Study of grain filling components of chickpea (Cicer arietinum L.) using segmented model under irrigation withholding condition, Methanol application and seed inoculation with bio fertilizers

Drought stress is the most influential factors affecting crop yield particularly in irrigated agriculture in arid and semiarid regions. Drought, being the most important environmental stress, severely impairs plant growth and development, limits plant production and the performance of crop plants, more than any other environmental factor. The impact of the drought on plant species depends on variety, severity and duration of the stress as well as on the development stage. The closing stomata which reduce transpiration and conserve water in plants is the first mechanism of plants against dehydration stress, which in turn limits CO2 fixation. One of the important strategies for increasing of carbon dioxide concentration in plants is using compounds such as methanol that can increase the concentration of CO2 in a plant will improve photosynthesis rate and growth under water deficit conditions. Among the numerous microorganisms in the rhizosphere, some have positive effects on plant growth promotion. These microorganisms are bio fertilizers such as plant growth promoting rhizobacteria (PGPR), which colonize the rhizosphere and roots of many plant species and confer beneficial effects to plants. Using rhizosphere microorganisms, particularly beneficial bacteria are an alternative strategy that can improve plant performance under stress environments and, consequently, enhance plant growth through different mechanisms. Mycorrhiza is a symbiotic association between plant roots and fungi and form symbiotic association with terrestrial as well as aquatic plants. They also impart other benefits to them including production/accumulation of secondary metabolites, osmotic adjustment under osmotic stress, improved nitrogen fixation, enhanced photosynthesis rate, and increased resistance against biotic and abiotic stresses. The mechanisms used by mycorrhiza to enhance the water relations of host plants are not amply clear, however, this may occur by increasing water absorption by external hyphae, regulation of stomatal apparatus, increase in activity of antioxidant enzymes and absorption of nutrients particularly phosphorus. Hence, application of bio fertilizers and methanol presumably looks to be a promising practice in plant yield optimization under suboptimal growth conditions. So, better understanding of chickpea physiological responses under water limitation may help in programs which the objective is to improve the grain yield under water limitation. Therefore, the aim of this study was to evaluate of grain filling components of chickpea (Cicer arietinum L.) using segmented model under irrigation withholding condition, methanol application and seed inoculation with bio fertilizers. 

 A factorial experiment was conducted based on randomized complete block design with three replications at the farm of Piralger from Ardabil provence in 2017-2018. The experimental factors included: application of methanol (foliar application with water as control, application 20 and 30 volume percent), bio fertilizers at four levels (no application as control, Mesorhizobium ciceri application, both application mycorhyza with Mesorhizobium ciceri, application of mycorhyza with Mesorhizobium ciceri and Psesomonas putida) and three irrigation levels (full irrigation as control, severe water limitation or irrigation withholding at flowering stage, moderate water limitation or irrigation withholding at podding). To investigate grain filling parameters in each sampling, two plants in each plot were taken. The first sampling was taken on day 12 after podding, and other samplings were taken in 5-days intervals to nv xfrikh determine the accumulation of grain weight. At each sampling, grains were removed from pods manually and were dried at 80°C for 48 h. We applied grain dry weight and number to estimate the mean grain weight per sample. Following Borrás and Otegui (2001), we calculated total duration of grain filling for each treatment combination through fitting a bilinear model: Where GW is the grain dry weight; a, -intercept; b, the slope of grain weight indicating grain filling rate. Borrás, Slafer, and Otegui (2004) determined grain filling using a bilinear model. Effective grain filling period (EFP) was calculated from the following equation:Where MGW: the highest grain weight (g) and b: grain filling rate (g day-1). Conversely, an increase in kernel weight in filling period was calculated using the above-cited equation in statistical software SAS 9.2 via Proc NLIN DUD method. The analysis of variance and mean comparisons were performed using SAS computer software packages. The main effects and interactions were tested using the least significant difference (LSD) test at the 0.05 probability level.

 A two part linear model was used to quantify the grain filling parameters. The highest number and weight of noduls per plant (11.6 and 113.21 mg per plant, respectively), chlorophyll index (50.28), grain filling rate (0.0117 g/day), grain filling period (39.57 days), effective grain filling period (32.2 days) and grain yield (1455 kg/ha) were obtained in full irrigation and high levels of methanol and application of mycorhyza, Mesorhizobium ciceri with Psesomonas which, there were 237 and 148 increases, respectively in number and weight of nodule per plant, 84.17% in chlorophyll index, 34.48% in grain filling rate, 21.38 and 25.3% in grain filling period and effective grain filling period respectively and 111% in grain yield in comparison with no application of methanol and bio fertilizers under irrigation withholding at flowering stage conditions. 

Based on the results, it seems that seed inoculation by bio-fertilizers and foliar application of methanol in order to increasing of grain yield, rate and grain filling period under water limitation is effective.