Suitability of crops,fruit trees/plants to plant parasitic nematodes

Fifteen economically important plant species were tested for their suitability to commonly occurring plant parasitic nematodes viz, Hoplolaimus indicus, Helicotylenchus indicus, Tylenchus filiformis, Rotylenchulus reniformis, Tylenchorhynchus brassicae, Pratylenchus zeae and Meloidogyne incognita. The plants reacted differently to different nematodes. Moreover, eight fruit trees/plants were also tested for their suitability to nematodes.     

Relative efficacy of different cropping sequences integrated with ploughing for the management of plant parasitic nematodes: Relative wirksamkeit verschiedener beim pflügen integrierter fruchtfolgen zur bekämpfung von pflanzenparasitären nematoden

The relative efficacy of 25 different cropping sequences was tested at the end of the experiment. It appears that for Hoplolaimus indicus sequence number 16, 20, 8 and 10 gave high reduction in rate of reproduction, for Helicotylenchus indicus sequence No. 6, 11, 17 and 3, for Rotylenchulus reniformis sequence No. 2, 8, 13 and 14, for Tylenchorhynchus brassicae sequence No. 6, 24, 3 and 13, for Meloidogyne incognita larvae sequence No. 1, 2, 4 and 24, for Pratylenchus coffeae sequence No. 1, 2, 3 and 5; for Tylenchus filiformis sequence No. 2, 3, 4 and 5.     

Role of plant parasitic nematodes and abiotic soil factors in growth heterogeneity of sugarcane on a sandy soil in South Africa

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.     

Effectors of root sedentary nematodes target diverse plant cell compartments to manipulate plant functions and promote infection

Sedentary plant-parasitic nematodes maintain a biotrophic relationship with their hosts over a period of several weeks and induce the differentiation of root cells into specialized feeding cells. Nematode effectors, which are synthesized in the esophageal glands and injected into the plant tissue through the syringe-like stylet, play a central role in these processes. Previous work on nematode effectors has shown that the apoplasm is targeted during invasion of the host while the cytoplasm is targeted during the induction and the maintenance of the feeding site. A large number of candidate effectors potentially secreted by the nematode into the plant tissues to promote infection have now been identified. This work has shown that the targeting and the role of effectors are more complex than previously thought. This review will not cover the prolific recent findings in nematode effector function but will instead focus on recent selected examples that illustrate the variety of plant cell compartments that effectors are addressed to in order reach their plant targets.     

Occurrence and correlations of nematodes,Fusarium oxysporum and edaphic factors on banana plantations

Problems caused by nematodes and Fusarium wilt (Panama disease) on banana plantations are responsible for yield losses and are limiting to its cultivation. In the state of Goias, there is little information about the nematode occurence on this crop, and its relation with the incidence of Fusarium oxysporum f.sp. cubense (Foc). This research had the purpose to identify the occurrence of plant‐parasitic nematodes on banana plantations and to verify its correlation with the Fusarium wilt and with the soil attributes (pH, texture, nutrients). Twelve banana orchards in the state of Goias were sampled in the municipalities of Anapolis, Caiaponia, Goiatuba, Itaguaru, Itumbiara (two areas), Jatai, Morrinhos, Ouro Verde, Palestina, Taquaral and Uruana. All sampled areas, except Morrinhos, revealed contamination with Foc, and all areas had different genera of nematodes either in the soil or in the roots samples. Meloidogyne sp., Helicotylenchus sp. and Rotylenchus sp. were the main genera of plant‐parasitic nematodes found in the samples, with Meloidogyne sp. and Rotylenchus sp. being the most dominant and abundant genera. The presence of Pratylenchus sp. increases the population levels of F. oxysporum. Helicotylenchus sp. is highly correlated with high concentrations of Mn. High population density of Meloidogyne sp. was found in irrigated areas with low concentrations of P, Ca, Mg and soil pH.     

The effects of Brassica green manures on plant parasitic and free living nematodes used in combination with reduced rates of synthetic nematicides

Brassica plants once incorporated into soil as green manures have recently been shown to have biofumigant properties and have the potential of controlling plant-parasitic nematodes. In Washington State, plant-parasitic nematodes are successfully managed with synthetic nematicides. However, some of the synthetic nematicides became unavailable recently or their supply is limited leaving growers with few choices to control plant-parasitic nematodes. The objective of this project was to evaluate the effects of Brassica green manures on their own and in combination with reduced rates of synthetic nematicides on plant-parasitic nematodes and free living nematodes. In a greenhouse experiment and field trials in three seasons, Brassica green manures in combination with half the recommended rate of 1,3-dichloropropene (1,3-D, Telone) reduced root knot nematode, Meloidogyne chitwoodi to below detection levels, and reduced lesion nematodes, Pratylenchus penetrans and stubby root nematodes, Paratrichodorus allius, to below economic thresholds. The combination treatments did not affect the beneficial free-living nematode populations and the non-pathogenic Pseudomonas. The total cost of growing and soil-incorporating Brassica crops as green manures in combination with reduced rates of 1,3-D was approximately 35% lower than the present commercial costs for application for the full rate of this fumigant. Integrating conventional management practices with novel techniques fosters sustainability of production systems and can increase economic benefit to producers while reducing chemical input.     

Plant parasitic nematodes associated with the roots of wind toppled trees at the Royal Botanic Gardens, Kew

Root and soil samples from 21 trees blown down in Kew Gardens during the gales of October 1987 yielded 29 species of plant parasitic nematodes. Pratylenchus crenatus, P. thornei and P. penetrans were the only endoparasitic nematodes found. The common occurrence of P. crenatus and the root ectoparasitic nematodes, such as Merlinius microdorus, Paratrichodorus pachydermus and Rotylenchus robustus reflected the predominantly sandy nature of most of the soil samples. Species rarely recorded in Britain included Hemicriconemoides pseudobrachyurum, Paralongidorus maximus and Xiphinema pseudocoxi, all of which may be introductions.     

Effect of tillage,subsidiary crops and fertilisation on plant‐parasitic nematodes in a range of agro‐environmental conditions within Europe

The overall goal in nematode management is to develop sustainable systems where nematode populations are kept under the economic damage threshold. Conservation tillage and subsidiary crops, applied as cover crops and living mulches, generally improve soil health by increasing soil organic matter content and stimulating soil microbial activity. However, more permanent crop and weed cover associated with subsidiary crops and noninversion tillage, respectively, may benefit plant‐parasitic nematodes with broad host spectra such as Meloidogyne and Pratylenchus. These genera are major constraints to many field crops throughout Europe and there is a need to identify effective and reliable management options that can be applied to avoid excessive infestations. The dynamics of the indigenous fauna of plant‐parasitic nematodes were studied in eight coordinated multi‐environment field experiments (MEEs) under four agro‐environmental conditions in Europe (Continental, Nemoral, Atlantic North and Mediterranean North). The MEEs consisted of a 2‐year sequence of wheat combined with a living mulch or subsequent cover crops and second main crops maize, potatoes or tomatoes depending on site. Additionally, the effects of inversion tillage using the plough were compared with various forms of conservation tillage (no‐tillage, shallow and deep noninversion tillage). Overall, Helicotylenchus, Paratylenchus, Pratylenchus and Tylenchorhynchus were the most frequent genera across sites while Meloidogyne occurred only in Germany at very low densities. During the wheat–maize sequences in Switzerland, the populations of Pratylenchus increased from 63 to 146 nematodes per 100 mL soil and Helicotylenchus from 233 to 632 nematodes per 100 mL soil. The effects of tillage on plant‐parasitic nematodes were generally minor, although no tillage in Italy supported higher densities of Pratylenchus (184 nematodes per 100 mL soil) than inversion tillage (59 nematodes per 100 mL soil). Furthermore, Pratylenchus densities were 160 nematodes per 100 mL soil when leguminous subsidiary crops were grown, 122 nematodes per 100 mL soil in the green fallow and 84 nematodes per 100 mL soil after growing black oat (Avena strigosa) or oilseed radish (Raphanus sativus). The differences were greatest in Italy, in a sandy soil with low organic matter. Application of compost or nitrogen fertiliser had no consistent effects on plant‐parasitic nematodes. We conclude that crop rotations including specific subsidiary crops are prominent factors affecting the indigenous nematode community, while tillage and fertiliser are of lower importance.     

From pathogen genomes to host plant processes: the power of plant parasitic oomycetes

Recent pathogenomic research on plant parasitic oomycete effector function and plant host responses has resulted in major conceptual advances in plant pathology, which has been possible thanks to the availability of genome sequences.     

Impacts of a native parasitic plant on an introduced and a native host species: implications for the control of an invasive weed

Background and Aims: While invasive species may escape from natural enemies in thenew range, the establishment of novel biotic interactions withspecies native to the invaded range can determine their success.Biological control of plant populations can be achieved by manipulationof a species' enemies in the invaded range. Interactions weretherefore investigated between a native parasitic plant andan invasive legume in Mediterranean-type woodlands of SouthAustralia. Methods: The effects of the native stem parasite, Cassytha pubescens,on the introduced host, Cytisus scoparius, and a co-occurringnative host, Leptospermum myrsinoides, were compared. The hypothesisthat the parasitic plant would have a greater impact on theintroduced host than the native host was tested. In a fieldstudy, photosynthesis, growth and survival of hosts and parasitewere examined. Key Results: As predicted, Cassytha had greater impacts on the introducedhost than the native host. Dead Cytisus were associated withdense Cassytha infections but mortality of Leptospermum wasnot correlated with parasite infection. Cassytha infection reducedthe photosynthetic rates of both hosts. Infected Cytisus showedslower recovery of photosystem II efficiency, lower transpirationrates and reduced photosynthetic biomass in comparison withuninfected plants. Parasite photosynthetic rates and growthrates were higher when growing on the introduced host Cytisus,than on Leptospermum. Conclusions: Infection by a native parasitic plant had strong negative effectson the physiology and above-ground biomass allocation of anintroduced species and was correlated with increased plant mortality.The greater impact of the parasite on the introduced host maybe due to either the greater resources that this host providesor increased resistance to infection by the native host. Thisdisparity of effects between introduced host and native hostindicates the potential for Cassytha to be exploited as a controltool.     

Variation for host range within and among populations of the parasitic plant Striga hermonthica

Striga hermonthica is an angiosperm parasite that causes substantial damage to a wide variety of cereal crop species, and to the livelihoods of subsistence farmers in sub-Saharan Africa. The broad host range of this parasite makes it a fascinating model for the study of host-parasite interactions, and suggests that effective long-term control strategies for the parasite will require an understanding of the potential for host range adaptation in parasite populations. We used a controlled experiment to test the extent to which the success or failure of S. hermonthica parasites to develop on a particular host cultivar (host resistance/compatibility) depends upon the identity of interacting host genotypes and parasite populations. We also tested the hypothesis that there is a genetic component to host range within individual S. hermonthica populations, using three rice cultivars with known, contrasting abilities to resist infection. The developmental success of S. hermonthica parasites growing on different rice-host cultivars (genotypes) depended significantly on a parasite population by host-genotype interaction. Genetic analysis using amplified fragment length polymorphism (AFLP) markers revealed that a small subset of AFLP markers showed 'outlier' genetic differentiation among sub-populations of S. hermonthica attached to different host cultivars. We suggest that, this indicates a genetic component to host range within populations of S. hermonthica, and that a detailed understanding of the genomic loci involved will be crucial in understanding host-parasite specificity and in breeding crop cultivars with broad spectrum resistance to S. hermonthica.     

Anatomy and ultrastructure of epidermal cells in the haustorium of a parasitic flowering plant,Cuscuta japonica, during attachment to the host

Changes of epidermal cells in the haustorium of the parasiticCuscuta japonica during its attachment to the host plantimpatiens balsamina were studied with light and electron microscopy. In the transverse sections of dodder stems not in contact with the host, epidermal cells had rounded outlines. However, when haustorial initials developed in the cortex of the parasite stem at the contact site, the epidermal cells had more dense cytoplasm and conspicuous nuclei than before, and their outline was flat in the longitudinal section. As meristem cells developed from those initials, the epidermal cells became more elongated. When the haustorium was fully matured, the apical tips of the elongated epidermal cells at the contact site branched like toes, producing numerous projections via cell wall invaginations. This event caused spaces to form between the projections; coincidently, the surface area of the apical ends of the epidermal cells increased. The dense cytoplasm at those projections contained prominent nuclei and abundant other organelles, suggesting a active metabolism. Osmiophilic particles, releasing into the cell walls from the cytoplasm, were though to be associated with the loosening and elongating of the epidermal cell walls. Dense and homogeneous materials were secreted within the spaces between the projections. These materials could play an important role in cementing the haustorium onto the surface of the host organ.     

Role of oil‐seed cakes for the management of plant‐parasitic nematodes and soil‐inhabiting fungi on lentil and mungben

The oil‐seed cakes of neem (Azadirachta indica), castor (Ricinus communis), linseed (Linum usitatissimum), groundnut (Arachis hypogaea), mustard (Brassica campestris) and duan (Eruca sativa) were tested for their efficacious nature against plant‐parasitic nematodes and soil‐inhabiting fungi infesting lentil and also on the subsequent crop, mungbean in field trials. The population of plant‐parasitic nematodes such as Meloidogyne incognita, Rotylenchulus reniformis, Tylenchorhynchus brassicae, Helicoty‐lenchus indicus etc., and the frequency of pathogenic fungi Macrophomina phaseolina, Fusarium oxysporum f. lentis, Rhizoctonia solarii, Septoria leguminum, Sclerotium rolfsii, etc., were significantly reduced by the incorporation of oil‐seed cakes, however, the frequency of saprophytic fungi Aspergillus niger, Trichoderma viridae, Penicillium degetatum, etc., was increased. A several‐fold improvement was observed in plant‐growth parameters such as plant weight, percent pollen fertility, pod numbers, chlorophyll content, nitrate reducíase activity in leaves and root‐nodulation. The residual effects of different oil‐seed cakes were also noted in the subsequent crop, mungbean, in the next growing season. The population of plant‐parasitic nematodes and frequency of soil‐inhabiting fungi also influenced by the depth of ploughing.     

Probing behavior of the tea green leafhopper on different tea plant cultivars

The probing behaviors of the tea green leafhopper, Empoasca vitis (Gothe), on 9 tea cultivars were studied using video-text Direct Current-Electrical Penetration Graph, i.e., DC-EPG. The following 7 types of waveforms produced by the leafhopper stylet probing were determined: A, stylet pathway formation; S, salivation when stylets pierce into and stay in phloems; C, active ingestion before stylets reach phloems; E and F, passive ingestion in phloems; R, the insect resting with its stylet inserted into the leaf tissue and NP without probing. The 9 tested tea cultivars were categorized into 3 groups by the cluster analysis according to the number of probes per insect, waveform durations, or duration per probe of various waveforms on different tea cultivars. Waveforms S, E and F correlated to the main feeding activity of the leafhopper and may provide valuable information on predicting the resis-tance level of the tea plants to the leafhopper. The resistance level of the 9 tea cultivars to the leafhopper was ranked based on the durations of waveforms S, E and F, as well as the duration per probe including various waveforms. The ranking order of the resis-tance was: Longjingchangye > Hangdan > Zhenghedabaicha > Qianmei 601 > Hongyafoshuo > Zhongcha 102 > Zhongcha 302 > Longjing 43 > Anjibaicha, which corresponded to the resistance level determined by the population density (infestation) of the leaf-hopper on the 9 tea cultivars in the tea fields. Our study suggests that this simple and convenient DC-EPG technique might have great potential as a reliable tool to predict the resistance of tea cultivars to the tea leafhopper.     

Probing behavior of the tea green leafhopper on different tea plant cultivars

The probing behaviors of the tea green leafhopper, Empoasca vitis (Gothe), on 9 tea cultivars were studied using video-text Direct Current-Electrical Penetration Graph, i.e., DC-EPG. The following 7 types of waveforms produced by the leafhopper stylet probing were determined: A, stylet pathway formation; S, salivation when stylets pierce into and stay in phloems; C, active ingestion before stylets reach phloems; E and F, passive ingestion in phloems; R, the insect resting with its stylet inserted into the leaf tissue and NP without probing. The 9 tested tea cultivars were categorized into 3 groups by the cluster analysis according to the number of probes per insect, waveform durations, or duration per probe of various waveforms on different tea cultivars. Waveforms S, E and F correlated to the main feeding activity of the leafhopper and may provide valuable information on predicting the resis-tance level of the tea plants to the leafhopper. The resistance level of the 9 tea cultivars to the leafhopper was ranked based on the durations of waveforms S, E and F, as well as the duration per probe including various waveforms. The ranking order of the resis-tance was: Longjingchangye > Hangdan > Zhenghedabaicha > Qianmei 601 > Hongyafoshuo > Zhongcha 102 > Zhongcha 302 > Longjing 43 > Anjibaicha, which corresponded to the resistance level determined by the population density (infestation) of the leaf-hopper on the 9 tea cultivars in the tea fields. Our study suggests that this simple and convenient DC-EPG technique might have great potential as a reliable tool to predict the resistance of tea cultivars to the tea leafhopper.     

The Aphelenchoides genomes reveal substantial horizontal gene transfers in the last common ancestor of free-living and major plant-parasitic nematodes

Aphelenchoides besseyi is a plant-parasitic nematode (PPN) in the family Aphelenchoididae capable of infecting more than 200 plant species. A. besseyi is also a species complex with strains exhibiting varying pathogenicity to plants. We present the genome and annotations of six Aphelenchoides species, four of which belonged to the A. besseyi species complex. Most Aphelenchoides genomes have a size of 44.7–47.4 Mb and are among the smallest in clade IV, with the exception of A. fujianensis, which has a size of 143.8 Mb and is one of the largest. Phylogenomic analysis successfully delimited the species complex into A. oryzae and A. pseudobesseyi and revealed a reduction of transposon elements in the last common ancestor of Aphelenchoides. Synteny analyses between reference genomes indicated that three chromosomes in A. besseyi were derived from fission and fusion events. A systematic identification of horizontal gene transfer (HGT) genes across 27 representative nematodes allowed us to identify two major episodes of acquisition corresponding to the last common ancestor of clade IV or major PPNs, respectively. These genes were mostly lost and differentially retained between clades or strains. Most HGT events were acquired from bacteria, followed by fungi, and also from plants; plant HGT was especially prevalent in Bursaphelenchus mucronatus. Our results comprehensively improve the understanding of HGT in nematodes.     

Selection of insect parasitic nematodes for biological control of the garden chafer,Phyllopertha horticola

Larvae ofPhyllopertha horticola L. (Coleoptera: Scarabaeidae) cause increasing problems on sports fields and lawns in NW-Europe. A biological control programme using insect parasitic nematodes is being developed. This paper contains the results of bioassays with various species and isolates of the nematode generaHeterorhabditis andSteinernema. In bioassays in small pots with moist sand, most of the nematode isolates gave 30–60% mortality against each of the three larval stages. The susceptibility of the grubs for nematode infection generally increased with larval development.H. bacteriophora, H. heliothidis, H. megidis, a DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 showed the highest mortality rates, with nearly 100% mortality of third instar grubs. The DutchHeterorhabditis isolate NLH-E87.3 andS. glaseri 326 were selected as candidates for further studies on their potential as biological control agents forP. horticola grubs in the field.     

不同离体寄主及其成熟度对亚洲柑桔木虱存活的影响

【目的】亚洲柑桔木虱Diaphorina citri Kuwayama的虫口密度及活动与柑桔黄龙病的田间传播、流行有十分密切的关系,寻找合适的室内饲养条件能够便于观察和研究其生物学特性和传病机制。【方法】本文以九里香Murraya exotica(L.)Mant.、酸桔Citrus sunki Hort.ex Tanaka和马水桔Citrus reticulata Blanco.cv.Mashuiju 3种寄主植物不同成熟度离体梢为研究材料,(1)比较亚洲柑桔木虱卵分别在3种寄主植株和离体嫩梢上的孵化率;(2)比较3种寄主不同成熟度离体梢对各龄若虫存活率和蜕皮的影响;(3)比较3种寄主不同成熟度离体梢对成虫存活率的影响。【结果】(1)亚洲柑桔木虱在植株嫩梢上卵的孵化率高于离体嫩梢,九里香表现最明显;(2)低龄若虫在叶片未完全展开的离体嫩梢上存活率最高,而高龄若虫在完全展开的嫩梢上最高;(3)用离体成熟梢饲养柑桔木虱成虫存活率高于离体嫩梢,酸桔和马水桔离体梢饲养的存活率较九里香高。【结论】用寄主植物离体梢饲养的亚洲柑桔木虱卵孵化率和若虫、成虫存活率都较高而且较稳定,该方法可用于这种木虱的室内繁殖中。     

Hand position on the bunch and source–sink ratio influence the banana fruit susceptibility to crown rot disease

The postharvest development of crown rot of bananas depends notably on the fruit susceptibility to this disease at harvest. It has been shown that fruit susceptibility to crown rot is variable and it was suggested that this depends on environmental preharvest factors. However, little is known about the preharvest factors influencing this susceptibility. The aim of this work was to evaluate the extent to which fruit filling characteristics during growth and the fruit development stage influence the banana susceptibility to crown rot. This involved evaluating the influence of (a) the fruit position at different levels of the banana bunch (hands) and (b) changing the source–sink ratio (So–Si ratio), on the fruit susceptibility to crown rot. The fruit susceptibility was determined by measuring the internal necrotic surface (INS) after artificial inoculation of Colletotrichum musae. A linear correlation (r = −0.95) was found between the hand position on the bunch and the INS. The So–Si ratio was found to influence the pomological characteristics of the fruits and their susceptibility to crown rot. Fruits of bunches from which six hands were removed (two hands remaining on the bunch) proved to be significantly less susceptible to crown rot (INS = 138.3 mm ²) than those from bunches with eight hands (INS = 237.9 mm ²). The banana susceptibility to crown rot is thus likely to be influenced by the fruit development stage and filling characteristics. The present results highlight the importance of standardising hand sampling on a bunch when testing fruit susceptibility to crown rot. They also show that hand removal in the field has advantages in the context of integrated pest management, making it possible to reduce fruit susceptibility to crown rot while increasing fruit size.