Control of root-knot nematode,Meloidogyne incognita and reniform nematode,Rotylenchulus reniformis on pigeonpea and linseed

Abstract

Pigeonpea (Cajanus cajan) and linseed (Linum usitatissimum) are susceptible to Meloidogyne incognita and Rotylenchulus reniformis nematodes. Reduction in different growth parameters (length and weight of plant, number of pods), bulk density of pigeonpea stem, oil content of linseed, chlorophyll content of leaf and water absorption of roots caused by M. incognita and R. reniformis were statistically significant. Similar effects were also observed in plants raised from seeds soaked in different concentrations of water soluble fractions (WSF) of rice polish and pyridoxine solutions, however, the reductions were of a comparatively lesser extent. Higher concentrations of the solutions were more effective when compared to lower ones and pyridoxine was more beneficial than WSF for improving plant growth and reducing disease incidence.     

Extraction of Root-associated Meloidogyne incognita and Rotylenchulus reniformis

A technique based on physical maceration of root tissue was developed to extract vermiform and swollen stages of Meloidogyne incognita and Rotylenchulus reniformis. Experiments conducted on soybean and tomato evaluated the efficiency of method (stir, grind), NaOC1 concentration (0%, 0.5%), and duration (lx, 2x) on extraction of nematodes and eggs from 60-day-old populations. Root-associated populations of R. reniformis were considerably lower than those of M. incognita, so development of the method focused on the latter. Grinding liberated more nematodes than stirring, but the reverse was true for egg extraction. Among grinding treatments, a duration of 10 seconds in 0.5% NaOCl provided the most efficient extraction of nematodes and eggs. Among stirring treatments, a duration of 10 minutes in 0.5% NaOCl provided the most efficient extraction of eggs. These techniques were compared on soybean roots 30 days older than those on which the procedures were first evaluated, with consistent results.     

Tolerance to Rotylenchulus reniformis and Resistance to Meloidogyne incognita Race 3 in High-Yielding Breeding Lines of Upland Cotton

Field experiments in 1992 and 1994 were conducted to determine the effect of Rotylenchulus reniformis, reniform nematode, on lint yield and fiber quality of 10 experimental breeding lines of cotton (Gossypium hirsutum) in untreated plots or plots fumigated with 1,3-dichloropropene. Controls were La. RN 1032, a germplasm line possessing some resistance to R. reniformis, and Stoneville 453, a cultivar that is susceptible to reniform nematode. Several breeding lines produced greater lint yields than Stoneville 453 or La. RN 1032 in both fumigated and untreated plots. Average lint yield suppression due to R. reniformis for six of the 10 breeding lines was less than half of the 52% yield reduction sustained by Stoneville 453. In growth chamber experiments, R. reniformis multiplication factors for La. RN 1032 and breeding lines N222-1-91, N320-2-91, and N419-1-91 were significantly lower than on Deltapine 16 and Stoneville 453 at 6 weeks after inoculation. R. reniformis populations increased by more than 50-fold on all entries within 10 weeks. In growth chambers, the breeding lines N220-1-92, N222-1-91, and N320-2-91 were resistant to Meloidoglyne incognita race 3; multiplication factors were ≤1.0 at both 6 weeks and 10 weeks after inoculation compared with 25.8 and 26.5 for Deltapine 16 at 6 and 10 weeks after inoculation, respectively, and 9.1 and 2.6 for Stoneville 453. Thus, the results indicate that significant advances have been made in developing improved cotton germplasm lines with the potential to produce higher yields in soils infested with R. reniformis or M. incogaita. In addition to good yield potential, germplasm lines N222-1-91 and N320-2-91 appear to possess low levels of resistance to R. reniformis and a high level of resistance to M. incognita. This germplasm combines high yield potential with significant levels of resistance to both R. reniformis and M. incognita.     

Polarographische Bestimmung von Chlorat-Rückständen im Boden und in der Pflanze

An increase in the inoculum level of root‐knot nematode, Meloidogyne incognita and the reniform nematode, Rotylenchulus reniformis resulted in a relative decrease in plant growth parameters of chickpea. Consequently water absorption capability of roots was impaired. M. incognita caused greater reduction than R. reniformis at the same inoculum level. In concomitant inoculation of M. incognita and R. reniformis there was greater suppression in plant growth of chickpea. The suppression in concomitant inoculations was less than the sum of the suppression caused by the same levels of inoculations of the individual species. The multiplication rate of the nematodes decreased as the inoculum level increased. The results also suggest competition for feeding sites between the two nematode species. The multiplication rate of one species progressively decrease with the increase in the inoculum levels of the other nematode.     

Interrelations between Meloidogyne javanica,Rotylenchulus reniformis,and Rhizobium Sp. on Vigna sinensis

The interactions of Meloidogyne javanica, Rotylenchulus reniformis, and Rhizobium sp. on cowpea seedlings were investigated. Upon simultaneous inoculation with the two nematode species, M. javanica invaded first but did not affect root invasion by R. reniformis. M. javanica populations increased less in competition with R. reniformis than when present alone. Preinvasion by R. renilormis significantly suppressed the number of M. javanica in the roots. Inoculation of M. javanica and/or R. reniformis with rhizobia did not affect nodulation. Nodule formation was hindered only when R. reniformis infection preceded rhizobial inoculation. Nitrogen nodules were formed on M. javanica galls. Nodules and M. javanica galls served as infection sites for both nematodes. Although R. reniIormis on the roots reduced the space for M. javanica infection, M. javanica is more competitive than R. reniformis and ultimately predominates as a result of its higher reproductive potential and shorter time spent in the soil before infection.     

Effects of Acibenzolar-S-Methyl Application to Rotylenchulus reniformis and Meloidogyne javanica

Effects of acibenzolar-s-methyl, an inducer of systemic acquired resistance in plants, on Rotylenchulus reniformis and Meloidogyne javanica in vitro and in vivo were determined. A single foliar application of acibenzolar at 50 mg/liter (5 ml of solution per plant) to 7-day-old cowpea or soybean seedlings decreased R. reniformis and M. javanica egg production by 50% 30 days after inoculation. The mechanism of acibenzolar on plant-parasitic nematodes was then investigated. Acibenzolar at 50 to 200 mg/liter did not affect movement of R. reniformis and M. javanica or penetration of second-stage juveniles (J2) of M. javanica on cowpea. However, M. javanica development was slowed and fecundity was reduced in plants treated with acibenzolar. On average, 50% of J2 that penetrated acibenzolar-treated cowpeas developed into mature females with eggs, whereas the other 50% exhibited arrested development. The number of eggs per egg mass was 450 in water-treated cowpeas, whereas the number declined to 250 in acibenzolar-treated plants. Acibenzolar may be responsible for stimulating the plants to express some resistance to the nematodes.     

Cotton Root Protection from Plant-Parasitic Nematodes by Abamectin-Treated Seed

Abamectin is nematicidal to Meloidogyne incognita and Rotylenchulus reniformis, but the duration and length of cotton taproot protection from nematode infection by abamectin-treated seed is unknown. Based on the position of initial root-gall formation along the developing taproot from 21 to 35 d after planting, infection by M. incognita was reduced by abamectin seed treatment. Penetration of developing taproots by both nematode species was suppressed at taproot length of 5 cm by abamectin-treated seed, but root penetration increased rapidly with taproot development. Based on an assay of nematode mobility to measure abamectin toxicity, the mortality of M. incognita associated with a 2-d-old emerging cotton radicle was lower than mortality associated with the seed coat, indicating that more abamectin was on the seed coat than on the radicle. Thus, the limited protection of early stage root development suggested that only a small portion of abamectin applied to the seed was transferred to the developing root system.     

A screening technique to evaluate pigeonpea for resistance to Rotylenchulus reniformis*

Rotylenchulus reniformis is one of the most important nematode pests of pigeonpea. A simple greenhouse technique has been developed to aid evaluation of pigeonpea genotypes for resistance to R. reniformis. In greenhouse pot experiments, eggsacs of R. reniformis in pigeonpea (cv. ICPL 87) roots were counted by eye and with the aid of a stereoscopic microscope at 15, 30 and 45 days after seedling emergence in soils infested with various numbers of vermiform R. reniformis. Seedlings were rated for the number of eggsacs per root system on a one (no eggsacs) to nine (more than 50 eggsacs) scale. Eggsac ratings were more uniform when roots were evaluated at 30 – 45 days than at 15 days and an inoculum of 15 to 30 individuals/cm³ soil also helped reduce variability. Eggsacs were not easily visible without the aid of a stereoscopic microscope. Of the 14 stains tested, exposure of nematode-infected roots to 0.25% trypan blue for three min was effective in staining the eggsacs blue without staining the roots. Using the stain, the assessment of infestation by R. reniformis was equally accurate with or without the aid of a stereoscopic microscope. Exposure of eggsacs to trypan blue enhanced the emergence of juveniles from the eggsacs.     

Effects of Concomitant Development on Reproduction of Meloidogyne incognita and Rotylenchulus reniformis on Sweet Potato

The influence of various factors on reproduction of concomitant Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) on sweet potato were studied in the greenhouse. Reproduction of Rr was reduced by Mi at all inoculum levels and experiment durations used, while Mi reproduction was not inhibited. Both species failed to affect each other when inoculated simultaneously onto root systems developed in separate pots from different nodes of the same plant. Reproduction of each species was not significantly greater when inoculation of the second species was delayed 1-2 weeks compared to simultaneous inoculation. After shoot excision, Rr increased in the soil but Mi decreased. Fibrous root weights of plants inoculated with Rr + Mi in some tests were higher than those inoculated with Mi alone, indicating an early suppression of Mi and/or root stintulation by Rr. Drought stress delayed Rr egg hatching and movement of larvae into the soil, but had little effect on Mi reproduction.     

Relationship between Meloidogyne incognita and Rotylenchulus reniformis as Influenced by Soybean Genotype

The effect of soybean genotype on competition between Meloidogyne incognita race 2 (Mi) and Rotylenchulus reniformis (Rr) was evaluated in greenhouse and microplot replacement series experiments. Soil in pots containing seedlings of ''Davis'' (susceptible to Mi) or ''Buckshot 66'' (resistant to Mi) was infested with 1,000 vermiform individuals in the following Mi:Rr ratios: 0:0, 100:0, 75:25, 50:50, 25:75, or 0:100. After 91 days, the relative nematode yields (number of nematodes in mixed culture divided by the number in nonmixed culture) of each species were calculated based on soil and root nematode populations expressed as nematodes per gram of dry root tissue. To define the relationship between the two species, calculated relative nematode yields were compared with a theoretical noncompetition model using lack-of-fit regression. In the greenhouse, Mi populations on ''Davis'' were stimulated in the presence of Rr. In microplots, low Mi and Rr population densities likely resulted from severe galling and destruction of feeder roots that probably occurred early in the season. Enhanced susceptibility to Mi was not observed on ''Buckshot 66'', which remained resistant to Mi even when colonized by Rr. Host resistance is a key factor in determining the nature of the relationship between Mi and Rr.     

Effect of Temperature on the Embryogenesis of Geographic Populations of Rotylenchulus reniformis

The effect of temperature on the embryonic development of three populations of reniform nematode (Rotylenchulus reniformis) from the southeastern United States was studied. The development of eggs from single-cell stage to eclosion of second-stage juvenile was monitored at 20, 25, 30, and 35°C. All populations completed embryogenesis in 7 days at 25°C. The greatest differences among populations in time to completion of embryogenesis were observed at 20 and 35°C. Results at the intermediate temperatures (25 and 30°C) were similar for the three populations. The optimal temperature for embryogenesis was calculated to be 31.4°C for the population from Alabama, 28.4°C for the one from Mississippi, and 37.5°C for the one from South Carolina.     

Postinfection Development of Rotylenchulus reniformis on Resistant Gossypium barbadense Accessions

The reniform nematode (Rotylenchulus reniformis) causes significant cotton (Gossypium hirsutum) losses in the southeastern United States. The research objective was to describe the effects of two resistant G. barbadense lines (cultivar TX 110 and accession GB 713) on development and fecundity of reniform nematode. Nematode development and fecundity were evaluated on the resistant lines and susceptible G. hirsutum cultivar Deltapine 16 in three repeated growth chamber experiments. Nematode development on roots early and late in the infection cycle was measured at set intervals from 1 to 25 d after inoculation (DAI) and genotypes were compared based on the number of nematodes in four developmental stages (vermiform, swelling, reniform, and gravid). At 15, 20, and 25 DAI, egg production by individual females parasitizing each genotype was measured. Unique reniform nematode developmental patterns were noted on each of the cotton genotypes. During the early stages of infection, infection and development occurred 1 d faster on susceptible cotton than on the resistant genotypes. Later, progression to the reniform and gravid stages of development occurred first on the susceptible genotype, followed by G. barbadense cultivar TX 110, and finally G. barbadense accession GB 713. Egg production by individual nematodes infecting the three genotypes was similar. This study corroborates delayed development previously reported on G. barbadense cultivar TX 110 and is the first report of delayed infection and development associated with G. barbadense accession GB 713. The different developmental patterns in the resistant genotypes suggest that unique or additional loci may confer resistance in these two lines.     

Nematicides Enhance Growth and Yield of Rotylenchulus Reniformis Resistant Cotton Genotypes

Rotylenchulus reniformis resistant LONREN-1×FM966 breeding lines developed at Auburn University have demonstrated that the nematode resistance is accompanied by severe stunting, limited growth, and low yields. The objectives of this study were to evaluate the effects of applying nematicides to selected LONREN breeding lines on R. reniformis nematode populations, plant stunting, and yield. Four resistant breeding lines from the LONREN-1×FM966 cross, one susceptible line from the LONREN-1×FM966 cross, as well as LONREN-1, BARBREN-713, and the susceptible cultivar DP393 were evaluated with and without nematicides in the presence of R. reniformis. In the greenhouse, nematicides increased plant height across all genotypes compared with no nematicide. Rotylenchulus reniformis populations were 50% lower in the resistant lines compared with the susceptible lines at 45 days after planting (DAP). In microplot and field trials, the phenotypic stunting of all genotypes was reduced by aldicarb with increases in plant heights at 30 and 75 DAP. Increases in yields were evident across all genotypes treated with aldicarb. In all three trial environments, BARBREN-713 outperformed the LONREN-derived lines as well as ‘DP393’ in seed cotton yields, while having significantly lower R. reniformis egg densities than the susceptible genotypes.     

Rice root-knot nematode (Meloidogyne graminicola) infestation in rice

Rice (Oryza sativa) is an important staple food crop for majority of human population in the world in general and in Asia in particular. However, among various pests and diseases which constitute important constraints in the successful crop production, plant parasitic nematodes play an important role and account for yield losses to the extent of 90%. The major nematode pests associated with rice are Ditylenchus angustus, Aphelenchoides besseyi, Hirschmanniella spp., Heterodera oryzicola and Meloidogyne graminicola. However, rice root-knot nematode (M. graminicola) happens to be the most important pest and is prevalent in major rice producing countries of the world. In India, the distribution of M. graminicola in rice growing areas of different states has been documented in nematode distribution atlas prepared by All India Coordinated Research Project (Nematodes) and published by Directorate of Information and Publications of Agriculture, Indian Council of Agricultural Research, New Delhi, India during 2010. M. graminicola affected rice plants show stunting and chlorosis due to the characteristic terminal swellings/galls on the roots which ultimately result in severe reduction in growth and yield. Number of eco-friendly management technologies against M. graminicola have been developed and demonstrated, including the use of bioagents for minimising the losses due to rice root-knot nematode. This review is focused on collating information to understand the current scenario of rice root-knot nematodes with greater emphasis on its ecological requirements, damage symptoms, biology, morphology, host range and management strategies.