M. Daneel

Achievements and challenges (Nematology in South Africa: a view from the 21st century)

This chapter highlights the core achievements within the science of Nematology in South Africa since 1982. In addition, the editors have attempted to highlight for the benefit of future decision makers and researchers, the key challenges for the future such that the progress achieved since 1982 can be built upon in the coming decades.

Identification of Meloidogyne spp. associated with agri- and horticultural crops in South Africa

The four major and globally widespread Meloidogyne spp., M. arenaria (Neal, 1889), M. hapla Chitwood, 1949, M. incognita (Kofoid & White, 1919) and M. javanica (Treub, 1885) (see Jones et al., 2013), are also abundant in South African crop production areas (Kleynhans et al., 1996). Many other species parasitise crops in South Africa, including M. enterolobii Yang & Eisenback, 1983 (see Kleynhans et al., 1996; Marais, 2014). Meloidogyne enterolobii, reported from only a few crop production areas in South Africa (Van den Berg et al., 2017), is very aggressive, has a wide host range and is known to overcome various root-knot nematode resistance genes (Castagnone-Sereno, 2012). As it is morphologically similar to M. incognita and other thermophilic species, it is prone to being misidentified (Adam et al., 2007; Karssen et al., 2013). Various authors have emphasised the limitations in using only morphological characteristics (particularly perineal pattern morphology) for accurate identification of Meloidogyne spp. (Karssen & Van Aelst, 2001; Carneiro et al., 2004; Hunt & Handoo, 2009), and as discriminating Meloidogyne spp. is crucial to optimise control strategies (Adam et al., 2007), the use of accurate isoenzyme and molecular deoxyribonuclease (DNA) methods became popular (Esbenshade & Triantaphyllou, 1985; Karssen et al., 2013). The sequencederived-amplified region (SCAR) polymerase chain reaction (PCR) technique has been proven to be a fast, reliable and accurate method to discriminate Meloidogyne spp. (Zijlstra et al., 2000). This study aims to update distribution knowledge by identifying Meloidogyne spp. from 28 populations isolated from diagnostic samples or experimental sites through the use of the SCAR-PCR technique and perineal-pattern morphology. Meloidogyne spp. eggs and second-stage juveniles (J2) were extracted from infected root samples of various crops cultivated in different crop production areas during the 2013-2014 summer-growing season (Table 1). Root samples (50 g) of each crop were subjected to the adapted NaOCl method (Riekert, 1995) for extraction of eggs and J2. The latter life stages of each of the 28 populations were inoculated on roots of individual rootknot nematode-susceptible tomato seedlings (‘Rodade’) grown in 5000 cm3 capacity pots containing Telone II (a.s. 1-3 dichloropropene; dosage of 150 l ha–1) fumigated sandy-loam soil (5.3% clay, 93.6% sand, 1.1% silt, 0.47% organic matter and pH (H2O) 7.47) in a glasshouse

Genetic diversity and phylogeny of South African Meloidogyne populations using genotyping by sequencing

Meloidogyne species cause great crop losses worldwide. Although genetic host plant resistance is an effective control strategy to minimize damage caused by Meloidogyne, some resistant genes are ineffective against virulent species such as Meloidogyne enterolobii. Detailed knowledge about the genetic composition of Meloidogyne species is thus essential. This study focused on genotyping-by-sequencing (GBS) and Pool-Seq to elucidate the genetic relation between South African M. enterolobii, M. incognita and M. javanica populations. Hence, 653 common single nucleotide polymorphisms (SNPs) were identified and used to compare these species at genetic level. Allele frequencies of 34 SNPs consistently differed between the three Meloidogyne species studied. Principal component and phylogenetic analyses grouped the M. enterolobii populations in one clade, showing a distant relation to the M. javanica populations. These two species also shared genetic links with the M. incognita populations studied. GBS has been used successfully in this study to identify SNPs that discriminated among the three Meloidogyne species investigated. Alleles, only occurring in the genome of M. enterolobii and located in genes involved in virulence in other animal species (e.g. a serine/threonine phosphatase and zinc finger) have also been identified, accentuating the value of GBS in future studies of this nature.

Nematode Pests of Banana

The banana industry in South Africa is established in the low-lying and frost-free areas of the KwaZulu-Natal, Limpopo and Mpumalanga provinces. The Cavendish subgroup of cultivars are used for production, with the most popular being Grand Nain, Williams, Chinese Cavendish and Dwarf Cavendish. The chapter deals with the economically important nematode pests of banana in South Africa. These are Meloidogyne incognita and Meloidogyne javanica, Helicotylenchus multicinctus, Radopholus similis and Pratylenchus coffeae. Surveys in commercial plantations showed that Meloidogyne were present in more than 90 % of the samples, had the highest average population levels and together with species of Helicotylenchus constitute 72 % of the nematode complex. Damage symptoms, distribution of the economically important nematode pests as well as their host ranges in local banana plantings are discussed. This is followed by control strategies, which include legislation that is aimed at preventing the transport of infected planting material to new areas, the use of R. similis-free planting material, cultural control measures and biological and chemical control.