effect of three species of mycorrhiza inoculation on yield and some physiological properties of two potato cultivars under drought stress in controlled conditions

introduction in recent years, rainfall deficiency was an increasing problem in most countries; which limited the production of agricultural crops. among abiotic stresses the plants encountered, drought stress is considered as the most important limiting factor in plants growth and reproduction in natural and agricultural systems through most parts of the world; while drought stress causes 45% increase in the crops among various stress making factors (biotic and abiotic). a suitable procedure for controlling drought stress in agriculture is making the symbiotic relation between plants and mycorrhizal fungi. mycorrhizal fungi decrease the plant ability in absorbing nutrients, ion balance, keeping enzyme activity, increasing chlorophyll density and root-soil connection; they decline the hazards caused by stress and decrease the plant tolerance to biotic and abiotic stresses. potato is one of the most valuable sources to provide human food in the developing countries and is one of the most productive crops, while its production is twofold to rice and wheat. producing more than 5 million tones potato makes this crop as the first utilizable nutrient after wheat, in this country. potato is sensitive to soil humidity caused by limited and low-deep root system. materials and methods thus, an investigation was conducted to examine the effect of three of mycorrhizal fungi (glomus mosseae, glomus intraradices and glomus fasciculatum) on two potato cultivars (agria and fontana) under drought stress and control conditions, in factorial experiment based on complete randomize block with three repetitions in research greenhouse of ferdowsi university in 2012. in control treatment, irrigating was done when field capacity got 80% and it was conducted to 100% field capacity. stress treatment was done when the field capacity got 60% and continued to 80% field capacity. fungus treatment was done with a 100g mixture of inoculum including mycorrhizal root sections of corn, soil and mycorrhizal active parts (spore and hyphae) provided by corn root during a four-month period, in root space. results and discussion the results indicated that agria cultivar in higher than fontana. the drought stress decreased bush height, totally fungi resulted in increasing bush height in both cultivars. however, leaf area of fontana was more than agria; drought stress decreased leaf area but using glomus fasciculatum and glomus mosseae fungi increased the plant height in both cultivars. among the treatments, the effect of cultivar on chlorophyll fluorescence was significant and there was no significant difference with each other. only the effect of cultivar on chlorophyll fluorescence was significant among the treatments and there was no significant difference among other treatments. the amount of spad index in agria was 10% more than fontana. this parameter was observed much more in control treatment than fungal treatments; drought stress indicated higher spad. there was a significant difference between agria and fontana cultivars for tuber weight. fontana increased the production to 36% by producing 129g tuber to agria cultivar. this difference was observed in control treatment and drought stress. among various cultivars, glomus fasciculatum and glomus mosseae were significantly different from other treatments with 120 and 123gr tuber, respectively; and control treatment contained the least one with a 75g tuber. the interaction of fungus and stress indicated that there was no significant difference in fontana cultivar and in mycorrhizal treatments for single-bush yield; but in control treatment, this rate was the least and had significant difference with other treatments. the most significant difference among stress levels was observed in glomus intraradices; in this fungus, control treatment indicated 44% yield more than drought stress. fontana indicated a significant difference to agria cultivar for four tubers in a bush, averagely. control treatment indicated a significant difference to drought stress for four tubers in a bush and 20% increase, but there was no significant difference among various mycorrhizal fungi for tuber numbers in a bush. totally, glomus fasciculatum affected the studied potato properties more positively than other species.