Silicon (Si) is known to alleviate biotic and abiotic stresses in many crops. Much of the researc... more Silicon (Si) is known to alleviate biotic and abiotic stresses in many crops. Much of the research on the biotic influence of Si has dealt with insects and fungi, with no proper studies on the effect of Si on plant-parasitic nematodes. To investigate this effect, a replicated field trial was planted with sugarcane in KwaZulu-Natal, comparing Si carriers, bagasse, filtercake and fly ash, added either by themselves or in combination with condensed molasses stillage (CMS), thume, CMS alone and aldicarb (a synthetic nematicide) to untreated plots. Applying the Si carriers to the soil was not always sufficient to increase levels of Si in the sugarcane leaves. Uptake of Si by sugarcane required a particular chemical balance in the soil, which was not found uniformly in this field. As a consequence,the addition of Si carriers, per se, had no effect on the nematode community. However, a comparison between Si-rich and Si-poor plots, selected independently of the treatments, showed that total numbers of plant-parasitic nematodes and numbers of Pratylenchus zeae and Helicotylenchus dihystera in the soil were significantly lower in plots where foliar Si levels were higher. The same trend was true for the number of P. zeae in the roots, but the difference was not significant. Multivariate analysis showed that while numbers of some of the nematodes in the soil were depressed in the higher Si plots, numbers of the more damaging nematodes were unaffected. As a result there was still a potential risk in the long term for damage to the crop caused by these nematodes.
Philosophical transactions of the Royal Society of London, Jul 3, 1979
Data from a general survey of the soil and litter arthropods of Aldabra have been analysed in an ... more Data from a general survey of the soil and litter arthropods of Aldabra have been analysed in an attempt to reveal patterns in the distribution of the species. Analysis by means of a similarity index suggests that their distribution within 14 sites that were sampled quantitatively is to a large extent independent of vegetation type. This is supported by the results of a correspondence analysis of the faunal content of a total of 70 sites representing a variety of vegetation types from several localities around the atoll. It is suggested that this apparent lack of any clear association between vegetation type and fauna may be due to niche expansion by the immigrant species.
It is suggested that the bacterium Burkholderia tropica might be used to reduce nematode damage i... more It is suggested that the bacterium Burkholderia tropica might be used to reduce nematode damage in sugarcane by promoting certain nematode species to create a less pathogenic nematode community. This suggestion arises from an investigation of the plant parasitic nematodes and their relationship with Burkholderia species along a sugarcane row. During the course of this analysis sugarcane root and soil samples were taken at intervals (15, 45, 55, 75, 80, 85, 120, 150, 185, 190, 195 m) along a 200 m cane row across a cane field for nematode and bacterial analyses at various times after planting. Soil physical and chemical characteristics were similar at all sampling points. The numbers of culturable bacteria and Burkholderia were significantly greater during the early part of the crop cycle when plants were younger. The diversity of the Burkholderia communities was characterized by groups using Amplified Ribosomal 16S rDNA Restriction Analysis. Six groups were present. Burkholderia species in each group were identified using 16S rDNA sequencing. It was observed that B. ambifaria and B. cenocepacia, were dominant at all sampling dates, although less so as the crop aged. The common nematode species were Pratylenchus zeae, Paratrichodorous minor, Xiphinema elongatum and Helicotylenchus dihystera. A spatial association of nematodes and Burkholderia species along the cane row was identified using Principle Component Analysis (ADE-4 software). The more pathogenic X. elongatum, was associated with B. graminis, B. silvatlantica, B. gladioli, B. fungorum and was dominant at the beginning of the cane row where planting started. In contrast the less pathogenic species H. dihystera and P. zeae, were associated with B. tropica and were more common towards the end of the cane row where planting ended. Coinertia analysis revealed that B. tropica was positively correlated with H. dihystera and P. zeae, but negatively correlated with X. elongatum.
Pests and diseases flourish where a susceptible host is abundant in both time and space. Hence mo... more Pests and diseases flourish where a susceptible host is abundant in both time and space. Hence monocropping can lead to considerable crop loss and even crop failure where no attempt is made to contain the pathogens. Conventionally, pathogens are controlled by means of chemicals, resistant cultivars and various agronomic practices that reduce infection. For some years interest has been given to cultivating mixtures of cultivars, or varieties, of the same plant species to reduce the incidence of disease. Combining cultivars that have different levels of disease susceptibility can disproportionately reduce the level of the disease in the field and thus improve yield. This short communication reports on outcomes of planting mixtures of sugarcane varieties. In one field trial, a combination of four varieties, N12, N21, N27 and N29, was planted in the same furrow. The yields of the second and third ratoons were greater than the averages of the varieties planted alone. The total yield bene...
A study was made of the root development of twelve sugarcane varieties, some of which are known t... more A study was made of the root development of twelve sugarcane varieties, some of which are known to differ in their response to nematodes. The number and mass of sett and shoot roots produced by the varieties were recorded at intervals up to 14 weeks after planting in pots. Root length was estimated and indices of root hair abundance and frequency of branching were calculated. Number and mass of sett roots generally increased up to 10 weeks and then declined. In NCo 382 and N6 however, there was a progressive increase up to 14 weeks. Shoot root production was initiated after 2 weeks. The number and mass of shoot roots of each variety increased with time but there were relatively large differences betwieen varieties. Shoot root mass was greatest in N55/805 and NCo310 and least in N6. Estimated total root length at 14 weeks was greatest in N55/805 and Co331 and least in CB36/14 and NCo293. In most varieties the number of root hairs per unit length of sett or shoot root decreased from 6 to 14 weeks. There was little difference in the degree of branching of the sett or shoot roots between varieties. Varieties that generally grow well on soils subject to moisture deficiency tended to have a greater total root length than those that require better growing conditions. The variety N8, which has shown some degree of tolerance to nematode damage in field trials, did not develop more roots nor a greater mass or length of roots than some other less tolerant varieties.
The importance of growing sugarcane varieties that minimise losses from nematodes is linked to th... more The importance of growing sugarcane varieties that minimise losses from nematodes is linked to the effect that the nematodes have on the cane. Revised estimates of crop loss from nematodes in South Africa indicate a reduction in yield equivalent to more than 1.6 million tons cane per annum. The most pathogenic species on sugarcane, Meloidogyne javanica, is restricted to very sandy soils. The other pathogenic and much more widespread nematodes are Pratylenchus zeae, Xiphinema elongatum and species of Paratrichodorus. The varieties generally tolerant of these nematodes can be identified by their smaller response to treatment with nematicide. The contribution that tolerant varieties make in minimising losses from nematodes was quantified by comparing their yield with susceptible varieties in six field trials conducted on sandy soil in three regions of the sugar industry, with between three and six crops per trial. Where a nematicide was not used, growing a tolerant variety increased yields by between 25 and 124% (average 83%) over that of a susceptible variety. The benefit was broadly equivalent to the increased yield achieved by treating the susceptible variety with a nematicide. In the six trials this represented an average increase of 34 t cane/ha. It is also shown that nematode tolerant varieties can sustain yields over time through the continued production of high yielding ratoon crops.
A species of Heterorhabditis and two species of Steiner nema were isolated from soil in Natal. A... more A species of Heterorhabditis and two species of Steiner nema were isolated from soil in Natal. A third species of Steinernema was obtained from a dead beetle grub. Larvae of Eldana saccharina Walker were more susceptible to the Heterorhabditis and, to a lesser extent, one of the Steiner nemaspecies than to the other species. Pupae of eldana were less susceptible than larvae to the Heterorhabditis and this Steinernema species. The Heterorhabditis sp. was tested against eldana in the field by spraying infested sugarcane with various concentrations and volumesof an aqueoussus pensionof the infective stage of the nematode. Theseranged from 50 to 8 000 infectives ml- ' and 50 to 200 ml stalk'. Large volumes of water and very large numbers of nema todes were required to achieve moderate control of eldana.
Summary -Eldana saccharifia Wa1ker (Lepidoptera : Pyralidae) is the most important insect pest of... more Summary -Eldana saccharifia Wa1ker (Lepidoptera : Pyralidae) is the most important insect pest of sugarcane in South Africa. Previous field tests had shown that, at best, only moderate control of this stalk borer could be achieved by spraying infested cane with an aqueous suspension of the infective stage juveniles of a species of Hecerorhabditis, designated Hspl. A description is given of six field tests to assess the effect of adding a water thickener, Methocel ]75, on the performance of the nematodes. A mean of 20 % morta1iry of E. saccharina larvae was achieved in four tests when the nematodes were applied at a rate of 11-13 x 10 9 infectives in 3380-7800 10.1 % Triton X lOO/ha. With the addition of 0.5 % Methocel the mortaliry of E. saccharina was increased to a mean of 33 %. In one test increasing the rate at which the nematodes were applied from 13 x 10 9 to 65 X 10 9 infectives in 3900 10.1 % Triton X lOO/ha almost doubled the effectiveness of the nematodes, from 26 % to 49 ...
Nematology in South Africa: A View from the 21st Century
Sugarcane in South Africa hosts more than 90 species of 28 genera of plant-parasitic nematodes. T... more Sugarcane in South Africa hosts more than 90 species of 28 genera of plant-parasitic nematodes. The more common include Helicotylenchus dihystera, Pratylenchus zeae, Xiphinema elongatum and, on sandy soils, Meloidogyne javanica. Root damage caused by nematodes reduces the number and length of cane stalks and yield of sucrose. Nematodes cause an estimated 9 % loss of production. Crop loss is reduced by using nematicides and nematode-tolerant cultivars. Helicotylenchus dihystera seemingly mitigates the pathogenicity of other plant-feeding nematodes and is associated with higher-yielding crops. Management practices that favour H. dihystera should provide a sustainable means of reducing the effect of more pathogenic species.
This chapter highlights the core achievements within the science of Nematology in South Africa si... more 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.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
SUMMARY Observations were made on the distribution, level of parasitism and host preference of Ba... more SUMMARY Observations were made on the distribution, level of parasitism and host preference of Bacillus penetrans infecting Meloidogyne in sugarcane fields in South Africa. Infected female Meloidogyne were found in 34% of 73 fields and occurred more frequently in coarse than fine textured soils. Fields of coarse textured soi1 infested with B. penetrans had been cultivated for more years than such fields without the parasite. Meloidogyne populations were generally larger in infested fields and data collected from one field show that the level of parasitism was greater at higher densities of the host. B. penetrans spores derived from M. jauanica infected a much larger proportion of the larvae of this species than larvae of M. incognita and larvae of an unidentified species of Meloidogyne. In contrast, spores from M. incognita were equally infective on al1 three species. An undescribed species of Meloidogyne was not infected by spores from M. javanica. RESUME
Silicon (Si) is known to alleviate biotic and abiotic stresses in many crops. Much of the researc... more Silicon (Si) is known to alleviate biotic and abiotic stresses in many crops. Much of the research on the biotic influence of Si has dealt with insects and fungi, with no proper studies on the effect of Si on plant-parasitic nematodes. To investigate this effect, a replicated field trial was planted with sugarcane in KwaZulu-Natal, comparing Si carriers, bagasse, filtercake and fly ash, added either by themselves or in combination with condensed molasses stillage (CMS), thume, CMS alone and aldicarb (a synthetic nematicide) to untreated plots. Applying the Si carriers to the soil was not always sufficient to increase levels of Si in the sugarcane leaves. Uptake of Si by sugarcane required a particular chemical balance in the soil, which was not found uniformly in this field. As a consequence,the addition of Si carriers, per se, had no effect on the nematode community. However, a comparison between Si-rich and Si-poor plots, selected independently of the treatments, showed that total numbers of plant-parasitic nematodes and numbers of Pratylenchus zeae and Helicotylenchus dihystera in the soil were significantly lower in plots where foliar Si levels were higher. The same trend was true for the number of P. zeae in the roots, but the difference was not significant. Multivariate analysis showed that while numbers of some of the nematodes in the soil were depressed in the higher Si plots, numbers of the more damaging nematodes were unaffected. As a result there was still a potential risk in the long term for damage to the crop caused by these nematodes.
Philosophical transactions of the Royal Society of London, Jul 3, 1979
Data from a general survey of the soil and litter arthropods of Aldabra have been analysed in an ... more Data from a general survey of the soil and litter arthropods of Aldabra have been analysed in an attempt to reveal patterns in the distribution of the species. Analysis by means of a similarity index suggests that their distribution within 14 sites that were sampled quantitatively is to a large extent independent of vegetation type. This is supported by the results of a correspondence analysis of the faunal content of a total of 70 sites representing a variety of vegetation types from several localities around the atoll. It is suggested that this apparent lack of any clear association between vegetation type and fauna may be due to niche expansion by the immigrant species.
It is suggested that the bacterium Burkholderia tropica might be used to reduce nematode damage i... more It is suggested that the bacterium Burkholderia tropica might be used to reduce nematode damage in sugarcane by promoting certain nematode species to create a less pathogenic nematode community. This suggestion arises from an investigation of the plant parasitic nematodes and their relationship with Burkholderia species along a sugarcane row. During the course of this analysis sugarcane root and soil samples were taken at intervals (15, 45, 55, 75, 80, 85, 120, 150, 185, 190, 195 m) along a 200 m cane row across a cane field for nematode and bacterial analyses at various times after planting. Soil physical and chemical characteristics were similar at all sampling points. The numbers of culturable bacteria and Burkholderia were significantly greater during the early part of the crop cycle when plants were younger. The diversity of the Burkholderia communities was characterized by groups using Amplified Ribosomal 16S rDNA Restriction Analysis. Six groups were present. Burkholderia species in each group were identified using 16S rDNA sequencing. It was observed that B. ambifaria and B. cenocepacia, were dominant at all sampling dates, although less so as the crop aged. The common nematode species were Pratylenchus zeae, Paratrichodorous minor, Xiphinema elongatum and Helicotylenchus dihystera. A spatial association of nematodes and Burkholderia species along the cane row was identified using Principle Component Analysis (ADE-4 software). The more pathogenic X. elongatum, was associated with B. graminis, B. silvatlantica, B. gladioli, B. fungorum and was dominant at the beginning of the cane row where planting started. In contrast the less pathogenic species H. dihystera and P. zeae, were associated with B. tropica and were more common towards the end of the cane row where planting ended. Coinertia analysis revealed that B. tropica was positively correlated with H. dihystera and P. zeae, but negatively correlated with X. elongatum.
Pests and diseases flourish where a susceptible host is abundant in both time and space. Hence mo... more Pests and diseases flourish where a susceptible host is abundant in both time and space. Hence monocropping can lead to considerable crop loss and even crop failure where no attempt is made to contain the pathogens. Conventionally, pathogens are controlled by means of chemicals, resistant cultivars and various agronomic practices that reduce infection. For some years interest has been given to cultivating mixtures of cultivars, or varieties, of the same plant species to reduce the incidence of disease. Combining cultivars that have different levels of disease susceptibility can disproportionately reduce the level of the disease in the field and thus improve yield. This short communication reports on outcomes of planting mixtures of sugarcane varieties. In one field trial, a combination of four varieties, N12, N21, N27 and N29, was planted in the same furrow. The yields of the second and third ratoons were greater than the averages of the varieties planted alone. The total yield bene...
A study was made of the root development of twelve sugarcane varieties, some of which are known t... more A study was made of the root development of twelve sugarcane varieties, some of which are known to differ in their response to nematodes. The number and mass of sett and shoot roots produced by the varieties were recorded at intervals up to 14 weeks after planting in pots. Root length was estimated and indices of root hair abundance and frequency of branching were calculated. Number and mass of sett roots generally increased up to 10 weeks and then declined. In NCo 382 and N6 however, there was a progressive increase up to 14 weeks. Shoot root production was initiated after 2 weeks. The number and mass of shoot roots of each variety increased with time but there were relatively large differences betwieen varieties. Shoot root mass was greatest in N55/805 and NCo310 and least in N6. Estimated total root length at 14 weeks was greatest in N55/805 and Co331 and least in CB36/14 and NCo293. In most varieties the number of root hairs per unit length of sett or shoot root decreased from 6 to 14 weeks. There was little difference in the degree of branching of the sett or shoot roots between varieties. Varieties that generally grow well on soils subject to moisture deficiency tended to have a greater total root length than those that require better growing conditions. The variety N8, which has shown some degree of tolerance to nematode damage in field trials, did not develop more roots nor a greater mass or length of roots than some other less tolerant varieties.
The importance of growing sugarcane varieties that minimise losses from nematodes is linked to th... more The importance of growing sugarcane varieties that minimise losses from nematodes is linked to the effect that the nematodes have on the cane. Revised estimates of crop loss from nematodes in South Africa indicate a reduction in yield equivalent to more than 1.6 million tons cane per annum. The most pathogenic species on sugarcane, Meloidogyne javanica, is restricted to very sandy soils. The other pathogenic and much more widespread nematodes are Pratylenchus zeae, Xiphinema elongatum and species of Paratrichodorus. The varieties generally tolerant of these nematodes can be identified by their smaller response to treatment with nematicide. The contribution that tolerant varieties make in minimising losses from nematodes was quantified by comparing their yield with susceptible varieties in six field trials conducted on sandy soil in three regions of the sugar industry, with between three and six crops per trial. Where a nematicide was not used, growing a tolerant variety increased yields by between 25 and 124% (average 83%) over that of a susceptible variety. The benefit was broadly equivalent to the increased yield achieved by treating the susceptible variety with a nematicide. In the six trials this represented an average increase of 34 t cane/ha. It is also shown that nematode tolerant varieties can sustain yields over time through the continued production of high yielding ratoon crops.
A species of Heterorhabditis and two species of Steiner nema were isolated from soil in Natal. A... more A species of Heterorhabditis and two species of Steiner nema were isolated from soil in Natal. A third species of Steinernema was obtained from a dead beetle grub. Larvae of Eldana saccharina Walker were more susceptible to the Heterorhabditis and, to a lesser extent, one of the Steiner nemaspecies than to the other species. Pupae of eldana were less susceptible than larvae to the Heterorhabditis and this Steinernema species. The Heterorhabditis sp. was tested against eldana in the field by spraying infested sugarcane with various concentrations and volumesof an aqueoussus pensionof the infective stage of the nematode. Theseranged from 50 to 8 000 infectives ml- ' and 50 to 200 ml stalk'. Large volumes of water and very large numbers of nema todes were required to achieve moderate control of eldana.
Summary -Eldana saccharifia Wa1ker (Lepidoptera : Pyralidae) is the most important insect pest of... more Summary -Eldana saccharifia Wa1ker (Lepidoptera : Pyralidae) is the most important insect pest of sugarcane in South Africa. Previous field tests had shown that, at best, only moderate control of this stalk borer could be achieved by spraying infested cane with an aqueous suspension of the infective stage juveniles of a species of Hecerorhabditis, designated Hspl. A description is given of six field tests to assess the effect of adding a water thickener, Methocel ]75, on the performance of the nematodes. A mean of 20 % morta1iry of E. saccharina larvae was achieved in four tests when the nematodes were applied at a rate of 11-13 x 10 9 infectives in 3380-7800 10.1 % Triton X lOO/ha. With the addition of 0.5 % Methocel the mortaliry of E. saccharina was increased to a mean of 33 %. In one test increasing the rate at which the nematodes were applied from 13 x 10 9 to 65 X 10 9 infectives in 3900 10.1 % Triton X lOO/ha almost doubled the effectiveness of the nematodes, from 26 % to 49 ...
Nematology in South Africa: A View from the 21st Century
Sugarcane in South Africa hosts more than 90 species of 28 genera of plant-parasitic nematodes. T... more Sugarcane in South Africa hosts more than 90 species of 28 genera of plant-parasitic nematodes. The more common include Helicotylenchus dihystera, Pratylenchus zeae, Xiphinema elongatum and, on sandy soils, Meloidogyne javanica. Root damage caused by nematodes reduces the number and length of cane stalks and yield of sucrose. Nematodes cause an estimated 9 % loss of production. Crop loss is reduced by using nematicides and nematode-tolerant cultivars. Helicotylenchus dihystera seemingly mitigates the pathogenicity of other plant-feeding nematodes and is associated with higher-yielding crops. Management practices that favour H. dihystera should provide a sustainable means of reducing the effect of more pathogenic species.
This chapter highlights the core achievements within the science of Nematology in South Africa si... more 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.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
SUMMARY Observations were made on the distribution, level of parasitism and host preference of Ba... more SUMMARY Observations were made on the distribution, level of parasitism and host preference of Bacillus penetrans infecting Meloidogyne in sugarcane fields in South Africa. Infected female Meloidogyne were found in 34% of 73 fields and occurred more frequently in coarse than fine textured soils. Fields of coarse textured soi1 infested with B. penetrans had been cultivated for more years than such fields without the parasite. Meloidogyne populations were generally larger in infested fields and data collected from one field show that the level of parasitism was greater at higher densities of the host. B. penetrans spores derived from M. jauanica infected a much larger proportion of the larvae of this species than larvae of M. incognita and larvae of an unidentified species of Meloidogyne. In contrast, spores from M. incognita were equally infective on al1 three species. An undescribed species of Meloidogyne was not infected by spores from M. javanica. RESUME
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