Evaluation of resistance to root-knot nematode (Meloidogyne incognita) in okra cultivars

The root-knot nematode, Meloidogyne incognita, is one of the major limiting factors affecting plant growth and yield causing an estimated $100 billion loss per year worldwide. Synthetic pesticides, though instantaneously effective, are usually prohibitively expensive, not readily available, may cause hazards to both man and livestock, and inflict injury to the environment. Notable among the alternatives to nematicides is the use of resistant cultivars which are inexpensive and eco-friendly. In the present studies, twelve okra (Abelmoschus esculentus L) cultivars were evaluated for their resistance against M. incognita under field conditions. Ten-day old okra plants of test cultivars were inoculated with 3000 freshly hatched second stage juveniles of M. incognita. The nematode caused reductions in various growth parameters of all the cultivars to varying levels over their respective controls. None of the cultivars was found completely resistant. The cultivar ‘Sharmeeli’ was highly susceptible as >100 galls were recorded on the roots. Sharmeeli also showed maximum reductions in growth among the cultivars evaluated. The cultivars Anmol and Sindha were susceptible with 71–100 galls. The cultivars Sabz Pari, Super Star, PMS-55 and PMS Beauty were moderately susceptible with 31–70 galls and comparatively less reductions in growth. Cultivars Sanam, Dikshah, Arka Anamika, Ikra-1 and Ikra-2 with 11–30 galls were rated as moderately resistant and showed less damage by the nematode as compared to susceptible cultivars and their planting could provide a useful tool to control root-knot nematodes.     

Response of selected okra cultivars to Meloidogyne incognita

Root–knot nematodes (Meloidogyne spp.) are major pests of vegetables especially in the tropics and subtropics. All commercial okra varieties are susceptible to root knot nematodes and cause substantial losses. The objective of this study is to find out resistant germplasm in order to facilitate our breeders for gene manipulation. A greenhouse study was conducted to evaluate 28 okra cultivars against Meloidogyne incognita inoculated with 5000 eggs. Five cultivars (Bamya Yalova, 19,232, 19,236, 1,922,121, and Green Wonder) had significantly fewer root galls and eggs and less reduction in plant growth (shoot weight and root length), than most of the other entries. A positive relationship was demonstrated between root galls and reduction in plant growth parameters measured. These cultivars may improve okra production in fields infested with M. incognita. During our study, none of the cultivars tested were observed to be immune or resistant to nematode infection according to a scale where: good host [susceptible] when Pf/Pi (Pf = Final population of nematodes after harvest and Pi = Initial population of nematodes which was used as inoculum during experiment) > 5.0, fair, better [moderately resistant] if 5.0 ≥ Pf/Pi > 1, poor if 1 > Pf/Pi > 0, and non-host [resistant] when Pf/Pi = 0. The cultivars, including 19,224, 19,235, Pusa Sawami, Ikra-1, Ikra-2 and Sabzperi China Red, were found to be susceptible with Pf/Pi > 5.0, and they were declared as good hosts of M. incognita. While all the other cultivars were moderately resistant, with 0 ≥ Pf/Pi > 1 but still a significant penetration of nematodes was found. The regression studies showed positive and significant relationships between the number of galls and the reduction in shoot weight (r² = 0.95), number of galls and reduction in shoot length (r² = 0.81), and number of galls and decrease in root length (r² = 0.89).     

Histopathological changes induced by Meloidogyne incognita in some ornamental plants

Histopathological changes induced by the root-knot nematode (Meloidogyne incognita) in five ornamental plants, specifically, Calendula (Calendula officinalis), Centaurea (Centaurea montana), Papaver (Papaver somniferum), Chrysanthemum (Chrysanthemum morifolium) and Dianthus (Dianthus caryophyllus), were investigated. Based on the galling index (GI), Centaurea was classified as susceptible, Calendula as moderately susceptible, and Papaver as moderately resistant, while Chrysanthemum and Dianthus were highly resistant to M. incognita infection. The histopathology of the galled roots of Centaurea, Calendula, and Papaver during later stages of infection showed that nematodes were localized entirely within the cortex and generally oriented horizontally to the vascular cylinder. Most of the females were mature, and a few of them were associated with egg masses. Giant cells with a variation in cell sizes were observed in the galled roots of all three of the plant species and exhibited a granular cytoplasm and hypertrophied nuclei as a typical reaction to nematode feeding.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

Root-knot and reniform nematode reproduction on kenaf and sunn hemp compared with that on nematode resistant and susceptible cotton

Kenaf (Hibiscus cannabinus L.) and sunn hemp (Crotalaria juncea L.) are industrial fiber crops that are being grown increasingly in areas where cotton (Gossypium hirsutum L.) is the major crop. The nematodes causing most cotton yield losses in the USA are the southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, and the reniform nematode, Rotylenchulus reniformis Linford and Oliveira. For nematode management, knowledge about the comparative effects of kenaf, sunn hemp, and cotton on nematode population densities in the soil is important. The objective of this study was to clarify the host status of kenaf and sunn hemp to M. incognita and R. reniformis by directly comparing reproduction of each nematode on each crop with the same nematode's reproduction on nematode-resistant and nematode-susceptible cotton. Comparisons were made in six experiments under growth chamber, microplot, and field conditions. The results showed that sunn hemp is resistant, but not equally resistant to M. incognita and R. reniformis. Reproduction of R. reniformis on sunn hemp was nearly undetectable, whereas reproduction of M. incognita was greater than on resistant cotton (Auburn 623, Auburn 634) and up to 20% of that on susceptible cotton (Deltapine 16, Deltapine 50, or Deltapine 5409). Kenaf was confirmed to elevate populations of M. incognita to levels that devestate cotton, but found to support substantially less reproduction by R. reniformis than cotton does. Two populations of R. reniformis differed substantially in reproduction on kenaf even though the same populations reproduced similarly on cotton. In conclusion, distinguishing M. incognita from R. reniformis is essential to the management of nematodes in rotations involving kenaf, sunn hemp and cotton.     

Amendment of soil with African marigold and sunn hemp for management of Meloidogyne incognita in selected legumes

Field experiments were conducted in 2008 and 2009 in the tropical rainforest zone of Nigeria to investigate the effects of amendment of soil with seedlings of African marigold (Tagetes erecta) and sunn hemp (Crotalaria juncea) incorporated singly in plots on Meloidogyne incognita and yield of cowpea and soybean. The experimental field, which was naturally free of plant-parasitic nematodes, was inoculated with chopped roots of M. incognita race 2-infected Celosia argentea roots and planted to tomato to increase M. incognita population at the site.Eight week-old marigold seedlings were incorporated in cowpea or soybean field and eight week-old sunn hemp seedlings were also incorporated in cowpea or soybean field. At the ends of the experiments, M. incognita population densities were significantly higher in control plots than those of the plots amended with marigold or sunn hemp with correspondingly higher grain yield in the amended plots in both cowpea and soybean fields in both years. A significantly higher population of the nematode and consequently, lower yield was associated with cultivar Ife Brown than cultivar Ife Bimpe of cowpea for each treatment whereas in soybean cultivars, the pattern was not definite. Also twelve seedlings of marigold or sunn hemp per plot incorporated into the soil produced significantly higher grain yield in cultivar Ife Brown of cowpea and cultivar TGX 1440 of soybean compared to six seedlings per plot. The results of this study suggest that incorporating marigold or sunn hemp in M. incognita-infected cowpea or soybean field has potentials to suppress M. incognita population and reduce nematode damage on yield of the associated leguminous crops.     

Infestation assessment of root-knot nematodes (Meloidogyne spp.) associated with cucumber in the Pothowar region of Pakistan

Studies to estimate root-knot nematode infestations on cucumber were conducted during mid- to late-season at 378 randomly selected sites in 126 villages of the four districts across the Pothowar zone of the country. The overall mean infestation of root-knot nematodes in the region was found to be 15.66%. The studies revealed variations in the incidence and severity of root-knot nematodes in the four districts. The incidence of root-knot nematodes was the highest in Rawalpindi district (21.86%), followed by 13.89% in Attock. Of the four districts, the minimum incidence of 10.97% was recorded in Jhelum district. The maximum mean severity (3.79), measured in terms of the galling index, was found in Rawalpindi district, while the minimum (1.86) was observed in Jhelum district. The mean severities of root-knot nematodes in the districts of Attock and Chakwal were 2.66 and 2.19 respectively. Variations in incidence and severity were also observed among subdivisions of the districts. Of all the associated species of root-knot nematodes, Meloidogyne incognita constituted 78.53%, Meloidogyne javanica 19.03%, Meloidogyne arenaria 1.82% and Meloidogyne hapla 0.62%. M. incognita and M. javanica were recorded in all of the districts, with M. incognita predominating. M. incognita as a pure population was recorded in 29.63% of the villages, while the other three species were found as mixtures. The most common mixed population was M. incognita and M. javanica, observed in 70.37% of villages in the region. M. arenaria and M. hapla were not found together in any of the population mixtures. The results indicate that cucumber is severely attacked by root-knot nematodes, warranting adoption of strict control measures for its management.     

部分国内外小麦种质资源对燕麦孢囊线虫的抗病性

燕麦孢囊线虫是小麦生产上的重要病原线虫。为筛选抗燕麦孢囊线虫的小麦种质资源,采用室内接种方法测试了104个国外小麦品种（系）和37个国内小麦品种对燕麦孢囊线虫的抗病性,并利用不同抗性评价标准在自然病田对37个国内小麦品种的抗病性进行了评价。室内接种试验表明,104份国外小麦品种（系）中有高抗品种（系）14个,中抗品种（系）12个,中感品种（系）27个,其他均属高感,37个国内参试品种均属感病品种。自然病田鉴定结果表明,采用不同的评价标准对37个国内品种的评价结果具有较大差异。依据Andersen等的评价标准,37个小麦品种中有7个品种表现感病,30个品种表现抗病,与室内接种测试结果差异较大;依据Ireholm的标准,仅良星66表现抗病,其他品种均表现感病,与室内测试结果接近;依据Soriano等的标准,37个品种均表现感病,与室内测试结果相同。建议在筛选抗孢囊线虫小麦资源时首先采用Andersen等的标准进行初筛,然后利用Soriano等的标准进行田间评价。     

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.     

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.     

Differential response of two pineapple cultivars (Ananas comosus (L.) Merr.) to SAR and ISR inducers against the nematode Rotylenchulus reniformis

We hypothesized that inducing systemic resistances can contribute to the control of the nematode Rotylenchulus reniformis in pineapple. In greenhouse experiments conducted in Martinique, the pineapple cultivars Smooth Cayenne and MD-2 were treated with methyljasmonate (JAME) and salicylic acid (SA), elicitors of induced systemic resistance (ISR) and systemic acquired resistance (SAR). The efficacy of the elicitors was tested by inoculating plantlets grown in individual pots with a monospecific population of R. reniformis reared on Vigna unguiculata. The final nematode populations, 45 days after inoculation on MD-2 treated with JAME were reduced by 67.0% (p = 0.006). Nematode populations on MD-2 plants treated with SA were reduced by 55.8% (p = 0.016). Nematode populations on SC were not reduced by the elicitors. In a second experiment, using split-root systems, JAME was applied to MD-2 plantlets and enzymatic activities involved in plant defense and stress responses were monitored for 14 h after treatment. Additional pots were inoculated with nematodes 24 h after JAME treatment and examined ten days later. Transient stress was observed along with an increase in enzymatic response after inoculation with nematodes. These results showed that the MD-2 was primed through an ISR by JAME. The question now arises whether ISR can be specifically induced only in certain pineapple cultivars. Results are discussed from the perspective of introducing new strategies to manage pineapple nematodes.     

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.     

Interactive effects of Meloidogyne incognita race 2, Bradyrhizobium japonicum and crude extracts of Cucumis myriocarpus fruit on Vigna unguiculata

Crude extracts of wild cucumber (Cucumis myriocarpus) fruit, without information on their effects on nodulation, had been touted as having potential as a nematicide and a fertiliser in low-input cowpea (Vigna unguiculata) production systems. Interactive effects of the southern root-knot nematode (Meloidogyne incognita), Bradyrhizobium japonicum and crude extracts of wild cucumber (C. myriocarpus) fruit on each other and growth of cowpea variety Eureka were investigated in a 23 factorial experiment. At harvest, 70 days after initiating the treatments, significant (P ≤ 0.05) first order interactions between any two of the three main factors on variables measured were observed, with interactive effects being either stimulatory or inhibitory. Crude extracts of C. myriocarpus fruit were basically suppressive on nematode numbers but stimulated nodulation and growth of cowpea. Consequently, the material is suitable for use in managing population densities of M. incognita on cowpea production in low-input cowpea production systems.     

Nemato-toxic potential of Betel (Piper betle L.) (Piperaceae) leaf

In vitro and in-planta trials were conducted to determine the nemato-toxic potential of aqueous leaf extracts of Betel (Piper betle L.) against the root-knot nematode species, Meloidogyne incognita, at five concentrations, standard extract (S) [1:2 (w/v] and its four dilutions, 20%, 40%, 60%. 80% of S. In the in vitro trials, second-stage juveniles (J₂s) and eggs of M. incognita were directly exposed to the extract while in the in-planta trials, the effect of the extract was evaluated as a root dip treatment using tomato plants. The findings indicated that the extract was lethal to J₂s but also inhibited egg hatch. The seedling dip treatments reduced root infestations in terms of gall formation, egg production and J₂ population densities in soil while simultaneously enhancing the growth of tomato plants. All these effects varied in a dose-dependent manner. Based on the LC₅₀ value, the eggs were found to be less sensitive to the extract than J₂s. One hundred percent of mortality of J₂s was recorded at four concentration levels, 40%, 60% and 80% of S and S, while 100% egg inhibition was only recorded at S. The highest reductions in gall formation (i.e., number of galls/root system), egg production and J₂ population were all recorded at S as 83%, 87% and 84% compared to the untreated water control. The maximum growth enhancement, which was 235% of the control, was detected in the root length of treated tomato plants. It appears the aqueous leaf extract of P. betle shows promise as a sustainable eco-friendly nematicide for the management of M. incognita.     

小麦品种对禾谷孢囊线虫（Heterodera avenae） 江苏沛县群体的抗性鉴定

为了筛选对禾谷孢囊线虫病(Cereal cyst nernatode,CCN)具有抗性的小麦品种,采用室内二龄幼虫接种法、网室卵接种法和田间病圃法测定了收集自5个省份的40个小麦品种对小麦孢囊线虫江苏沛县群体的抗性。室内二龄幼虫接种测定结果表明,供试材料中无免疫品种,华麦1号、温粮58和豫麦66-18系表现为高抗,扬麦13和徐麦7086表现为中抗,烟农5158表现最感病,平均单株白雌虫数达104.7个;田间病圃测定表明,上述5个品种仅华麦1号表现为抗病。网室卵接种法测定结果与室内二龄幼虫接种法及田间病圃法测定结果差异较大,显示该方法不适用小麦品种的CCN抗性鉴定。     

Rapid detection of Meloidogyne spp. by LAMP assay in soil and roots

Loop-mediated isothermal amplification (LAMP), a novel DNA amplification technique, has been used to detect a variety of pathogens including viruses, fungi, bacteria and parasites. However, diagnosis of sedentary plant-parasitic nematode (PPN) species has not yet been attempted. In this study, we developed a universal LAMP set (RKN-LAMP) for the diagnosis of four common Meloidogyne species (Meloidogyne incognita, M. arenaria, M. javanica and M. hapla), and M. incognita-specific LAMP set (Mi-LAMP). In both assays, a typical ladder-like pattern on gel electrophoresis was observed in all positive samples but not in the negative controls. Amplification products were further confirmed using restriction analysis of the Hpa II enzyme, detection by visual inspection using SYBR Green I and the lateral flow dipstick (LFD) assay. The two LAMP sets were specifically able to detect four common Meloidogyne species and M. incognita populations having several different geographical origins and pathotypes. No cross reaction with DNA of other PPNs was observed. Sensitivity of the RKN- and Mi-LAMP was 10 and 100 fg of pure genome DNA respectively. Both LAMP sets could also amplified crude DNA isolated from the galled root tissue and from soil containing juveniles of M. incognita. The RKN- and Mi-LAMP sets offer the advantages of simplicity, rapidity and cost effectiveness. Both LAMP sets will be instrumental for the diagnosis of Meloidogyne spp. by local extension and regulatory personnel.     

Managing Meloidogyne incognita and Bemisia tabaci with thiacloprid in cucumber crops in China

Field trials were conducted to determine the potential use of thiacloprid for integrated Meloidogyne incognita and Bemisia tabaci B biotype control in cucumber (Cucumis sativus Linn.) in China. The following five treatments were evaluated: three thiacloprid doses (7.5, 15, and 30 kg ha⁻¹), an avermectin treatment (7.5 L ha⁻¹) and an untreated control. All thiacloprid application rates were effective for reducing the M. incognita and B. tabaci B biotype populations. M. incognita was reduced by 51.0%∼86.7% on 60th day and B. tabaci B biotype was reduced by about 37.2%∼95.3% within 21 days, respectively. In addition, greater thiacloprid doses resulted in fewer nematodes and whiteflies. Over two successive years, the cucumber plants that were treated with thiacloprid at a dose of 15 kg ha⁻¹ had the greatest plant height, plant vigor and marketable yield, which were 134.1 cm, 91, 1514.3 g plant⁻¹, respectively in 2010–2011 and 151.9 cm, 93, 1651.4 g plant⁻¹, respectively in 2011–2012. In addition, thiacloprid was superior to avermectin. The results of this study demonstrated that thiacloprid could be used in cucumber production for the integrated control of M. incognita and B. tabaci B biotype. Furthermore, a dose of 15 kg ha⁻¹ of thiacloprid was recommended for controlling nematode and whitefly populations according to the control effect and marketable cucumber yield.     

Differential effect of delayed planting on soybean cultivars varying in susceptibility to bacterial pustule and wildfire in Korea

In 2009 and 2010, the effect of delayed planting on bacterial pustule (Xanthomonas axonopodis pv. glycines) and wildfire (Pseudomonas syringae pv. tabaci) in four soybean cultivars was evaluated in fields in Suwon and Naju, Korea. Soybean was planted on 15 May as the first (traditional) planting date; then, planting was delayed at approximately 15-day intervals (three times) after the first planting. In plots planted approximately 15 or 30 days after the traditional planting date, the disease incidence in highly (Saeolkong and Taegwangkong) and moderately (Pungsannamulkong) susceptible cultivars was significantly reduced under moderate disease pressure, but disease reduction in highly susceptible cultivars was sometimes diminished especially against bacterial pustule under high disease pressure. Altered planting date had no effect on disease incidence in the least susceptible (resistant) cultivar (Cheongja-3-ho), regardless of disease pressure. Consistent differences in disease occurrence were not observed between planting locations. The results from this study indicate that delayed soybean planting reduced the bacterial disease incidence and differentially affected resistant and susceptible cultivars. Thus, planting resistant cultivars at the optimal planting date is desirable, but in the case of susceptible cultivars, delayed planting could be considered along with application of other control measures such as agrochemicals.     

水稻抗纹枯病育种成效的初步评价

以广东省和江苏省里下河农科所新近育成的部分籼稻品种（系）、扬州大学农学院的研究组以不同抗源杂交后代向抗感两个极端选育的9份籼稻品系以及另一组合向抗病方向选育的5份籼稻品系为材料,设置抗感病对照,进行田间纹枯病菌接种试验。结果表明品种间对纹枯病的抗性存在极显著差异;聚类分析将参试材料按抗性水平高低聚为6类：高度感病、感病、中等感病、中等抗病、抗病和更高水平抗病。广东品种在6种类型中均有分布,但属于抗和更抗类型的品种只有3个。扬州大学农学院对抗×抗杂交向抗感两个极端选育的品系在病级的中间类型中几乎没有分布;而向抗病方向选育的品系则仅分布于中抗至抗病的范围内,且属于抗的品种数占此类品种的60%。江苏省里下河农科所近些年育成的几个品种则只分布于后4类之中,且最高水平抗性的3个品种中,其品种占2/3。表明水稻对纹枯病的抗性是可遗传的性状,对抗性的选择有效。     

Management of the root-knot nematode Meloidogyne incognita on tomato with combinations of different biocontrol organisms

The nematicidal effect of Pseudomonas fluorescens, Paecilomyces lilacinus, Pichia guilliermondii and Calothrix parietina singly or in combination was tested against root-knot nematode, Meloidogyne incognita. Treatments with P. fluorescens and P. lilacinus caused mortality of M. incognita as 45% and 30% of juveniles after 48 h of exposures, respectively compared to water control in vitro. Under greenhouse conditions, all treatments reduced the disease severity and enhanced plant growth compared to untreated control. Application of P. fluorescens, P. lilacinus and P. guilliermondii Moh 10 was more effective compared to C. parietina. There was a negative interaction between C. parietina and either P. lilacinus or P. guilliermondii. Fresh and dry weight of shoots and roots of plants were significantly reduced as a result of infection with M. incognita, however application of biocontrol agents singly or in mix recovered this reduction. Moreover, they enhanced the growth parameters compared with the control. Our results proved that application of different biocontrol agents (P. fluorescens, P. lilacinus and P. guilliermondii) not only has a lethal effect on nematode, but also enhances the plant growth, supplying many nutritional elements and induction the systemic resistance in plants. Presence of C. parietina as a soil inhabitant cyanobacterium could antagonize biocontrol agents leading to the reduction of their practical efficiency in soil.