The interaction and co-existence of alien plant species Populus alba L. with native grass species

Abstract

The cycad genus, Encephalartos, is endemic to Africa with more than half of its species occurring in South Africa. Seventy-three percent of South African Encephalartos species are threatened with extinction with four species already extinct in the wild. The major threat to Encephalartos species in South Africa is the illegal trade of cycads. In addition, biotic factors, such as insect pests and microbial diseases that affect these plants, are on the increase. The aim of this study was to identify diseases and insect pests of Encephalartos species in South Africa. Symptomatic plant material and insects were collected from diseased cycad species in the KwaZulu-Natal, Limpopo and Gauteng provinces. Microbial isolates obtained were identified based on morphology and DNA sequence data. Species of Alternaria, Phoma and Pseudocercospora were often isolated from leaf spots and Bionectria and Fusarium species from dying cycads. The plant pathogen, Phytophthora cinnamomi, was isolated from dying Encephalartos tranvenosus plants in the Modjadji cycad reserve in Limpopo. Insect pests observed causing the most damage to cultivated cycads were the beetle, Amorphocerus talpa, and the scale insect, Aspidiotus capensis. A. talpa was observed infesting cycad cones in the Pretoria Botanical Gardens, causing discolouration and death of the cones. The scale insect, A. capensis, was found on the leaflets of many cycads, causing chlorosis and premature death of leaves. In this study we also report, for the first time, the scale insect, Aulacaspis yasumatsui, infesting cycads in South Africa. A. yasumatsui was identified based on morphology and DNA sequence data. Plants infested by this scale insect showed symptoms of severe leaf chlorosis and necrosis. The presence of A. yasumatsui on South African Encephalartos species is of much concern and efforts should be made to manage this pest in the country.