Using relative penetration and maleness indices in Meloidogyne incognita to establish resistance type in Cucumis myriocarpus

Resistance in plant-parasitic nematodes is broadly classified as pre-infectional or post-infectional. Prebreeding establishment of resistance type in plant-parasitic nematodes is essential where germplasm is to be introgressed into the rootstock breeding lines since only post-infectional resistance is introgressible. A study was conducted to determine whether resistance in wild cucumber (<i>Cucumis myriocarpus</i>) rootstocks to the southern root-knot nematode (<i>Meloidogyne incognita</i>) was pre- or postinfectional. Seven treatments: 0, 200, 600, 1000, 1400, 1800 and 2200 eggs and juveniles, were arranged in a randomised complete block design with 10 replicates. At harvest, 56 days after inoculation, therelative penetration index [RPI = (Pfin root/Pfin soil) – 1] and the relative maleness index [RMI = (Pftotal males/Pftotal females) – 1] were each greater than one, with the reproductive factors of M. incognita alsobeing less than one at all levels, without any yield loss. The RPI and RMI suggested that resistance in C. myriocarpus to M. incognita was  post-infectional. Thus, the resistance germplasm in this plant couldbe introgressed into wild watermelons in the development of nematode-resistant rootstock lines for the management of M. incognita race 2 in highly nematode-susceptible watermelon cultivars.Key words: Citrullus lanatus, nematode resistance, reproductive potential, watermelon

Control of whiteflies and aphids in tomato (Solanum lycopersicum L.) by fermented plant extracts of neem leaf and wild garlic

Whitefly (Bemisia tabaci, Homoptera: Aleyrodidae) and aphid (Homoptera) on tomato (Solanum lycopersicum L.) are economically important insect pests that are difficult to manage due to their resistance to a wide range of chemical pesticides. Field experiments were conducted to assess the effects of fermented plant extracts of neem (Azadirachta indica A. Juss.) leaf and wild garlic (Tulbaghia violacea) on whitefly and aphid population. The population of both insect pests showed two different patterns with higher counts observed during summer than winter monitoring. During both seasons, numbers of whiteflies and aphids increased regardless of the treatment, but the numbers remained significantly lower within treated than untreated plots. The mixture of neem and wild garlic was more effective in reducing population densities of whitefly and aphid than either plant extract applied alone. In conclusion, results of this study suggested a synergistic effect of fermented plant extracts of neem and wild garlic as a bio-pesticide.Key words: Aphid, bio-pesticide, fermented plant extract (FPE), Solanum lycopersicum, whitefly

Management of Meloidogyne incognita in nematodesusceptible watermelon cultivars using nematoderesistant Cucumis africanus and Cucumis myriocarpus rootstocks

Watermelon (Citrullus lanatus) cultivars are highly susceptible to the southern root-knot nematode (Meloidogyne incognita), with considerable yield losses when this nematode is not managed. Empirical evidence suggested that wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus) were highly resistant to M. incognita race 2. The objective of this study was two-fold; viz. to determine whether (1) C. africanus and C. myriocarpus seedling rootstocks would be compatible with watermelon cv. ‘Congo’ and ‘Charleston Gray’ and (2) the two Cucumis spp. rootstocks would retain their nematode-resistance capabilities when grafted with the two highly nematode-susceptible watermelon cultivars. The eight treatment combinations were arranged in a randomised complete block design, with six replications. At harvest, 56 days after transplanting the grafted seedlings, with highly susceptible watermelon cultivars had no effect on nematode-resistance capabilities of C. africanus and C. myriocarpus. Also, the two Cucumis spp. were compatible with the two watermelon cultivars. Consequently, C. africanus and C. myriocarpus rootstocks have the potential for use as resistant rootstocks in the management of M. incognita race 2 in watermelon production.Key words: Cucumis spp., root galls, resistant rootstocks, reproductive factor, watermelon cultivars

Baseline information on using fermented crude extracts from Cucumis africanus fruit for suppression of Meloidogyne incognita and improving growth of tomato plants

Bio-pesticides, when used as a post-planting pesticide, are limited by their potential ability to suppress the pest and their degree of phytotoxicity. Baseline information on the suitability of fermented crude extracts (FCE) of Cucumis africanus fruit as a post-planting bio-nematicide was determined on Meloidogyne incognita and growth of tomato in pot trials. Seedlings were inoculated with 1,130 eggs and juveniles/pot, while FCE  were applied weekly at 0, 10, 20, 30, 40, 50 and 60% dilutions. At harvest, nematode and plant data were  subjected to analysis of variance and the curve-fitting allelochemical response data (CARD) computer-based  model, respectively. Relative to inoculation level, final nematode population density (Pf) at the same level of  inoculation was reduced, while increasing dosages had no effect on Pf and reproductive factor values. Since  increasing dosages had no effect on Pf, the material could possibly still reduce this variable when applied below  10% dilutions. Dosages used were phytotoxic to tomato plants, but CARD model demonstrated that the material stimulated plant growth at dosages below 10%. In conclusion, baseline information from CARD  model suggested that FCE from C. africanus fruit have the potential to serve as a bio-nematicide and  bio-fertiliser on tomato provided the material was applied below 10% dilutions.Key words: Cucumis africanus, bionemagation, effective microbe organisms, ground leaching technology, root-knot nematode

Genetic analysis among selected vernonia lines through seed oil content, fatty acids and RAPD DNA markers

Vernonia (Vernonia galamensis) is a new potential industrial oilseed crop. The seeds of this crop contain unusual naturally epoxidised fatty acids which are used in the production of various industrial products. The objective of this study was to evaluate and select vernonia lines in Limpopo province through seed oil content, fatty acid content and RAPD DNA markers. Significant differences were observed for the content of seed oil (22.4 - 29.05%), vernolic acid (73.09 - 76.83%), linoleic acid (13.02 - 14.05%), oleic acid (3.77 - 5.28%), palmitic acid (2.48 - 2.98%) and stearic acid (2.26 - 2.75%). Among the 13 RAPD DNA primers screened, primer OPA10 amplified DNA samples and resulted in 4 distinct groupings among tested lines. Four promising lines were selected; Vge-16, Vge-20, Vge-27 and Vge-32 using seed oil content, fatty acids and RAPD markers. The lines will be used for strategic breeding of vernonia as an alternative industrial oil crop in Limpopo province of South Africa or other similar environments

Sensitivity of Meloidogyne incognita second-stage juvenile hatch, motility and viability to pure cucurbitacins and cucurbitacin-containing phytonematicides

© 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.status: publishe

Responses of entomopathogenic nematode Steinernema feltiae to cucurbitacin-containing Nemafric-BL phytonematicide

Cucurbitacin-containing phytonematicides have potent nematicidal effects on plant-parasitic nematodes, but their effects on entomopathogenic nematodes (EPN) are unknown. The objective of our study was to determine the effects of cucurbitacin-containing Nemafric-BL phytonematicide on the viability (survival and mortality) of the EPN Steinernema feltiae. Infective juveniles (IJ) of S. feltiae were exposed to dilutions of the phytonematicide at 0.0, 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0% for 24, 48 and 72 h. Survival and mortality of IJ over increasing concentrations of the test phytonematicide exhibited negative and positive quadratic relations, respectively. Since y-intercepts in mortality curves were higher than zero, observations were adjusted for corrected mortality and subjected to lines of the best fit. Corrected IJ mortality over increasing phytonematicide concentrations exhibited positive quadratic relations, with y-intercept being equivalent to zero. Infective juvenile survival and corrected mortality over increasing Nemafric-BL phytonematicide concentrations exhibited quadratic relations, with survival relations explained by 93, 93 and 90% COD at 24, 48 and 72 h exposure durations, respectively. The optimum concentration for corrected IJ mortality and minimum concentration for IJ survival were almost equivalent. In conclusion, within the tested concentration ranges, the sensitivity of S. feltiae IJ to the phytonematicides was low as shown by the gradual increase in corrected IJ mortality and the gradual decrease in IJ survival, without intersection of the two curves.status: publishe