The Effects of Root-knot Nematode Infection and Mi-mediated Nematode Resistance in Tomato on Plant Fitness

The Mi-1.2 resistance gene in tomato (Solanum lycopersicum) confers resistance against several species of root-knot nematodes (Meloidogyne spp.). This study examined the impact of M. javanica on the reproductive fitness of near-isogenic tomato cultivars with and without Mi-1.2 under field and greenhouse conditions. Surprisingly, neither nematode inoculation or host plant resistance impacted the yield of mature fruits in field microplots (inoculum=8,000 eggs/plant), or fruit or seed production in a follow-up greenhouse bioassay conducted with a higher inoculum level (20,000 eggs/plant). However, under heavy nematode pressure (200,000 eggs/plant), greenhouse-grown plants carrying Mi-1.2 had more than ten-fold greater fruit production than susceptible plants and nearly forty-fold greater estimated lifetime seed production, confirming prior reports of the benefits of Mi-1.2. In all cases Mi-mediated resistance significantly reduced nematode reproduction. These results indicated that tomato can utilize tolerance mechanisms to compensate for moderate levels of nematode infection, but that the Mi-1.2 resistance gene confers a dramatic fitness benefit under heavy nematode pressure. No significant cost of resistance was detected in the absence of nematode infection.     

Changes in populations of soil microorganisms,nematodes, and enzyme activity associated with application of powdered pine bark

Evaluation of enzyme activities in combination with taxonomic analyses may help define the mechanisms involved in microbial decomposition of orgaic amendments and biological control of soilborne pathogens. In this study, powdered pine bark was added to nematode-infested soil at rates of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 g kg^–1. Total fungal populations did not differ among treatments immediately after application of pine bark. After 7 days, fungal populations were positively correlated with increasing levels of pine bark. This increase was sustained through 14 and 21 days.Penicillium chrysogenum andPaecilomves variotii were the predominant fungal species isolated from soil amended with pine bark. Total bacterial populations did not change with addition of pine bark at 0, 7, and 14 days after treatment. At 21 and 63 days, total bacterial populations declined in soil receiving the highest rates of pine bark. Addition of pine bark powder to soil caused a shift in predominant bacterial genera fromBacillus spp. in nonamended soil, toPseudomonas spp. in amended soil. Soil enzyme activities were positively correlated with pine bark rate at all sampling times. Trehalase activity was positively correlated with total fungal populations and with predominant fungal species, but was not related to bacterial populations. The number of non-parasitic (non-stylet bearing) nematodes andMeloidogyne arenaria in soil and roots were not correlated with pine bark rate. However,Heterodera glycines juveniles in roots, and the number of cysts g^–1 root, declined with increasing levels of pine bark.Journal Series Series No. 18-933598 Alabama Agricultural Experiment Station     

番茄‘Ls-89’和‘坂砧2号’幼苗活性氧代谢对南方根结线虫侵染的反应

为了解番茄(Lycopersicon esculentum)砧木幼苗活性氧代谢与抗南方根结线虫(Meloidogyne incognita)的关系,以高感品种‘Ls-89’与高抗品种‘坂砧2号’为材料,采用盆栽人工接种法,研究了南方根结线虫侵染对番茄砧木幼苗活性氧代谢的影响。结果表明,未接种南方根结线虫的番茄砧木幼苗,其根系与叶片活性氧水平及相关酶活性在品种间没有显著差异。接种南方根结线虫后,两品种幼苗根系与叶片的O_2·~–生成速率和H_2O_2含量均升高,且‘坂砧2号’显著高于‘Ls-89’,但‘Ls-89’的MDA含量则显著高于‘坂砧2号’。两品种幼苗根系与叶片的SOD活性均在侵染早期降低,以‘坂砧2号’降幅较大;但POD、CAT活性在侵染早期变化不大,至侵染中后期则显著升高。因此,番茄抗性品种砧木幼苗的膜脂抗氧化能力较强,活性氧水平较高,且SOD活性对南方根结线虫侵染敏感。     

Interaction of Fusarium oxysporum f. sp. ciceri and Meloidogyne javanica on Cicer arietinum

Interaction of Meloidogyne javanica and Fusarium oxysporum f. sp. ciceri was studied on Fusarium wilt-susceptible (JG 62 and K 850) and resistant (JG 74 and Avrodhi) chickpea cultivars. In greenhouse experiments, inoculation of M. javanica juveniles prior to F. oxysporum f. sp. ciceri caused greater wilt incidence in susceptible cultivars and induced vascular discoloration in roots of resistant cultivars. Nematode reproduction was greatest (P = 0.05) at 25 °C. Number of galls and percentage of root area galled increased when the temperature was increased from 15 °C to 25 °C. Wilt incidence was greater at 20 °C than at 25 °C. Chlorosis of leaves and vascular discoloration of plants did not occur at 15 °C. The nematode enhanced the wilt incidence in wilt-susceptible cultivars only at 25 °C. Interaction between the two pathogens on shoot and root weights was significant only at 20 °C, and F. o. ciceri suppressed the nematode density at this temperature. Wilt incidence was greater in clayey (48% clay) than in loamy sand (85% sand) soils. The nematode caused greater plant damage on loamy sand than on clayey soil. Fusarium wilt resistance in Avrodhi and JG 74 was stable in the presence of M. javanica across temperatures and soil types.     

Plantago lanceolata and Plantago rugelii Extracts are Toxic to Meloidogyne incognita but not to Certain Microbes

Extracts from the plants Plantago lanceolata and P. rugelii were evaluated for toxicity to the root-knot nematode Meloidogyne incognita, the beneficial microbes Enterobacter cloacae, Pseudomonas fluorescens and Trichoderma virens, and the plant-pathogenic fungi Fusarium oxysporum f. sp. gladioli, Phytophthora capsici, Pythium ultimum, and Rhizoctonia solani. Wild plants were collected, roots were excised from shoots, and the plant parts were dried and ground to a powder. One set of extracts (10% w/v) was prepared in water and another in methanol. Treatments included extract concentrations of 25%, 50%, 75% and 100%, and water controls. Meloidogyne incognita egg hatch was recorded after 7-day exposure to the treatments, and second-stage juvenile (J2) activity after 48 hours. All extracts were toxic to eggs and J2, with P. lanceolata shoot extract tending to have the most activity against M. incognita. Numbers of active J2 remained the same or decreased in a 24-hour water rinse following the 48-hour extract treatment, indicating that the extracts were lethal. When data from water- and methanol-extracted roots and shoots of both plant species were combined for analysis, J2 tended to be more sensitive than eggs to the toxic compounds at lower concentrations, while the higher concentrations (75% and 100%) were equally toxic to both life stages. The effective concentrations causing 50% reduction (EC₅₀) in egg hatch and in J2 viability were 44.4% and 43.7%, respectively. No extract was toxic to any of the bacteria or fungi in our assays.     

南方根结线虫对不同砧木嫁接番茄苗活性氧清除系统的影响

采用盆栽人工接种方法,对番茄嫁接苗进行了抗性评价,研究了番茄嫁接苗叶片中抗氧化酶活性和活性氧代谢的动态变化。结果表明,接种南方根结线虫(J2)后,砧木嫁接苗表现为高抗,自根嫁接苗为高感。通过嫁接换根,与自根嫁接苗相比,砧木嫁接苗明显提高了接穗叶片的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性,降低了超氧阴离子(O.2-)产生速率以及过氧化氢(H2O2)和丙二醛(MDA)含量。表明番茄植株体内的活性氧水平和抗氧化酶活性的高低与其抗根结线虫的能力密切相关,较低的活性氧水平和较高的抗氧化酶活性有利于减轻对膜系统的伤害,提高番茄植株的抗根结线虫能力。     

Managing Nematode Population Densities on Tomato Transplants Using Crop Rotation and a Nematicide

Millet, milo, soybean, crotalaria, and Norman pigeon pea were used in conjunction with clean fallow and a nematicide (fensulfothion) for managing nematode populations in the production of tomato transplants (Lycopersicon esculentum Mill.). Glean fallow was the most effective treatment in suppressing nematode numbers. After 2 years in tomato, root-knot nematodes increased in numbers to damaging levels, and fallow was no longer effective for complete control even in conjunction with fensulfothion. After 4 years in tomato, none of the crops used as summer cover crops alone or in conjunction with fensulfothion reduced numbers of root-knot nematodes in harvested tomato transplants sufficiently to meet Georgia certification regulations. Milo supported large numbers of Macroposthonia ornata and Pratylenchus spp. and crotalaria supported large numbers of Pratylenchus spp. Millet, milo, soybean, crotalaria, and pigeon pea are poor choices for summer cover crops in sites used to produce tomato transplants, because they support large populations of root-knot and other potentially destructive nematodes.     

Effects of Rapeseed and Vetch as Green Manure Crops and Fallow on Nematodes and Soil-borne Pathogens

In a rapeseed-squash cropping system, Meloidogyne incognita race 1 and M. javanica did not enter, feed, or reproduce in roots of seven rapeseed cultivars. Both nematode species reproduced at low levels on roots of the third crop of rapeseed. Reproduction of M. incognita and M. javanica was high on squash following rapeseed, hairy vetch, and fallow. The application of fenamiphos suppressed (P = 0.05) root-gall indices on squash following rapeseed, hairy vetch, and fallow; and on Dwarf Essex and Cascade rapeseed, but not Bridger and Humus rapeseed in 1987. The incorporation of 30-61 mt/ha green biomass of rapeseed into the soil 6 months after planting did not affect the population densities of Criconemella ornata, M. incognita, M. javanica, Pythium spp., Rhizoctonia solani AG-4; nor did it consistently increase yield of squash. Hairy vetch supported larger numbers of M. incognita and M. javanica than rapeseed cultivars or fallow. Meloidogyne incognita and M. javanica survived in fallow plots in the absence of a host from October to May each year at a level sufficient to warrant the use of a nematicide to manage nematodes on the following susceptible crop.     

Influence of Initial Population Densities of Meloidogyne incognita on Three Chile Cultivars

The effects of Meloidogyne incognita on the Big Jim, Jalapeno, and New Mexico No. 6 chile (Capsicum annuum) cultivars were investigated in microplots for two growing seasons. All three cultivars were susceptible to M. incognita and reacted similarly to different initial populations of this nematode. Severe stunting and yield suppressions occurred at all initial M. incognita densities tested ranging from 385 to 4,230 eggs and larvae/500 cm³ soil. Regression analysis of the microplot data from a sandy loam soil showed yield losses of 31% for the 1978 season and 25% for the 1979 season for the three cultivars for each 10-fold increase in the initial population of M. incognita.     

Resistance of Cucumis spp. to the Root-knot Nematode,Meloidogyne incognita acrita

The nature of resistance in Cucumis ficifolius and C. metuliferus to the root-knot nematode, Meloidogyne incognita acrita, was studied under greenhouse conditions. Although as many larvae penetrated the roots of these species as those of the susceptible C. melo, few developed to the adult female stage. Resistance in C. ficifolius and C. metuliferus was associated with hindrance of larval development beyond the second stage, delayed development of larvae to adults and stimulation toward maleness. Tissue necrosis or hypersensitivity was not associated with larval penetration. Comparisons of the histopathology of 26-day-old infections of C. melo and C. metuliferus roots showed no observable differences in the type of giant cell development in regions of roots associated with adult females. However, in C. rnetuliferus immature nematodes were associated with small giant cells which were limited to a few cells near the head of the nematode.