Botryosphaeriaceae species associated with blueberry dieback and sources of primary inoculum in propagation nurseries in New Zealand

Sampling at blueberry farms found Botryosphaeriaceae fungi in five of seven farms sampled; overall incidence was 41.4%, with Neofusicoccum australe (79.0%), N. luteum (8.0%), N. ribis (8.0%) and N. parvum (5.0%). Sampling of nursery plants found infections in all four nurseries with 45% incidence in mainly asymptomatic plants, which were infected with N. australe (66.0%), N. parvum (31.5%) and N. ribis (2.5%). Asymptomatic propagation cuttings from one nursery were found to have external contamination of Botryosphaeriaceae DNA (90.0%) and internal infection (65.0%) by the four main species found in the blueberry farms and nurseries. For propagation media nested PCR showed that out of the 98 samples received, 43 samples were positive for the presence of Botryosphaeriaceae DNA (44.0%). Results from the SSCP indicated that N. australe, N. luteum, N. parvum/ N. ribis and Diplodia mutila were present in the propagation media received. Isolates of the four main species recovered from farms and nurseries were pathogenic on blueberry stems but pathogenicity differed significantly between species and isolates within a species, with N. ribis being the most pathogenic, then N. parvum, N. luteum and N. australe. Overall, the high rate of infection in nursery plants indicated that nurseries can be a major source of infection for blueberry farms. Since propagating cuttings are the likely sources of infection for nurseries, these should be targeted in the control strategies.