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Summary Our objective was to discover the stages (pre- or post-infection) in which the resistance to burrowing nematode (Radopholus similis) occurs in two resistant banana (Musa spp.) cultivars. An autotrophic in vitro culture system was used to compare R. similis migration towards, and penetration into, the banana roots. A new two-compartment autotrophic in vitro model system was developed using agar-based medium to examine the migration of R. similis to either the susceptible ‘Grande Naine’ or the resistant ‘Yangambi km5’ (‘Ykm5’), when both the Musa genotypes were present at equal distance. The autotrophic in vitro model system was advantageous, because it supported continuous root growth due to the actively photosynthesising shoots growing in the open air, while the in vitro root conditions make it possible to observe and assess the nematode chemotaxis in the transparent medium. Significantly fewer nematodes migrated towards the resistant ‘Ykm5’ plants when compared to both the susceptible ‘Grande Naine’, and another resistant cultivar, ‘Saba’, at 1 h after infection. This signals a possibility of a lower concentration or different composition of nematode attractants in ‘Ykm5’ root exudates. No significant differences were observed in the percentage of R. similis that migrated towards the roots of the susceptible and resistant banana plants at 3, 4 and 6 h after inoculation. No significant differences were observed in the percentages of female penetration in the resistant and susceptible plant roots at 1 and 2 days after inoculation. The results of the two-compartment system confirmed that when a choice is given to migrate towards the resistant and susceptible genotypes, no differences were observed in the percentage of female migration towards both the genotypes.

The bio-protective effect of either single or dual mycorrhizal (AMF) and rhizobial colonisation of the roots of non-leguminous and leguminous banana intercrops differing in host response to Radopholus similis on the reproduction of this important migratory endoparasitic nematode was examined. Included in the study were sorgho-Sudan grass (good R. similis host), sweet potato and common bean (intermediate hosts), soybean and sunn hemp (poor hosts), and marigold (non-host). Significant plant growth-promoting effect of single AMF and rhizobial colonisation in the good and intermediate R. similis hosts sorgho-Sudangrass (AMF) and common bean (AMF and rhizobium), respectively, was observed whereas this plant growth-promoting effect was absent in the other intercrops with the exception of sunn hemp with significant plant growth-promoting effect of AMF colonisation on fresh root weight. An additive plant growth-promoting effect of dual AMF and rhizobial colonisation (on fresh shoot weight) was only observed in the poor R. similis host soybean. Single AMF and rhizobial colonisation also resulted in a significant bio-protective effect against R. similis in sorgho-Sudangrass (AMF), sweet potato cv. Inzovu (AMF) and common bean (AMF and rhizobium). The growth-promoting and bio-protective effects of AMF colonisation were clearly present in the good and intermediate R. similis hosts with moderate to high relative mycorrhizal dependency (RMD) values ranging from 47% (sorgho-Sudangrass) to 65% (common bean) but absent in the intermediate R. similis host sweet potato, which had a negative RMD value, and in the poor and non- R. similis hosts. Overall, no suppressive effect of R. similis infection on AMF and rhizobial colonisation was observed except in soybean and sunn hemp in which AMF colonisation was significantly reduced.

Heterodera schachtii (Tylenchida: Heteroderidae), also called the sugar beet cyst nematode, are of economic importance worldwide. Oilseed rape (Brassica napus L.), which is a crop of global importance, suffers yield loss when it is infected with H. schachtii. The first report of the occurrence of H. schachtii in South Africa was made in 1968 on the Greater Cape Flats of the Western Cape province of South Africa, showing the widespread occurrence and the high nematode numbers on cabbage, cauliflower, beetroot and Brussels sprouts. The penetration, development and life cycle of a local H. schachtii population on seven vegetables (beetroot, broccoli, Brussels sprout, cabbage, cauliflower, lettuce and turnip) and three weeds (black nightshade, purslane and shepherd’s purse) commonly grown, or found, in the Greater Cape Flats region of the Western Cape, South Africa, and two candidate trap crops (white mustard and oilseed radish) were examined under laboratory conditions. All the vegetables and weeds were found to be good hosts of H. schachtii, with the exception of lettuce, which was found to be a non-host. Oilseed radish and white mustard allowed penetration and some nematode development, but no, or little, cyst formation. Female bodies filled with eggs were observed from 31 to 34 days after inoculation onwards on all the vegetables and weeds, except for on beetroot, on which female bodies filled with eggs were observed a few days later. The results from this study are important, especially in terms of the adaptation of vegetable crop rotation cycles that are practised on the Cape Flats, so as to prevent the build-up of H. schachtii populations in agricultural settings.

The host status of South African adapted, genetically modified (GM) glyphosate-tolerant soybean genotypes to root-knot (field and glasshouse) and lesion (field) nematodes were assessed. Analyses of root and soil samples of 29 genotypes (collected from seven production areas during the 2014/15 season) enabled the identification of nine plant-parasitic nematode genera and 10 species. Predominant endoparasitic genera in root samples were Meloidogyne (Meloidogyne incognita and M. javanica) and Pratylenchus (Pratylenchus brachyurus, P. zeae and P. teres). Rotylenchulus parvus was the predominant semi-endoparasite in soil, followed by Scutellonema brachyurus and Helicotylenchus sp. Only ‘PAN 1583 R’ and ‘PAN 1521 R’ maintained less than 10% of the Meloidogyne spp. densities present in roots of the most susceptible genotype, while all genotypes were susceptible to the Pratylenchus spp. The host status of 36 soybean genotypes to M. incognita infection, evaluated in two follow-up glasshouse experiments terminated 56 days after inoculation of ca. 1000 M. incognita eggs and second-stage juveniles (J2) per seedling, varied substantially for final population density (Pf), reproduction factor (Rf) and relative percentage susceptibility (%S). Only ‘PRF-GCI7’ and the resistant reference ‘LS 5995’ had Rfs

Summary The bio-protective effect of a root-nodulating strain (CNPAF 512) of the nitrogen-fixing rhizobium, Rhizobium etli, against both a sedentary (Meloidogyne incognita) and a migratory (Radopholus similis) endoparasitic nematode in common bean (Phaseolus vulgaris) was examined using an in vitro autotrophic tripartite culture system. Two in vitro assays were carried out with each of the nematode species. Each assay consisted of two treatments: the plants were either inoculated with the rhizobial strain or remained non-inoculated (control plants). To examine the effect of either pre- or simultaneous inoculation of the rhizobial strain on the reproduction of M. incognita and R. similis, one assay was carried out in which the nematodes were inoculated 3 weeks after rhizobial inoculation while another assay was carried out in which the nematodes were inoculated simultaneously with the rihizobial strain. Both pre-inoculation and simultaneous inoculation with R. etli CNPAF 512 significantly suppressed the reproduction of both M. incognita and R. similis.

Summary The host response to Meloidogyne javanica infection of selected Oryza sativa and NERICA (New Rice for Africa) genotypes that are commonly grown in Tanzania and East Africa was examined. The O. sativa genotypes ‘Komboka’ and ‘Supa’ appeared to be partially resistant. A further experiment showed that both genotypes are also partially resistant to M. graminicola infection. The host response of ‘Komboka’ and ‘Supa’ to M. javanica and M. graminicola was further examined and compared in indoor growth chamber conditions. The genotypes ‘TOG5674’, ‘TOG5675’, ‘CG11’ and ‘CG14’ (both O. glaberrima) were included as the resistant reference genotypes for M. graminicola and the genotype ‘UPLRi-5’ (O. sativa) was included as the susceptible reference genotype for both species of root-knot nematodes. Meloidogyne graminicola was more aggressive on ‘Komboka’ and ‘Supa’ than M. javanica. Significantly less root galling was observed on ‘Komboka’ and ‘Supa’ than on ‘UPLRi-5’. In ‘Komboka’ and ‘Supa’ significantly fewer second-stage juveniles (J2) were able to penetrate the roots, to develop into adult females and to reproduce compared with ‘UPLRi-5’. Differential emigration of J2 from the roots of ‘Komboka’ and ‘Supa’ compared with ‘UPLRi-5’ contributed to the observed partial resistance in these genotypes to M. graminicola and M. javanica. Nematodes that successfully penetrated and developed in ‘Komboka’ and ‘Supa’ showed aberrant phenotypes. ‘Supa’ and ‘Komboka’ may be recommended for use by farmers in M. javanica and M. graminicola-infested fields.

Information about the non-target effects of glyphosate, a broad-spectrum systemic herbicide on soil-borne nematodes is scarce and not well documented for South African agricultural fields. In the present study, the abundance and identity of plant-parasitic nematodes in roots and rhizosphere soil of commercial glyphosate- tolerant (genetically modified; GM) and conventional (non-glyphosate-tolerant) soybean cultivars from cultivated fields were obtained for two consecutive growing seasons. Grass and soil from adjacent natural vegetation were sampled, representing the reference system. Thirty plant-parasitic nematode species, belonging to 13 genera were identified in the roots and rhizosphere soil of soybean cultivars and natural vegetation. In rhizosphere soil, Meloidogyne (for glyphosate-tolerant and conventional soybean), followed by Helicotylenchus (for glyphosate-tolerant soybean) and Scutellonema (for conventional soybean), were the predominant genera. Seven species, namely Pratylenchus flakkensis, Pratylenchus scribneri, Pratylenchus vulnus, Rotylenchus brevicaudatus, Telotylenchus avaricus, Tylenchorhynchus brevicaudatus and Quinisulcius capitatus are first reports for soybean in South Africa. Although it was not possible to define the impact of each ecosystem on the plant-parasitic nematode assemblages, this study suggested that glyphosate had no deleterious effects on plant-parasitic nematodes

Information on the effect of the herbicide glyphosate on nematodes in the field is limited and contradictory. A small field experiment was conducted during two consecutive summer-growing seasons to investigate the response of plant-parasitic nematode communities on the application of glyphosate to genetically-modified glyphosate-tolerant soybean (cultivar ‘LS 6164 R’) and maize (cultivar ‘DKC 80-30 RR’). A mixed Meloidogyne incognita and Meloidogyne javanica population dominated both crops during both seasons. Five other plant-parasitic nematode genera (Criconema, Helicotylenchus, Nanidorus, Pratylenchus and Tylenchorhynchus) were also identified. Glyphosate application had no effect on M. incognita, M. javanica and Pratylenchus spp. numbers. No significant differences were observed between the glyphosate-treated and non-treated plots for Meloidogyne population densities per 50 g roots for both soybean and maize. Significant (p ≤ 0.05) differences recorded between glyphosate-treated and non-treated plots from 5 g roots and 200 g rhizosphere soil for other genera were mainly due to absence during some sampling dates

Summary Host response of BC2F3 recombinant inbred line (RIL) population derived from a cross between African rice (CG14) and Asian rice (IR64) genotypes was evaluated in the field and quantitative trait loci (QTLs) that confer resistance and tolerance to Meloidogyne graminicola were mapped using SSR markers. Of the 155 BC2F3 progenies evaluated, 23 were resistant and six were partially resistant based on the number of second-stage juveniles (J2) per root system and J2 per g roots. Based on yield reduction, 23 progenies were identified as tolerant and 14 were less sensitive to M. graminicola infection. QTLs related to resistance were detected on chromosomes 6, 7 and 12. QTL for tolerance linked to percentage yield reduction was mapped on chromosome 5. QTLs linked to fresh root weight, dry root weight, dry shoot weight, percentage filled grains per panicle and yields were also mapped. QTLs identified will be useful in a breeding programme to develop M. graminicola-resistant and tolerant rice cultivars.

The mechanism of resistance of selected recombinant Oryza sativa inbred lines (RILs) resistant and partially resistant to Meloidogyne graminicola, and their resistant (IR78877–208-B-1-2) and susceptible (IR64, Dinorado) parents was examined by comparing the penetration and development of the second-stage juveniles (J2) and females with the nematode infection process in the resistant Oryza glaberrima genotype TOG5674. Lignification and total phenolic content of infected and uninfected plants were also studied. Less J2 were able to penetrate the roots of the partially resistant and resistant O. sativa genotypes included in the study. The development of J2 that had penetrated in the roots of the RILs was delayed resulting in turn in a delay in the development of egg-laying females and the second generation. Lignification was more intense in infected plants compared with uninfected plants and in the resistant genotypes (especially TOG5674) compared with the susceptible genotypes. This observation suggests that lignification, at least in some rice genotypes, is constitutively expressed and that this expression may differ in time. The accumulation of lignin in the epidermis of some RILs and the endodermis of TOG5674 at 1 day after inoculation suggests that lignification may act as a constitutive post-penetration mechanism of resistance to M. graminicola infection at least in some rice genotypes. On the other hand, higher intensity of lignification in resistant vs susceptible genotypes and the accumulation of lignin in the endodermis at the site of giant cell formation may suggest that lignification also acts as an inducible post-penetration mechanism of resistance to M. graminicola infection. A higher total phenolic content was observed in infected plants of some RILs compared with uninfected plants during the first weeks of observation.

Meloidogyne graminicola is one of the most important plant-parasitic nematodes in rice. Breeding for natural resistance and tolerance is considered one of the most economical and sustainable approaches to control this damaging pathogen. Quantitative trait loci (QTL) mapping was carried out in a recombinant inbred line (RIL) population derived from a cross between the Asian rice genotypes IR78877-208-B-1-2 and Dinorado. IR78877-208-B-1-2 is an aerobic rice genotype that is resistant and tolerant to M. graminicola. Dinorado is a traditional upland rice genotype from the Philippines that is characterized by its aroma and prized for its cooking quality. The host response of 300 F4 lines derived from this cross was evaluated in both nematode infested and non-infested concrete beds in the dry seasons of 2013 and 2014. Five genotypes were found consistently resistant while 13 genotypes were consistently partially resistant to M. graminicola. QTL mapping for M. graminicola resistance/tolerance, yield-contributing traits, and yield revealed four main effect QTLs (qJ2RS2.1, qJ2GRT2.1, qJ2RS3.1, and qJ2GRT3.1) associated with reduced nematode reproduction on chromosomes 2 and 3 and two QTLs (qGR3.1 and qGR5.1) associated with reduced root galling on chromosomes 3 and 5. Twenty main effect QTLs associated with yield-contributing traits and yield were also found. Our study further identified co-locating QTLs associated with nematode resistance, yield-contributing traits, and yield on chromosomes 3 and 5. QTLs harboring candidate genes, such as OsBAK1, OsDST, OsIPT4, and DUF26, for higher grain yield and tolerance to abiotic and biotic stress, were identified. These QTLs and the RILs that are consistently resistant and tolerant to M. graminicola, and which are high-yielding in nematode-infested fields, can be utilized in breeding programs to improve the resistance and tolerance of Asian rice to this important pathogen.

The nematicidal activity of crudely milled powders of stems, leaves, and bulbs of Cassia abbreviata, Cissus cactiformis, Euphorbia ingens, Ipomoea kituiensis, Synadenium cupulare, Senna petersiana, Urigenia sanguinea, Maerua angolensis, and Tabernaemontana elegans on eggs and J2 population densities of Meloidogyne incognita race 2 on tomato was examined under glasshouse conditions. These plant species have medicinal properties and are being used in South Africa by traditional healers as so-called "muti." All plant species showed a suppressive effect. Relative to untreated control, the soil amendments consistently suppressed M. incognita population densities in tomato roots and the reproductive potential (RP) of the nematode. When compared to fenamiphos, a commercial systemic chemical nematicide, the soil amendments performed comparable or better in suppressing nematode populations in the root systems in 2008 and 2009, but fenamiphos performed better than all soil amendments in 2011. The RP of M. incognita was comparable for both soil amendment- and fenamiphos-treated plants. No consistent trend in the effect of the soil amendments on plant root and shoot bioweight was observed, except when plants were treated with T. elegans-based soil amendments and both root and shoot bioweight were consistently higher compared with untreated control plants. Our results show that the plant species examined are potential sources of phytonematicides effective against M. incognita race 2. The nematicidal activity of crudely milled powders of stems, leaves, and bulbs of Cassia abbreviata, Cissus cactiformis, Euphorbia ingens, Ipomoea kituiensis, Synadenium cupulare, Senna petersiana, Urigenia sanguinea, Maerua angolensis, and Tabernaemontana elegans on eggs and J2 population densities of Meloidogyne incognita race 2 on tomato was examined under glasshouse conditions. These plant species have medicinal properties and are being used in South Africa by traditional healers as so-called “muti.” All plant species showed a suppressive effect. Relative to untreated control, the soil amendments consistently suppressed M. incognita population densities in tomato roots and the reproductive potential (RP) of the nematode. When compared to fenamiphos, a commercial systemic chemical nematicide, the soil amendments performed comparable or better in suppressing nematode populations in the root systems in 2008 and 2009, but fenamiphos performed better than all soil amendments in 2011. The RP of M. incognita was comparable for both soil amendment- and fenamiphos-treated plants. No consistent trend in the effect of the soil amendments on plant root and shoot bioweight was observed, except when plants were treated with T. elegans-based soil amendments and both root and shoot bioweight were consistently higher compared with untreated control plants. Our results show that the plant species examined are potential sources of phytonematicides effective against M. incognita race 2.

Soil amendments, constituting of various plant and animal sources, were evaluated in pits for their effects on Meloidogyne spp. infecting tomato in comparison to the synthetic nematicide fenamiphos and the untreated control. Fifty-six days after transplanting, soil and root samples were collected for nematode extraction and counting while fruit mass and the number of fruits were also recorded and the average yield per treatment calculated. The plant-based pit-composting treatments decreased nematode population densities, from 43% to 94%; with the citrus fruit-pit compost being the most effective (reducing nematode densities by up to 94%). Conversely, chicken and cattle manure treatments generally resulted in increased nematode densities (up to 141% and 159%, respectively). Increases in tomato yield ranged from 7% to 94% in response to compost, cattle and chicken manure treatments while all pit-composting significantly enhanced yield ranging from 100% to 400%; except for the shrub-pruning pit compost which decreased yield. Pit-composting is a promising strategy that can be used by especially subsistence farmers to grow crops sustainably in the presence of lower nematode pest densities

Interactive effects of alternatives to methyl bromide on root-knot (Meloidogyne species) nematodes could provide information on whether to use the products combined or singularly. The objective of ...

Resistance and tolerance to Meloidogyne graminicola infection of introgressed rice genotypes derived from crosses between M. graminicola-resistant Oryza glaberrima genotype CG14 and -susceptible O. sativa genotype IR64 were evaluated in an indoor growth chamber and outdoor raised beds. None of the 44 introgressed genotypes: 24 first backcross F2 generation (BC1F2) and 20 first backcross F3 generation (BC1F3) evaluated did express the same level of resistance as the resistant O. glaberrima reference genotypes included in the experiments for comparison. Lower nematode multiplication factor on the BC1F3 genotypes suggests that M. graminicola resistance trait segregated among the 3rd generation progeny of the backcross population. The majority of the introgressed genotypes were susceptible and sensitive to M. graminicola infection, some genotypes were susceptible but tolerant and few were both resistant and tolerant to nematode infection. Several genotypes with resistance and/or tolerance to M. graminicola were identified that could either be further developed into advanced breeding lines to produce resistant and/or tolerant cultivars or in the short-term developed into M. graminicola-resistant and/or –tolerant cultivars for use by resource-poor farmers.

The host response to Meloidogyne graminicola infection of 30 advanced breeding lines developed from crosses between high-yielding and drought-tolerant Oryza sativa genotypes was evaluated i...

The rice root-knot nematode (RKN), Meloidogyne graminicola, is an important pathogen affecting rice production in South and Southeast Asia. Efficacy of resistance and tolerance in selected M. graminicola-resistant African rice genotypes TOG5674, TOG5675 and CG14 and -susceptible Asian rice genotypes IR64 and UPLRi-5 were examined under a range of initial population densities (Pi) and water regimes. Resistance to M. graminicola in resistant rice genotypes was not broken with increasing pathogen pressure (Pi = 15,000 to 60,000 J2/plant). Resistant rice genotypes were even tolerant to the damage and yield loss caused by high pathogen pressure. On the other hand, increasing Pi levels caused more damage on susceptible rice genotypes. Final nematode population densities in the root systems of resistant and susceptible rice genotypes were significantly lower under flooded conditions than under upland and drought conditions. TOG5674, TOG5675 and CG14 were more tolerant to M. graminicola infection even whe...

The effect of different rice-based crop rotation sequences on the population densities of Meloidogyne graminicola and on the yield of rice was evaluated in a microplot experiment under lowland rice field conditions. Ten treatments of cropping sequences were grown in four successive growing seasons: continuous growing of the susceptible rice cultivar Thihtatyin (rice-rice-rice-rice), four treatments of 1- season crop rotation sequences (rice-rice-chickpea-rice, rice-rice-black gram-rice, rice-rice-soybean-rice, rice-rice-cowpea-rice), and five treatments of 2-season crop rotation sequences (groundnut-rice-chickpea-rice, green gram-rice-black gram-rice, cowpea-rice-soybean-rice, sesame-rice-cowpea-rice, sunflower-rice-sesame-rice). Population densities of M. graminicola recovered from the rice plants and the nematode multiplication factors (Mf) in the soil in the continuous rice cropping sequence (rice-rice-rice-rice) was the highest among the ten cropping sequences. Lowest nematode Mf in the soil was observed in the 2-season crop rotation sequence sunflower-rice-sesame-rice and the highest was observed in the 1-season crop rotation sequence rice-rice-cowpea-rice among the nine crop rotation sequences. Highest rice yield was obtained in the 2-season crop rotation sequences green gram-rice-black gram-rice, sesame-rice-cowpea-rice and sunflower-rice-sesame-rice, which were about 2 times higher compared with the 1-season crop rotation sequences and about 3 times higher compared with the continuous rice cropping sequence

© 2019, © 2019 Southern African Plant & Soil Sciences Committee. Previous claims suggested that pure active ingredients from botanicals were less effective in pest management than their fermented crude-extracts. The objective of this study was to compare the toxicity of pure (98%) cucurbitacin A and B on nematode bioactivities with those of their fermented crude-extracts, the Nemarioc-AL and Nemafric-BL phytonematicides, respectively. Purified active ingredients were each diluted to 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, 2.25 and 2.50 μg ml‒1 and their fermented crude-extracts to 0.0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5% and 5.0% phytonematicide. The exposure time for second-stage juveniles (J2) hatch, motility and viability of the J2 to each concentration was 24, 48 and 72 h. The overall sensitivities (Σk) of J2 hatch to Nemarioc-AL, cucurbitacin A, Nemafric-BL and cucurbitacin B were 1, 30, 5 and 2 units, respectively, for motility 7, 12, 2 and 12 units, respectively, and for viability 2, 4, 1 and 4 units, respectively. Generally, nematodes displayed high sensitivities to cucurbitacin-containing phytonematicides than to their respective purified active ingredients (cucurbitacins). In conclusion, the cucurbitacin-containing phytonematicides were more effective in nematode suppression than their purified active ingredients. ispartof: South African Journal of Plant and Soil vol:36 issue:1 pages:29-32 status: published

Rotation with nonhost crops is an important practice used for root-knot nematode (RKN) management. Screenhouse experiments were conducted to evaluate the response infection of 27 cultivars belonging to 14 crops (blackgram, cabbage, cauliflower, chickpea, cowpea, garlic, ginger, greengram, groundnut, maize, potato, sesame, soybean, sunflower), which are grown in rotation with rice in lowland and upland rice-based ecosystems, to the RKN Meloidogyne graminicola. Root galling indices observed on all crop rotation cultivars were significantly lower compared with the rice cv. Thihtatyin, used as positive control. Differences in host response to M. graminicola infection were observed between cultivars. All 27 cultivars were poor or non-hosts of M. graminicola, except cv. Yezin 4 of chickpea considered as good host. No significant differences in plant growth were observed between non-inoculated and inoculated plants of all plant/species cultivars, with the exception of a reduction in root length in the chickpea cv. Yezin 4 (good host) and the garlic cv. Shan (poor host). Rotation crops identified as poor or non-hosts of M. graminicola could be useful in the management of RKN in rice-based cropping systems.

The aim of this study was to examine the nematicidal properties of two defence inducers against the root-knot nematode Meloidogyne incognita. A direct-contact bioassay was applied to evaluate the nematicidal effects of acibenzolar-S-methyl (ASM) and methyl jasmonate (MEJA) on second-stage juveniles (J2). Nematodes were incubated in different concentrations of these compounds, and the numbers of immobile nematodes were counted after 24 and 48 h post incubation. Tap water was then added to verify whether the nematodes recovered or remained dead at 72 h. The percentage of dead nematodes was used as indicator for the toxicity of the different solutions. Our results show that ASM, in the formulation of Bion®, and MEJA have nematicidal properties.

Ditylenchus africanus affects peanut quality, which leads to downgrading of consignments and economic losses for producers. This nematode is difficult to control and host-plant resistance may be the most effective way to control it. Recently, the peanut breeding line PC254K1 has been identified as resistant to a D. africanus population from Vaalharts and will be included into the peanut breeding program. The objectives of our study were to compare the reproduction potential of D. africanus geographic populations from five different areas in the peanut production area of South Africa and to assess whether PC254K1 is resistant to all five D. africanus populations. Reproduction of the D. africanus populations was evaluated on peanut callus in growth cabinets at 21°C, 28°C, and 35°C. The peanut cv. Sellie was included in the study as the D. africanus-susceptible reference genotype in the greenhouse and microplots. Reproduction potential of all five of the D. africanus populations was similar. Resistance of PC254K1 was confirmed to all five D. africanus populations. The resistance trait of a D. africanus-resistant cultivar developed from PC254K1 should, therefore, be sustainable over the five localities tested during this study.

Information about the effects of glyphosate on nematodes is limited and contradictory, while none existing for South African agricultural fields. The abundance and identity of non-parasitic nematodes in the rhizospheres of commercial glyphosate-tolerant and conventional (non-glyphosate-tolerant), soybean cultivars from cultivated fields, and adjacent natural vegetation (reference system) were obtained for two growing seasons. The impact of glyphosate was also investigated on non-parasitic nematodes in a 2-year soybean-maize cropping system. Thirty-two non-parasitic nematode genera were identified from soils of the three field ecosystems, with most of the genera occurring in natural vegetation (28), and less in conventional (23) and glyphosate-tolerant soybean (21). Bacterivores had the greatest diversity in soils of all three ecosystems during both seasons, while fungivores tended to be more abundant in glyphosate-tolerant soybean fields especially during the second season. Soils from the three ecosystems were disturbed and degraded with low abundance and diversity of omnivores and predators. Of the 14 genera identified from the soybean-maize cropping experiment, bacterivores dominated in terms of diversity in non-treated, and fungivores in glyphosate-treated plots. Soils from glyphosate-treated plots were degraded, less enriched and fungal-mediated, while those from non-treated plots were disturbed, enriched, and bacterial-mediated.

Rice production in Southeast Asia is significantly affected by root-parasitic nematodes (RPN). The Green Revolution has encouraged new agricultural practices (e.g. intensive monoculture, high yielding rice variety) to respond to the high rice demand; however, these methods have promoted the spread of these pests. The recent banning of chemical nematicides resulted in a need for alternative sustainable control strategies. In the present study, we assessed the effects of a direct-seeding mulch-based cropping system (DMC) vs conventional plough-based tillages (CT) on soil properties, rice yield and RPN communities during a two-year trial in Cambodia. Our results show that on average the population densities of RPN were significantly higher in DMC than in CT. Molecular identification revealed only two RPN species associated with roots: Meloidogyne graminicola, not previously reported from Cambodia, was predominant and was present throughout the plant’s development, whereas Hirschmanniella mucronata was only found at the tillering and milky stages. We conclude that DMC had a significant positive impact on rice yield, despite higher RPN short-term pressure. In order to increase the efficiency of such cropping systems, further studies and an evaluation of the long-term relationships between DMC, the nature of cover crops used, the soil biota including RPN, and rice yield should be conducted.

Background The root-knot nematode Meloidogyne graminicola is an obligate biotrophic pathogen considered to be the most damaging nematode species that causes significant yield losses to upland and rainfed lowland rice production in South and Southeast Asia. Mapping and identification of quantitative trait loci (QTL) for resistance to and tolerance for M. graminicola may offer a safe and economic management option to farmers. In this study, resistance to and tolerance for M. graminicola in Asian rice (Oryza sativa L.) were studied in a mapping population consisting of 300 recombinant inbred lines (RILs) derived from IR78877–208-B-1-2, an aerobic rice genotype with improved resistance to and tolerance for M. graminicola, and IR64, a popular, high-yielding rice mega-variety susceptible to M. graminicola. RILs were phenotyped for resistance and tolerance in the dry seasons of 2012 and 2013. QTL analysis was performed using 131 single nucleotide polymorphism (SNP) and 33 simple sequence repeat (SSR) markers. Results Three QTLs with main effects on chromosomes 4 (qMGR4.1), 7 (qMGR7.1) and 9 (qMGR9.1) and two epistatic interactions (qMGR3.1/ qMGR11.1 and qMGR4.2/ qMGR8.1) associated with nematode reproduction that were consistent in the two seasons were detected. A QTL affecting root galling was found on chromosomes 4 (qGR4.1) and 8 (qGR8.1), and QTLs for nematode tolerance were found on chromosomes 5 (qYR5.1) and 11 (qYR11.1). These QTLs were consistent in both seasons. A QTL for grain yield was found on chromosome 10 (qGYLD10.1), a QTL affecting filled grains per panicle was detected on chromosome 11 (qFG11.1) and a QTL for fresh root weight was found on chromosomes 2 (qFRWt2.1), 8 (qFRWt8.1) and 12 (qFRWt12.1) in both seasons. The donor of the alleles for qMGR4.1, qMGR7.1, qMGR9.1, qGR4.1, qGR8.1, qYR5.1 and qFRWt2.1 was IR78877–208-B-1-2, whereas for qYR11.1, qGYLD10.1 and qFG11.1, qFRWt8.1 and qFRWt12.1 was IR64. Lines having favorable alleles for resistance, tolerance and yield provided better yield under nematode-infested conditions and could be a starting point of marker-assisted breeding (MAB) for the improvement of M. graminicola resistance and tolerance in Asian rice. Conclusion This study identified a total of 12 QTLs with main effects and two epistatic interactions in the 1st season and 2nd season related to M. graminicola resistance and tolerance, and other agronomic traits such as plant yield, percentage of filled grains, and fresh and dry root weight. Rice genotypes that have the favorable alleles for resistance (qMGR4.1, qMGR7.1, qMGR9.1, qGR4.1, qGR8.1) and tolerance (qYR5.1, and qYR11.1,) QTLs, and which are either resistant or partially resistant and tolerant, were also selected. These selected genotypes and the identified QTLs are vital information in designing MAB for the improvement of high-yielding rice genotypes but are susceptible to M. graminicola infection. Electronic supplementary material The online version of this article (10.1186/s12863-018-0656-1) contains supplementary material, which is available to authorized users.

International audience; Meloidogyne graminicola is a major plant-parasitic nematode affecting rice cultivation in Asia. Resistance to this nematode was found in the African rice genotypes Oryza glaberrima and O. longistaminata; however, due to interspecific hybrid sterility, the introgression of resistance genes in the widely consumed O. sativa varieties remains challenging. Recently, resistance was found in O. sativa and, here, we report for the first time the histological and genetic characterization of the resistance to M. graminicola in Zhonghua 11, an O. sativa variety. Bright-light microscopy and fluorescence observations of the root tissue of this variety revealed that the root cells surrounding the nematode displayed a hypersensitivity-like reaction with necrotic cells at early stages of infection when nematodes are migrating in the root's mesoderm. An accumulation of presumably phenolic compounds in the nematodes' neighboring root cells was also observed. In addition, at a later stage of infection, not only were few feeding sites observed but also the giant cells were underdeveloped, underlining an incompatible interaction. Furthermore, we generated a hybrid O. sativa population by crossing Zhonghua 11 with the susceptible O. sativa variety IR64 in order to describe the genetic background of this resistance. Our data suggested that the resistance to M. graminicola infection was qualitative rather than quantitative and, therefore, major resistance genes must be involved in this infection process. The full characterization of the defense mechanism and the preliminary study of the genetic inheritance of novel sources of resistance to Meloidogyne spp. in rice constitute a major step toward their use in crop breeding.

SummaryFive populations ofMeloidogyne graminicolaisolated from different rice-growing areas in the Philippines were characterised. The populations showed little phenotypic variability of second-stage juveniles and female perineal pattern. Differences in reproduction amongM. graminicolapopulations were not observed on mature resistantOryza glaberrimavarieties ‘TOG5674’, ‘TOG5675’, ‘RAM131’ and ‘CG14’, or on susceptibleO. sativavarieties ‘IR64’ and ‘UPLRi-5’. In all infected rice varieties, plant growth and yield-contributing traits showed no differences among the populations. A search onM. graminicolapopulations from the Philippines for single-nucleotide polymorphism on the sequences of Internal Transcribed Spacer (ITS) of rDNA genes and mtDNA indicated only few points of heteroplasmy. Nematode reproduction and disease induction of the fiveM. graminicolapopulations in the Philippines exerted the same level of aggressiveness and virulence. The absence of resistance-breaking populations ofM. graminicolais important for the maintenance of durability of resistance to this important rice pathogen.

Sunflower ranks first among the legume and oilseed crops produced in South Africa, followed by soybean. The production of Bambara groundnut, cowpea, dry bean, groundnut and lupin is practised on a much smaller scale. The omnipresence of economically important plant-parasitic nematodes poses a threat to the sustainable production and expansion of leguminous and oilseed crops, with Meloidogyne and Pratylenchus spp. as generally the most damaging nematode pests. Ditylenchus africanus (indigenous to Southern Africa) is the predominant nematode pest of groundnut. The discovery of Aphelenchoides arachidis individuals in groundnut pods also poses a threat to producers. In this chapter, symptoms of damage inflicted by particular plant-parasitic nematodes on leguminous and oilseed crops are described, as are the management strategies available to local producers. These typically include the use of chemical control, crop rotation and to a lesser extent host plant resistance. Of particular interest are discussions on root-knot nematode resistance breeding in soybean and the development of molecular markers to expedite the breeding process. The same applies for D. africanus and groundnut. Although nematode research focused mainly on groundnut and soybean, information for Bambara groundnut, cowpea, dry bean, lupin and sunflower is also presented.

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.

In South Africa, about 48 % of the people live in rural areas. A large portion (35 %) of this rural population lives below the poverty line. Most of these communities depend on the production of grain, leguminous and vegetable crops, mainly in household or communal gardens, as their main food source. Available land is often limited and, therefore, frequently reused, which aggravates soil disease and pest problems and soil degradation. In agricultural production more than 10 % of the crop yields can be lost due to diseases and pests. However, in rural areas this percentage is much higher. Diseases and pests, including plant-parasitic nematodes, can even cause crop failures. In general, root-knot nematodes (Meloidogyne spp.) are the most abundant and damaging nematode pests in local smallholding farming. To alleviate the nematode problem and secure food production in such a way that it is affordable for smallholding farmers, alternative low-input, cost-effective and environmentally friendly nematode management strategies need to be developed. In South Africa, research related to such strategies for smallholding farming is mainly focused on the discovery of local botanical nematicides (phytonematicides) and their use as soil amendments to manage root-knot nematodes. Also the use of natural sources of resistance or tolerance, the application of crop rotation and intercropping, the use of organic amendments and the use of cover crops as biofumigants are being investigated.

Maize is the most important cereal crop grown in South Africa, followed by wheat and grain sorghum. Yields of grain crops usually vary considerably between years, mainly due to highly variable rainfall. The most widespread and frequently encountered nematode pests of maize are root-knot nematodes, with Meloidogyne incognita and M. javanica dominating. Lesion nematodes follow, with Pratylenchus zeae generally being the predominant of a range of species from this genus. However, other plant-parasitic nematodes of the families Criconematidae, Dolichodoridae and Hoplolaimidae and species of Longidorus, Nanidorus, Paratrichodorus and Xiphinema have also been recorded from maize-producing areas. The response to treatment with nematicides in field experiments generally has not given consistent results, due in part to fluctuating rainfall. As a result, nematodes are not considered by maize farmers as a primary yield constraint. In contrast with an extensive body of information being available for maize nematodes, limited nematology research has been done on other cereal crops. The most commonly occurring nematode pests associated with barley, grain sorghum, millet, wheat and rice are also referred to in this chapter.

Banana and plantains (Musa spp.), the second largest fruit crop in the world, are important staple foods in tropical regions of Africa, America, Asia and the Pacific. It is the most widely consumed and exported fruit in the world. Plant parasitic nematodes are one of the major biotic stresses affecting banana production. Breeding works carried out at the Department of Fruit Crops, Tamil Nadu Agricultural University, India. The potential diploids and hybrids developed were crossed with commercial triploids to develop primary tetraploids and improved diploids. The susceptible check cultivar used was ‘Rasthali’ (AAB), while the resistant reference cultivar used ‘Pisang Lilin’ (AA). Banana suckers of uniform size and weight were collected, pared and planted in earthen part containing 5 kg sterilized pot mixture. Egg masses of M. incognita were picked from roots, allowed to hatch in a beaker of distilled water and the hatched juveniles (J2) were inoculated in the rhizosphere of the hybrids by soil injection method at 5,000 nematodes/pot. Same set of replicated banana hybrids were also maintained as uninoculated check. The reactions of nineteen new synthetic banana phase II hybrids to M. incognita was studied under field conditions as well as in controlled inoculation tests in pots. Hybrid H 531 (‘Poovan’ × ‘Pisang Lilin’) was found to be resistant and six hybrids, H-02-34, H-03-05, H-03-13, H-04-12, H-04-24 and NPH-02-01 were found to be tolerant to the root-knot nematode, M. incognita while the remaining were rated as susceptible and highly susceptible ones. Total phenols and PO, PPO, PAL and enzymatic activity of the hybrids in defense mechanism in response to nematode invasion indicated higher activities in resistant genotypes compared to susceptible ones. The total phenol in the roots was estimated using Folin Ciocalteau reagent and measuring absorption at 660 nm in a spectrophotometer. For enzyme extraction, one gram of root sample per replicate was homogenized with 2ml of 0.1 M sodium phosphate buffer (pH 7.0) at 4°C. The supernatant was used as crude enzyme extract for assaying PO and PPO. Enzyme extracted in borate buffer was used for estimation of PAL. The PO activity was assessed according to Hammer-Schmidt and the PPO activity was assessed using the modified method of Mayer. Hybrid H 531 had the maximum biochemical content and enzyme activity among the hybrids included in this study. The resistant and tolerant hybrids had enhanced contents of total phenol, PO, PPO and PAL.

The root-knot nematode,Meloidogyne graminicola, can cause substantial rice yield losses. Understanding the mechanisms of resistance to this nematode species in known resistant rice genotypes may help to improve rice genotypes, aiming at developing and implementing environment-friendly and cost-effective nematode management strategies. Using susceptible and resistant rice genotypes, a comparative analysis of histological response mechanisms was made during two phases of the nematode colonisation:i) root penetration; andii) subsequent establishment and development byM. graminicolasecond-stage juveniles (J2). Two types of defence response mechanisms could be distinguished in the resistant rice genotypes. The early defence response consisted of a hypersensitive response (HR)-like reaction in the early stage of infection characterised by necrosis of cells directly affected by nematode feeding. This HR-like reaction was observed only in theM. graminicola-resistantOryza glaberrimagenotypes and not in theM. graminicola-susceptibleO. sativagenotypes. The late defence response took place after the induction of giant cells by the J2. Giant cells usually collapsed and degenerated before J2 developed into adults. Structural features of the roots of the susceptibleO. sativashowed greater root and stele diam. and cortex thickness than the resistantO. glaberrimagenotypes. Desired features of plants with resistance toM. graminicolaelucidated in this study can be used for selection of plants for breeding programmes.

The role of lignin and phenols in plant defence ranges from preformed characteristic to inducible physical and chemical response against nematode infection. Our study shows the involvement of lignin and phenols in the defence of two newly identified resistant banana (Musa) genotypes to burrowing nematode Radopholus similis infection. Results were compared with reference resistant and susceptible banana cultivars. Histochemical analysis of root cross sections showed a more extensive secondary cell wall lignification of vascular bundles in R. similis-infected plants than in the nematode non-infected plants. Increased extensive lignification was not associated with the cortex cells that are directly attacked by the nematode. This showed that the increased lignification is a general defence response to protect the vascular bundle from damage rather than resisting the nematode development and reproduction at the root cortex. Histochemical localisation showed no preformed phenolic cells in the cortex of the non-infected, R. similis-resistant and -susceptible Musa genotypes. By contrast, phenolic substances were the major constituents of the nematode-infected necrotic cells. Phenols and lignin contents were also quantitatively assayed. The Folin-Ciocalteu assay confirmed the increase in phenol content of nematode-infected root cells. Phenol content in nematode-infected plants was twice the amount of phenol content in nematode non-infected plants at 3 weeks after infection. This is possibly due to the biosynthesis or accumulation of secondary metabolites such as phenolic phytoalexins in the nematode infection sites of all the banana genotypes. This study clearly demonstrates that phenols and lignin play an important role in the defence mechanisms of Musa to R. similis infection.

The life cycle of the rice root-knot nematode, Meloidogyne graminicola, was studied in an indoor growth chamber on the susceptible Asian rice cultivar UPLRi-5 at 29/26 and 36/32 °C (day/night temperature) under non-flooded and flooded conditions. Adult females were observed 11 days after inoculation (DAI) at 36/32 °C under non-flooded conditions and at 29/26 °C under flooded conditions. At 29/26 °C under non-flooded conditions, adult females were observed at 13 DAI. Completion of the life cycle from the second-stage juvenile (J2) to the second-generation J2 at 29/26 °C under non-flooded conditions was 20 days, and 19 days at 29/26 and 36/32 °C under flooded and non-flooded conditions, respectively. At 36/32 °C under non-flooded conditions, about one-third more adult females were observed compared with the other treatments but this did not result in more second-generation J2. The number of second-generation J2 was significantly higher (more than 15 times) at 29/26 °C under flooded conditions compared with ...

The rice root-knot nematode Meloidogyne graminicola is considered one of the most potentially important nematode pathogens of rice, especially in South and Southeast Asia, in a range of rice production systems. Identification of M. graminicola-resistant or -tolerant rice varieties will enable breeding programmes to develop rice varieties which are able to limit yield losses caused by this nematode species. The host response to M. graminicola infection of 15 lowland rice varieties and 9 upland rice varieties, which are being grown in the summer-irrigated lowland and rainfed upland rice ecosystems in Myanmar, was evaluated in two experiments under screenhouse conditions. The lowland rice experiment was carried out under intermittently flooded conditions in a clay loam soil (i.e. simulating the summer-irrigated lowland rice ecosystem) and the upland rice experiment was carried out at field capacity in a sandy loam soil (i.e. simulating the monsoon rainfed upland rice ecosystem). None of the15 lowland and 9 u...

Host and yield responses of soybean genotypes resistant to Meloidogyne incognita were verified in semi-field and field trials at four different localities in South Africa. The resistant cultivar LS5995 and susceptible cultivars Prima and Prima2000 were used and each trial consisted of two treatments: fumigated (control) and nematode-infected plots. The number of rootknot nematode eggs and J2 in roots of nematode-infected plants was significantly higher in Prima and Prima2000 compared with those of the resistant genotypes in all trials. Low root and soil nematode population densities were consistently recorded for LS5995 in all trials. Yield of the resistant genotypes did not differ significantly between the fumigated and the nematode-infected plants for all trials, while yields of the susceptible Prima and Prima2000 grown in fumigated plots were significantly higher than those in nematode-infected plots for one microplot as well as one field trial. LS5995 is no longer commercially available in South Africa but is used as a superior source of M. incognita-resistance in breeding programmes for introgression of resistance into high-yielding, locally adapted soybean cultivars. http://www.tandfonline.com/toc/ttpm20/current#.Va36xPlGRfk