Pathogen Infection and Host-Resistance Interactively Affect Root-Associated Fungal Communities in Watermelon

Abstract

Interactions of pathogen infection, host plant resistance, and fungal communities are poorly understood. Although the use of resistant watermelon cultivars is an effective control measure of watermelon wilt disease, fungal communities may also have significant effects on the development of the soil-borne pathogen complexes. We characterized the root and rhizosphere fungal communities associated with healthy and diseased watermelons of three different cultivars with different susceptibilities toward wilt disease by paired-end Illumina MiSeq sequencing. Thirty watermelon plants including highly wilt-resistant, moderately resistant, and susceptible cultivars were collected from a greenhouse, half of which showing clear wilt symptoms and the other half with no symptoms. Patterns of watermelon wilt disease and the response of the fungal communities varied among the three cultivars. The amount of the pathogen Fusarium oxysporum f. sp. niveum was higher in diseased root and rhizosphere samples, particularly in the susceptible cultivar, and was significantly positively correlated with the disease index of Fusarium wilt. Plant health had significant effects on root-associated fungal communities, whereas only the highly resistant cultivar had significant effects only on the rhizosphere fungal communities. Co-occurrence networks revealed a higher complexity of fungal communities in the symptom-free roots compared to diseased roots. In addition, networks from roots of the highly resistant plants showing symptoms had a higher complexity compared to the susceptible cultivars. Keystone species were identified for the plants with different symptom severity and the different cultivars in the root and rhizosphere, such as Fusarium oxysporum, Monosporascus cannonballus, and Mortierella alpina. Overall, the most important factor determining fungal communities in the roots was plant symptom severity, whereas in the rhizosphere, plant genotype was the most important factor determining fungal communities.

Seed-Transmitted Bacteria and Fungi Dominate Juvenile Plant Microbiomes

“…Sequence the bacterial populations in soybean root nodules, and by far the most abundant members observed are Bradyrhizobium, which are the preferred nitrogen-fixing endosymbionts of those plants (Sharaf et al, 2019). Watermelon cultivars which are susceptible to fusarium wilt, will accumulate much higher levels of Fusarium in their roots than will resistant cultivars (Xu et al, 2020). Identify soils with high levels of plant pathogens (such as Fusarium solani, Verticillium dahliae, Rhizoctonia solani, and Colletotrichum truncatum), and it is possible to identify the part of the field the sickest strawberry plants will develop (Mirmajlessi et al, 2018).…”

Effects of maize variety on the structure of maize phyllosphere fungal communities

“…We found that the complexity of the fungal community networks for the HR variety was relatively higher than the other three varieties, which indicated higher stability of the fungal community. This is supported by the notion that a resistant plant genotype frequently possessed a more complex microbial network in the rhizophsere and phyllosphere (Xu et al 2020;Zhong et al 2019). More positive associations in the HR fungal community included more cross feeding, co-aggregation, co-colonization and niche overlap in the community (Faust and Raes 2012), suggesting a relatively healthy community.…”

Effects of maize resistance and leaf chemical substances on the structure of phyllosphere fungal communities

“…We found that the complexity of the fungal community networks for the HR variety was relatively higher than the other three varieties, which indicated higher stability of the fungal community. This is supported by the notion that a resistant plant genotype frequently possessed a more complex microbial network in the rhizophsere and phyllosphere ( Zhong et al., 2019 ; Xu et al., 2020 ). More positive associations in the HR fungal community included more cross feeding, co-aggregation, co-colonization and niche overlap in the community ( Faust and Raes, 2012 ), suggesting a relatively healthy community.…”