The significance of nematode communities in South African citrus decline orchards

Abstract

Citrus slow decline is a slow developing disease occurring in citrus orchards rendering the citrus orchards uneconomical in a decade or two. Causal agents have not been identified and therefore a study was initiated to identify parameters or combination of parameters that could be useful in early detection of the disease. Four citrus orchards in Mpumalanga Province, South Africa, were identified where citrus slow disease decline was present. Twenty trees of each of the three disease categories including healthy, slight sick and sick trees, were randomly selected and sampled in each orchard. Among the many parameters measured, nematode communities were evaluated as they might show differences between the three tree categories. Results showed that Tylenchulus semipenetrans was the most abundant nematode species present in the three tree categories making up more than 90% of the nematode communities. Nine other plant-parasitic and 21 free-living nematodes were identified among the three tree categories with Acrobeloides being the most abundant nematode genus followed by Prismatolaimus. Among the feeding groups, 73% belonged to bacterivores followed by about 10% to the fungivores. Metabolic foot prints for the three tree categories were very small and closely together in the depleted and degraded quadrat.