Population dynamics of potato cyst nematodes and associated damage to potato.

Population dynamics of potato cyst nematodes (PCN; Globoderarostochiensis (Woll.) Skarbilovich and G. pallida Stone) and their interactions with potato plants are insufficiently understood to explain variations of population increase and yield reduction among years and locations. This thesis describes experiments and simulation studies to elucidate mechanisms of PCN population increase and associated damage to potato. Models of potato crop growth and PCN population development, driven by radiation and ambient and soil temperatures, were linked through effects of second-stage juveniles on photosynthesis and through interactions among root growth, hatching and root invasion of second-stage juveniles. Photosynthesis reduction by second-stage juveniles during syncytial initiation could fully explain yield loss due to PCN. Population increase was explained by effects of the density of second-stage juveniles in roots on the sex ratio and on root death and concomitant death of the nematodes within. Simulated mechanisms of crop resistance and tolerance agreed with experimental observations. Tolerance was enhanced by resistance, acting upon or before the stage of syncytial initiation. The potential use of the model for development and evaluation of PCN control strategies in sustainable production systems is discussed