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Schoeman M.H.,Agricultural Research Council Institute for Tropical and Subtropical Crops | Labuschagne N.,University of Pretoria
South African Journal of Plant and Soil | Year: 2014

Guava wilt disease (GWD), caused by Nalanthamala psidii, is a serious disease occurring in the guava-producing areas of the Mpumalanga and Limpopo provinces of South Africa. Two resistant guava rootstocks, TS-G1 and TS-G2, were developed by the ARC-ITSC in 1995. In 2009, a renewed outbreak of GWD was reported, which also affected the resistant TS-G2 cultivar, placing the guava industry under threat again. The aim of this study was to seek resistant guava selections by means of in vitro screening of guava seedlings and subsequently testing the most promising selections in inoculation studies with N. psidii. A culture filtrate of N. psidii was used to screen guava seedlings in vitro. Promising selections were multiplied in tissue culture, hardened-off and planted in bags before inoculation with the GWD fungus in a shadehouse trial. The number of plants surviving nine months after inoculation was recorded. Although none of the selections showed complete resistance, selection MS44 showed some tolerance against the G2 isolate of the pathogen obtained from diseased TS-G2 trees, whilst selection MS70 showed some tolerance against the G1 isolate obtained from diseased TS-G1 trees. These selections were also resistant to the original Fan Retief isolate of the pathogen. © 2014 © Southern African Plant and Soil Sciences Committee. Source


Schoeman P.S.,Agricultural Research Council Institute for Tropical and Subtropical Crops
African Entomology | Year: 2014

Physical aspects of macadamia orchards appear to play an important role in the distribution patterns of indigenous heteropterans. Increasing tree density and tree height appear to be associated with increases in insect damage. Very dense orchards not only provide these insects with an ideal sheltered habitat, it also reduces the efficacy of many air-assisted sprayers commonly used for insect control in this crop. Macadamias are very tall trees and heteropterans seem to have a preference for nuts occurring in the higher tree strata. The reason for this is unclear at the moment but it might be related to thermoregulation or lekking behaviour. Heteroptera damage was also confined to the edges of many orchards especially during the early season and it is speculated that perimeter trees may temporarily act as a barrier, preventing migration deeper into the orchards. Implications of these findings for an IPM programme are discussed and include: perimeter spraying during the early season as opposed to a full cover spray, tree pruning as well as tree height management. Source


Masevhe M.R.,Agricultural Research Council Institute for Tropical and Subtropical Crops | Masevhe M.R.,University of Pretoria | Soundy P.,Tshwane University of Technology | Taylor N.J.,University of Pretoria
South African Journal of Plant and Soil | Year: 2015

Wheat straw has generally been used as the main substrate for cultivating oyster mushrooms (Pleurotus ostreatus); however, in South Africa it is becoming expensive for small-scale farmers to utilise. Therefore, the main objective of the study was to investigate the use of alternative, but suitable substrates for planting oyster mushrooms. Wheat straw (control), wood chips and thatch grass, selected on account of their year-round availability and low cost, were tested with two drainage treatments (drained or not drained) and replicated four times. Wheat straw showed no contamination, whereas there was contamination in thatch grass and wood chips from weeks 1 to 4. At harvest, a significantly higher cumulative number of flushes, caps and fresh mass of oyster mushrooms was observed in wheat straw and thatch grass compared with wood chips. The results demonstrated that thatch grass could be used as a viable alternative to the commonly used wheat straw. © 2015 Taylor & Francis Source


Fourie H.,North West University South Africa | Ahuja P.,North West University South Africa | Lammers J.,Wageningen University | Daneel M.,Agricultural Research Council Institute for Tropical and Subtropical Crops
Crop Protection | Year: 2016

Nematode pests parasitise and cause substantial crop yield and quality losses to a wide range of crops worldwide. To minimize such damage, the exploitation and development of alternative nematode control strategies are becoming increasingly important, particularly as a result of global efforts to conserve the ozone layer as well as our soil and water substrates. Inclusion of Brassicaceae crops in cropping systems is one such alternative and has been demonstrated in most cases to be effective in managing the top-three rated economically important nematode pests, viz. root-knot (Meloidogyne), cyst (Heterodera and Globodera) and lesion (Pratylenchus) nematodes as well as others. In the past nematode pests were and still are generally managed successfully by the use of synthetically-derived nematicides, which are progressively being removed from world markets. However, fragmented and limited information about the use of Brassicaceae crops as a nematode management tool exists in various countries. The need thus arose to summarize, compare and discuss the vast amount of information that has been generated on this topic in a concise article. This paper therefore represents a comprehensive, practical and critical review of the use and effect(s) of Brassicaceae-based management strategies and the biofumigation and cover-crop/rotation characteristics of Brassicaceae in reducing nematode-pest population levels in global cropping systems. © 2015 Elsevier Ltd. Source


Ntidi K.N.,Agricultural Research Council ARC Grain Crops Institute | Ntidi K.N.,North West University South Africa | Fourie H.,North West University South Africa | Daneel M.,Agricultural Research Council Institute for Tropical and Subtropical Crops
International Journal of Pest Management | Year: 2016

Since weeds serve as hosts for nematode pests, the host status of 20 weed species (commonly occurring in fields of developing farmers) to Meloidogyne incognita and M. javanica, respectively, were investigated. Greenhouse studies showed that seven weed species had Rf values >1 for both nematode species indicating susceptibility, while 13 had Rf values ≤ 1 indicating resistance. Greenhouse results showed that Hibiscus trionum and Amaranthus tricolor were identified as the most susceptible and Chenopodium carinatum and Datura ferox the poorest hosts for M. incognita and M. javanica. For field experiments at Kuruman, Solanum retroflexum was the most susceptible weed to a M. javanica population, while the same was evident for H. trionum at Nelspruit, where a mixed population of M. incognita and M. javanica occurred and at Potchefstroom, where a population of M. incognita was present. Results from this study indicated that certain weed species are highly susceptible to root-knot nematodes and should be removed timely and effectively to prevent population level increases of root-knot nematode pests in the fields of farmers. © 2015 Agricultural Research Council. Source

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