Abstract:

In this study， seeds of oat （Avena sativa） were soaked in a broth without fungi （CK） or in the borth of a culture of one of four plant endophytic fungi （three Penicillium and one Trichoderma species） isolated from the Qinghai-Tibetan Plateau. Then， the growth， physiology， and root endophytic fungal community structure of the oat under osmotic stress were evaluated. After seed-soaking treatments， seeds were germinated in Petri dishes， grown in pots under normal conditions for 30 days， and then grown under different osmotic stress treatments for a further 10 days. The plants were subjected to osmotic stress treatments， which were established by adding 50 mL of a solution containing polyethylene glycol at concentrations （V/V） of 5%， 10% and 15% （mild stress）； 20% and 25% （moderate stress）； 30% and 35% （severe stress）. Sterile water was added to the unstressed control （0% polyethylene glycol）. The plant height， fresh weight， dry weight and chlorophyll contents of the oat seedlings generally decreased with increasing severity of drought stress， and peroxidase activity and the contents of malondialdehyde and proline varied widely depending on which endophytic fungus had been used for seed soaking. Illumina Miseq data were obtained from the 40-day-old plants grown from fungal broth-soaked seeds. In total， 192944 valid sequences obtained， corresponding to 1140 operational taxonomic units belonging to 9 phyla， 15 classes， 34 orders， 56 families， and 148 genera. Compared with the CK group， seed-soaking changed the community structure of endophytic fungi in the oat roots. Soaking seeds in fungal broth increased the relative abundance of Russulaceae （Basidiomycota）. The dominant genus was Lactarius， whereas the dominant genus in the CK was Alternaria. Principal component analysis divided Penicillium and Trichoderma strains used for seed-soaking into three categories： growth-promoting strains， stress-enhancing strains， and strains that increase microbial diversity. Trichodermaalni increased the diversity of endophytic fungi in roots， whereas Penicillium spp. and Penicilliumgoetzii significantly promoted oat growth and stress resistance. These results show that soaking seed in the culture broth of endophytic fungi from the Qinghai-Tibet Plateau can enhanced the response of oat plant to drought stress by promoting growth， reducing drought-induced oxidative damage， and changing the community structure of endophytic fungi in the roots.

Key words: seed soaking of endophytic fungi, Avena sativa, drought stress, physiology and biochemistry, fungal community structure