Screening for drought tolerance in lentil genotypes (Lens culinaris Medik) with emphasis on comparing old and new indices of stress tolerance in order to introduce promising genotypes

Introduction Drought stress is one of the main problems in agriculture of Iran and the world. Among the environmental limiting factors of the yield crops, drought is the most important factor to reduce production, especially in arid and semi-arid regions. Drought stress reduces water content in plant tissues, lead to growth shrinkage and some physiological and metabolic changes in them. Food legumes, as one of the most important protein-rich vegetable sources, played a major role in providing human protein, especially in low-income and developing countries, and after cereals are the second most important source of human food. These plants, with bio-stabilization of nitrogen, provide a large portion of their nitrogen, and because they require low water and nutrients, they are highly desirable for cultivation in poor lands. Lentil (Lens culinaris Medik) is one of the beans that had more than 20% protein content and characteristics such as the ability to grow in inappropriate conditions and poor soils, has been able to play an important role in the low-income diet of people in developing countries. Regarding to the success of a breeding program depends on the size and diversity of genetic resources, genetic diversity lead to succeeding in selection, so identification of cultivars with high yield, as well as limiting factors of yield potential and genotypes tolerant to these factors in lentil seems to be necessary.   Materials & Methods This research was carried out in the research farm of Ferdowsi University of Mashhad in 2014. In this experiment, 73 lentil genotypes including native genotypes and lines from other countries were cultivated in two separate plots under non stress and stress conditions in Augmented design. Five genotypes used as control (Kimia, Gachsaran, Cabralinta, ILL325 and ILL857). Controls were cultivated in all blocks. Before planting, field soil was sampled from a depth of 30 cm and pH values, organic matter, EC, macro elements (N, P and K) and soil texture were measured. The planting was carried out on March 20, 2014. At the same time, according to the fertilizer recommendation, the amount of required elements was added to the soil and immediately after cultivation, an irrigation step was conducted to ensure the emergence of all the seeds for both dry conditions (drought stress) and non-stress. Afterwards, irrigation was performed only for non-stress treatments and every 10 days.   Results & Discussion The results showed that mean and standard deviation of lentil genotype yields under drought stress and non stress conditions revealed significant differences. Accordingly, the average yield of genotypes under conditions of stress was 20.4 g.m-2, which showed a decrease of 70.3% in non-stress conditions with 68.6 g.m-2. According to 147 mm rainfall from planting to harvest, this yield reduction was not expected, indicating the need for supplementary irrigation. High standard deviation between genotypes indicates a large variety of lentil genotypes, and this wide variety can be used as a valuable genetic resources for later studies. According to the results, there was a significant correlation between yield and stress (P≤0.01) (r=0.71**). Also, there was a positive and significant correlation between performance in non stress conditions with the old indices HARM, TOL, MP, STI, GMP, SSPI, ATI and the new SNPI index (P≤0.01), and the correlation between yield in non stress conditions and SSI and RDI were not significant. There was also a positive and significant correlation between performance in non-stress conditions and ATI, GMP, HARM, RDI, STI, SSI, TOL and MP, and the new SNPI index (P≤0.01), but between yield in non stress conditions and the SSI was a significant negative correlation (P≤0.01). Old indices of HARM, TOL, STI, GMP, MP, ATI, and two new indicators of SSPI and SNPI, all have a positive and significant correlation (p≤0.01) with performance under stress and non stress conditions and can be considered as suitable indicators for screening stress tolerant genotypes.   Conclusion The results of current study showed that the new SNPI index, which has a very high correlation (99.9%) with yield in stress conditions, as well as the old indices of HARM, STI and GMP, which have the positive and significant correlation with each other and with performance in two. The conditions of non stress and stress have been identified as the most suitable and effective criteria for identifying and selecting genotypes tolerant to drought stress. The results obtained from the three-dimensional, biplot, and cluster analysis methods are in agreement with each other for selection of high yielding and drought tolerant lines. Accordingly, it seems that genotypes 40, 48, 71, 73, 3, 8 , 45 and 52 are the promising and proposing genotypes in the Mashhad climate for further studies.