Co-infection by Neofusicoccum luteum and N.parvum influences direction of lesion expansion but not total lesion size

Abstract

In a national survey of symptomatic vines a total of 238 samples were collected yielding 336 isolates of botry-osphaeriaceous species. From this collection 18 lesions were systematically sampled to determine if multiple species were present. Twelve lesions contained multi-ple species. Diplodia seriata was found most frequently in combination with other species (40%) but Neofusico-cum luteum and N. parvum were found most frequently together (20%). To determine whether co-infection by these two Neofusicoccum species was synergistic, trunks of 1-year-old Sauvignon blanc vines were co-inoculated with two isolates each of N. luteum and N. parvum, either together or alone. Each pair of isolates for each species consisted of a weakly virulent and highly virulent isolate, with virulence established in previous experiments. Following inoculation the presence of both species in one lesion was confirmed by PCR. The results showed that in co-inoculated lesions mean total lengths were not larger than the lesion length produced by the most virulent of the isolate pair (P≤0.05), irrespective of the virulence of the second isolate. However, when the distances from the inoculation points to lesion edges were analysed, results showed that there were significantly greater lengths below than above inoculation points for all combinations (P≤0.05). In addition, co-inoculation of two weakly virulent isolates reduced upward movement (P≤0.05). A decrease in the endophytic movement of N. luteum beyond the lesion was also observed in all co-inoculations. Overall, the results demonstrated that there were no synergistic effects of co-inoculation with these two common species.