Identification of Sources of Resistance to Four Species of Root-knot Nematodes in Tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.     

红麻种质资源根结线虫病抗性鉴定

为鉴定我国红麻种质资源对根结线虫病的抗病性,在对120份红麻遗传资源进行田间自然发病鉴定的基础上,选择25份有代表性(22份高抗和3份感病)的种质进行盆栽根结线虫病接种鉴定。田间自然发病鉴定结果:120份红麻遗传资源中5个高感、19个中感、25个中抗、71个高抗;其侵染的根结线虫主要为南方根结线虫(Meloidogyne incognita)、爪哇根结线虫(Meloidogyne javanica)和花生根结线虫(Meloidogyne arenria)的混合种群。进行盆栽接种鉴定的25份遗传资源中,7份为中抗,其余分别为中感和高感品种,未发现高抗或免疫品种。本研究可为红麻种质资源发掘利用提供科学依据。     

番木瓜和西番莲根结线虫病记述

本文对番木瓜根结线虫病和西番莲根结线虫病的症状作了描述。病原线虫经鉴定确认,侵染番木瓜的虫种为南方根结线虫(Meloidogneincognita),侵染西番莲的根结线虫是由南方根结线虫、高弓根结线虫(M. acrita)和花生根结线虫(M. arenaria)3个种组成的混合群体,南方根结线虫为优势种。     

Effect of Soils from Six Management Systems on Root-knot Nematodes and Plant Growth in Greenhouse Assays

The effects of soil management systems on root-knot nematode (Meloidogyne incognita) eggs and gall incidence on tomato (Lycopersicon esculentum) and cucumber (Cucumis sativus) following tomato were evaluated. Soil was collected from a replicated field experiment in which six management systems were being assessed for vegetable production. Soil management systems were conventional production, organic production, bahiagrass (Paspalum notatum) pasture, bahiagrass: Stylosanthes (Stylosanthes guianensis) pasture, bare ground fallow, and weed fallow. Soil was collected from field plots and used in greenhouse experiments. Identification of egg-parasitic fungi and the incidence of root-knot nematode galling were assessed both on tomato and cucumber planted in the same pots following the removal of tomato plants. Organic, bare ground fallow and conventional production treatments reduced galling both on tomato and on cucumber following tomato. Although no treatment consistently enhanced egg-parasitic fungi, management system did affect egg viability and the types of fungi isolated from parasitized eggs.     

High and Low Throughput Screens with Root-knot Nematodes Meloidogyne spp.

Root-knot nematodes (genus Meloidogyne) are obligate plant parasites. They are extremely polyphagous and considered one of the most economically important plant parasitic nematodes. The microscopic second-stage juvenile (J2), molted once in the egg, is the infective stage. The J2s hatch from the eggs, move freely in the soil within a film of water, and locate root tips of suitable plant species. After penetrating the plant root, they migrate towards the vascular cylinder where they establish a feeding site and initiate feeding using their stylets. The multicellular feeding site is comprised of several enlarged multinuclear cells called ''giant cells'' which are formed from cells that underwent karyokinesis (repeated mitosis) without cytokinesis. Neighboring pericycle cells divide and enlarge in size giving rise to a typical gall or root knot, the characteristic symptom of root-knot nematode infection. Once feeding is initiated, J2s become sedentary and undergo three additional molts to become adults. The adult female lays 150-250 eggs in a gelatinous matrix on or below the surface of the root. From the eggs new infective J2s hatch and start a new cycle. The root-knot nematode life cycle is completed in 4-6 weeks at 26-28°C.Here we present the traditional protocol to infect plants, grown in pots, with root-knot nematodes and two methods for high-throughput assays. The first high-throughput method is used for plants with small seeds such as tomato while the second is for plants with large seeds such as cowpea and common bean. Large seeds support extended seedling growth with minimal nutrient supplement. The first high throughput assay utilizes seedlings grown in sand in trays while in the second assay plants are grown in pouches in the absence of soil. The seedling growth pouch is made of a 15.5 x 12.5cm paper wick, folded at the top to form a 2-cm-deep trough in which the seed or seedling is placed. The paper wick is contained inside a transparent plastic pouch. These growth pouches allow direct observation of nematode infection symptoms, galling of roots and egg mass production, under the surface of a transparent pouch. Both methods allow the use of the screened plants, after phenotyping, for crossing or seed production. An additional advantage of the use of growth pouches is the small space requirement because pouches are stored in plastic hanging folders arranged in racks.     

Vertical Distribution of Plant-parasitic Nematodes in Sandy Soil under Soybean

Vertical distribution of five plant-parasitic nematodes was examined in two north Florida soybean fields in 1987 and 1988. Soil samples were collected from 0-15 cm, 15-30 cm, and 30-45 cm deep at each site. Soil at the three depths consisted of approximately 96% sand. More than 50% of Belonolaimus longicaudatus population densities occurred in the upper 15-cm soil layer at planting, but the species became more evenly distributed through the other depths as the season progressed. Criconemella sphaerocephala was evenly distributed among the three depths in one field but was low (< 20% of the total density) in the upper 15 cm at a second site. Maximum population densities of Pratylenchus brachyurus were observed at 15-30 cm on most sampling dates. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed seasonal variation. A diagnostic sample from the upper 0-15 cm of these soybean fields revealed only a minority of the populations of most of the phytoparasitic species present.     

七种我国昆虫病原线虫共生菌的分离与鉴定

昆虫病原线虫共生菌是一类具有广阔发展前景的生物防治资源,由于这类菌的分类鉴定工作起步晚,存在分类混乱和不系统的现象,在本土资源十分丰富的我国尤为突出.本文对本实验室分离的7个共生菌菌株进行了分类描述,建立了以生理形态,生化特征为分类基础,结合16 SrDNA序列分析的有效鉴定方法.     

七种我国昆虫病原线虫共生菌的分离与鉴定

昆虫病原线虫共生菌是一类具有广阔发展前景的生物防治资源, 由于这类菌的分类鉴定工作起步晚, 存在分类混乱和不系统的现象, 在本土资源十分丰富的我国尤为突出。本文对本实验室分离的7个共生菌菌株进行了分类描述, 建立了以生理形态, 生化特征为分类基础, 结合16S rDNA序列分析的有效鉴定方法。     

Distribution of Field Corn Roots and Parasitic Nematodes in Subsoiled and Nonsubsoiled Soil

A field trial was conducted for 2 years in an Arredondo fine sand containing a tillage pan at 15-20 cm deep to determine the influence of subsoiling on the distribution of corn roots and plant-parasitic nematodes. Soil samples were taken at various depths and row positions at 30, 60, and 90 days after planting in field corn subsoiled under the row with two chisels and in non-subsoiled corn. At 30 and 60 days, in-row nematode population densities to 60 cm deep were not affected by subsoiling compared with population densities in nonsubsoiled plots. After 90 days, subsoiling had not affected total root length or root weight at the 20 depth-row position sampling combinations, but population densities of Meloidogyne incognita and Criconemella spp. had increased in subsoiled corn. Numbers of Pratylenchus zeae were not affected. Subsoiling generally resulted in a change in distribution of corn roots and nematodes in the soil profile but caused little total increase in either roots or numbers of nematodes. Corn yield was increased by subsoiling.     

The Effects of Soil Salinity and Meloidogyne javanica on Tomato

A non-sodic, non-saline sandy loam soil was salinized to anion-cation ratios similar to those naturally occurring in Iraq and California. The interactions of saline soils (conductivities 4, 8, 12 and 16 mmhos/cm) with a moderately salt-tolerant plant (Lycopersicon esculentum ''Marimond'') and a plant parasitic nematode (Meloidogyne javanica) were investigated. Plant parasitic nematodes were shown to be an important modifying influence within the plant environment, either accentuating or ameliorating salinity stress effects.     

Management of Root-knot Nematodes by Phenamiphos Applied through an Irrigation Simulator with Various Amounts of Water

Phenamiphos (6.7 kg a.i./ha) was applied via an irrigation simulator to squash at planting (AP) and 2 weeks after planting (PP), and to corn AP and 1 week PP to manage root-knot nematodes (Meloidogyne incognita). The nematicide was applied with 0.25, 0.64, 1.27, and 1.91 cm surface water/ ha to a Lakeland sand in which the soil moisture was at or near field capacity. Based on efficacy and crop response, no additional benefits resulted when phenamiphos was applied in volumes of water greater than 0.25 crn/ha. The cost of applying each 0.25 cm of water over a hectare is approximately $1.08, or a 92% reduction in nematicide application cost over conventional methods ($13.50/ha). Low root-gall indices and high yields from squash and corn indicate more effective nematode management when phenamiphos was applied AP rather than PP. Results from this method of applying phenamiphos suggest that certain nematicides could be used as salvage alternatives when nematodes are detected in crops soon after planting. For multiple-pest management, nematicides, other compatible biocides, and fertilizers could be applied simultaneously with sprinkler irrigation.     

1株根结线虫拮抗放线菌新种的分离与鉴定

从海南东寨港红树林底泥中分离到206株放线菌。利用24孔板法进行抗线虫活性筛选,获得根结线虫拮抗菌HAlll66。该菌株16SrDNA序列与Nocardiopsis trehalosi VKM Ac-942^T相似性最高（98．3％）,并在系统发育树上聚为同一分支,二者DNA—DNA杂交率38．8％。形态和生理生化特征也表现出一定差异。基于表型与分子特征,鉴定菌株HA11166为Nocardiopsis属新种,命名为东寨港拟诺卡氏菌（Nocardiopsis dongzhaigangensis sp. nov. ）。     

Portable Cyst Extractor: Detecting Cyst Nematodes in the Field

For on-site detection of cysts, a portable cyst extraction kit was constructed from nine readily available items. The portable cyst extractor detected cysts in a range of 1-117 cysts/100 g soil from 42 fields. Samples processed by this kit in fields were clean and easy to examine, possibly because the kit is a compact version of the standard wet-sieving technique used in the laboratory. The portable cyst extractor has several advantages over traditional survey methods: i) diagnosis of cyst infestations in the field accurately and rapidly most of the year and ii) reduction in the labor of samplings and transportation of soil samples.     

Effects of Temperature and Root Leachates on Embryogenic Development and Hatching of Meloidogyne chitwoodi and M. hapla

At 20 C the duration of the embryogenic development of Meloiclogyne chitwoodi and M. hapla was about 20 days. At 10 C the embryogenic development was 82-84 days for M. chitwoodi and 95-97 days for M. hapla. The effect of distilled water and root leachates of potato cv. Russet Burbank, tomato cv. Columbian, and wheat cv. Hyslop on the hatching of eggs of the two root-knot nematode species was investigated at 4, 7, 10, 15, 20, and 25 C (± 1 C). Cumulative egg taatch was no greater in root leachates titan in distilled water, but temperature did significantly affect egg hatch (P = 0.05). Less than 1% of the eggs of both nematode species hatched at 4 C. The percent cumulative hatch at 10 C was significantly less (P = 0.05) than at higher temperatures for both nematodes and significantly more (P = 0.05) M. chitwoodi eggs hatched than did M. hapla eggs. At 15 G the percent cumulative hatch of both species was significantly lower (P = 0.05) than that at 20 and 25 C. The percent cumulative egg hatch of two species did not differ at 25 C, but was higher (P = 0.05) at 25 C than at 20 C. At 7 C the emergence of M. chitwoodi juveniles was about seven times (P = 0.01) greater than that of M. hapla in distilled water.     

Progression of Root-knot Nematode Symptoms and Infection on Resistant and Susceptible Cottons

Progressive development in cotton root morphology of resistant A623 and susceptible M-8 cotton (Gossypium hirsutum L.) lines following infection by the root-knot nematode Meloidogyne incognita was studied in glass front boxes. Symptom development and radicle growth were observed; degree of galling, gall and egg mass diameter, and number of eggs per egg mass were recorded; and root segments were examined histologically. Small cracks caused by M. incognita appeared in the root epidermis and cortex soon after the cotyledons expanded on day 4. The cracks were longer and wider and extended through the cortex when the first true leaf became visible at day 8. Galls had formed on taproots by this time. When exposed to M. incognita, A623 had faster radicle growth (22%), fewer and smaller cracks in the root epidermis and cortex, fewer and smaller root galls, one-twelfth as many egg masses, and one-fourth as many eggs per egg mass as M-8. Root cracking, galling, and giant cell formation are major effects of M. incognita that may predispose cotton roots to pathogens resulting in synergistic interactions and diseases.     

Competition between the Plant-parasitic Nematodes Pratylenchus neglectus and Meloidogyne chitwoodi

In experiments on competition between Pratylenchus neglectus and Meloidogyne chitwoodi in barley, the species that parasitized the roots first inhibited penetration by the latter species. Prior presence of P. neglectus impeded the development of M. chitwoodi. Pratylenchus neglectus reduced egg production, final population levels, and reproductive index of M. chitwoodi. The reduction was linearly related to initial population densities of P. neglectus. Initial population densities of M. chitwoodi had no effect on final population levels of P. neglectus. Carbon assimilation by barley plants was reduced when either nematode species was present alone, but not when both were present together. Both nematode species assimilated lower amounts of carbon when present together than when present alone. A split-root experiment demonstrated that translocatable chemicals were not involved in the competition between the two species.