Influence Of Transgenic Bt Cotton On Symbiotic Characteristics And Effect Of AM Fungi

Arbuscular mycorrhiza(AM) fungi are a kind of functional micro-organisms,which can form symbiotic association with more than 80% of land plants. The symbiotic relationship can facilitate plant mineral nutrient uptake, enhance tolerance of environmental stress and plant disease. AM fungi play an important role on maintaining plant species diversity and ecosystem stability.In recent years, Bt-transgenic crops are widely planted in the world, which may lead to many environmental issues. During different growth stage, Bt-transgenic crops will constantly release insecticidal crystal proteins into soils. These insecticidal crystal proteins can accumulate in soil and keep insecticidal activity for 180-234 days,which will have much impact on non-target organisms.This study investigated the effect of Bt protein on germination of AM fungal spore and hyphal differentiation under sterile culture. With 5 transgenic Bt cotton cultivars and their corresponding parental non-transgenic lines, a pot experiment was conducted to investigate the impact of Bt cotton on the germination of AM fungal spore, hyphal differentiation and mycorrhizal symbiosis. The impact of decomposed Bt cotton leaves on the symbiotic activity of AM fungi was also examined. The main results are as followed:(1) Bt protein significantly inhibited the germination of AM fungal spores. Bt protein had a negative impact on hyphal differentiation. When the concentration of Bt protein was over 100 ng ml-1, the germination of G. intraradices spore was significantly inhibited, and when over 50 ng ml-1, the germination of G. mosseae spore was inhibited.(2) Rhizosphere substances of Bt cotton had much influence on the germination of AM fungal spore and hyphal differentiation. Except s GK321 and Zhong41, the germination rate, number of hyphal branch and hyphal length with parental non-transgenic cotton were significantly higher than those with Bt cotton. While s GK321 promoted such indexes, Zhong41 had no significant influence.(3) Bt cotton had much influence on symbiotic characteristics and symbiotic effect of AM fungi. The appressoria number on the root epidermis of parental non-transgenic cotton are more than those of Bt cotton. Except s GK321, the infection rate and arbuscular abundance of G. intraradices with parental cotton are much higher than those of Bt cotton from the 15 th day post inoculation. Except Zhong 41, the infection rate and arbuscular abundance of G. mosseae with parental cotton are much higher. Inoculation of AM fungi improved phosphate uptake and enhanced the biomass of Bt cotton and conventional cotton.(4) Decomposed leaves of Bt cotton inhibited G. intraradices infection with A sinicus and decreased arbuscular abundance. Decomposed leaves of Bt cotton also decreased SDH, ALP activity of AM fungi. Inoculation of AM fungi improved phosphate uptake and enhanced the biomass of A sinicus.