Effects of uniconazole and bio fertilizers on grain filling period and contribution of remobilization in grain yield of wheat under different moisture regimes in greenhouse condition

Introduction Drought stress is the most influential factors affecting crop yield particularly in arid and semiarid regions. This stress induces various biochemical and physiological responses in plants as a survival mechanism (Tas and Tas 2007). 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 (Shao et al. 2008.( Under stress condition, high yield of wheat grain is as a result of the grain filling rate and the ability to transfer assimilates stored to the grain (Santiveri et al., 2002). Borrás et al. (2004) reported that dramatic decrease in grain filling period and grain yield are related to lack of assimilate supply during the grain filling period. Santiveri et al. (2002) found that grain filling period appears to be greatly affected by environmental factors than grain filling rate. Most of the assimilates used for grain filling is produced by the upper canopy, which develops mainly from the spike, the flag leaf, and its sheath (Loss & Siddique, 1994). Dry matter and stem reserves provide a powerful resource for grain filling under any type of stress (Wang et al., 2009). Ehdaie et al. (2008) suggested that wheat in dry land areas may rely more on stem reserves for grain filling than on the current photosynthesis. Xue et al. (2006) reported that after anthesis, when photosynthetic activity is reduced by drought or salinity, grain filling becomes more dependent on mobilized of the dry matter (22 to 80%) that accumulates in the grain stem reserves. Application of bio- fertilizers and uniconazole are proper methods for increasing wheat yield under water limitation conditions. Materials and methods  In order to study the effects of uniconazole and bio- fertilizers on grain filling period and contribution of remobilization in grain yield of wheat under different moisture regimes, a factorial experiment was conducted based on randomized complete block design with three replications at research greenhouse of faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili in 2015. Experimental factors included foliar application of uniconazole at two levels (without uniconazole as control and foliar application of 0.1 g.L-1), bio fertilizers in four levels (application of mycorrhiza, application of Azotobacter+Psedomunas, co-inoculation with PGPR+mycorrhiza and no application of biofertilizers as control), and irrigation in three levels (full irrigation, irrigation until%50 of heading and booting stages as moderate and severe water limitations, respectively). Mycorrhiza fungi (Glomus mosseae) was purchased from the Zist Fanavar Turan institute and soils were treated based on the manufacturer’s protocol 10 g of inoculums per 1 kg soil. Azotobacter chrocoococum and Psedomunas putida were isolated from the rhizospheres of wheat by Research Institute of Soil and Water, Tehran, Iran. The strains and cell densities of microorganisms used as PGPR in this experiment were 107 bacteria per milliliter (108 cfu/ml-1). uniconazole were sprayed prior to booting stage. To investigate grain filling parameters in each sampling, three plants in each pot were taken. The first sampling was taken on the 15th day after heading and other samplings were taken in 4 days’ intervals for determining the accumulation of grain weight .   Results and Discussion The results showed that the maximum contribution of remobilization from aaboveground organs (57.6%), contribution of stem reserves at grain yield (53.4%) and also the minimum of grain filling period (26.6 days) were obtained with irrigation until 50% of booting, no usage of biofertilizers and without uniconazole. The Maximum single grain weight and grain filling period (0.052 g and 34.5 days respectively) were observed with full irrigation and application of both biofertilizers and uniconazole, whereas the lowest amounts of these traits (0.03 g and 26.6 days) were observed with irrigation till 50% of booting stage, and no usage of both bio fertilizers and uniconazole. The maximum grain filling rate (0.00248 g.day-1) was obtained with irrigation until 50% of booting stage and application of both biofertilizers and uniconazole, whereas its minimum rate(0.00016 g.day)was obtained with full irrigation and no usage of biofertilizers. Conclusion Generally, it seems that application of bio-fertilizers and uniconazole can be considered as appropriate management factors for increasing grain yield and grain filling period under water limitation conditions.