Initial Inoculum and Spatial Dispersal of Colletotrichum gloeosporioides, the Causal Agent of Strawberry Anthracnose Crown Rot

Abstract

Anthracnose crown rot (ACR), caused by Colletotrichum gloeosporioides, is a serious disease of strawberry (Fragaria × ananassa) in nurseries and fruiting fields in the southeastern United States. This study was conducted to determine the potential of alternative hosts for initial inoculum source and spread that causes ACR in strawberry nurseries. Results indicated that Parthenocissus quinquefolia is a noncultivated host of C. gloeosporioides in North Carolina and may serve as an initial inoculum source for planting material. Sources of inoculum data were complemented with a 2-year study of disease incidence and spread in simulated nursery production experiments. Sixty days after inoculation of the mother plants in the nursery, three different inoculation levels showed a significant positive correlation (r = 0.78, P < 0.004) with the quiescent infection (QI) incidence on the runner or daughter plants at the end of the nursery production cycle. Runner plant counts from different proportion of mother plants' inoculation treatments indicated that runner plant production was negatively and significantly (P < 0.001) affected by C. gloeosporioides. Infected tips used to produce transplants destined for fruit production resulted in 29.3 and 16.8% mortality in plug trays in 2007 and 2008, respectively. Tracking foliar QI incidence that resulted from dispersal of inoculum from an introduced point source in the nursery showed a sharp decline at 1 m and beyond from the inoculation focus. Although the exponential model (R2 = 0.92 to 0.94) had slightly higher coefficients of determination than the modified power law (R2 = 0.89 to 0.90), residual plots indicated that the modified power law model fit the disease gradient data better than the exponential model in both years. Results from our dispersal study indicated that rogueing of infected plants within a 4-m radius of infection foci would reduce the risk of transferring infected runner plants from the nursery to the fruiting field.