Population development of both sexes of Heterodera schachtii is diminished in a beet cyst nematode-suppressive soil

The population development of females and males of Heterodera schachtii Schmidt on Swiss chard (Beta vulgaris L. subsp. cicla (L) cv. Large White Ribbed) in suppressive and conducive soil was monitored for two generations in a greenhouse experiment. No significant differences were detected between the number of second-stage juveniles in Swiss chard roots grown in suppressive soil and conducive soil 75 degree-days (DD) after soil infestation with beet cyst nematodes. After the first nematode generation (440 DD), the beet cyst nematode populations in the suppressive and the conducive soil were not significantly different as indicated by the number of males and cysts as well as by the number of eggs and second-stage juveniles within those cysts. However, after two beet cyst nematode generations (880 DD), the number of all monitored life stages were significantly lower in the suppressive soil than in the conducive soil. The reproduction index of H. schachtii was 33.9 in conducive soil and 1.0 in suppressive soil. After each generation, the population of soil-dwelling second-stage juveniles was significantly smaller in suppressive than in conducive soil. After both generations, more than half the cysts in the suppressive soil were colonized by fungi, while less than 25% of the cysts in the conducive soil were colonized. Egg parasitism was very low in conducive soil, and significantly more eggs were parasitized in suppressive soil after both nematode generations.