Interaction Effect of Arbuscular Mycorrhiza and Redroot Pigweed (Amaranthus retroflexus L.) on Growth and Yield of Sunflower under Water Stress Conditions

The management of soil elements by biological fertilizers is considered as an important attribute of sustainable agriculture. In order to evaluate the interaction effects of Arbuscular mycorrhizal fungi and redroot pigweed (Amaranthus retroflexus L.) on growth and yield of sunflower (Helianthus annuus L.) under water stress conditions, a field study was conducted in 2015 at School of Agriculture, Shiraz University, Shiraz, Iran. Water stress at three levels (60, 80 and 100% FC) as main factor, mycorrhizal fungi at two levels (with and without fungi) and redroot pigweed at two levels (weedy and weed free) were used in three replications based on factorial in sub plots. Results showed that seed yield reduced the by 42% under weedy conditions and applying mycorrhizal fungi compensated the grain yield decrease by 29%. Weed in moderate and severe water stress conditions caused seed yield reductions of 35 and 52%, and applying mycorrhizal fungi compensated grain yield loss by 4 and 51%, respectively. Mean comparisons for severe water stress and weedy treatment interaction showed oil yield, biological yield and harvest index reduced by 57, 36 and 25% and applying mycorrhizal fungi compensated oil yield, biological yield and harvest index decreases by 63, 25 and 20%, respectively. In general, it seems that the application of mycorrhiza can improve growth and yield characteristics of sunflower under water stress and weedy conditions.