Influence of the pruning system on the fungal community of grapevine (Vitis vinifera)

Abstract

The novel grapevine training system “semi minimal pruned hedge” (SMPH), enables farmers to reduce their production costs by replacing the time and labour intensive winter pruning, usually done by hand, with a mechanical pruning approach. Due to its economic benefits, SMPH became more popular in Germany over the last decade and the number of SMPH vineyards is still increasing. However, due to the lack of extended monitoring in the field, some cultivation aspects of SMPH are poorly understood. One important issue is related to the incidence of fungal grapevine diseases and the respective protection of the vines. Therefore, it was the aim of this study to investigate on a long term basis (2015–2018) the influence of the pruning system on the fungal community of grapevine, with special regard to phytopathogenic fungi.

One part of this study compared the canopy architecture and microclimate of SMPH and “vertical shoot positioning” (VSP) trained vines. The incidence of major fungal grapevine diseases, i.e. Downy Mildew (DM), Powdery Mildew (PM) and Botrytis Bunch Rot (BR) was surveyed over four consecutive years. Within this time frame it was noted that SMPH trained vines were more susceptible to DM and PM compared to VSP trained vines. It is assumed that the comparatively slower drying process of SMPH canopies produces a microclimate that favours growth and spread of these diseases. By contrast, SMPH bunches were less susceptible to BR compared to VSP bunches, which is probably linked to the more loose bunch architecture.

An analysis of the temporal development of the fungal community in healthy grapevine branches covering two months to eight years old branches revealed that fast growing fungi like Alternaria spp., Aureobasidium pullulans, Botrytis cinerea, Cladosporium spp., Diaporthe spp., Epicoccum nigrum, Penicillium spp., and Truncatella angustata are characteristic for young branches (two months to one year old). However, in older branches (> one year) the fungal community is more characterized by grapevine trunk disease (GTD) associated fungi, with Cadophora luteo-olivacea, Diplodia seriata and Eutypa lata as predominant species. These data show that grapevines with older branches, as found in SMPH trained vines, are more threatened by GTDs than grapevines with only annual branches, as in VSP trained vines.

In four consecutive years a monitoring for Esca related foliar symptoms was performed in twelve vineyards each subdivided in SMPH and VSP trained sections to investigate the influence of the training system on symptom occurrence. Significant differences between the two training systems regarding the incidence of Esca foliar symptoms were found in three out of the four years. However, overall the results are inconsistent. While in 2016 SMPH trained vines expressed more symptoms than VSP trained vines, the opposite was the case in 2017 and 2018.

Spore traps were placed in a vineyard subdivided into SMPH and VSP trained sections to monitor the incidence of the Esca associated fungus Phaeomoniella chlamydospora over the year. Besides P. chlamydospora also other species of the Phaeomoniellales were isolated, including one known species, Neophaeomoniella zymoides, and six unknown species, which were newly described. The number of fungal strains and species of the Phaeomoniellales tend to be higher for spore traps attached to SMPH trained vines. A pathogenicity test made with potted plants in the greenhouse revealed that of the eight isolated species of the Phaeomoniellales only P. chlamydospora was able to induce significant lesions in the wood.

Data collected in this study shall help to developing a plant protection regime adapted to SMPH.