Abstract
In this work we analyzed the relationship among native arbuscular mycorrhizal fungi (AMF) and vine roots affected by esca, a serious grapevine trunk disease. The AMF symbiosis was analyzed on the roots of neighboring plants (symptomatic and asymptomatic to esca) in 14 sites of three vineyards in Marche region (central–eastern Italy). The AMF colonization intensity, identified by non-vital staining, showed higher value in all esca symptomatic plants (ranging from 24.6% to 61.3%) than neighboring asymptomatic plants (from 17.4% to 57.6%). The same trend of Glomeromycota phylum abundance was detected by analyzing fungal operational taxonomic units (OTUs) linked to the AMF community, obtained by amplicon high throughput analysis of ITS 1 region. Overall, the highest amount of OTUs was detected on roots from symptomatic plants (0.42%), compared to asymptomatic roots (0.29%). Specific primer pairs for native Rhizophagus irregularis and Funneliformis mosseae AMF species, were designed in 28S rRNA and large subunit (LSU) ribosomal RNA, respectively, and droplet digital PCR protocol for absolute quantification was set up. A higher number of DNA copies of both fungal species were detected more frequently in symptomatic than asymptomatic vines. Our study suggests a relationship between esca and native AMF in grapevine. These results underline the importance of native rhizosphere microbial communities for a better knowledge of grapevine esca disease.
Highlights
Esca, together with Eutypa dieback and Botryosphaeria dieback, are considered the most destructive trunk diseases of grapevine, and are a rapidly growing concern in all wine producing countries [1]
Related to non-vital staining, native arbuscular mycorrhizal fungi (AMF) colonization was detected in all analyzed root samples of both esca symptomatic and asymptomatic plants with a frequency (F%)
Relating to each of the 14 sites identified in the vineyards, all the esca symptomatic plants showed higher significative native mycorrhizal colonization related to both mycelium colonization (M%) (p < 0.0001, Student’s paired t-test) and arbuscular abundance (A%), (p = 0.0005, Student’s paired t-test) than the neighboring asymptomatic plants (Figure 1a,b)
Summary
Together with Eutypa dieback and Botryosphaeria dieback, are considered the most destructive trunk diseases of grapevine, and are a rapidly growing concern in all wine producing countries [1]. This disease involves several xylem-inhabiting fungi [2,3,4,5,6,7]. More than 80% of plant species in natural conditions are mycorrhized This exceptionally ancient (>450 million years) and coevolutionary relationship is considered the key factor in early plant colonization of land and has been verified to be generally beneficial to both partners [11,12]. In addition to this nutritional function, AMF field and pot inoculation can enhance plant tolerance to both biotic and abiotic stresses including drought, salinity, herbivory, temperature, metals, and diseases, relative to their non-mycorrhizal counterparts in experimental studies [15]
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