Pathozone dynamics of Meloidogyne incognita in the rhizosphere of tomato plants in the presence and absence of the nematophagous fungus, Pochonia chlamydosporia

Pathozone dynamics were derived for approx. 50 Meloidogyne incognita juveniles infecting a single root of tomato under controlled conditions from a point source of inoculum and described using simple, non-linear models. The pathozone decayed sigmoidally with distance, but increased over time as progressively more nematodes were able to infect the root. Despite the reported ability of M. incognita juveniles to travel up to 50 cm in some conditions, the maximum width of the pathozone for a single tomato root was estimated as 18·1 mm. It is conjectured that this was because of (i) diffusion from a point source of inoculum, (ii) a small infection court (a single root tip) and (iii) the limited life span of the nematode. A second experiment was used to assess the effect of the nematophagous fungus Pochonia chlamydosporia on the pathozone dynamics of the nematode. This fungus is known to produce nematicidal products in vitro , which may affect invasion of roots by the free-living nematode. To examine the possibility of a change in the position of the site of infection, changes in the probability of gall formation along the root length were also examined. In the absence of P. chlamydosporia , the pathozone dynamics of M. incognita were very similar to those of the first experiment. It was shown that P. chlamydosporia did not significantly affect the pathozone dynamics of M. incognita nor the site of gall formation, which appear to have little importance for the role of the fungus as a biological control agent.     

温度和初始种群密度对象耳豆根结线虫侵染番茄的影响

通过室内接种方法,研究了不同温度和接种密度对象耳豆根结线虫侵染番茄能力的影响。研究结果表明,28~30 ℃是象耳豆根结线虫侵染番茄的最适温度。随着温度的下降,其侵染能力明显降低。当象耳豆根结线虫2龄幼虫接种密度大于10条/100 cm3土壤时,番茄的生长会受到显著的抑制,随着线虫接种密度的增加,根结指数显著增加、线虫对番茄的危害也逐渐加重。研究结果将为广东省蔬菜产区制定象耳豆根结线虫防治指标提供理论依据。     

聚多曲霉Snef210对南方根结线虫毒性的研究

蔬菜根结线虫病在我国乃至世界危害日益严重,安全防控该病害成为目前急需解决的农业生产问题。本研究筛选到一株可毒杀南方根结线虫Meloidogyne incognita的生防真菌Snef210,经形态学和分子生物学鉴定为聚多曲霉Aspergillus sydowii(Bain.et Sart.) Thom et Church。该菌株发酵液对南方根结线虫2龄幼虫(J_2)具有很强的毒杀作用,原液处理24 h后校正死亡率达90.1%,处理3 d后对卵孵化的抑制率达92.8%。盆栽试验中,与对照相比,菌株发酵液10倍稀释液土壤处理对番茄根部的根结减退率为66.7%。聚多曲霉代谢产物丰富,多用于抗菌和抗肿瘤的研究,本文首次发现其对南方根结线虫有效,是一类潜在的控制植物线虫病害的新型生防因子。     

不同植物秸秆对番茄及南方根结线虫的影响

为有效防治南方根结线虫,本试验研究了添加不同剂量的玉米秸秆(8.32、4.16、2.08g/kg)、辣椒秸秆(4.16、2.08、1.04g/kg)和茵陈蒿秸秆(4.16、2.08、1.04g/kg)对温室大棚番茄及根结线虫的影响。结果显示,在根结线虫侵染的土壤中添加植物秸秆后30d,玉米秸秆(4.16、2.08g/kg)对番茄株高有显著影响,辣椒(4.16、1.04g/kg)和茵陈蒿(4.16、2.08g/kg)秸秆对番茄茎粗影响显著;60d时经茵陈蒿处理的番茄植株比对照生长发育良好,对形态指标的影响程度依次为茎粗开花分枝;120d时番茄的茎粗、分枝和果实重量均显著高于对照。末次接种后20d调查,每种作物秸秆处理以高剂量对根结线虫的防治效果最好,防治效果依次为:茵陈蒿秸秆辣椒秸秆玉米秸秆,分别为79.60%、71.32%、68.89%,表明茵陈蒿秸秆处理既可降低根结线虫危害程度,又可提高番茄产量。本研究为温室大棚有效防治根结线虫提供了依据。     

华南地区主要番茄品种对南方根结线虫的抗性评价

通过人工接种方式, 对华南地区番茄主要栽培品种对优势根结线虫——南方根结线虫（Meloidogyne incognita）的抗性进行了评价。结果表明,广东栽培品种年丰、红宝石、新星、福安、粤红玉、穗丰、金丰、益丰、丰顺、大丰顺、满丰和法国品种SAINT PIERRE均高度感病; 而法国品种 PIERSOL VFN高度抗病,根结率为0。根据SAS8.0多重比较分析表明,在F0.01的水平上, 品种PIERSOL VFN与其余品种之间对根结线虫的抗性均存在显著性差异,而其他12个品种间对根结线虫的抗性差异不显著。     

Mobility of oxathiapiprolin in and between tomato plants

BACKGROUND

Oxathiapiprolin (OXPT; FRAC code 49) is a new piperidinyl-thiazole isooxazoline anti-oomycete fungicide that targets oxysterol-binding proteins. The fungicide is known to translocate acropetally from root to shoot to protect plants against fungal attack.

RESULTS

OXPT is ambimobile. It can also translocate basipetally from shoot to root. OXPT exhibits an unprecedented capacity for trans-plant protection. When two tomato plants are grown in one pot, and one is treated with OXPT (on the stem, leaves or apex), while the other plant and soil surface are adequately covered, both plants become protected against late blight caused by Phytophthora infestans.

CONCLUSION

Trans-plant systemic protection induced by OXPT involves translocation of the fungicide from the shoot of the treated plant to its root, exudation into the soil and uptake by the root of the neighboring untreated plant to protect it against the disease. Liquid chromatography–tandem mass spectrometry analyses confirmed the occurrence of OXPT in root exudates of OXPT-treated tomato plants in quantities sufficient to protect detached tomato leaves and intact plants against P. infestans. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Lack of synergistic effects in tomato plants co-infected with tomato severe rugose virus and tomato chlorosis virus

The begomovirus Tomato severe rugose virus (ToSRV) and the crinivirus Tomato chlorosis virus (ToCV), in single and co-infections, are very common in tomato crops in Brazil. Both viruses are transmitted by the whitefly Bemisia tabaciMEAM1 (biotype B). The objective of this study was to analyse the interaction between ToSRV and ToCV in tomato plants of cultivars Santa Clara and Kada. Plants at 15, 30 and 45 days after emergence were inoculated with 30 viruliferous B. tabaci per plant. The following treatments were compared: plants inoculated with ToSRV, ToCV, ToSRV + ToCV, and healthy (control). The interaction between these viruses was analysed by measuring the virus titre by qPCR and the fresh and dry weights of the aerial parts of the tomato plants. Based on two independent assays, no significant effects for co-infection of ToSRV and ToCV on virus titres and plant development were observed compared to single infections. The dry weight of tomato plants of both cultivars infected with ToSRV, ToCV, or co-infected did not differ significantly. However, the dry weight of Santa Clara tomato plants infected with ToSRV, ToCV and ToSRV + ToCV showed mean reductions of 21.5%, 25.5% and 32%, respectively, compared to healthy plants, and mean reductions for Kada were 31.7%, 37.5% and 38%, respectively.     

Occurrence of a new resistant breaking pathotype of Meloidogyne incognita on tomato in Greece

Journal of Plant Diseases and Protection - In a pot assay, a population of Meloidogyne incognita from Northern Greece, reproduced on the resistant tomato cv. Silvana carrying the Mi gene and on...     

10种植物提取物对南方根结线虫毒杀活性研究

采用触杀法研究了10种植物干材料无水乙醇提取物、乙酸乙酯提取物和石油醚提取物对南方根结线虫2龄幼虫的毒杀活性。结果表明,这10种植物材料的3种有机溶剂提取物对根结线虫都有不同程度的毒杀活性。其中,牡丹皮、丁香、八角茴香、何首乌和地肤子的无水乙醇和乙酸乙酯提取物的毒杀活性最强,48h校正死亡率均大于90%;八角茴香石油醚提取物也表现出较高毒杀活性,48h校正死亡率也达到了80%以上。     

Increased resistance to Verticillium dahliae in Arabidopsis plants defective in auxin signalling

Auxin signalling and transport participate in plant–microbe interactions as positive or negative regulators of disease resistance. The present study investigated the responses of Arabidopsis thaliana plants impaired in the auxin receptors TIR1, AFB1 and AFB3 and the auxin transporter AXR4, upon infection by the soilborne root pathogen Verticillium dahliae. Fewer symptoms were recorded in afb1, afb3 and axr4 plants compared to the wild type (wt). qPCR analysis revealed that the decrease in symptom severity in afb1, afb3 and axr4 was correlated with reduction in the growth of the pathogen in the plants. Therefore, afb1, afb3 and axr4 are partially resistant to V. dahliae. Upon V. dahliae infection, the expression of TIR1, AFB1, AFB3 and AXR4 was up‐regulated in roots, while indole‐3‐acetic acid levels were similar to mocks. The partial resistance of afb1, afb3 and axr4 against V. dahliae can be attributed in part to the up‐regulation of defence‐related genes, as it was observed that afb1 and axr4 had higher PR1 levels than wt, while afb3 had higher PDF1.2 levels than wt. The findings of the present study suggest that the auxin signalling defective mutants afb1, afb3 and axr4 show increased resistance against V. dahliae.     

The influence of the nematode Meloidogyne incognita on competition between Solanum nigrum and tomato

The effect of Meloidogyne incognita (Kofoid & White) Chitwood, 1949, on the competitive relationship between tomato (Lycopersicon esculentum Mill.) and black nightshade (Solanum nigrum L.) was investigated under glasshouse conditions. Two intraspecific competition treatments were set up for the crop and the weed, and five interspecific treatments where the emergence of S. nigrum plants was progressively delayed in relation to tomato. Nematodes reproduced in all inoculated plants, their multiplication rates being much higher in tomato than in S. nigrum plants. Under nematode-free conditions, intraspecific competition of tomato was more severe than the interspecific competition shown by the weed S. nigrum. Tomato was as tronger competition with S. nigrum than the weed was with itself. However, when infested by M. incognita, both species displayed a similar competitive ability. Tomato yield losses increased with prolonged weed competition but were greater under nematode-infested conditions.     

Suppression of Meloidogyne incognita by the endophytic fungus Acremonium implicatum from tomato root galls

Specific endophytes with biocontrol potential might occur in diseased plant tissues. We isolated an endophytic fungus from tomato root galls infected with Meloidogyne incognita and identified it as Acremonium implicatum based on morphology and internal transcribed spacer sequences. Its biocontrol potential was tested in vitro and in pot and field experiments. In the in vitro test, 96.0% of second-stage juveniles of M. incognita were killed by a culture filtrate of A. implicatum after 48 h. The fungus also suppressed egg hatching, with only 36.3% of treated eggs hatching compared with 87.3% of control eggs. Pot experiments showed that A. implicatum inhibited the formation of root galls, with 40.6 galls per treated plant compared with 121.6 on control plants. A. implicatum reduced the nematode population in soil, with 151.1 nematodes per 100 g treated soil and 375.1 in control soil. Field experiments demonstrated that the root gall index of treated plants (25) was markedly lower than that of control plants (96). In conclusion, A. implicatum has excellent potential for the biocontrol of M. incognita.     

Variability in infection and reproduction of Meloidogyne javanica on tomato rootstocks with the Mi resistance gene

The response of 10 commercial or experimental tomato rootstocks with the Mi resistance gene to an initial inoculum of a Mi‐avirulent population of Meloidogyne javanica was determined in pot tests conducted in spring and summer. In a field test, the rootstocks were subjected to continuous exposure to high initial population densities (2050 ± 900 second‐stage juveniles (J2) per 250 cm³ soil) of the nematode. The presence of the Mi locus in the resistant rootstocks and cultivars was confirmed using the PCR co‐dominant markers REX‐1 and Mi23. Nematode infectivity (egg masses) and reproduction (eggs g^?1 root) were highly variable in the spring tests. Rootstocks PG76, Gladiator and MKT‐410 consistently responded as highly resistant, with nematode multiplication rate (Pf/Pi) < 1 and reproduction index (RI) < 10%, and they were as efficient as standard resistant tomato cultivars at nematode suppression. The relative resistance levels of rootstocks Brigeor, 42851, 43965, Big Power and He‐Man varied depending on the susceptible standard used for reference or the duration of the test. Rootstocks Beaufort and Maxifort were susceptible to M. javanica (Pf/Pi > 50 and RI > 50%). Rootstocks PG76 and He‐Man, and the resistant tomato cv. Caramba showed high levels of resistance in the test conducted in summer, whereas MKT‐410 and 42851 and the resistant tomato cv. Monika were moderately resistant. In the field, seven rootstocks showed high levels of resistance and one (He‐Man) showed an intermediate level, whereas Beaufort and Maxifort were susceptible.     

Variation in resistance to the root-knot nematode Meloidogyne incognita in tomato genotypes bearing the Mi gene

Root-knot nematodes ( Meloidogyne spp.) are among the main pathogens of tomato ( Lycopersicon esculentum ) worldwide. Plant resistance is currently the method of choice for controlling these pests and all the commercially available resistant cultivars carry the dominant Mi gene, which confers resistance to the three main species Meloidogyne arenaria , M. incognita and M. javanica . However the emergence of virulent biotypes able to overcome the tomato resistance gene may constitute a severe limitation to such a control strategy. To date, little was known of the possible influence of the homozygous vs heterozygous allelic state of the Mi locus, or the tomato genetic background, on the expression of the resistance. In order to test both these factors, the resistance was evaluated of a large panel of L. esculentum genotypes (selected from the Vilmorin germplasm stock collection) to seven M. incognita lines avirulent or virulent against the Mi gene. Plant resistance was estimated by counting the egg masses on the root systems after inoculation with second-stage juveniles (J₂). Reproduction of the nematodes was similar or, more often, significantly higher on heterozygous tomato genotypes than on homozygous ones, suggesting a possible dosage effect of the Mi gene. Data also indicated that the tomato genetic background had a major effect on the variations observed in nematode reproduction, especially when tomato genotypes were heterozygous for the Mi gene. These results have important consequences in terms of breeding strategies and durability of the resistance conferred by the Mi gene.     

Adverse effect of the chitinolytic enzyme PjCHI‐1 in transgenic tomato on egg mass production and embryonic development of Meloidogyne incognita

A novel chitinase gene (PjCHI‐1) isolated from Paecilomyces javanicus, a non‐nematophagous fungus, and driven by a CaMV35S promoter, was delivered into CLN2468D, a heat‐tolerant cultivar of tomato (Solanum lycopersicum). T₁ tomato plants exhibited high endochitinase activity and reduced numbers of eggs and egg masses when infected with the root‐knot nematode (RKN) Meloidogyne incognita. The eggs found in transgenic tomato had lower shell chitin contents than eggs collected from control plants. Egg masses from transgenic plants exhibited higher chitinase activity than those from control plants. Moreover, only 30% of eggs from transgenic plants were able to develop to the multi‐cell/J1 stage, compared with more than 96% from control plants. The present study demonstrated that the expression of the PjCHI‐1 chitinase gene can effectively reduce the production of egg masses and repress the embryonic development of M. incognita, presenting the possibility of a novel agro‐biotechnological strategy for preventing crop damage by RKN.     

Investigation of alternatives to methyl bromide for management of Meloidogyne javanica on greenhouse grown tomato

The root galling index and the densities of eggs in roots and juveniles in soil of the root-knot nematode Meloidogyne javanica (Treub) Chitwood on tomato, and the effect of these on crop yield were assessed in greenhouse experiments applying various treatments at two different sites in Crete, Greece. Tomato crops were grown for four cycles by rotating nematode-resistant (first and third spring crops) with susceptible (second and fourth autumn crops) cultivars and receiving the following treatments: (a) untreated control; (b) methyl bromide application before the first and third crops; (c) application of the fungus Pochonia chlamydosporia (Goddard) Zare, Gams & Evans before planting the first, third and fourth crops with a supplementary application three weeks after the beginning of the fourth crop; (d) application of oxamyl in both sites and fenamiphos in site 1 only at the second and fourth crops; (e) combination of treatments (c) and (d). The fungus density in soil was monitored three weeks after application and at the end of each crop, when roots were lifted. Pochonia chlamydosporia had a variable establishment and did not control the nematode. Its pathogenicity on eggs was not demonstrated, as in all cases galls were big, with all egg masses inside and protected from infection. The methyl bromide treatment significantly reduced root galling and egg production compared to other treatments in all crop cycles and the yield of the fourth crop was significantly greater. Nematicides reduced nematode densities compared with untreated controls and the fungus treatment, but they were less effective than methyl bromide and resulted in increased yield in one site only.     

Resistance of Brassicaceae plants to root-knot nematode (Meloidogyne spp.) in northern Australia

Abstract

Brassicaceae plants have the potential as part of an integrated approach to replace fumigant nematicides, providing the biofumigation response following their incorporation is not offset by reproduction of plant-parasitic nematodes on their roots. Forty-three Brassicaceae cultivars were screened in a pot trial for their ability to reduce reproduction of three root-knot nematode isolates from north Queensland, Australia: M. arenaria (NQ1), M. javanica (NQ2) and M. arenaria race 2 (NQ5/7). No cultivar was found to consistently reduce nematode reproduction relative to forage sorghum, the current industry standard, although a commercial fodder radish (Raphanus sativus) and a white mustard (Sinapis alba) line were consistently as resistant to the formation of galls as forage sorghum. A second pot trial screened five commercially available Brassicaceae cultivars, selected for their biofumigation potential, for resistance to two nematode species, M. javanica (NQ2) and M. arenaria (NQ5/7). The fodder radish cv. Weedcheck, was found to be as resistant as forage sorghum to nematode reproduction. A multivariate cluster analysis using the resistance measurements, gall index, nematode number per g of root and multiplication for two nematode species (NQ2 and NQ5/7) confirmed the similarity in resistance between the radish cultivar and forage sorghum. A field trial confirmed the resistance of the fodder radish cv. Weedcheck, with a similar reduction in the number of Meloidogyne spp. juveniles recovered from the roots 8 weeks after planting. The use of fodder radish cultivars as biofumigation crops to manage root-knot nematodes in tropical vegetable production systems deserves further investigation.     

Reaction of a heterozygous tomato hybrid bearing the Mi-1.2 gene to 15 Meloidogyne species

Many root-knot nematode (RKN) species (Meloidogyne spp.) are polyphagous and cultivated tomato (Solanum lycopersicum) is one of their preferential hosts, leading to significant losses. It is known that the dominant Mi-1.2 gene in tomato confers resistance to the three most important RKN species—M. incognita, M. javanica, and M. arenaria, and minor species—M. ethiopica, M. hispanica, and M. luci. However, little information is available about resistance of tomatoes carrying this gene to other tomato-infecting RKN species. In this study, resistance conferred by the Mi-1.2 gene/locus was evaluated against populations of 15 Meloidogyne species, employing tomato cultivars Santa Clara (homozygous recessive mi-1.2/mi-1.2, susceptible) and Debora Plus (heterozygous Mi-1.2/mi-1.2, resistant). Debora Plus was susceptible only to M. enterolobii and M. hapla, and was resistant to the other Brazilian populations of M. arenaria, M. ethiopica, M. exigua, M. hispanica, M. incognita, M. inornata, M. izalcoensis M. javanica, M. konaensis, M. luci, M. morocciensis, M. paranaensis, and M. petuniae. Mi-1.2 is located on tomato chromosome 6 within a cluster of seven homologous genes of the nucleotide-binding site leucine-rich repeat (NBS-LRR) family; further research is required to confirm if this multiple Meloidogyne spp. resistance phenotype is controlled exclusively by Mi-1.2 or by combined action of other closely linked genes. This evaluation of resistance of the Debora Plus cultivar to several Meloidogyne species suggests that the Mi-1.2 gene/locus may reduce losses induced by a wide range of Meloidogyne spp. Further studies using additional resistant cultivars and other populations of Meloidogyne spp. are needed to confirm these results.