The influence of parasitism of young Heterodera schachtii-females on later cyst content
1992
Thomas, E. (Landwirtschaftskammer Rheinland, Bonn (Germany). Pflanzenschutzamt)
One hundert cysts each, from three Heterodera schachtti populations of different ages, were selected and were subjected to a hatching test. Relevant for the determination of the age of the cysts was the period between the last sugarbeet crop and sampling as well as the visual quality of the cysts under the microscope. Hatch levels were determined and then the remaining cyst content ascertained as to quality and quantity. Population development was strongly influenced by total or partial destructions of the cyst content, due to fungal egg parasites. On the one hand they restricted the increase in population on the other hand they furthered the spontaneous hatch of viable juveniles in partially infected cysts with the result that, within a few years, these no longer showed viable content. In contrast the number of juveniles remained the same for several years in uninfested cysts, which had more robust 'dense' cyst cuticles. After only two years, the difference in hatching intensity led to a selection of predominantly 'healthy cysts', filled with large numbers of hatchable juveniles. The simultaneous increase of cysts without viable content resulted in a progressive differentiation of filling levels
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