Suppression of Meloidogyne hapla by arbuscular mycorrhiza fungi (AMF) on pyrethrum in Kenya

Two arbuscular mycorrhiza fungi (AMF) isolated from a pyrethrum-growing region in Kenya were screened for efficacy against a nematode, Meloidogyne hapla, in greenhouses. The fungi were identified at INVAM (International Culture Collection of Vesicular Arbuscular Mycorrhizal Fungi) as Glomus etunicatum (Isolate KS18) and Glomus sp. (Isolate KS14). Isolate KS14 (Glomus sp.) significantly suppressed nematode population, growth and development by up to 54%, egg production by up to 75% and disease severity by up to 71%. Glomus etunicatum (Isolate KS18) suppressed nematode growth and development by up to 50%, egg production by up to 75% and disease severity by up to 57%. In addition, G. etunicatum and Isolate KS14, significantly improved top dry biomass of pyrethrum by up to 33% and 47%, respectively. Glomus etunicatum and M. hapla were mutually inhibitory as root colonization by G. etunicatum was significantly reduced (up to 24%) by the presence of the nematode. The presence of the nematodes, on the other hand, did not significantly affect root colonization by Isolate KS14.     

Protection of olive planting stocks against parasitism of root-knot nematodes by arbuscular mycorrhizal fungi

The effects were investigated, under controlled conditions, of single and joint inoculation of olive planting stocks cvs Arbequina and Picual with the arbuscular mycorrhizal fungi (AMF) Glomus intraradices , Glomus mosseae or Glomus viscosum , and the root-knot nematodes Meloidogyne incognita and Meloidogyne javanica , on plant performance and nematode infection. Establishment of the fungal symbiosis significantly increased growth of olive plants by 88·9% within a range of 11·9–214·0%, irrespective of olive cultivar, plant age and infection by M. incognita or M. javanica . In plants free from AMF, infection by Meloidogyne spp. significantly reduced the plant main stem diameter by 22·8–38·6%, irrespective of cultivar and plant age. Establishment of AMF in olive plants significantly reduced severity of root galling by 6·3–36·8% as well as reproduction of both Meloidogyne spp. by 11·8–35·7%, indicating a protective effect against parasitism by root-knot nematodes. Infection by the nematodes influenced root colonization by AMF, but the net effect depended on the AMF isolate–olive cultivar combination. It is concluded that prior inoculation of olive plants with AMF may contribute to improving the health status and vigour of cvs Arbequina and Picual planting stocks during nursery propagation.     

Effect of <Emphasis Type="Italic">Meloidogyne ethiopica</Emphasis> parasitism on water management and physiological stress in tomato

Root-knot nematodes (RKN) are obligate endoparasites that severely damage the host root system. Nutrient and water uptake are substantially reduced in infested plants, resulting into altered physiological processes and reduced plant growth. The effect of nematode infestation on the morphological changes of roots and subsequent physiological plant responses of infested tomatoes with the RKN Meloidogyne ethiopica was studied in a pot experiment. Plants were infested with two inoculum densities (10 or 50 eggs per cm³ substrate) and its effect was evaluated 74 and 102 days post inoculation (DPI). Morphological changes and root growth was determined by analysing scanned images of the whole root system. Nematode infestation reduced the portion of fine roots and increased that of coarse roots due to gall formation. Fine roots of non-infested control plants represented around 51% of the area of the whole root system at 74 and 102 DPI. In comparison to controls, plants inoculated with low and high nematode density had 2.1 and 3.2-times lower surface area of fine roots at 102 DPI. Root analyses revealed that plants had a very limited ability to mitigate the effects of the root-knot nematodes infestation by altering root growth. Root galls had a major influence on the hydraulic conductivity of the root system, which was significantly reduced. The low leaf water potential of infested plants coincided with decreased stomatal conductivity, transpiration and photosynthesis. The latter two were reduced by 60–70% when compared to non-infested control plants.     

Effect of Temperature on and Histopathology of the Interaction Between Meloidogyne incognita and Thielaviopsis basicola on Cotton

ABSTRACT Controlled environments were used to study the relationship between the root-knot nematode (Meloidogyne incognita) and Thielaviopsis basicola on cotton. Temperature treatments were continuous 20, 24, and 28 degrees C or two cyclic linear regimes with ranges of 14 to 32 or 18 to 28 degrees C over 24 h. Cotton seeds were planted in fumigated soil infested with T. basicola, M. incognita, or both. After 42 days, pathogen effects on plant growth and pathogen development were evaluated. Histology was conducted on roots collected 14, 28, and 42 days after planting in the continuous 24 degrees C treatment. Reductions in plant height-to-node ratio and total fresh weight were observed for soils infested with both pathogens compared with the control or with soils infested with either pathogen, except for M. incognita-infested soil at 28 degrees C. T. basicola reduced root galling and reproduction of the nematode at all temperatures. Vascular discoloration caused by T. basicola was greater in the presence of M. incognita compared with that by T. basicola alone. At 2 and 4 weeks, histological studies showed that plants grown in all T. basicola-infested soils contained chlamydospore chains on the root surface and in cortical cells. The fungus was not observed inside the vascular cylinder. Roots from 4-week-old plants from soils infested with T. basicola and M. incognita showed fungal sporulation in vascular tissue and localized necrosis of vascular tissue adjacent to the nematodes. At 6 weeks, plants grown in soil infested with T. basicola alone exhibited no remaining cortical tissue and no evidence of vascular colonization by the fungus. Six-week-old plants grown in T. basicola + M. incognita-infested soils exhibited extensive vascular necrosis and sporulation within vascular tissue. These studies suggest that coinfection expands the temperature ranges at which the pathogens are able to cause plant damage. Further, M. incognita greatly increases the access of T. basicola to vascular tissue.     

Root‐knot nematodes do not affect black root rot disease severity on watermelon and bottle gourd

The effects of root‐knot nematodes on black root rot of watermelon and bottle gourd were studied using field surveys and co‐inoculation tests with Meloidogyne incognita (southern root‐knot nematode) and Diaporthe sclerotioides. The results of the field survey suggested that root‐knot nematodes had little effect on either the severity of black root rot or infection with D. sclerotioides. None of the three fields showed a significant positive correlation between disease severity and nematode gall index, with low correlation coefficients. Co‐inoculation experiments under controlled conditions found no significant effect of root‐knot nematodes on black root rot of watermelon and bottle gourd based on area under disease progress curves (AUDPC). These results were supported by the quantities of DNA of the two agents in root tissues because no significant difference was found between dual‐ and single‐inoculation treatments with M. incognita and/or D. sclerotioides. These findings suggest that root‐knot nematodes probably do not affect the infection of watermelon or bottle gourd roots by D. sclerotioides or the incidence of black root rot in these crops caused by this fungus.     

Effects of root- and stolon-infecting fungi on root-colonizing nematodes of white clover

The effects on white clover ( Trifolium repens ) of different combinations of the nematodes Meloidogyne trifoliophila , Helicotylenchus dihystera and Heterodera trifolii and nine stolon-infecting and three root-infecting fungi were studied in a glasshouse experiment. The presence of the fungus Phytophthora megasperma alone increased ( P  < 0·001) root-rot severity and reduced ( P  < 0·001) plant growth. Other species combinations, such as Phoma nebulosa and Alternaria alternata , interacted and increased root-rot severity. Combinations of P. megasperma with Pythium irregulare , and P. nebulosa with Phoma medicaginis or A. alternata , increased M. trifoliophila populations. Several other fungi ( P. irregulare , P. nebulosa , Colletotrichum coccodes , Macrophomina phaseolina , P. medicaginis and Phoma sp.) interacted with the nematode M. trifoliophila causing severe root-knot symptoms. The results indicated that fungi and nematodes interacted to cause root and stolon rot and reduced yields, and that poor persistence of white clover in pastures is likely to be a problem with a complex etiology.     

Parasitism of the root-lesion nematode Pratylenchus thornei on chickpea

Pratylenchus thornei -chickpea interactions were investigated under controlled and fluctuating environmental conditions in the growth chamber, greenhouse and shadehouse. Under controlled conditions, P. thornei infected chickpea lines 12071/10054 and P2245 and cultivars Andoum 1, JG62 and UC27. Line P 2245 and cv. JG 62 were the most susceptible genotypes on the basis of root damage and nematode reproduction, but nematode infection did not significantly reduce root and shoot weights. Cultivars Andoum 1 and UC27 and line 12071/10054 showed the least root damage and nematode reproduction. Inoculation of cv. Andoum 1 with 2500, 5000 or 10000 nematodes per plant in pots did not affect shoot weight, regardless of the conditions of water stress of the plants. However, root weight was significantly reduced by nematode infection in plants grown under water stress and fluctuating temperature conditions in the greenhouse, but was not affected by any other treatment. The nematode reproduction index was not affected by soil water content under shadehouse conditions, but was greater on plants watered to soil water-holding capacity than in water-stressed plants under greenhouse conditions. For both environments, the nematode reproduction index decreased when inoculum density was greater than 5000 nematodes per plant.     

Effect of root-knot nematodes on cajanol accumulation in the vascular tissues of pigeonpea after stem inoculation with Fusarium udum

The effect of root-knot nematodes ( Meloidogyne javanica and M. incognita ) on production of the isoflavonoid phytolexin, cajanol, was investigated in pigeonpea ( Cajanus cajan ) plants infected with Fusarium udum , the causal organism of Fusarium wilt. Seven-day-old seedlings of a wilt-resistant pigeonpea cultivar, ICP 9145 and a wilt-susceptible cultivar, Malawi Local, both of which were moderately susceptible to the nematode, were grown in soil infested with 2000 Meloidogyne juyeniles per plant. A duplicate set of plants remained free from nematodes. Twenty-one days later, all the plants were inoculated with F. udum by stem puncture. Quantitative estimates of cajanol in the vascular tissues were made at intervals up to 15 days after inoculation with the fungus. No external symptoms of wilt appeared in any plants of the wilt-resistant cultivar in the absence of the nematode. However, when inoculated with the nematode, two thirds of the plants developed wilt symptoms. Cajanol levels were lower in both the wilt-resistant and wilt-susceptible plants in the presence of the nematode than in its absence, although this effect was considerably more marked in the wilt-resistant cultivar. These results indicate that the root-knot nematode is capable of breaking resistance of ICP 9145 to Fusarium wilt and that at least part of the mechanism of this effect is retarded cajanol accumulation.     

Interactions Between Trichoderma harzianum Strain T22 and Maize Inbred Line Mo17 and Effects of These Interactions on Diseases Caused by Pythium ultimum and Colletotrichum graminicola

ABSTRACT Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation of soil with Pythium ultimum had little effect upon growth of Mo17. The presence of T22 increased protein levels and activities of beta-1,3 glucanase, exochitinase, and endochitinase in both roots and shoots, even though T22 colonized roots well but colonized shoots hardly at all. With some enzymes, the combination of T22 plus P. ultimum gave the greatest activity. Plants grown from T22-treated seed had reduced symptoms of anthracnose following inoculation of leaves with Colletotrichum graminicola, which indicates that root colonization by T22 induces systemic resistance in maize.     

食线虫真菌蠕虫埃斯特菌对植物寄生线虫的侵染特性

为评价食线虫真菌蠕虫埃斯特菌Esteya vermicola菌株NKF 13222的生防应用价值,采用2%水琼脂培养基平板接种法测定了该菌株对7种植物寄生线虫的诱引、黏附和侵染能力,并比较了其对不同线虫的侵染特性.结果显示,该菌株的菌丝对松材线虫、拟松材线虫、腐烂茎线虫和水稻干尖线虫均有诱引作用,而对南方根结线虫、禾谷孢囊线虫和穿刺短体线虫无诱引作用;菌株的粘性分生孢子对有诱引现象的4种线虫都能黏附,接种24 h后的黏附率达到82%～99%,对无诱引现象的3种线虫不能黏附;粘性分生孢子黏附虫体后对不同线虫的侵染力存在差异,接种7 d后的松材线虫死亡率可达98%,而拟松材线虫、腐烂茎线虫和水稻干尖线虫死亡率分别为43%、35%和9%.表明蠕虫埃斯特菌不仅是松材线虫的强内寄生真菌,而且对其它重要植物寄生线虫也具有一定的应用潜力.     

Differential effect of nematicide treatments on tuber yields in early- and late-maturing potato cultivars

A 3-year field study examined the effects of 1,3-dichloropropene or oxamyl on tuber yields in four early- and five late-maturing potato cultivars. The nematicide treatments increased total tuber yield by ≈ 12% for early-maturing cultivars, but by less than 2% for the late-maturing cultivars. The treatments reduced the numbers of root lesion nematodes (primarily Pratylenchus penetrans ), which were the dominant plant parasitic nematodes at the site. Covariance analysis indicated that treatment effects on total tuber yield were no longer significant after adjusting for root lesion nematodes in soil at harvest, confirming that these nematodes had a direct effect on the host. As expected, there were significant inverse relationships ( P  = 0·05) between total tuber yields and numbers of root lesion nematodes in soil and in roots. However, the application of nematicides in late-maturing cultivars was found to be of no practical value. Crop production systems designed to reduce or optimize pesticide applications can form one criterion in the development of more environmentally sensitive management strategies. The merit of utilizing chemicals for root lesion nematode control are considered with regard to cultivar maturity.     

Interactions of Pratylenchus thornei and Fusarium oxysporum f. sp. ciceris on Chickpea

ABSTRACT Fusarium oxysporum f. sp. ciceris and the root-lesion nematode Pratylenchus thornei coinfect chickpeas in southern Spain. The influence of root infection by P. thornei on the reaction of Fusarium wilt-susceptible (CPS 1 and PV 61) and wilt-resistant (UC 27) chickpea cultivars to F. oxysporum f. sp. ciceris race 5 was investigated under controlled and field conditions. Severity of Fusarium wilt was not modified by coinfection of chickpeas by P. thornei and F. oxysporum f. sp. ciceris, in simultaneous or sequential inoculations with the pathogens. Root infection with five nematodes per cm(3) of soil and 5,000 chlamydospores per g of soil of the fungus resulted in significantly higher numbers of propagules of F. oxysporum f. sp. ciceris with the wilt-susceptible cultivar CPS 1, but not with the wilt-resistant one. However, infection with 10 nematodes per cm(3) of soil significantly increased root infection by F. oxysporum f. sp. ciceris in both cultivars, irrespective of fungal inoculum densities (250 to 2,000 chlamydospores per g of soil). Plant growth was significantly reduced by P. thornei infection on wilt-susceptible and wilt-resistant chickpeas in controlled and field conditions, except when shorter periods of incubation (45 days after inoculation) were used under controlled conditions. Severity of root necrosis was greater in wilt-susceptible and wilt-resistant cultivars when nematodes were present in the root, irrespective of length of incubation time (45 to 90 days), densities of nematodes (5 and 10 nematodes per cm(3) of soil), fungal inocula, and experimental conditions. Nematode reproduction on the wilt-susceptible cultivars, but not on the wilt-resistant one, was significantly increased by F. oxysporum f. sp. ciceris infections under controlled and field conditions.     

Effects of arbuscular mycorrhizal fungi on severity of root rot of bananas caused by Cylindrocladium spathiphylli

The interaction between four arbuscular mycorrhizal (AM) fungi, Glomus sp., G. proliferum , G. intraradices and G. versiforme , and the root-rot fungus Cylindrocladium spathiphylli , and subsequent effects on growth and phosphorus nutrition of banana ( Musa acuminata , AAA, cv. Grande Naine) were investigated under glasshouse conditions. Overall, root infection by C. spathiphylli reduced the growth of banana plants, but preinoculation with AM fungi significantly attenuated this detrimental effect. Lower disease severity, stimulation of growth and increase of shoot P content were observed for the plants inoculated with one of the four AM fungi. Glomus sp. and G. proliferum induced the largest increase in growth parameters and shoot P content as compared to G. intraradices and G. versiforme , in the presence as well as in the absence of C. spathiphylli . Root damage caused by C. spathiphylli was decreased in the presence of AM fungi, but the inoculation of mycorrhizal plants with C. spathiphylli also decreased the intensity of AM fungal root colonization, indicating a clear interaction between the two organisms.     

Systemic nematicidal activity of fluensulfone against the root-knot nematode Meloidogyne incognita on pepper

BACKGROUND: Fluensulfone, a new nematicide of the fluoroalkenyl group, has proved to be very effective in controlling root‐knot nematodes, Meloidogyne spp., by soil application. The systemic activity of this compound against M. incognita on peppers via soil drenching and foliar spray was evaluated. RESULTS: Root application of fluensulfone via soil drenching showed slight and no nematode control activity when applied 4 and 10 days, respectively, after inoculation. A single foliar spray of peppers with a fluensulfone solution at 3.0 g L^?1 prior to inoculation reduced the galling index by 80% and the number of nematode eggs by 73–82% of controls. The reduction in these parameters by fluensulfone was much higher than that obtained with oxamyl or fenamiphos at the same concentration. This activity was also observed when the plants were sprayed 21 days before inoculation. A series of experiments suggested that foliar spray with fluensulfone prior to inoculation reduces nematode invasion. However, foliar spray after inoculation did not inhibit nematode development inside roots. CONCLUSION: Fluensulfone showed relatively high nematode control activity when sprayed on the foliage before inoculation. Fluensulfone may be used as a foliar application, in addition to soil application, for root‐knot nematode control. Copyright © 2011 Society of Chemical Industry     

Effects of Potato-cyst Nematodes (Globodera pallida) and Soil pH on Root Growth, Nutrient Uptake and Crop Growth of Potato

Potato-cyst nematodes (Globodera pallida) cause severe yield losses in potato. Plants infected with potato-cyst nematodes generally have reduced concentrations of nitrogen, phosphorus and potassium in the foliage. This study investigated whether reduced growth of nematode-infected potato is caused by nutrient limitation.Experiments in the field and in containers showed that phosphorus concentration correlated best with total crop biomass at early stages of growth. The role of phosphorus in nematode damage was further investigated in the field and in the Wageningen Rhizolab. The experimental field was infested with potato-cyst nematodes and two levels of nematode density were established by fumigation with a nematicide. Prior applications of calcium carbonate resulted in pHKCl levels of 4.8 and 6.1. Two levels of phosphorus fertiliser were applied: either 0 or 225kgPha–1. In the Wageningen Rhizolab, soil of both pH levels from the field was used after treatment with 1MRad gamma irradiation to kill the nematodes. Subsequently, half of the soil was inoculated with cysts to give a nematode density of 30 viable juveniles per gram of soil.In the field, nine weeks after planting, the total crop biomass ranged from 107gm–2 for the treatment with nematodes at pHKCl 6.1 without phosphorus fertiliser to 289gm–2 for the fumigated treatment at pHKCl 4.8 with phosphorus fertiliser. The differences in total biomass for the various treatments were explained by differences in foliar phosphorus concentration. Nematodes induced or aggravated P deficiency and reduced total biomass. This was not the only damage mechanism as at high, non-limiting levels of foliar phosphorus concentration, nematodes still reduced total biomass.In the Wageningen Rhizolab, directly after planting, the number of roots visible against minirhizotrons was reduced by nematodes. However, the increase of root number in the nematode treatment continued longer than in the control, until root number was higher than that of the control. The compensary root growth of the nematode treatment was restricted to the top 30cm and nematodes reduced rooting depth.High soil pH reduced growth, mainly by reducing the availability of phosphate. Both nematodes and high soil pH reduced nutrient uptake per unit root length. Our results lead us to suggest an interaction between nematodes and soil pH, with nematode damage being higher at pHKCl 6.1 than at pHKCl 4.8.     

Differential expression of a β-1,4-endoglucanase induced by diet change in the foliar nematode Aphelenchoides fragariae

We identified and characterized a β-1,4-endoglucanase, Afr-ENG-1, in the foliar nematode Aphelenchoides fragariae that is differentially expressed when the nematode feeds on fungi or plants. When individuals from hosta plants were transferred to a fungus culture, expression of the enzyme decreased 1,812-fold after five generations on the fungus diet. Afr-eng-1 was readily detected in the genome of 75% of nematodes from the plant population but only in 38% of the diet-changed population. The gene cannot be detected in nematodes maintained on fungus for over 100 generations. Diet was also associated with changes in nematode body size and in the severity of symptoms caused on hosta leaves. Plant-diet nematodes caused larger lesions and were longer and thinner than fungus-diet nematodes. Nematodes moved from a plant diet to a fungus diet for five generations had the same body size as the nematodes that had fed on the fungus for 100 generations. Full-length sequences of Afr-eng-1 were obtained and found to encode a glycosyl hydrolase family 5 protein. This is the first β-1,4-endoglucanase and plant-parasitism-related gene described in the genus Aphelenchoides.     

河南省小麦根腐线虫病的发生危害及病原鉴定

为明确河南省小麦根腐线虫病的发生危害情况及其病原线虫种类,对14个县(市)45个采样点小麦根腐线虫进行了分离调查,分别通过人工接种测定其致病性和杀线剂处理研究其危害性,并采用形态学和分子生物学方法鉴定其病原。结果显示:小麦根腐线虫在河南省的分布具有一定的区域性,中北部的10个县(市)34个沙质土壤采样点均分离出小麦根腐线虫,而在南部土壤粘重地区的小麦根内和土壤中均没有分离出根腐线虫;15%涕灭威颗粒剂处理土壤后小麦的穗粒数、千粒重和单位面积产量较对照明显上升,产量增加13.6%;该线虫能够侵染小麦,并明显抑制小麦生长;河南省小麦根腐线虫以敏捷短体线虫Pratylenchus agilis为主。     

Influence of Ring Nematode Infestation and Calcium, Nitrogen, and Indoleacetic Acid Applications on Peach Susceptibility to Pseudomonas syringae pv. syringae

ABSTRACT Two field experiments were conducted to study the effects of added nitrogen, calcium, and indoleacetic acid, in the presence or absence of ring nematodes (Mesocriconema xenoplax), on susceptibility of peach to bacterial canker. When noninfested soil was inoculated with ring nematodes, peach tree susceptibility to bacterial canker infection caused by Pseudomonas syringae pv. syringae was dramatically increased after a period of 2 years. However, no evidence was found that ring nematode infestation increased tree water stress or, in turn, altered plant calcium uptake. Soil fumigation with methyl bromide prior to planting in a commercial orchard significantly reduced both nematode populations and peach tree susceptibility to bacterial canker infection when compared with nonfumigated treatments. In both experiments, tree susceptibility, as measured by canker length following inoculation of stems with P. syringae pv. syringae, was negatively correlated with plant tissue nitrogen content and positively correlated with tissue calcium content. A principal components analysis showed that tissue nitrogen and calcium levels were negatively correlated, and that high-nitrogen, low-calcium tissues were less susceptible to bacterial canker than low-nitrogen, high-calcium tissues. These results indicate that the increased susceptibility of peach to P. syringae pv. syringae under nematode infestation conditions is mediated by both nutritional effects (primarily nitrogen) and nutritional-independent effects, but do not support previous reports of beneficial effects of calcium for reducing bacterial canker.     

Interactions Between the Soybean Cyst Nematode and Fusarium solani f. sp. glycines Based on Greenhouse Factorial Experiments

ABSTRACT The soybean cyst nematode, Heterodera glycines, and the fungus that causes sudden death syndrome (SDS) of soybean, Fusarium solani f. sp. glycines, frequently co-infest soybean (Glycine max) fields. The interactions between H. glycines and F. solani f. sp. glycines were investigated in factorial greenhouse experiments with different inoculum levels of both organisms on a soybean cultivar susceptible to both pathogens. Measured responses included root and shoot dry weights, H. glycines reproduction, area under the SDS disease progress curve, and fungal colonization of roots. Both H. glycines and F. solani f. sp. glycines reduced the growth of soybeans. Reproduction of H. glycines was suppressed by high inoculum levels but not by low levels of F. solani f. sp. glycines. The infection of soybean roots by H. glycines did not affect root colonization by the fungus, as determined by real-time polymerase chain reaction. Although both pathogens reduced the growth of soybeans, H. glycines did not increase SDS foliar symptoms, and statistical interactions between the two pathogens were seldom significant.