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A SURVEY OF PLANT-PARASITIC NEMATODES ASSOCIATED WITH WHEAT CROPS IN SOUTH AFRICA

Siphamandla Lamula

Grain farming in Africa, especially in Sub-Saharan Africa, faces the combined effects of abiotic (including drought and poor crop management technology) and biotic (fungal diseases and pests) stresses. Among these, the cereal cyst nematodes (CCNs) (Heterodera spp.), root-knot nematodes (RKN) (Meloidogyne spp.), and root-lesion nematodes (RLN) (Pratylenchus spp.) are the main limiting factor for grain production and are considered as economically important for wheat worldwide and major facilitators of fungal infections such as fusarium species. Loses of cereals as a result of plant-parasitic nematodes (PPNs) are estimated up to 6.9 to 50% ($US 125 billion) worldwide. The damage caused by these PPNs, their behavior, and control has received little attention in many African countries, especially Sub-Saharan African, despite indications by other countries that the productivity of grains can be severely reduced. The current study aims to identify the plant-parasitic nematode assemblages in South African wheat-producing areas, emphasizing morphological and molecular identification. A total of 776 composite rhizosphere soil and root samples have been collected from 24 localities over two seasons in the Free State (4), KwaZulu-Natal (1), Northern Cape (6), and Western Cape (13) provinces. Nematodes were extracted from soil and root samples by using the adapted decanting and sieving method, followed by an adapted sugar centrifugal method. Nematodes were extracted from kernels employing soaking the samples in water for 24 hours and decanting the extract through a 20μm sieve. Nematode species were identified based on morphometrics and morphological features, while Prominence Values (PV) were calculated for each genus or family. Individuals from the following genera/families/orders were identified from the following provinces: Free State: Pratylenchus, Rotylenchus, Scutellonema, Helicotylenchus, Criconema, and Dolichodorus; KwaZulu-Natal: Meloidogyne, Pratylenchus, Criconema, Spiral, and Longidorus; Northern Cape: Pratylenchus, Criconema, and Spiral; Western Cape: Pratylenchus, Rotylenchus, Scutellonema, Helicotylenchus, Coslenchus, Tylenchus and Xiphinema. According to PV-value, the predominant genera identified across the localities to date are Pratylenchus, Meloidogyne, Spiral, Coslenchus, Tylenchus, Criconema, Longidorus, and Xiphinema. Cedara in KwaZulu-Natal had a high number of Meloidogyne (420 second-stage juveniles /200 g soil) compared to the other sampled localities. Western Cape (Malmesbury) showed a high number of Pratylenchus sp. (8750/200 g soil). In root samples, the PV of Meloidogyne in Cedara was 183 followed by De Vlei (PV=943), Tygerhoek (PV=490), Kopporfontein (PV=134), and Wellington (PV=57) for Pratylenchus sp. No plant-parasitic nematodes were found in kernel samples. However, a bacterivore species of Panagrolaimus was identified from wheat kernels from Clarens in the Free State, being the first record both in South Africa and worldwide. The D2-D3, 18S rRNA, ITS, PCR, and SCAR-PCR for amplification of detected genera is ongoing and thus far, among other economically important, species such as Pratylenchus thornei Pratylenchus neglectus and Pratylenchus Bolivian have been amplified and the data corresponds with that of morphological and morphometrical identifications. Due to their microscopic size, nematode pests are commonly overlooked or misdiagnosed.