Evaluation of the Antifungal Activity of Endophytic and Rhizospheric Bacteria against Grapevine Trunk Pathogens

Abstract

Grapevine trunk diseases (GTDs) are caused by multiple unrelated fungal pathogens, and their management remains difficult worldwide. Biocontrol is an attractive and sustainable strategy given the current need for a cleaner viticulture. In this study, twenty commercial vineyards were sampled across California to isolate endophytic and rhizospheric bacteria from different grapevine cultivars with the presence and absence of GTD symptoms. A collection of 1344 bacterial isolates were challenged in vitro against Neofusicoccum parvum and Diplodia seriata, from which a subset of 172 isolates exerted inhibition levels of mycelial growth over 40%. Bacterial isolates were identified as Bacillus velezensis (n = 154), Pseudomonas spp. (n = 12), Serratia plymuthica (n = 2) and others that were later excluded (n = 4). Representative isolates of B. velezensis, P. chlororaphis, and S. plymuthica were challenged against six other fungal pathogens responsible for GTDs. Mycelial inhibition levels were consistent across bacterial species, being slightly higher against slow-growing fungi than against Botryosphaeriaceae. Moreover, agar-diffusible metabolites of B. velezensis strongly inhibited the growth of N. parvum and Eutypa lata, at 1, 15, and 30% v/v. The agar-diffusible metabolites of P. chlororaphis and S. plymuthica, however, caused lower inhibition levels against both pathogens, but their volatile organic compounds showed antifungal activity against both pathogens. These results suggest that B. velezensis, P. chlororaphis and S. plymuthica constitute potential biocontrol agents (BCAs) against GTDs and their application in field conditions should be further evaluated.

Biocontrol of almond canker diseases caused by Botryosphaeriaceae fungi

“…53 Other strains of Pseudomonas spp. and B. velezensis have also demonstrated their efficacy against fungal trunk diseases in other crops, such as grapevine, 37,39,55 as well as in the control of apple and pear ring rot disease caused by B. dothidea. 48,[74][75][76] Isolation of endophytic bacteria from healthy, asymptomatic trees, growing in an infested orchard has been described as a powerful technic to obtain bacterial species to be used as (A) (B) Figure 3.…”

“…87 In this context, these genera have also been used against trunk pathogens in various woody crops, particularly in grapevines. 55,81,88 Additionally, they have shown promising results as BCAs against various insect species that are pests of almond. 89 Also, different species of Trichoderma and Clonostachys have been successfully used as BCAs for the protection of almond, cherry and grapevine pruning wounds against infection by fungal canker pathogens, including N. parvum.…”

“…and B . velezensis have also demonstrated their efficacy against fungal trunk diseases in other crops, such as grapevine, 37,39,55 as well as in the control of apple and pear ring rot disease caused by B . dothidea 48,74–76 …”

“…Furthermore, endophytic bacteria from the plant microbiota represent an important source of biocontrol agents displaying beneficial activities. 55 Given the considerable variability within the Botryosphaeriaceae family, 56 it is crucial to possess a wide variety of phytosanitary products to control the disease. Considering this, our study focuses on evaluating the effect of rhizospheric and endophytic bacteria on the in vitro growth of four Botryosphaeriaceae species that cause almond canker diseases: Neofusicoccum parvum, Botryosphaeria dothidea, Diplodia seriata and Macrophomina phaseolina.…”

“…However, to the best of our knowledge, no control agents based on bacterial strains have been successfully tested against canker diseases caused by Botryosphaeriaceae in almond. Furthermore, endophytic bacteria from the plant microbiota represent an important source of biocontrol agents displaying beneficial activities 55 . Given the considerable variability within the Botryosphaeriaceae family, 56 it is crucial to possess a wide variety of phytosanitary products to control the disease.…”