Hypersensitive-like reaction conferred by the Mex-1 resistance gene against Meloidogyne exigua in coffee

The response of a susceptible coffee cultivar (Caturra) to infection by the root-knot nematode Meloidogyne exigua was compared histologically with that of cv. Iapar 59 possessing the recently identified Mex-1 resistance gene. The reproductive behaviour of the nematode was also compared in the two cultivars. Penetration and development in resistant plants were reduced in comparison with susceptible plants. Several cell features, including dark-stained cytoplasm and altered organelle structure, were observed in the resistant cultivar, indicating a hypersensitive-like (HR) response of the infested host cells. Features of giant cells were sometimes found beside necrotic-like areas, but the corresponding feeding sites were frequently associated with nematodes displaying abnormal shape. Six weeks after inoculation, root systems of cv. Caturra contained significantly more nematodes than those of cv. Iapar 59 (mean values 1574 and 41, respectively). The susceptible cultivar presented a minimum of 11 galls per plant, compared with only one or two galls per plant in the resistant cultivar. The findings are discussed in the context of plant–pathogen interactions.     

Nematode quantitative resistance conferred by the pepper genetic background presents additive effects and is stable against different isolates of Meloidogyne incognita

Root‐knot nematodes (RKNs), Meloidogyne spp., are a major disease problem in solanaceous crops worldwide, including pepper (Capsicum spp.). Genetic control provides an economically and environmentally sustainable protection alternative to soil fumigants. In pepper, resistance to the main RKN species (M. incognita, M. javanica and M. arenaria) is conferred by the major genes (R genes) Me1, Me3 and N. However, RKNs are able to develop virulence, thus endangering the efficiency of R genes. Quantitative resistance (QR) against Meloidogyne spp. is expected to provide an alternative to R genes, or to be combined with R genes, to increase the resistance efficiency and durability in pepper. In order to explore the ability of QR to protect pepper against RKNs, five pepper inbred lines, differing in their QR level, were tested directly, or after combination with the Me1 and Me3 genes, for their resistance to a panel of M. arenaria, M. javanica and M. incognita isolates. The M. arenaria and M. javanica isolates showed low pathogenicity to pepper, unlike the M. incognita isolates. The QR, controlled by the pepper genetic background, displayed a high resistance level with a broad spectrum of action, protecting pepper against Me3‐virulent as well as avirulent M. incognita isolates. The QR was also expressed when combined with the Me1 and Me3 genes, but presented additive genetic effects so that heterozygous F₁ hybrids proved less resistant than homozygous inbred lines. The discovery of this QR is expected to provide promising applications for preserving the efficiency and durability of nematode resistance.     

有机酸类化合物对南方根结线虫的生物活性

采用室内离体测定方法,测试了15种有机酸对南方根结线虫(Meloidogyne incognita) 2龄幼虫致死率和卵孵化抑制率。结果表明,甲酸和丙酸对2龄幼虫和卵的生物活性最高,明显优于其他供试有机酸,但是活性低于对照药剂阿维菌素。对生物活性结果及有机酸化学结构进行比对发现,小分子量化合物对南方根结线虫具有较高生物活性。     

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.     

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。     

Screening of Urfa pepper landraces for resistance to Meloidogyne incognita

Journal of Plant Diseases and Protection - The root-knot nematodes (Meloidogyne spp.) are significant pathogens that affect the yield and fruit quality in pepper cultivars (Capsicum spp.)....     

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。     

New sources of resistance to Meloidogyne incognita race 3 in wild cotton accessions and histological characterization of the defence mechanisms

Accessions of Gossypium spp., some of them never previously tested, were evaluated for resistance to a local isolate of Meloidogyne incognita race 3 in greenhouse experiments. Nematode infection was characterized based on the galling and egg mass indexes and the reproduction factors (RF). Root‐knot nematode reproduction among the newly tested accessions varied from highly susceptible (AS0188, AS0189) to moderately resistant (MT123 no. 3), and some accessions showed highly reduced nematode reproduction (CIR1343, CIR1348, Fai Mui). Histological observations of two resistant accessions (G. barbadense CIR1348 and G. hirsutum TX‐25, respectively) showed that resistance occurs through a two‐stage mechanism in the first accession and through a single‐stage mechanism in the second. Parasitism is blocked early after second‐stage juvenile (J2) penetration or during its initial tissue migration (CIR1348) and the development of later‐stage juveniles into female adults is suppressed at a later stage (TX‐25 and CIR1348). Fluorescence and bright light microscopy showed that root cells surrounding nematodes exhibit a hypersensitivity‐like reaction, with the accumulation of presumably phenolic compounds and the presence of necrotic cells that limit the development of nematodes and the formation of giant cells. Underdeveloped giant cells with degenerated cytoplasmic content were found in small numbers in CIR1348 and in large numbers in TX‐25, along with deformed nematodes. The full characterization of the defence mechanisms of novel sources of resistance to the root‐knot nematode in cotton constitutes a first step towards their use in crop improvement.     

产生几丁质酶的交枝顶孢(Acremonium implicatum)对南方根结线虫生防潜力

 由于化学杀线剂给环境带来了污染问题,寄生线虫的生防真菌成为研究热点。为进一步鉴定和筛选高效食线虫真菌,从山东日照五莲烟草北方根结线虫卵中分离到1株较高应用潜力菌株WLE1。根据形态学和rDNA-ITS序列分析方法鉴定该菌为交枝顶孢Acremonium implicatum。该菌是1株能够产生几丁质酶的食线虫真菌,在第4天几丁质酶活性到达高峰,为18.49 μmol·h^-1·mL^-1 ,直到第16天依然维持较高活性;活性电泳测定其几丁质酶分子量分别为98.0、82.9、70.2和35.9 kDa;交枝顶孢几丁质粗酶液处理南方根结线虫卵,第7天卵的孵化抑制率为80.17%。该菌能够寄生南方根结线虫卵、2龄幼虫和雌虫。第6天卵和2龄幼虫的寄生率分别为82.11%和73.97%。说明具有高效产生几丁质酶特性且能寄生南方根结线虫不同生活史阶段的交枝顶孢WLE1对南方根结线虫具有巨大生防潜力。     

响应面法优化根结线虫生防真菌Snef5的发酵工艺

为提高生防真菌Simplicillium chinense Snef5的杀线虫活性,本研究采用响应面法对其发酵条件进行优化。首先,采用Plackett?Burman法筛选出有显著效应的3个因素：初始pH值、蔗糖和MgSO₄·7H₂O用量,而后通过Box?Benhnken设计和响应面分析法对其进行分析,获得了优化的最佳初始pH值为6.74,蔗糖含量4.19%,MgSO₄·7H₂O含量0.04%。经摇瓶和发酵罐发酵验证,该理论预测值与实测值无显著差异;优化后的发酵液杀线虫活性与原始发酵液相比,摇瓶发酵与30 L发酵罐产出的发酵液对南方根结线虫2龄幼虫的致死率分别提高了20.6%和21.3%,显示出较好的优化效果。试验结果对生防真菌的发酵及实际应用具有重要指导作用。     

长枝木霉对南方根结线虫致死和寄生作用的显微观察及测定研究

对不同时期长枝木霉(Trichoderma longibrachiatum)分生孢子悬浮液对南方根结线虫(Meloidogyne incognita)2龄幼虫的致死和寄生作用过程进行了显微观察和室内测定.显微观察结果表明,侵染初期长枝木霉分生孢子吸附或寄生在虫体的表面,并且分生孢子萌发产生大量的菌丝穿透虫体体壁.侵染后期被分生孢子寄生的虫体开始出现畸形,且寄生的部位出现缢缩和溶解,甚至有的虫体完全溶解.室内测定结果表明,不同浓度长枝木霉分生孢子悬浮液对2龄幼虫具有明显的致死和寄生作用,并且不同浓度长枝木霉分生孢子悬浮液之间存在显著的差异.第14天浓度为1.5×107个/mL的长枝木霉分生孢子悬浮液对2龄幼虫的寄生率为87.33％,以及72 h后2龄幼虫的死亡率和校正死亡率分别为90.00％和88.81％.     

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     

Characterization of mechanisms of resistance against Didymella pinodes in Pisum spp.

Ascochyta blight caused by Didymella pinodes is a serious disease of pea (Pisum sativum ssp. sativum) to which little resistance has been identified so far. Only incomplete resistance is available in pea germplasm although higher levels of resistance have been reported in related Pisum species. In this study we characterized histochemically the underlying resistance mechanisms in these wild species and in the pea cv. Radley, the pea cultivar with the highest level of resistance to D. pinodes. Resistance was characterized by a reduced success of colony establishment and lesion size. Histologically this was associated with higher frequency of epidermal cell death and protein cross-linking in infected epidermal cells but not with H₂O₂ accumulation and peroxidase activity.     

Diversity of Meloidogyne incognita populations from cotton and aggressiveness to Gossypium spp. accessions

The root-knot nematode (RKN) Meloidogyne incognita is the main nematode causing losses to the cotton crop in Brazil. In order to implement control strategies within integrated management, an accurate identification of the nematode populations prevailing in the cotton production areas is necessary. This study aimed to assess the genetic variability and aggressiveness of RKN populations from cotton production areas in Bahia state, Brazil. All populations were characterized biochemically and molecularly and identified as M. incognita. RAPD and AFLP markers detected 44% of polymorphic fragments among the 13 populations of this species. The 10 M. incognita populations collected in Bahia presented 33.7% of diversity when compared to each other, and 25% when the population from Barreiras (the most polymorphic) was excluded. This polymorphism increased when populations from other Brazilian states were included. The aggressiveness and virulence among populations from Bahia towards different cotton accessions (susceptible/resistant) was also studied. None of the populations showed virulence against the moderately resistant (Clevewilt 6, Wild Mexican Jack Jones and LA 887) and highly resistant (CIR1348 and M-315 RNR) cultivars. Two M. incognita populations from Barreiras were the most aggressive, reaching reproduction factors of 539 and 218, respectively, in the susceptible cultivar FiberMax 966. The most aggressive population (8) was also the most genetically divergent in phylogenetic analyses. These results demonstrate that diversity of M. incognita populations from cotton farms in Bahia is not related to virulence against resistant accessions, which suggests that cultivars containing one or two resistance genes with good agronomic characteristics could be used in infested commercial areas in Bahia state, Brazil.     

酸黄瓜南方根结线虫病抗性的解剖学及其细胞学研究

为探明酸黄瓜南方根结线虫病抗性的内在机理,以抗病材料酸黄瓜与感病材料北京截头为试材,对南方根结线虫侵入与幼虫发育、根的解剖学及线虫侵入诱导形成的取食位点的细胞学结构进行了比较研究。结果表明,抗病材料酸黄瓜根系中线虫侵入率极显著低于感病材料北京截头(P0.01),酸黄瓜能够有效抵抗南方根结线虫的侵入;抗、感材料根系中雌雄虫个体比例分别为1∶12和1∶5(P0.01),抗性反应能够抑制线虫取食和幼虫发育;酸黄瓜根的解剖结构与普通栽培黄瓜相似,酸黄瓜的根不具有结构抗性;抗病反应中细胞发生过敏性坏死,感病反应中无此类现象发生。抗侵入、抑制取食和坏死反应是抗病材料酸黄瓜抗性反应的主要特征。