Treatment With Wheat Root Exudates and Soil Microorganisms From Wheat/Watermelon Companion Cropping Can Induce Watermelon Disease Resistance Against Fusarium oxysporum f. sp. niveum.

Companion cropping with wheat (Triticum aestivum L.) can enhance watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] wilt disease resistance against Fusarium oxysporum f. sp. niveum. However, the mechanism of resistance induction remains unknown. In this study, the effects of microbial community dynamics and the interactions between wheat and watermelon plants, particularly the effect of wheat root exudates on watermelon resistance against F. oxysporum f. sp. niveum, were examined using a plant-soil feedback trial and plant tissue culture approach. The plant-soil feedback trial showed that treating watermelon with soil from wheat/watermelon companion cropping decreased watermelon wilt disease incidence and severity, increased lignin biosynthesis- and defense-related gene expression, and increased ß-1,3-glucanase activity in watermelon roots. Furthermore, soil microbes can contribute to increasing disease resistance in watermelon plants. Tissue culture experiments showed that both exogenous addition of wheat root exudates and companion cropping with wheat increased host defense gene expression, lignin and total phenols, and increased ß-1,3-glucanase activity in watermelon roots. In conclusion, both root exudates from wheat and the related soil microorganisms in a wheat/watermelon companion cropping system played critical roles in enhancing resistance to watermelon wilt disease induced by F. oxysporum f. sp. niveum.

Physiological response and sulfur metabolism of the V. dahliae-infected tomato plants in tomato/potato onion companion cropping.

Companion cropping with potato onions (Allium cepa var. agrogatum Don.) can enhance the disease resistance of tomato plants (Solanum lycopersicum) to Verticillium dahliae infection by increasing the expressions of genes related to disease resistance. However, it is not clear how tomato plants physiologically respond to V. dahliae infection and what roles sulfur plays in the disease-resistance. Pot experiments were performed to examine changes in the physiology and sulfur metabolism of tomato roots infected by V. dahliae under the companion cropping (tomato/potato onion). The results showed that the companion cropping increased the content of total phenol, lignin and glutathione and increased the activities of peroxidase, polyphenol oxidase and phenylalanine ammonia lyase in the roots of tomato plants. RNA-seq analysis showed that the expressions of genes involved in sulfur uptake and assimilation, and the formation of sulfur-containing defense compounds (SDCs) were up-regulated in the V. dahlia-infected tomatoes in the companion cropping. In addition, the interactions among tomato, potato onion and V. dahliae induced the expression of the high- affinity sulfate transporter gene in the tomato roots. These results suggest that sulfur may play important roles in tomato disease resistance against V. dahliae.

[Effects of Chinese onion' s root exudates on cucumber seedlings growth and rhizosphere soil microorganisms].

Taking the Chinese onion cultivars with different allelopathy potentials as the donor and cucumber as the accepter, this paper studied the effects of Chinese onion' s root exudates on the seedlings growth of cucumber and the culturable microbial number and bacterial community structure in the seedlings rhizosphere soil. The root exudates of the Chinese onion cultivars could promote the growth of cucumber seedlings, and the stimulatory effect increased with the increasing concentration of the root exudates. However, at the same concentrations of root exudates, the stimulatory effect had no significant differences between the Chinese onion cultivars with strong and weak allelopathy potential. The root exudates of the Chinese onion cultivars increased the individual numbers of bacteria and actinomyces but decreased those of fungi and Fusarium in rhizosphere soil, being more significant for the Chinese onion cultivar with high allelopathy potential (L-06). The root exudates of the Chinese onion cultivars also increased the bacterial community diversity in rhizosphere soil. The cloning and sequencing results indicated that the differential bacteria bands were affiliated with Actinobacteria, Proteobacteria, and Anaerolineaceae, and Anaerolineaceae only occurred in the rhizosphere soil in the treatment of high allelopathy potential Chinese onion (L-06). It was suggested that high concentration (10 mL per plant) of root exudates from high allelopathy potential Chinese onion (L-06) could benefit the increase of bacterial community diversity in cucumber seedlings rhizosphere soil.