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A study was undertaken to investigate the effect of soil physical and chemical properties on nematodes associated with sugarcane. Principal component analysis (PCA) showed little or no change in the nematode community between nematicide treated and untreated plots or between sugarcane varieties. Analysis of the topsoil revealed very small differences in chemical elements between varieties. Soil of plots with the variety N16 had higher levels of Mg and Ca and lower levels of Fe. The study of soil characteristics of the topsoil and of the deeper layer revealed a heterogeneous situation alluding to the distinction of two zones over the area. However, the overall distribution of the entire nematode community, described by the factorial values of the PCA, was not related to the location of these two soil delimited zones. The coinertia analysis was then performed to identify the relationship between individual soil factors and individual species. These relationships were shown to be significant and concerned mainly the Mn level in the soil, the size of the plant–parasitic community and the abundance of Helicotylenchus dihystera and Xiphinema elongatum . All three decreased as the Mn content increased. To a lesser extent, pH and Na were positively associated with the numbers of free-living nematodes.

An attempt is made to quantify the long-term benefit from the sustained production of sugarcane in South Africa using nematicides to reduce the damage caused by nematodes in each crop. The study was conducted using data from the plant crop and four or five ratoon crops from two trials located on similar sandy soils. Treatments comprised aldicarb and an untreated control, applied to a total of 10 sugarcane cultivars. Two cultivars were common to both sites. The plant parasitic nematode communities were similar at both sites except that Meloidogyne javanica was absent from one site. Yield of ratoon crops was correlated with the yield of the plant crop. Annual losses from nematodes were similar over successive crops. Data from both sites showed there to be a significant, positive correlation between yield of the nematicide treated plots and size of the response to treatment. Over a 4-year period, M. javanica alone was responsible for 30% of the losses, equivalent to 15 t cane/ha per year. The long-term effect of nematodes on sugarcane production was measured after calculating a logarithmic function from the observed yields of successive ratoons. Without a nematicide the time taken for the yield to decline to a threshold of 40 t cane/ha per year ranged from a minimum of 1 year in the M. javanica infested site to a maximum of 9 years in the other site. Treatment with a nematicide increased this period considerably. On the site with M. javanica it took a projected 20 years before the yield of one of the cultivars reached the threshold and 43 years for the same cultivar at the other site. The use of a nematicide increased long-term production, on average, by a factor of 3 at the M. javanica infested site and a factor of 5 at the other site. Differences between cultivars in the rate at which ratoon yields declined meant that, over time, the best cultivars at both sites were not the ones which gave the greatest annual yields during the first few crops after planting.

A feature of many sugarcane fields is the patchy growth. This is often thought to be due to physical or chemical differences in the soil. In this paper we investigate the causes of growth heterogeneity of sugarcane on a sandy soil in KwaZulu-Natal, South Africa. To identify the factors that were associated with the good and poor areas, soil texture, pH, organic matter content and a number of soil chemical elements and nematode community data were subjected to principal component analysis (PCA). The numbers of each of the nematode species (Meloidogyne sp., Pratylenchus zeae, Helicotylenchus dihystera, Xiphinema elongatum and Paratrichodorus sp.) were first converted to relative proportions of ectoparasites and endoparasites. The data were collected from the 2nd ratoon crop of a nematicide trial, where half of the plots had been treated with aldicarb in the preceding two crops. Yields of control plots varied from 34.7 to 126.8 t cane ha−1 and from 85.4 to 138.7 for the treated plots. The yield data were centred and normalised separately for the treated and control plots and the values projected on the trial map to study spatial distribution. Plots with above-average yields, whether treated or untreated, occurred in the lower part of the trial site. The PCA factorial values were also projected onto the map of the trial. According to the first factor of the analysis of the abiotic soil characteristics in the 0–20 cm surface layer, the trial site could be divided into two areas, one on the left and one on the right. PCA of the soil data from the 0–20 and 20–40 cm layers showed that there was little or no difference between the two that might explain the two growth areas. However, analysis of the nematode community distinguished two main areas that largely corresponded to the distribution of the plots of low and high yielding cane. Correlation analysis confirmed the relationship between nematodes and yield. H. dihystera was positively correlated with yield of cane whereas the reverse was true for the Meloidogyne species.

Correspondance: shaun.berry@sugar.org.za; International audience; A number of different plant parasitic nematode species are found associated with sugarcane in South Africa. Of these, the root-knot nematode (Meloidogyne javanica), the lesion nematode (Pratylenchus zeae) and the dagger nematode (Xiphinema elongatum) are potentially the most damaging pests. Identification and enumeration of the number of these nematodes are necessary for providing advice to farmers as well as studying the effects of various treatments in field and glasshouse trials. We report on the development, use, and extent of specificity of three sets of primers, for M. javanica, P. zeae and X. elongatum, and on tests to detect and quantify the number of these nematodes in soil samples using SYBR Green I dye and real-time PCR technology. Amplicons from the three target species (obtained with their respective primer sets) are discernible in size by gel electrophoresis (380 bp for M. javanica, 250 bp for P. zeae and 500 bp for X. elongatum). Also, these amplicons have characteristic melting temperatures of 83.8 °C (M. javanica), 86.6 °C (P. zeae) and 86.1 °C (X. elongatum). Investigations into multiplex reactions found competition between species with M. javanica competing with P. zeae and X. elongatum. Subsequent single tube (simplex) assays, enabled the construction of calibration curves for each of the three species. These were then used for quantification of the numbers of each of these species in nematode samples extracted from the field, with a high (R2 = 0.83) and significant positive correlation between real-time PCR and counts performed with microscopy.

On the sandy soils in South Africa damage by plant parasitic nematodes to sugarcane occurs equally in both the plant and ratoon crops. In Australia and Burkina Faso, ratoon crops are less susceptible than plant crops. The aim of the present work was to investigate whether differences in stubble or stool size, resulting from the different harvesting practices in Australia, Burkina Faso and South Africa, affected yield loss in ratoon crops under South African conditions. The Australian billing up method (producing a larger below-ground stool) had little effect on nematode abundance and population structure but did exhibit reduced yield loss from nematodes in ratoon crops. A large above-ground stubble (similar to that produced by the Burkina Faso harvest method), on its own, was not associated with reduced yield loss. However when a pretrashing treatment was performed just before harvest, then a significant reduction in yield loss occurred in the following crop. Harvest procedures that produced an above-ground stubble were associated with a significantly altered nematode community structure, with increased relative proportions of Helicotylenchus dihystera and decreased proportions of Xiphinema elongation. Such nematode communities are known to be less pathogenic to sugarcane.

Metadata only record Circular patches of exceptionally well-grown sugarcane, known as "isiduli" are a common feature of sandy sugarcane fields in South Africa. They correspond to termitaria of Macrotermes natalensis, leveled by ploughing of the field. Root and soil samples were collected at 0-30 and 30-60 cm depths along a 21m transect, which passed through an isiduli. Soil physical and chemical analyses were made. Nematodes in the soil and roots of cane were identified and counted and bacterial activities were measured. Plant characteristics were determined at the various points along the transect and chemical analyses of the leaves were performed. Estimated cane yield was five times greater within the isiduli than elsewhere along the transect. Levels of N, Si, S and Ca were higher in the leaves of cane within the isiduli than outside. The reverse was true for Mn, juice purity and % sucrose. Meloidogyne javanica was absent and Xiphinema elongatum less abundant in the isiduli than elsewhere. Greater numbers of Helicotylenchus dihystera, Pratylenchus zeae and Paratrichodorus spp. occurred within the isiduli than elsewhere along the transect. The limits of the contrasting nematode communities closely matched the limits of the isiduli as defined by the vegetative parameters. The levels of the different soil elements in the topsoil (0-30 cm) were always higher within the isiduli. However, the extent of the isiduli, when defined by the greater concentrations of soil elements, did not correspond well with the limits determined by the vegetative parameters. A better correspondence was observed with the soil characteristics of the deeper (30-60 cm) soil layer. Bacterial activity gave the poorest discrimination of the extent of the isiduli, high bacterial activity being observed in samples collected both inside and outside the isiduli. © 2003 Elsevier B.V. All rights reserved.