Effect of Arbuscular mycorrhizal on yield, yield components and plant characteristics of sunflower (Helianthus annuus L.) under drought stress conditions

Water stress is one of the most important factors limiting growth and production of field crops in arid and semi-arid regions. One approach to increase drought tolerance in crop plants is through the symbiotic effect of the arbescular mycorrhizal (AM) fungi.. Water deficit stress is typical to semi arid environments and most of the crop plants are affected by drought, during the flowering-grain filling periods. To study the symbiotic effect of the arbescular mycorrhizal (AM) fungi On drought tolerance and some plant characteristics in sunflower, a field experiment was conducted in split plot arrangements using randomized complete blocks with four replications at the Research Field of Tarbiat Moddres University, Tehran, Iran in 2006 cropping season. Three soil available soil moisture contents; 40%(w1), 60%(w2) and 80%(w3) were assigned to main plots and two mycorrhiza species; Glomus mosseae, Glomus hoi and a non- inoculated traetment were randomized in sub- plots. Results showed that the AM fungi species significantly affected all of measured plant traits, except 1000 seed weight, number of total seed m-2, number of filled seed number per m-2 and oil content. However, water stress affected significantly all of measured traits. Water stress  mycorrhiza interaction was negligible on all studied traits except on grain yield and number of unfilled seed per m2 and oil yield. Results indicated that the highest and lowest grain yield and dry matter was obtained in available soil moisture content of 80% and inoculation with G. mosseae and non-inoculated treatrments with 1230 and 990 kg.ha-1 of grain yield and 4400 and 3180 kg.ha-1 of dry matter, respectivly. Results also revealed that different AM fungi species had significantly diffrent effect on seed yield and root colonization under different soil moisture conditions. Seed yield and seed oil content were higher in well-watered with mycorrhiza and without mycorrhiza. Micorrhiza species affected seed yield of sunflower through their effect on seed weight and filled seed number m-2 under well -watered and water stress conditions.