Influence of morphological traits of xylem vessels on the response to Phaeomoniella chlamydospora of table- and wine-grape and rootstocks

Phaeomoniella chlamydospora causes heavy economic losses on grapevine under field and nursery conditions. Xylem structural features might be a key determinant of sensitivity or resistance of the host plant. Here the relationship between P. chlamydospora infection and xylem vessels features of ten table grape and seventeen wine grape varieties or clones, as well as three rootstocks, was investigated. The observations were based on image analysis of cross sections and fungal isolation of cuttings artificially inoculated with a conidial suspension (106 conidia mL-1) of the benomyl resistant-marked strain PCHCIA43.2 of P. chlamydospora at 30-90 days after inoculation (DAI). The average vessels diameters of table grape cultivars ranged from 58.8 ('Allison') to 70.5 µm ('Red Globe'); 'Allison', 'Sable' and 'Timco' showed higher vessel densities than 'Italia', 'Sugar Crisp' and 'Sugraone' in the diameter classes 151-180 μm and >180 μm. Vessel diameters of wine-grape varieties were in the range from 44.8 ('Nero di Troia') to 72.3 μm ('Merlot') and their densities ranged from 20.3 ('Nero di Troia') to 54.4 vessels/mm2 ('Sangiovese'). In rootstock, vessel diameters were 50.8, 54.0 and 60.9 μm for 34 E.M., 140 Ruggieri and 1103 Paulsen, in the order, and their density was always lower than 25.5 vessels/mm2. Regarding the bioassay in planta, at 90 DAI PCHCIA43.2 was isolated from 93.3% of ‘Timco’ cuttings and 13.3% of ‘Sugar Crisp’ and ‘Sugraone’. These data resulted positively correlated with the frequency of large vessels. With few exceptions, on wine-grape varieties, the percentage of isolation was related to the frequency of large vessels or vessel density. The pathogen was isolated from 33-51% of rootstock cuttings and infection data were more related to vessel densities than their size. These results highlight the relationship between the susceptibility to P. chlamydospora and the size and density of xylem vessels which are worthwhile of further research. This research was financially supported by the program "POR Puglia 2014/2020 – Asse X – Action 10.4. Research for Innovation – (REFIN)", project: "Applications of new technologies for developing IPM strategies on table and wine grape, stone fruit and pomegranate against pathogens of new introduction or mycotoxigenic to improve the sustainability of production processes and the produce quality and security of produce".