Grapevine adaptation to drought and resistance to Neofusicoccum parvum, causal agent of Botryosphaeria dieback

The sustainability of viticulture in response to climate change has been addressed mainly considering agronomic impacts, such as water management and diseases, either separately or together.

In grapevines, there is strong evidence that different genotypes respond differently to biotic and abiotic stresses. A screening was conducted on various local cultivars in response to drought and Neofusicoum parvum infection aiming to evaluate their susceptibility to abiotic stress and resistance to fungal diseases.

To characterize the varieties’ drought effect, physiological parameters were measured on 12 potted plants of each variety. Relative water content (RWC), leaf water potential (Ѱ_MD) and gas exchange parameters were measured at midday once the plants reached severe water stress levels, i.e. stomatal conductance (g_s) between 0,05 and 0,15 mol H₂O m^-2 s^-1.

Moreover, aiming to test the resistance of each variety to the pathogen N. parvum, agar and mycelium disks of 6 mm were placed in a marked wound between the two lower nodes of each plant, using sterile agar disks as controls. Six plants per variety were used as controls and the other 6 were inoculated with N. parvum. Four months after inoculation, the plants were evaluated by measuring the development of internal lesions produced by the fungus.

Under well-watered (WW) conditions, fungal infection provoked a strong reduction in g_s and, consequently, an increase in intrinsic water use efficiency (WUE_i, A_N/g_s) in infected plants compared with non-infected plants in all cultivars. However, no other parameters were affected by the fungus. Under water stress (WS) conditions, infection with N. parvum caused similar or even higher g_s values in infected than in non-infected plants, thus obtaining similar WUE values for both treatments.

This study may indicate that plants may adjust their physiology to counteract the fungal infection by maintaining a tight stomatal control and by sustaining a balanced carbon change.