Seasonal Availability of Inoculum for Constriction Canker of Peach in New Jersey

ABSTRACT The seasonal sporulation ability of Phomopsis amygdali was evaluated over a 2-year period by sampling twig cankers from commercial 'Encore' and 'Jerseyglo' peach orchards. Canker size, pycnidia per canker, percent pycnidia forming cirri, and spore production were evaluated once each month from January 1997 through December 1998. Average canker size and number of pycnidia per canker, which followed a sinusoidal pattern of change, were at lowest values in spring and at maximum values in fall. In 1997, the ability of pycnidia to sporulate (produce cirri) increased significantly from a minimum during winter to a maximum during summer. In contrast, pycnidia sporulation in 1998 increased slowly throughout the year with a maximum in the fall. Inoculum potential, measured as number of spores per canker, peaked between June and August and was lowest in winter. Although pycnidia numbers in 1997 were about 50% of that observed in 1998, approximately twice as many conidia per canker were produced in 1997; consequently, the number of conidia produced per canker was equivalent in both years. These results indicated that P. amygdali acts as an r strategist by maintaining abundant pycnidia and sporulation capability throughout much of the year. Therefore, infection is most likely not limited by the availability of inoculum.