Evaluation of six red grapevine cultivars inoculated with Neofusicoccum parvum in a “terroir” of La Mancha wine región (Spain)

Aim: Among Botryosphaeriaceae species associated with Botryosphaeria dieback of grapevines, Neofusicoccum parvum is one of the most virulent and fastest wood-colonizing fungi. This study aimed to evaluate the susceptibility of six red grapevine cultivars (“Bobal”, “Monastrell”, “Garnacha Tinta”, “Moravia Agria”, “Tinto Velasco” and “Moribel” to N. parvum, under field conditions.

Methods and Results: Pathogenicity studies were conducted, over two consecutive years, with one-year old grapevine rooted cuttings inoculated with a N. parvum isolate. Rooted cuttings were wounded between the two upper internodes with a cork borer. A mycelial agar plug, from a 3-weeks-old culture on potato dextrose agar (PDA), was placed in the wound. Wounds were sealed with parafilm and wrapped with foil paper to prevent drying. Ten rooted cuttings per cultivar were inoculated with the fungus and two others with uncolonized PDA plugs, as negative controls. After inoculating, rooted cuttings were planted in a plot and irrigated by a drip system with two drippers per plant. Plants were collected after eight months and inspected for lesion development. Extent of wood necrosis was measured upward and downward from the inoculation point. Three rooted cuttings for each cultivar were selected and small pieces, of necrotic tissue from de edge of each lesion, were cut and placed on malt extract agar supplemented with 0.5 g/L of streptomycin sulphate (MEAS), in an attempt to recover the inoculated fungus and complete Koch’s postulates. N. parvum was identified by morphological and molecular approaches. Mean percentage of infected rooted cuttings ranged from 42.1% (“Monastrell” cultivar) to 93.3% (“Tinto Velasco” cultivar). Mean lengths of the extent of wood necrosis caused by N. parvum on inoculated one-year-old grapevine wood ranged from 21.2 (“Bobal” cultivar) to 87.2 mm (“Tinto Velasco” cultivar). N. parvum was reisolated from the edge of each lesion in 90.3% of the cultivars. The results of statistical analysis showed that “Bobal” and “Monastrell” cultivars were significantly more tolerant than “Tinto Velasco”.  

Conclusions:

All tested grapevine cultivars were susceptible to infection by N. parvum, evidencing that there was no qualitative resistance to this fungus. “Bobal” and “Monastrell” cultivars highlighted for their lower wood response susceptibility to N. parvum.

Significance and Impact of the Study: Interactions between Botryosphaeriaceae species and grapevine cultivars are poorly understood and there is currently little data available. This study allowed classifying different Vitis vinifera cultivars based on their degree of quantitative resistance to N. parvum. “Bobal” and “Monastrell” cultivars could be potential candidates to create tolerant varieties to N. parvum fungus. Using tolerant varieties would be the safest, easiest, the least expensive and the most effective means of controlling this disease.