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Steenkamp S.,Agricultural Research Council Grain Crops Institute ARC GCI | Jordaan A.,North West University South Africa | Mc Donald A.H.,North West University South Africa | Waele D.D.,North West University South Africa | Waele D.D.,Laboratory of Tropical Crop Improvement
Nematology | Year: 2011

Ditylenchus africanus causes cellular breakdown in pod tissue of susceptible groundnut cultivars. The histopathology of this nematode on a resistant genotype was studied using light microscopy and compared with the histopathology of D. africanus on a susceptible genotype. Plants of breeding line PC254K1 and cv. Sellie were propagated in a glasshouse, inoculated with D. africanus at inoculum levels of 2000, 5000 and 7000 nematodes per plant and the pods were collected at 90, 120 and 150 days after planting. In contrast to the susceptible genotype, only a small number of nematodes were observed in restricted areas of the pod tissue of the resistant genotype. Furthermore, the resistant genotype showed neither external symptoms nor cellular breakdown in reaction to D. africanus. According to results of this study, the mechanism of resistance involved may be the inhibition of proper development, migration and reproduction of this nematode, thus preventing it building up to damaging population levels. © 2011 BRILL. Source


Steenkamp S.,Agricultural Research Council Grain Crops Institute | De Waele D.,Laboratory of Tropical Crop Improvement | De Waele D.,North West University South Africa | McDonald A.,North West University South Africa
Journal of Nematology | Year: 2016

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 218C, 288C, and 358C. 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. © The Society of Nematologists 2016. Source


Holscher D.,Nuclear Magnetic Resonance Research Group | Holscher D.,University of Kassel | Dhakshinamoorthy S.,Laboratory of Tropical Crop Improvement | Alexandrov T.,University of Bremen | And 27 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2014

The global yield of bananas - one of the most important food crops - is severely hampered by parasites, such as nematodes, which cause yield losses up to 75%. Plant-nematode interactions of two banana cultivars differing in susceptibility to Radopholus similis were investigated by combining the conventional and spatially resolved analytical techniques 1H NMR spectroscopy, matrixfree UV-laser desorption/ionization mass spectrometric imaging, and Raman microspectroscopy. This innovative combination of analytical techniques was applied to isolate, identify, and locate the bananaspecific type of phytoalexins, phenylphenalenones, in the R. similiscaused lesions of the plants. The striking antinematode activity of the phenylphenalenone anigorufone, its ingestion by the nematode, and its subsequent localization in lipid droplets within the nematode is reported. The importance of varying local concentrations of these specialized metabolites in infected plant tissues, their involvement in the plant's defense system, and derived strategies for improving banana resistance are highlighted. Source


Ndabamenye T.,University of Pretoria | Van Asten P.J.A.,International Institute Of Tropical Agriculture | Blomme G.,Bioversity International | Vanlauwe B.,Tropical Soil Biology And Fertility Institute of CIAT | And 3 more authors.
Scientia Horticulturae | Year: 2013

Numerous studies have been conducted on the effects of plant density on growth and yield of dessert bananas in the humid tropics, but effects of plant densities in relations with ecological characteristics in low input East African highland banana (Musa spp., AAA-EA genome) cropping systems have not been reported. On-station field experiments were conducted in three contrasting agro-ecological sites of Rwanda (Kibungo low rainfall with medium soil fertility, Rubona high rainfall with low soil fertility and Ruhengeri high rainfall with high soil fertility) to explore germplasm×environment interactions. Five different plant densities (plantsha-1): 1428, 2500, 3333, 4444 and 5000 and two cooking (" Ingaju" , " Injagi" ) and one beer (" Intuntu" ) cultivars were investigated. The effect of plant density on plant performance (growth and yield) over two cropping cycles in low input systems was determined. The effects of site×cultivar and site×density interactions on yield traits were significant (p<0.05). Annual yield increased with increasing plant density but strongly depended on agro-ecological site (from 6.1 to 9.2tha-1yr-1 at Kibungo, 9.5 to 21.5tha-1yr-1 at Rubona and 7.0 to 25.0tha-1yr-1 at Ruhengeri). Yields of beer cultivars increased with density, but those of cooking cultivars decreased. Maximum yields were attained at 4444plantsha-1 at Kibungo and Rubona whilst yields increased linearly beyond this level at Ruhengeri. Crop cycle duration was prolonged with increasing plant density. Relationships between bunch yield, the total above ground dry matter yields and soil chemical properties suggest that nutrient deficiencies were larger at Kibungo (e.g. K) and Rubona (e.g. K, P, Ca and Mg) compared with Ruhengeri, where yield correlated significantly with leaf area index (LAI). LAI increases up to 4, where 95% of solar radiation was intercepted by the crop canopy, indicating that increasing the LAI above 4 would have little effect on production. Evaporation was much greater at lower rainfall areas (e.g. Kibungo) and accompanied by negative annual water deficit (-135mmyr-1) than at high rainfall areas (e.g. Ruhengeri) with positive water surplus (382mmyr-1). Growing degree days from planting to bunch harvest were higher at Kibungo (3675°C days) but much less at the Ruhengeri cooler site (1729°C days), implying temperature is not restrictive at Ruhengeri. This study showed that the optimal density for bananas depends on water availability, soil fertility and cultivar, which serves as an entry point to maximize yield potential for the East African smallholder farmers rather than using a uniform blanket recommended density. We suggest that agronomic optimal plant density is lower (<4444plantsha-1) in low rainfall (<1000mmyr-1) and less fertile areas but seem to be higher (>5000plantsha-1) in areas with high fertility which receive high rainfall (>1300mmyr-1). © 2012 Elsevier B.V. Source


Ndabamenye T.,University of Pretoria | Van Asten P.J.A.,International Institute Of Tropical Agriculture | Vanhoudt N.,Laboratory of Tropical Crop Improvement | Blomme G.,Bioversity International | And 3 more authors.
Field Crops Research | Year: 2012

East African highland bananas (Musa spp., AAA-EA group) are a primary food and cash crop for smallholders in Rwanda and much of the East African highlands. Their production generally declines over time due to poor farm management and declining soil fertility. Farmers believe that among the bunch mass maintaining factors, plant density management offers some prospect. They often decrease banana mat (i.e. a single mother plant with interconnected suckers) density in an effort to increase bunch size, but the effectiveness and profitability of this practice has not been studied. In addition, not much research has been executed on the influence of climatic and edaphic factors on variations in on-farm plant density. An on-farm survey was conducted in contrasting agro-ecological sites of Rwanda (Ruhengeri, Rusizi, Karongi, Butare, Ruhango, Kibungo and Bugesera) to determine existing densities and their relationship to bunch mass. A plant density assessment method was used that measures the average distance of five mats to their respective nearest four mats to calculate average mat spacing. Plant density positively correlated with surplus/deficit water supply (i.e. difference between rainfall and water demand by bananas) (r 2=0.62), with highest plant densities (>1500matsha -1) found in high rainfall areas (>1200mmyr -1) with water surplus (218-508mmyr -1) and lowest plant densities (1000-1400matsha -1) found in lower rainfall areas (1000-1200mmyr -1) with water deficit (from -223 to -119mmyr -1). Heaviest bunches (18.1-20.8kgfreshmassplant -1) were found at lowest plant densities and medium sized bunches (14.7-15.5kg) at highest plant densities. Lower soil and banana leaf nutrient contents (especially N, K, Ca and Mg) were observed on weathered soils (Acrisols) and were associated with smaller bunch mass in comparison to fertile soils (Andosols, Nitisols). Farmers tended to reduce mat densities (i) if they wanted to intercrop bearing in mind site characteristics, and (ii) to increase bunch mass to adapt to market preferences. The plant densities generally recommended by extension bodies (3m×3m or 2m×3m; i.e. 1111 and 1666matsha -1, respectively) are seldom practiced by farmers, nor do they seem to be very appropriate, as higher densities seem productive in areas with high rainfall and relatively good soil fertility. © 2012 Elsevier B.V.. Source

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