Combined Heat and Drought Stress Induce Grapevine Defense Responses

Climate change leads to specific hydrothermal conditions, which alter the health of plants and their associated microbial communities. Abiotic conditions have both positive and negative effects on pathogen development due to the specific physiological responses of grapevines to drought and heat stress. The aim of the study was to investigate the defense responses of grapevine and the development of phytopathogens under the influence of abiotic stressors of vegetation period. The study was conducted on two grape (Vitis vinifera L.) varieties—‘Riesling’ and ‘Bianca’—infected with compatible pathogens, Plasmopara viticola and Alternaria alternata, respectively. The abundance of epiphytic micromycetes increased with increasing adverse hydrothermal conditions, particularly, lack of precipitation and temperature above the long-term average. ‘Riesling’ susceptibility to P. viticola was associated with down-regulation of most defense genes upon infection under optimal and drought conditions at 24 hpi. Combined abiotic stress stimulated high level of defense genes expression, vinifirin production, high hydrogen peroxide levels and high peroxidase activity during P. viticola infection. This corresponded to minimal P. viticola infection rate. Low expression levels of PDF1 appeared to be responsible for decreased susceptibility of grapes to A. alternata. Expression patterns during the least efficient infection of A. alternata were similar in ‘Bianca’ and ‘Riesling’. This work contributes to our understanding of the impact of a combination of stress factors on grapevine plants during vegetation period. This new knowledge can be used to develop and refine plant protection systems.