Alternative cropping systems can have contrasting effects on various soil-borne diseases: Relevance of a systemic analysis in vegetable cropping systems

Vegetable production makes an intensive use of pesticides, and a major challenge is to build alternative cropping systems that can control pests and diseases with fewer uses of chemical products. An on-farm analysis was conducted in Southeast France to assess the efficacy of several cropping systems in simultaneously controlling two major pests: root-knot nematodes (Meloidogyne spp.) and lettuce drop due to Sclerotinia sclerotiorum. Ten cropping systems resulting from the combinations of three crop sequences and two alternative techniques, solarization and green manure, were assessed during two years. The use of solarization once a year or once every two years limited the occurrence of S. sclerotiorum. Sorghum green manure tended to increase S. sclerotiorum incidence; the effect was positively correlated with green manure duration. Especially when no vegetable was cropped in summer, the green manure crop duration was lengthened and this probably created soil conditions favorable to the development of the fungus. The incidence of root-knot nematodes was largely dependent on crop rotation: a melon crop in summer increased its incidence on the subsequent lettuce crops whereas a summer sorghum cover crop had no effect. The cropping systems that limited Sclerotinia development in soil tended to support the root-knot nematode populations. These results should motivate farmers and advisers to adopt a systemic analysis and take into account the various interactions among inoculum level, soil characteristics, crop rotations, and technical management options for designing sustainable vegetable production systems.     

Nematodes as a Limiting Factor in Potato Production in Scandinavia

Plant parasitic nematodes associated with potato feed on roots and/or tubers. About 70 species, representing 24 genera, have been reported from potato. Since nematodes attack underground plant parts, there are no reliable foliar symptoms to show that nematodes may be the major cause of poor growth and reduced tuber yields. Potato roots damaged by nematodes may show lesions, abnormal proliferation of lateral roots, emerging white females and brown cysts. Nematode attacks may render plants vulnerable to other pathogens, so disease caused by microorganisms may have nematodes as an etiological component. Therefore, nematode damage may often have been attributed to other factors. In Scandinavia, potato cyst nematodes (Globodera rostochiensis and Globodera pallida) are by far the most important nematodes on potato. In Norway, the cost of compensations schemes due to imposed statutory regulations of potato cyst nematodes may some years exceed the compensation for any other pests or diseases organism in agriculture. Other important nematodes include root lesion nematodes (Pratylenchus spp.), stubby root nematodes (Trichodorus spp. and Paratrichodorus spp.), and potato rot and stem nematodes (Ditylenchus spp.). Root knot nematode Meloidogyne hapla is considered less important. Meloidogyne chitwoodi and Meloidogyne fallax are not known to be present in Nordic countries. In the control, crop rotations using non-host crops, alternating susceptible and resistant potato cultivars, are an important control measure. However, the use of resistant potato cultivars requires knowledge of the species and pathotypes present in the field.     

Transgenic Approaches to Disease Resistance in Ornamental Crops

Abstract

Viral, bacterial, and fungal diseases of ornamental plants cause major losses in productivity and quality. Chemical methods are available for control of fungal diseases, and to a lesser extent for bacterial diseases, but there are no economically effective chemical controls for viral diseases except to control vector species. Host plant resistance is an effective means of controlling plant diseases, and minimizing the necessity for the application of pesticides; however, there are many ornamentals in which no natural disease resistance is available. It is possible to introduce resistance derived from other species, or even from the pathogen itself, by genetic engineering. This allows the introduction of specific, or in some instances broad spectrum, disease resistance into plant genotypes that have been selected for desirable horticultural characters; in contrast, introduction of natural resistance by traditional breeding may take many cycles of breeding to combine disease resistance with desirable ornamental quality. This article briefly reviews existing work on transformation systems for ornamentals, and discusses the various approaches to introducing resistance to viral, bacterial, and fungal diseases, and to nematode infestations. These include pathogen-related proteins, R genes, and general pathogen resistance; anti-microbial peptides; expression of anti-pathogen antibodies; viral sequences; ribozymes; antiviral peptides; ribonucleases; and ribosome-inactivating proteins. Examples are given of application of these approaches to disease resistance in other types of crop and model plant systems, and actual or potential application to disease resistance in ornamentals. Future prospects for obtaining plants with multiple pest and disease resistances are discussed.     

加强热作线虫学研究 促进热作产业健康发展

植物线虫是危害热带作物生产的一大重要植物病原。由于适宜热带气候和土壤条件，热作线虫病害具有种类丰富、繁殖世代多和群体大的特点，掌握热作线虫发生规律，控制热作线虫病害发生对保障热作顺利生产必不可少。概述了热带作物线虫病害危害情况、热带作物线虫学研究及服务三农现状，提出提升热带作物线虫学研究水平及服务三农的策略。     

Brassicacea-based management strategies as an alternative to combat nematode pests: A synopsis

Nematode pests parasitise and cause substantial crop yield and quality losses to a wide range of crops worldwide. To minimize such damage, the exploitation and development of alternative nematode control strategies are becoming increasingly important, particularly as a result of global efforts to conserve the ozone layer as well as our soil and water substrates. Inclusion of Brassicaceae crops in cropping systems is one such alternative and has been demonstrated in most cases to be effective in managing the top-three rated economically important nematode pests, viz. root-knot (Meloidogyne), cyst (Heterodera and Globodera) and lesion (Pratylenchus) nematodes as well as others. In the past nematode pests were and still are generally managed successfully by the use of synthetically-derived nematicides, which are progressively being removed from world markets. However, fragmented and limited information about the use of Brassicaceae crops as a nematode management tool exists in various countries. The need thus arose to summarize, compare and discuss the vast amount of information that has been generated on this topic in a concise article. This paper therefore represents a comprehensive, practical and critical review of the use and effect(s) of Brassicaceae-based management strategies and the biofumigation and cover-crop/rotation characteristics of Brassicaceae in reducing nematode-pest population levels in global cropping systems.     

Integrated pest management in field vegetable crops in northern Europe — with focus on two key pests

Improvements in (1) insecticide application, (2) supervised control, and (3) pest forecasting systems have each helped to reduce considerably the amounts of insecticides required to control fly, caterpillar and aphid infestations in vegetable crops in northern Europe. By growing plants that are partially resistant to certain major pests, it is now possible to apply even less insecticide than the dose recommended for the crop. In crops where only small amounts of insecticides are applied, natural predators should prevent large increases in pest insect populations and natural parasitoids should reduce the numbers of pest insects entering subsequent generations. The possible impact of introducing transgenic plants and the use of physical (crop covers), cultural (crop rotation, undersowing) and microbial (e.g. fungi, bacteria and nematodes) methods of control are also discussed. The withdrawal of certain insecticides, as a result of environmental and commercial pressures, means that some crops may soon be without appropriate insecticides for controlling one or more of the major pest species. Whether such systems will be sustainable, remains to be seen.     

Pathogens for biological control of nematodes

This review briefly examines some of the earlier research that lists the natural soil enemies of plant-parasitic nematodes. The major emphasis is on research developments of the past decade that consider biological control of nematodes. The importance of biocontrol has arisen as a consequence of the loss of the two effective but hazardous nematicidal soil fumigants, namely dibromo-chloropropane and ethylene dibromide, and because of the urgent need for new control strategies that their passing has created. Reports of successful biocontrol of plant nematodes by the fungal agents Nematophthora gynophila, Dactylella oviparasitica and Paecilomyes lilacinus and by the bacterial agent Pasteuria penetrans are examined. These recent developments are analysed and their implications on future research of nematode biocontrol discussed.     

基因工程在植物根结线虫防治中的应用

综述基因工程在植物根结线虫防治中的应用。介绍了利用基因工程获得抗虫植物,实现对根结线虫防治的策略：植物抗体策略,蛋白酶抑制剂策略,抗线虫取食位点策略,抗虫基因的克隆以及RNAi技术的利用等。展望了抗虫基因的克隆和RNAi技术在根结线虫防治方面的研究前景。     

Row fumigation with Vorlex for control of a meadow nematode (Pratlylenchus penetrans) in potatoes

Row fumigation with Vorlex at 3 and 7 gallons per acre was applied for meadow nematode (Pratylenchus penetrans) control in potatoes. The material was applied 3 weeks before planting using one chisel per row at a depth of 8″, and ridged. The treatments resulted in a reduction in population ofP. penetrans in the soil and in the potato roots. On a soil with a relatively high population of meadow nematodes, row application of Vorlex at 3 and 7 gal per acre resulted in a yield increase of 10 and 14% respectively, and a lower incidence of tubers with vascular discoloration. By early October as many nematodes were present in treated rows as in untreated rows. Row fumigation is of value for only one potato crop.     

根结线虫与寄主植物互作机理的研究进展

根结属(Meloidogyne Gǒldi)线虫必须寄生于寄主植物根系并获取所需的全部营养，才能完成其完整的生活史。此种寄生行为会对植物造成一定的伤害，而寄主植物的反应也会对根结线虫产生显著的影响，从而引发线虫的种种高度专化性适应。寄生过程引起的根结线虫与寄主植物之间的一系列互作反应，包括根结线虫对寄主植物的致病现象，寄主植物的感病反应和抗病反应。根结线虫与寄主的关系是在长期进化过程中形成的。     

Biocontrol of bacterial wilt of potato with an avirulent strain ofpseudomonas solanacearum: interactions with root-knot nematodes

Field tests for biological control of bacterial wilt of potatoes, caused byPseudomonas solanacearum, were conducted in Florida in 1984 and 1985. Potato seedpieces of tolerant (Ontario) and susceptible (Pungo and/or Atlantic) cultivars were immersed in a suspension of the avirulent, non-bacteriocinogenic strain ofP. solanacearum, B82, prior to planting in naturally-infested soil. Relatively low populations ofP solanacearum (2 to 4 log cfu/g soil) and root-knot nematodes (0 to 33 larvae ofMeloidogyne incognita/100 cm³ soil) were present in the soil before planting. In 1984, there was approximately a 50% reduction in incidence of bacterial wilt and brown rot in B82-treated plants of cultivar Atlantic, as compared with controls. With cultivar Ontario, on the other hand, disease incidence was very low and differences between treatments were not significant. In 1985, the incidence of bacterial wilt was low in all plots. Treatment with strain B82 reduced incidence of tuber brown rot in all cultivars, but differences between treatments were not significant at P = 0.05. There was a significant correlation, however, between incidence of wilt and root-knot nematode populations in the soil. Therefore, the possibility that control of bacterial wilt in 1984 was indirect,i e, via an effect of B82 treatment on root infection byM incognita, was examined. Greenhouse tests were conducted to determine the potential effect of seedpiece treatment with strain B82 on nematode infection of cultivars Atlantic and Ontario. In two out of three trials, the B82 treatment significantly reduced incidence of root knot. These results suggest that interactions of the biocontrol agent with root-knot nematodes may determine the effectiveness of a treatment designed for bacterial wilt control in the field.     

Allelopathy in Agroecosystems in Spain

Summary

This paper reviews the effects of allelopathic interactions in agroecosystems in Spain on plant physiological activity and their ecological advantages. The phenological stage of growth of donor plants and the effective allelochemicals in the soil solution while studying the role of phenolic compounds were highlighting. Finally possible future prospects and conclusions regarding weed control by allelochemi-cals under integrated crop management strategies are discussed.     

Modelling nematode population growth and damage

Recent results on the population dynamics and damage relationships of root-knot nematode (RKN, Meloidogyne incognita) and of potato cyst nematode (PCN, Globodera pallida) are modelled, and a computer-based programme is used to explore different strategies for PCN control. Damage by RKN was shown to be density dependent, to increase with increasing duration of plant growth, and to be much greater for good than poor hosts. PCN populations both increase and decline more slowly than those of RKN, and modelling suggested that, when non-hosts are grown, differences in decline rates will have an accumulative effect on the effectiveness of rotation. Similarly, differences in nematicide effectiveness will have a major effect on post-harvest PCN populations, and nematicides were shown to be most effective when PCN populations are small. Host resistance is a key component of integrated management of nematodes and, because gene flow in soil is limited, it can be durable.     

Effects of emission reduction surface seal treatments on pest control with shank-injected 1,3-dichloropropene and chloropicrin

The phase-out of methyl bromide for preplant soil fumigation has resulted in an increased reliance on combinations of 1,3-dichloropropene and chloropicrin in many annual and perennial cropping systems in California. However, these fumigants also can have negative environmental and human health consequences and considerable research has been conducted on methods to minimize emission of these products from the soil to the atmosphere. To ensure that pest control efficacy is not compromised by emission reduction techniques, this research was conducted to simultaneously evaluate the effects of several surface seal techniques on fumigant emissions and the efficacy of soil-borne pest control with a mixture of 1,3-dichloropropene + chloropicrin. Results indicated that the interaction between emission reduction techniques and pest control efficacy can be complicated. For example in the 2006 trial, some surviving nematodes were observed in plots with both high (manure plus high density polyethylene film) and intermediate (pre-irrigation) 1,3-D cumulative emissions which suggested that emission loses are not solely responsible for some pest control failures. Weed control tended to be better with plastic film treatments and worse with pre-fumigation soil moisture manipulations but was affected less than expected by intermittent water seals. Although pest control clearly was affected by surface seal techniques, especially in shallow soil layers, some differences in nematode and weed control could not be explained solely by surface seals. These results underline the complex interactions among soil moisture and other environmental factors, application techniques, and emission reducing surface seal treatments. As new techniques and technologies become available to reduce fumigant emissions, we recommend that research include pest control efficacy evaluations before any emerging techniques are required by regulators or implemented by growers.     

Evaluation of bacterial biological control agents for control of root-knot nematode disease on tomato

Among 19 bacterial strains isolated in Yunnan from rhizosphere soils and plant tissues, Bacillus methylotrophicus strain R2-2 and Lysobacter antibioticus strain 13-6 exhibited the highest antagonistic activity against the tomato root-knot nematode Meloidogyne incognita in plate and greenhouse pot experiments. The two strains, when applied as soil drenches or seed treatments in greenhouse experiments, reduced root-knot severity and incidence on tomato compared to no-bacteria controls. In tomato field trials conducted in separate years, soil drench treatment with either strain reduced root-knot disease levels and increased yields compared to the control. Levels of disease control and yield enhancement provided by the strains were higher than those using the chemicals abamectin and carbofuran. This is the first report of B. methylotrophicus being used as a biocontrol agent against a plant parasitic nematode and the first demonstration that B. methylotrophicus and L. antibioticus can suppress disease caused by root-knot nematodes in the field.     

Management of Meloidogyne incognita in yam-based cropping systems with cover crops

The effect of intercropping cover crops was with yam was assessed for nematode management both in pot and field conditions in Nigeria. The cover crops were sown with yams in pots containing sterile soil and inoculated with 5000 eggs of Meloidogyne incognita. In the field, each cover crop was separately intercropped with yams inoculated with 10,000 nematodes. From both pot and field experiments, no nematode damage was observed on yam tubers that were intercropped with Aeschynomene histrix, Crotolaria juncea, and Tagetes erecta. Damage in intercropped tubers was reduced by 72.7% with Mucuna pruriens, Centrosema pubescens, and Pueraria phaseoloides and by 58.3% with Stylosanthes guianensis compared to yams planted without cover crops; they also had lower (p ≤ 0.05) nematode populations. Cajanus cajan, Lablab purpureus and Vigna unguiculata however, supported high nematode populations and led to nematode damage in intercropped yams. Tubers from M. incognita-inoculated plants were more damaged and lost 42% more weight (p ≤ 0.05) following three months of storage than tubers from uninoculated plants. Intercropping yams with selected cover crops can be useful in managing M. incognita without reducing yam yields.     

Repeated solarization and long-term effects on soil microbiological parameters and agronomic traits

Innovative methods less invasive for man and environment are needed to solve the problem of weeds, pests and diseases in cropping systems. Soil solarization is one practice that involves passively heating soil covered by a thin clear plastic film for several weeks during the periods of high solar radiation before the crop is planted. Soil solarization treatments were repeated to verify their long-term effectiveness on soil microbial biomass and its respiration activities, in addition to yield response and root-knot nematodes control in tomato and melon crops following soil heating. Experiments in greenhouse were carried out in Southern Italy (40°24′ N, 16°28′ E) during the summer of 1998, 1999 and 2000 on soil infested by the root-knot nematode Meloidogyne javanica. Crop yields and fruit quality of all vegetable crops were positively affected by repeating solarization for two and three years, compared to an untreated soil and soil treated once in 1998. Solarization was effective in controlling root-knot nematode damage, but solarization affected the soil biota populations and their activities as a consequence of repeated treatments.     

Pratylenchus spp. andVerticillium spp. in New Brunswick potato fields

A survey of New Brunswick potato fields with symptoms of early dying was conducted in September 1990 and 1991. Root lesion nematodes (Pratylenchus spp.) were detected in 43 of 46 fields in 1990 and in 37 of 43 fields in 1991. In 1990 and 1991 populations averaged 910 and 410 nematodes g-¹ dry root and 1030 and 720 nematodes kg¹ dry soil, respectively. Previous crops did not affect nematode populations, except in one comparison where the number of nematodes in potato roots in 1990 was higher when the previous crop was cereal than in 1991 when the previous crop was peas.Pratylenchus crenatus was more prevalent thanP. penetrans. Root-knot nematodes(Meloidogyne hapla) were detected at a few sites at low population levels only in 1991. In 1991,Verticillium albo-atrum was detected in all 37 potato fields where fungal analyses were conducted, and the average population was 350 propagules g¹ dry soil. Soil populations ofV. alboatrum did not differ in fields in which either Russet Burbank or Shepody were being grown, nor did previous crops have any effect.Verticillium dahliae was detected in 17 fields at very low populations, usually below 1 propagule g¹ dry soil. There were no significant correlations (P<0.05) between populations of P.crenatus orP. penetrans in soil or roots and populations ofV. albo-atrum orV. dahliae propagules in soil.     

Free-Living Plant-Parasitic Nematodes do not Affect the Efficiency of Seed Tuber Fungicide Treatment against <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

Stem canker on germinating potato sprouts is often caused by seed-borne inoculum of the fungus Rhizoctonia solani. However, high amounts of free-living plant-parasitic nematodes have been found in field patches of potato plants with stem canker. Fungicide treatment of the seed tubers can be used to avoid stem canker caused by seed-borne inoculum but it is unknown if nematodes can affect this. To investigate whether free-living plant-parasitic nematodes, the root-lesion nematode Pratylenchus penetrans or a combination of several plant-parasitic nematode genera in a full nematode community, may have a negative effect on the fungicide seed treatment, a pot experiment with seed tubers inoculated with R. solani, half of which were treated with fungicides, was performed. The seed-borne inoculum caused severe damage to the plants, while no fungal damages were observed on the fungicide treated plants. This shows that the nematodes did not affect the fungicide treatment. The probability of black scurf decreased in treatments with a full nematode community, which may be due to the action of fungal-feeding nematodes.     

Effects of infestation with Globodera rostochiensis (Wollenweber) Behrens Rol on the growth of four potato cultivars

Four potato cultivars were grown in plots which, following previous treatments, contained few or many Globodera rostochiensis (Wollenweber) Behrens Rol. Soil moisture content, leaf water potential and percentage ground cover were measured each week, and whole-plant samples (including roots) were taken $\text{6}\text{1}\text{2}$ and 9 weeks for planting. Leaf areas, fresh and dry weights and inorganic nutrient contents were measured on these samples. Stomatal resistance was measured on one occasion, 13 weeks after planting, and soil samples were taken midway between plants on the same date and roots extracted from them. Yields were measured 30 weeks after planting. In terms of yield Cara, which contains the resistance gene H₁, tolerated nematode attack better than the other cultivars. Of the non-resistant cultivars, Pentland Crown was the most tolerant and Pentland Dell the least; the fact that Maris Peer yielded less than Pentland Dell in heavily infested plots is probably attributable to its early maturity date and lower yield potential. The shoot:root ratio measured 9 weeks after planting was similar for all cultivars following the same previous treatment, but was decreased from 11·9 when the previous crop was Maris Piper to 5·6 when the previous crop was Pentland Crown. Good yields in the presence of nematodes were produced by Cara (and to a lesser extent Pentland Crown) because it produced extra roots in the heavily infested plots; Pentland Dell and Maris Peer produced fewer roots in heavily infested plots. Measuring leaf water potentials and soil water contents was of little value for estimating tolerance but the least tolerant cultivar, Pentland Dell, showed the largest increase in stomatal resistance in heavily infested plots, with Cara showing the smallest. Percentage ground-cover measurements through the growing season gave the best overall picture of the reactions of the four cultivars to nematode infestation, but were time-consuming. Concentrations of potassium in haulm dry matter were decreased and those of calcium increased by nematodes, with the magnitudes of the effects least in Cara and greatest in Pentland Dell. The prospect of developing an assay for tolerance sufficiently convenient for use by plant breeders must depend upon adapting a simple test of this type to a pot scale.