Search

This study employed single nucleotide polymorphisms (SNPs) to determine the genetic variability present in 26 isolates of Rotylenchulus reniformis from Louisiana, Mississippi, Arkansas, South Carolina, Georgia, Hawaii, and Alabama. Genomic DNA from reniform nematode was extracted and increased quantitatively using the process of whole genome amplification. More than 162 putative SNPs were identified, 31 of which were tested using a KASP kompetitive allele-specific PCR genotyping assay. Of the SNPs tested, 13, 17, and 19 SNPs revealed genetic variability within reniform nematode isolates from Louisiana, Mississippi, and Arkansas, respectively. Seven SNPs elucidated genetic differences among isolates of reniform nematode from Louisiana, Mississippi, and Arkansas. Eight SNPs determined genetic variability among individual isolates from South Carolina, Georgia, Hawaii, and Alabama. This study is the first to report genetic variability in geographic isolates of reniform nematode employing a SNP assay. This study also demonstrated that SNP markers can be used to evaluate isolates of R. reniformis and could be useful to assess their genetic diversity, origin, and distribution. Such information would be extremely useful in resistance breeding programs.

The factors that influence the ability of cotton to minimize yield loss despite parasitism by Rotylenchulus reniformis (i.e., tolerance) were evaluated for 12 cotton genotypes. Reproduction of R. reniformis and total length of the root system were measured under greenhouse conditions, and the relationship of those variables to yield loss caused by R. reniformis in infested fields was evaluated. Values for nematodes per gram of root and root length were standardized by setting the genotype with greatest value as 100% and then calculating a percentage for each genotype. There was significant variability among genotypes in yield loss, resistance, and root length. Average yield loss for the genotypes ranged from 10.4% for IAC 26RMD to 43.2% for IMACD 5675B2RF. The least nematode reproduction was on IAC 26RMD, which had 49.6% of the reproduction on the susceptible check, Deltapine 16. The genotype with the shortest total root length was 34% less than the genotype with the greatest length. There was a significant linear relationship between percentage yield loss caused by R. reniformis and root length and nematodes per gram of root, both expressed as a percentage of the maximum, represented by the following equation: Yield loss (%) = 16.1258 – 0.1918*(% maximum root length) + 0.3728*(% maximum eggs + vermiform/g of roots). We conclude that tolerance to R. reniformis in cotton is influenced by the size of the root system and the parasitic load on the plant (nematodes per gram of root). Management approaches that increase root growth may lower the parasitic load, thereby reducing losses in cotton to R. reniformis.

In Virginia during September 2002, the reniform nematode, Rotylenchulus reniformis Linford and Oliveira (1), was found for the first time following a grower's concern about poor growth and yield of cotton (Gossypium hirsutum L.) cv. Fiber Max 989BR. The infested field was planted with cotton each year for the last eight growing seasons. The field was located on Hall Road in Southampton County, Virginia at coordinates 77°16′28.8926″W, 36°37′10.6428″N near the town of Branchville. The soil was loamy sand, which is typical of sandy textured soils in the region. Rainfall from May to September at a nearby weather station was nearly 50% below normal, which may have contributed to the suppression of plant growth. The vermiform nematodes were extracted with a North Carolina State University model semiautomatic elutriator and centrifugation/sugar flotation. Populations were 30 to 150 per 500 cm3 of soil in areas with noticeable stunting. Cultures were established on cotton cv. Delta Pine 64 and tomato (Lycopersicon esculentum Mill. cv. Rutgers) and were maintained in a greenhouse. Reproduction was moderate on cotton and high on tomato. Identifications were based on morphology and measurements of vermiform females and males: immature female length (L) = 407 ± 22 (376 to 418) μm, stylet L = 18.5+1.7 (17.0 to 21.3) μm; and male L = 351 ± 17 (339 to 367) μm. Voucher specimens were placed and are maintained in the Virginia Tech Nematode Collection. Reference: (1) M. B. Linford and J. M. Oliveira. Proc. Helminthol. Soc. Wash. 7:35, 1940.

14 pages, 13 figures., Chickpea (Cicer arietinum) is a cool-season food legume second in importance as a pulse crop in the world after beans (Phaseolus vulgaris). It is an important protein source in many regions of the semi-arid tropics. Chickpea is grown in 47 countries and is a significant component of subsistence cropping systems for farmers in the Indian Subcontinent, West Asia, the Mediterranean Basin, and certain areas of East and North Africa. More than 90% of the chickpea crops are grown in eight countries, including India, Pakistan, Iran, Turkey, Ethiopia, Mexico, Australia and Canada, in decreasing order., Many species of plant-parasitic nematodes have been reported in the roots and rhizosphere of chickpea in the major growing regions in the world (Table 1). However, only certain nematode species are considered constraints to chickpea production, causing an estimated 14% in annual yield losses (61,68). The symptoms and signs of nematode parasitism on chickpea differ depending upon the nematode’s feeding habit. Moreover, nematode attacks can make plants more sensitive to other biotic and abiotic stresses, and overall result in stunting and poor yield., Original results from the authors reported in this article were derived from research supported by grants (AGL2003-0640, AGL2004-01231) from Dirección General de Investigación, Ministerio de Educación y Ciencia, Spain.

Reniform nematode (Rotylenchulus reniformis) is a relatively recent introduction into the continental United States that can cause major yield losses on a variety of important crops including cotton and soybeans. DNA sequences from the internal transcribed spacer (ITS) region of this nematode were used to design primers for conventional and real-time PCR, as well as a TaqMan probe. These primers amplified DNA of reniform nematode isolates from a wide geographic range but did not detect genetically related species or other pathogenic nematodes found in production fields including Meloidogyne incognita and Heterodera glycines. Both SYBR green and TaqMan assays reliably quantified as little as 100 fg of reniform nematode DNA, and could be used to quantify as few as five reniform nematodes. An inexpensive and rapid DNA extraction protocol for high throughput diagnostic assays is described.

Rotylenchulus reniformis, reniform nematode, is a polyphagous pest commonly found parasitizing cotton in the southeastern United States. We developed and optimized 10 polymorphic microsatellite loci found in reniform nematode and tested them on 160 individual reniform nematodes to determine informative genetic variation of isolates from the southeastern United States, Colombia, Japan, and from the species Rotylenchulus parvus. No significant gametic disequilibrium was detected between any pair of loci, and most loci were not in expected Hardy-Weinberg proportions. A positive FIS coefficient was observed at all 10 loci, suggesting a high level of inbreeding at these loci. Most isolate locations exhibited significant genotypic differentiation and moderate to very high genetic differentiation based on FST analysis. The most consistently differentiated isolates were found reproducing parthenogenetically in Japan. These isolates were also found to represent the most basal locality in this study based on unweighted pair group method with arithmetic mean (UPGMA) clustering analysis and were distinct from other localities based on STRUCTURE V 2.3 analysis. These results support previous reports suggesting that the parthenogenetically reproducing isolates from Japan are another species. Taken together, our results can serve as the foundation for more extensive characterization of population structure and genetic variation among isolates of R. reniformis variants to help discern the impact of alternative processes on genetic connectivity and differentiation in the genetically undercharacterized reniform nematode.

Leach, M., Agudelo, P., and Lawton-Rauh, A. 2012. Effect of crop rotations on Rotylenchulus reniformis population structure. Plant Dis. 96:24-29. Rotylenchulus reniformis is a highly variable nematode species and an economically important pest in many cotton fields across the southeastern United States. Rotation with resistant or poor host crops is a method for management of reniform nematode. We studied the effect of six planting schemes covering four 120-day planting cycles on the predominant genotype of R. reniformis. Rotations used were: (i) cotton to corn; (ii) susceptible soybean to corn; (iii) resistant soybean to cotton; (iv) corn to cotton; (v) continuous susceptible soybean; (vi) continuous cotton. After each 120-day cycle, amplified fragment length polymorphisms (AFLPs) produced from four primer pairs were used to determine the effect of crop rotation on the predominant genotype of reniform nematode. A total of 279 polymorphic bands were scored using four primer combinations. Distinct changes in genotype composition were observed following rotations with resistant soybean or corn. Rotations involving soybean (susceptible and resistant) had the greatest effect on population structure. The characterization of field population variability of reniform nematode and of population responses to host plants used in rotations can help extend the durability of resistant varieties and can help identify effective rotation schemes.

A new fungal parasite of the reniform nematode has been observed parasitizing nematode populations that have increased on cotton in a sandy loam field soil in the greenhouse. When enumerated, 46% of the stock reniform nematode population was colonized by this fungus. Egg, vermiform, and adult stages of the reniform nematode were observed with light microscopy and scanning electron micrography (SEM). The nematophagous fungus, Catenaria auxiliaries, was identified morphologically. There are no sequences on the GenBank to achieve a molecular identification. This nematophagous fungus has been previously reported on the beet cyst nematode in Europe (1,2); however, to our knowledge there are no reports of this fungus parasitizing the reniform nematode. In vermiform life stages of the nematode, rhizomycelium is observed in the initial phase of infection and is characterized by ovoid cells, 9.5 to 13.5 × 17.0 to 24.5 μm in diameter, separated by septa. Usually 10 to 15 ovoid cells lacking intercellular hyphal filaments are produced within each vermiform body. Rhizoids 3.5 to 4.0 μm wide develop from the rhizomycelium. Mature swollen cells produce precursor sporangia that may mature into resting spores or zoosporangia. Resting spores are yellow-to-cream, 20 to 40 μm in diameter with a reticulate appearance, and are common in the vermiform nematode life stages. Zoosporangia are ovoid, 9.5 to 13.5 × 17.0 to 24.5 μm, and will erupt from the cuticle of the vermiform nematode releasing zoospores via papillae. Zoospores are 2.9 to 4.9 μm with visible globules in the anterior region and single flagella that are 9 to 11 μm long. The zoospores swim short distances, maneuvering in the direction of the flagellum. Adult reniform females observed through SEM exhibit zoospores encysted in the metacorpus region of the nematode. Parasitized eggs are internally colonized with zoosporangia that are 20 to 25 μm in diameter. In advanced stages of infection, the eggs darken in color and zoosporangia erupt through the cuticle of the egg. Reniform nematodes visibly colonized with zoosporangia and resting spores were placed on corn meal, water, and potato dextrose agars. None of these media supported growth of the fungus, supporting our theory that this organism appears to be an obligate parasite of the nematode. Koch's postulates was completed when eggs colonized with rhizomycelium and resting spores or zoosporangia were added to cotton plants in sterile soil previously inoculated with 2,000 healthy vermiform reniform life stages. Plants were allowed to grow for 30 days in the greenhouse after which the next generation of vermiform nematodes were extracted from the soil and examined under the microscope. Rhizomycelium, resting spores, and zoosporangia were present in 42% of the reniform vermiform life stages. Morphological comparisons of the rhizomycelium, resting spores or zoosporangia, and zoospores colonizing the reniform nematodes were similar to the initial observations. Thus to our knowledge, this is the first report of Catenaria auxiliaries parasitizing the reniform nematode. References: (1) B. Kerry. J. Nematol. 12:253, 1980. (2) H. T. Tribe. Trans. Br. Mycol. Soc. 69:367, 1977.

An emulsifiable formulation of 1,3-dichloropropene (1,3-D SL) was tested for efficacy against Rotylenchulus reniformis, the reniform nematode, in pots and in the field. Nematode population densities were reduced by 50% at 25 μg a.i. per g of soil in pot trials. In the field, efficacy (posttreatment numbers divided by pretreatment numbers) was similar between 1,3-D SL and 1,3-D VL (volatile liquid) at 407 kg a.i./ha. At 204 kg a.i./ha, 1,3-D SL was less effective than 1,3-D SL or VL at 407 kg a.i./ha in controlling the nematode but gave better control than no treatment (P < 0.05). Postplant application of 113 kg a.i. 1,3-D SL per ha did not provide sufficient nematode control to prevent yield reduction compared with a postplant fenamiphos (1.7 kg a.i./ha) treatment. Preplant fumigation with 1,3-D reduced the numbers of reniform nematode, but the population resurged within 10 months. Thereafter, regardless of nematicide, soil population densities of R. reniformis did not differ among treatments.

Sharma, S. B. 1995. Resistance to Rotylenchulus reniformis, Heterodera cajani, and Meloidogyne javanica in accessions of Cajanus platycarpus. Plant Dis. 79:1033-1035. Rotylenchulus reniformis, Heterodera cajani, and Meloidogyne javanica are important nematode pathogens of pigeonpea (Cajanus cajan), a legume crop cultivated widely in the semiarid tropics. Accessions of Cajanus platycarpus, a wild relative of pigeonpea, were evaluated in the greenhouse for resistance to R. reniformis race A, H. cajani, and M. javanica races 1 and 3. Two accessions, ICPWs 60 and 62, were resistant to R. reniformis race A. ICPWs 62, 69, and 70 were resistant to H. cajani. All the accessions were susceptible to M. javanica races. Race I produced bigger galls than those produced by race 3. ICPW 64 had lower damage indices (7.7 for race 1, and 5.4 for race 3) than other accessions. ICPW 62 was the only accession with resistance to two nematode species, H. cajani and R. reniformis. Seed of ICPWs 62, 69, and 70 with high levels of resistance to H. cajani were collected and multiplied. These lines will be useful in breeding programs as well as in research to obtain an understanding of the mechanism of resistance.

Approximately 5% of the cotton hectarage in each of 16 counties in South Carolina was sampled in a postharvest survey of 1,219 cotton fields during 1989-1992. Eleven species of plant-parasitic nematodes were recovered from soil samples. Hoplolaimus columbus, Meloidogyne spp., and Rotylenchulus reniformis were recovered from 61, 25, and 12%, respectively, of samples. H. columbus and Meloidogyne spp. were found in all 16 counties, but R. reniformis was found in only 11. Populations of H. columbus were in excess of damage thresholds in 37% of fields, of Meloidogyne spp. in 7% of fields, and of R. reniformis in 3% of fields [...]

Wheat varieties Arthur 71, Coker 747, Coker 6815, Delta Queen, Double Crop, Florida 301, McNair 1813, McNair 1003, and Southern Belle were resistant to the root-knot nematode, Meloidogyne incognita. Sorghum varieties Funk G 421, Funk G 499 BR, Funk G 516 BR, Funk G 522 A, Funk G 522 BR, Funk G 550, Funk G 611, Funk G 623, and DeKalb D 55 were susceptible to M. incognita. All wheat and sorghum varieties tested were nonhosts of the reniform nematode, Rotylenchulus reniformis