leaf dry weight trait (8.86). In this study, Kermanshah130 and Azarbayjan175 were the most tolerant genotypes with the lowest decrease for leaf dry weight, stem dry weight, stem number, plant height, leaf number, and internode length. Conclusion: Since the wild genotypes Kermanshah 130 and Azarbayjan 175 were the most tolerant genotypes in this study, they can be used as new sources of resistance in future breeding programs.
