Effects of Host Resistance on the Fecundity of Globodera rostochiensis

The fecundity of Globodera rostochiensis (RA) females that developed on resistant Rosa and susceptible Katahdin potato cultivars were compared. Cysts collected from each cultivar were bulked, separated into four sizes (> 500 mum, 355-500 mum, 250-355 mum, and < 250 mum), and crushed to determine fecundity as measured by viable egg content (VEC). Fewer and generally smaller cysts developed on Rosa than on Katahdin. Although cyst size significantly (P = 0.01) influenced VEC, cyst age (8 or 13 weeks) had no effect. Regardless of size, cysts produced on Rosa contained significantly fewer viable eggs than did cysts produced on Katahdin. The fecundity of progeny from cysts produced on Rosa was significantly reduced compared with that of progeny from cysts produced on Katahdin. After two generations on Katahdin, the VEC of cysts from a population originating from Rosa was significantly less than that of cysts from a population originating from Katahdin, indicating that in the presence of a pure population of G. rostochiensis RA, the females that develop on the resistant cultivar Rosa represent a diminished rather than a superior selected population.