سید محمد علی مفیدیان

Climate change drastically reduces the amount of water available to plants and increases the severity and frequency of droughts. By the end of this century, it is anticipated that droughts will continue to increase significantly. Drought stress, as one of the major climate events, induces physiological and morphological alterations, which can restrict crop growth, yield, and quality. In recent years, separate research projects and studies in the country have evaluated the effects of drought stress on grain maize, forage maize, grain sorghum, forage sorghum, grain millet, alfalfa, and clover yields, as well as the effects of drought stress on their yield gap. However, if the results of these separate studies were evaluated together, it would have been possible to compare the drought sensitivity and tolerance of various crops. Consequently, the optimal crop to plant under drought-stress conditions in the nation's agroecosystems would be determined. The meta-analysis is a statistical analysis that can assess the aggregate effects of numerous studies conducted under varying conditions. In other words, meta-analysis is a statistical technique for integrating the findings of multiple studies in order to comprehend a problem. The purpose of this meta-analysis was to determine the impact of different drought stress levels on the yields of grain maize, forage maize, grain sorghum, forage sorghum, grain millet, alfalfa, and clover.

In this study, the data obtained from 145 final reports of the Agricultural Research, Education, and Extension Organization (AREEO) and published articles over the past decade were analyzed using the meta-analysis method. This included grain sorghum (18 studies), forage sorghum (21 studies), grain maize (28 studies), forage maize (23 studies), grain millet (18 studies), alfalfa (17 studies), and clover (20 studies). In addition to the difference in quantitative results between studies, the effect size variance was utilized in this method. Consequently, the means, standard deviations, and sample sizes (replications in each study) for the control and evaluated treatments were determined. After classifying the data, the reaction ratio (R) and its natural logarithm were calculated. Subsequently, the method determined which treatments have additive or decreasing effects on yield under drought stress conditions, as well as which treatments had no positive or negative impact on yield. Utilizing the T-test, a group comparison was conducted between the mean yield under drought stress conditions and the mean yield under normal irrigation conditions in order to determine the significance level of yield changes caused by drought stress. The statistical analysis and preparation of the figures were performed by Excel.

According to the findings of the meta-analysis, the overall effect of drought stress on the yield of all seven crops was significant for grain sorghum (-16.30%) (P<0.05), forage sorghum (-18.27%) (P<0.05), grain maize (-31.75%) (P<0.01), forage maize (-33.24%) (P<0.01), grain millet (-25.66%) (P<0.01), alfalfa (-30.79%) (P<0.01), and clover (-32.14%) (P<0.01). The yield reductions in grain maize, forage maize, alfalfa, and clover were significant under all levels of drought stress, whereas grain sorghum, forage sorghum, and grain millet yield reductions were significant only under severe drought stress. The yields of grain sorghum, forage sorghum, grain maize, forage maize, grain millet, alfalfa, and clover decreased by 10.03, 11.84, 18.21, 20.27, 14.13, 19.74, and 20.37%, respectively, under moderate drought stress, and 21.98, 25.41, 39.09, 41.37, 32.55, 40.13, and 42.08%, respectively, under severe drought stress.

As a result, it is impossible to cultivate and develop grain maize, forage maize, alfalfa, and clover in areas with limited water resources without significantly reducing yield. According to the findings of this meta-analysis, grain sorghum, forage sorghum, and grain millet with a moderate drought stress tolerance threshold could be recommended for cultivation in regions where drought stress conditions are likely to occur.

To identify the limiting factors in forage maize production in Iran, this study has been carried out in order to separate the effective and influential management factors in forage maize production in the country with data. It is obtained from 43 final reports or their derived extracted articles in Agricultural Research, Education and Extension Organization (AREEO) with meta-analysis method. According to the results, plant density (5.65%), drought stress (-13.44%), cultivar (0.31%), planting date (2.54%), and nitrogen fertilizer (24%) justify the amount of forage maize variation. Based on the results of this study, forage yield has increased by about 9.49%, increasing plant density between 80 to 100 thousand plants per hectare. Maize forage yield has decreased significantly under mild stress, severe stress, and very severe drought stress by 25.30%, 14.38% and 8.99%, respectively. Also, for different cultivars and different groups of maturity, group-700 has had a significant increase of 3.83% compared to other groups. For the planting dates of forage maize compared to the control, which is the first half of June, a decrease in forage yield is observed. Finally, the highest percentage of increase in maize forage yield has been obtained from the use of 450 kg ha-1 of urea fertilizer. Overall, nitrogen fertilizer, drought stress, and planting density are recognized as the most important factors affecting corn forage yield in Iran, respectively.

This study was executed to compare forage yield and leaf area index of different alfalfa genotypes for two years and also, to estimate of LAI via leaf weight and plant height during 2011 and 2012. Twenty local and forigen alfalfa genotypes were planted in a RCB design with three replications in spring, 2011 at Seed and Plant Research Institute (SPII), Karaj, Iran. Two-years analysis of variance indicated significant diferent among genotype's means for fresh and dry forage yield in which Bami x Yazdi, Mesa sersa and KFA17 genotypes with 41.99, 39.84 and 39.15 (t ha-1) fresh forage yield and 9.75, 9.41 and 9.16 (t ha-1) dry forage yield were the most forage production, respectively. Despite the significanat difference among genotypes for leaf to stem ratio, there was no significance difference for LAI. The results showed that the fast, accurate and low-cost estimation of LAI is possible through leaf weight and plant height. In this study, leaf weight trait (especially the fresh leaf weight) had more efficiency than plant height in estimating leaf area index through a linear model (without constant) with high coefficient of determination (R2 ≥ 94). It was resulted that every 100 gr of fresh and dry leaf and 10 cm of plant height of alfalfa had 0.33, 1.51 and 0.25 m2 leaf area, respectively.

To evaluate fall dormancy of twenty alfalfa local ecotypes and exotic cultivars, this study was conducted in two separate experiments (conventional or dense planting and spaced planting) using randomized complete block design with three replications in three growing seasons 2014, 2015 and 2016 in two locations (Karaj and Khoy), Iran. First growing season was considered as estabilishment season. Three ecotypes of Hamedani population, four ecotypes of Gharah-Yunjeh population, five ecotypes of warm region populations, two ecotypes from central part of the country and six exotic cultivars were included in this study. In conventional planting, each cultivar/ecotype was grown in two rows of 5 m length and 50 cm row spacing using 20 kg.ha-1 seeding rate, based on seed germination percentage. In spaced planting, each cultivar/ecotype was planted in two rows of 5 m length and 50 cm row spacing and 50 cm distance between plants on row. The recorded traits were plant height, stem number per plant/m-2, dry forage yield, and fall dormancy score. Combined analysis of variance of both experiments showed that mean squares of cultivar/ecotype was significant for dry forage yield, plant height and fall dormancy score. Genotype × location interaction efect was also significant for these traits. Mean comparison of dry forage yield of cultivars/ecotypes showed that Baghdadi with 15.02 t ha-1 and Kiseverdai with 12.3 t.ha-1 in conventional planting, and Bami-1 with 29.6 g.plant-1 and Sequel with 22.1 g.plant-1 had the highest and lowest dry forage yield over two locations and growing seasons, respectively. In both experiments, the local ecotypes related to warm region had the higher fall dormancy scores in comparison to ecotypes from cold region. In conventional planting, Nikshahri, Bami-1 and Baghdadi with 6.9, 6.8 and 6.7 scores, and in spaced planting, Baghdadi and Nikshahri with 6.1 and 6.0 scores showed the highest fall dormancy scores, respectively. Commandor had the lowest fall dormancy score with 3.5 and 3.3 in conventional and spaced planting experiments, respectively. In general, the fall dormancy scores were determined in ecotypes of Ghara-yunje and Hamedani populations (cold region) from 4 to 5, ecotypes from temperate region (KFA7 and Yazdi) from 6 to 7 and warm region (Bami, Baghdadi and Nikshahri) from 7 to 9 scores. Assessment of fall dormancy scores in conventaionl planting experiment led to better estimates, however, it did not affect the grouping of cultivars/ecotypes.

To identify the limiting factors in grain maize production in Iran, a study has been carried out to particulate effective and influential management factors of this crop’s production in the country. The data come from 95 final reports or extracted articles in Agricultural Research, Education, and Extension Organization (AREEO), undergoing meta-analysis. Based on this study, of all grain maize variation, 2.93% is justified by plant density, 6.81% by planting structure, 11.12% by planting rotation, 2.28% by conservation agriculture, 25.28% by drought stress, 4.99% by cultivar, 4.46% by planting date, and 25.84% by nitrogen fertilizer. Accordingly, 100 thousand plants per hectare, zigzag double rows planting structure, maize-leguminous crops planting pattern, cultivating in residue, optimum irrigation without drought stress (in case of water availability), 700 maturity group cultivar (in case of adequate growing season), planting in May and early August in temperate and tropical climate, and using maximum 100-300 kg urea fertilizer per hectare are recommended to decrease yield gap in grain maize production.

Study of potential of alfalfa ecotypes in biomass partitioning and harvestable and non-harvestable parts as well as induction of summer dormancy under water scarcity can lead to develop adapted cultivars for sustainable farming system andto meet targets of the breeding program. Therefore, this experiment was conducted with 10 alfalfa ecotypes under four irrigation managements at Seed and Plant Improvement Institute (SPII), Karaj, Iran, during 2016-2018. The irrigation treatments included; full irrigation and irrigation withhold for 20, 40 and 60 days. Under stress and on stress conditions, Nikshahri and Yazdi ecotypes had the highest regrowth rate, therefore, these two ecotypes as well as KFA6 ecotype with high stem number demonstrated the highest survival rate under induction of summer dormancy. The highest biomass belonged to normal irrigation with 17.31 t.ha-1 while the maximum unharvestable part yield with 7.02 t.ha-1was measured in irrigation withhold treatment for 40 days. Yazdi and KFA6 ecotypes showed the maximum total biomass (15.71 and 15.76 t.ha-1 respectively) among warm and cold region ecotypes with different fall dormancy scores and can be used as aprentsin alfalfa breeding programs. Regarding to biomass partitioning ratio, KFA17, KFA6 and Yazdi, which are landraces, had greater harvestable part to unharvestable part ratio with 1.63, 1.43 and 1.40, respectively. Therefore, these landraces can be selected for forage production under different irrigation managements. As the leaf to stem ratio has the main role in forage quality, Baghdadi ecotype with leaf: stem ratio of 1.29 had the highest forage quality among studied ecotypes. Baghdadi also maintained its high quality in all irrigation management treatments. In alfalfa breeding programs focused on improvement of forage and unharvestable yield for sustainable production in both optimum and stress environment conditions, Yazdi and KFA6 ecotypes seems to be suitable.

Water scarcity is one of the major limiting factors to agricultural production across the globe and it is predicted that drought spells will occur more frequently in the future due to the long-term effects of global warming (Rivero et al., 2007). This has led to a decrease in canopy size, loss in photosynthesis and consequently reduced crop yields. Alfalfa, being perennial and multi cut, as well as having an efficient root system, can tolerate water limited conditions by dormancy and is able to restart its biological activities after irrigating (Mc Williams, 2002). The mechanisms of response to water stress are complex and include activation of growth regulators in molecular and physiological levels. In addition, the yield potential and stability of some Iranian alfalfa ecotypes in different locations have been investigated previously (Mofidian & Moghaddam, 2013).

The experiment was carried out with 10 warm and cold region alfalfa ecotypes in two distinct environments at Seed and Plant Improvement Institute (SPII), Karaj, Iran, over the years 2016-2018. The environments included full irrigation and no watering for 20 days from 22th of June. To conduct a preliminary evaluation of the ecotypes response to water stress, stress susceptibility index (SSI) based on fresh forage yield was calculated. The most important physiological traits measured in this study were as follows: relative water content (RWC), chlorophyll content index (CCI), canopy temperature depression (CTD), and stomatal resistance (SR), Chlorophyll a and b contents and carotenoids. Combined analysis of variance and mean comparisons were done by SPSS Ver.22 and Excel 2016.

The effect of no watering stress on all of the physiological traits was significant (P<0.01). The ecotypes showed a significant difference in dry matter yield and all physiological measurements except for electrolyte leakage and chlorophyll b content. The year effect indicated a significant difference for chlorophyll b (P<0.05); carotenoids and dry matter yield (P<0.01) but it was not found to be significant for the rest of traits. Among the interactions, environment × year interaction showed no significant effect for all the studied traits. Although, ecotype × environment interaction was significant just for carotenoids (P<0.01), ecotype × year interaction was significant for Dry matter yield, RWC, CTD and SR (P<0.01); and CCI, chlorophyll a (P<0.05), as well. Under full irrigation regime and cut-off irrigation treatment, RWC was respectively 66.26 and 44.06 percent, which indicated that water stress decrease RWC by 32 percent. Electrolyte leakage averaged 26.51 percent under the stress environment, exhibiting a 72 percent decrease in cell membrane stability relative to full irrigation scenario. The chlorophyll content index in non-stress condition was 38 percent greater than that of under stress condition. The canopy temperature depression decreased by 43 percent during water stress imposition. No water shortage treatment led to the least stomatal resistance of 22.22 s/cm; however, this value was 37.87 s/cm under water-limited conditions, which showed a difference of 70 percent.

The minimum stress susceptibility index at the first and second year, 0.35 and 0.51, were observed in BAGHDADI and BAMI ecotype respectively, which, among the investigated alfalfa ecotypes, were found to be the most resistance to no watering for 20 days. Overall, KFA6 ecotype showed the minimum electrolyte leakage (13.79 s/cm) and stomatal resistance (23.69 s/cm), respectively. Moreover, KFA6 ecotype had the maximum photosynthetic pigments of 1.623 mg in fresh leaf (gr) that led to the production of 17.48 t/ha dry matter yield and superiority of 14 percent as compared to the two-year mean of all ecotypes under full irrigation and no watering conditions. Keywords: Canopy temperature, stomatal resistance, cell membrane stability, photosynthetic pigments, and alfalfa. References: Mc Williams, D. 2002. Drought strategies for alfalfa. Extension handbook, Department of Extension Plant Sciences, New Mexico State University, Las Cruces, New Mexico. P-1-5. Rivero, R.M., Kojima, M., Gepstein, A., Sakakibara, H., Mittler, R., Gepstein, S., and Blumwald, E.2007. Delayed leaf senescence induces extreme drought tolerance in a flowering plant. Proceeding of National Academic Science, USA 104:19631–19636. Mofidian, S.M.A., and Moghaddam, A. 2013. Analysis of ecotype location interaction in cold-region alfalfa ecotypes. Iranian Journal of Crop Sciences, 15(2): 71-85.