Penetration of Crotalaria juncea,Dolichos lablab,and Sesamum indicum Roots by Meloidogyne javanica

Penetration of Crotalaria juncea (PI 207657 and cv. Tropic Sun) Dolichos lablab cv. Highworth, and Sesamum indicum by juveniles (J2) of Meloidogyne javanica was assessed to investigate the mechanism by which these plants may reduce nematode numbers in the field. Growth chamber experiments were conducted at 25 C, with vials containing 90 g sand infested with 450 J2; tomato (UC 204 C) was included as a susceptible host. Fifteen days after inoculation, roots were stained and the nematodes within stained roots were counted. Both C. juncea lines were highly resistant to penetration, as they contained significantly fewer nematodes per cm of root and per root system than the other plants. Although containing more nematodes per cm of root than C. juncea, S. indicum and D. lablab had significantly fewer nematodes per root system and per cm of root than tomato. Roots were significantly longer in the plants with the lowest nematode penetration. Although C. juncea, D. lablab, and S. indicum may have potential utility as cover or rotation crops in soil infested with M. javanica, further quantitative information on the reproduction of M. javanica and other nematodes in these plants is needed.     

Resistance of Interspecific Arachis Breeding Lines to Meloidogyne javanica and an Undescribed Meloidogyne Species

Resistance to a peanut-parasitic population of Meloidogyne javanica and an undescribed Meloidogyne sp. in peanut breeding lines selected for resistance to Meloidogyne javanica was examined in greenhouse tests. The interspecific hybrid TxAG-7 was resistant to reproduction of Meloidogyne javanica, M. javanica, and Meloidogyne sp. An Meloidogyne javanica-resistant selection from the second backcross (BC) of TxAG-7 to the susceptible cultivar Florunner also was resistant to M. javanica but appeared to be segregating for resistance to the Meloidogyne sp. When reproduction of M. javanica and Meloidogyne javanica were compared on five BC4F3 peanut breeding lines, each derived from Meloidogyne javanica-susceptible BC4F2 individuals, all five lines segregated for resistance to M. javanica, whereas four of the lines appeared to be susceptible to Meloidogyne javanica. These data indicate that several peanut lines selected for resistance to Meloidogyne javanica also contain genes for resistance to populations of M. javanica and the undescribed Meloidogyne sp. that are parasitic on peanut. Further, differences in segregation patterns suggest that resistance to each Meloidogyne sp. is conditioned by different genes.     

Meloidogyne javanica Parasitic on Peanut

Peanut fields in four governorates of Egypt were surveyed to identify species of Meloidogyne present. Fourteen populations obtained from peanut roots were all identified as M. javanica based on perineal patterns, stylet and body lengths of second-stage juveniles, esterase phenotypes, and restriction fragment length polymorphisms of mtDNA. Three of 14 populations, all from contiguous fields in the Behara governorate, had individuals with a unique two-isozyme esterase phenotype. All populations of M. javanica tested on peanut had levels of reproduction on the M. arenaria-susceptible peanut cultivar Florunner that were not different from M. arenaria (P = 0.05), and had lower levels of reproduction on the M. arenaria-resistant genotype TxAG-7 than on Florunner (P = 0.05). Reproduction of the five Egyptian populations of M. javanica tested was lower on root-knot nematode resistant tomato cultivars Better Boy and Celebrity than on the root-knot nematode susceptible cultivar Rutgers (P = 0.05). These data are evidence that some populations of M. javanica are parasitic on peanut and that the peanut and tomato genotypes resistant to M. arenaria are also resistant to these populations of M. javanica.     

Meloidogyne javanica on Peanut in Florida

A mixed population of Meloidogyne arenaria race 1 and M. javanica race 3 is reported on peanut from a field in Levy County, Florida. Confirmation of M. javanica on peanut is based on esterase and malate dehydrogenase isozyme patterns resolved on polyacrylamide slab gels following electrophoresis, and perineal patterns. Up to 29% of 290 individual females collected from peanut roots in the field in autumn 2002 showed a typical esterase J3 phenotype for M. javanica. This is the third report of M. javanica infecting peanut in the United States.     

Host Status of Endophyte-Infected and Noninfected Tall Fescue Grass to Meloidogyne spp

Tall fescue grass cultivars with or without endophytes were evaluated for their susceptibility to Meloidogyne incognita in the greenhouse. Tall fescue cultivars evaluated included, i) wild-type Jesup (E+, ergot-producing endophyte present), ii) endophyte-free Jesup (E-, no endophyte present), iii) Jesup (Max-Q, non-ergot producing endophyte) and iv) Georgia 5 (E+). Peach was included as the control. Peach supported greater (P ≤ 0.05) reproduction of M. incognita than all tall fescue cultivars. Differences in reproduction were not detected among the tall fescue cultivars and all cultivars were rated as either poor or nonhosts for M. incognita. Suppression of M. incognita reproduction was not influenced by endophyte status. In two other greenhouse experiments, host susceptibility of tall fescue grasses to two M. incognita isolates (BY-peach isolate and GA-peach isolate) did not appear to be related to fungal endophyte strain [i.e., Jesup (Max-Q; nontoxic endophyte strain) vs. Bulldog 51 (toxic endophyte strain)]. Host status of tall fescue varied with species of root-knot nematode. Jesup (Max-Q) was rated as a nonhost for M. incognita (BY-peach isolate and GA-peach isolate) and M. hapla, a poor host for M. javanica and a good host for M. arenaria. Bulldog 51 tall fescue was also a good host for M. arenaria and M. javanica, but not M. incognita. Jesup (Max-Q) tall fescue may have potential as a preplant control strategy for M. incognita and M. hapla in southeastern and northeastern United States, respectively.     

Morphological Comparison of Three Host Races of Meloidogyne javanica

A morphological and morphometric comparison using light microscopy and scanning electron microscopy was made of six populations of Meloidogyne javanica belonging to three host races (infective on pepper, peanut, or noninfective on both). The variability of certain morphological characters was studied within these populations, and the reliability of these taxonomic traits was evaluated for usefulness in species identification. The most useful diagnostic characters of M. javanica were head and stylet morphology of males and stylet morphology and perineal patterns of females. Males have an offset head region, usually lacking annulations, and a distinct, narrow head cap with slightly raised labial disc. The stylet has a cone markedly wider than the shaft at the junction and large, transversely ovoid knobs that are offset from the shaft. Females have a robust stylet with a dorsally curved cone and large, transversely ovoid knobs. Perineal patterns are oval to squarish in shape, usually with coarse, broken striae and with conspicuous lateral lines. The host races could not be differentiated on a morphological basis.     

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.     

Reproduction and Development of Meloidogyne incognita and M. javanica on Guardian Peach Rootstock

Guardian peach rootstock was evaluated for susceptibility to Meloidogyne incognita race 3 (Georgia-peach isolate) and M. javanica in the greenhouse. Both commercial Guardian seed sources produced plants that were poor hosts of M. incognita and M. javanica. Reproduction as measured by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root were a better measure of host resistance than number of root galls per plant. Penetration, development, and reproduction of M. incognita in Guardian (resistant) and Lovell (susceptible) peach were also studied in the greenhouse. Differences in susceptibility were not attributed to differential penetration by the infectivestage juveniles (J2) or the number of root galls per plant. Results indicated that M. incognita J2 penetrated Guardian roots and formed galls, but that the majority of the nematodes failed to mature and reproduce.     

Influence of Inoculum Density,Host, and Low-temperature Period on Delayed Hatch of Meloidogyne javanica Eggs

Most eggs of M. javanica hatch within several days when incubated in water. Those that do not are said to show delayed hatching. Several experiments were conducted to determine the effect of specific conditions on the percentage of eggs with delayed hatch. Six initial inoculum densities ranging from 100 to 20,000 eggs per pot did not influence egg hatch within a 45-day incubation period. In a 60-day test, the percentage of eggs hatching after more than 20 days was low for egg masses removed from carrot and okra and high for those from pepper and bean. Increasing exposure to cold temperature (8 C) from 7 to 30 days tended to delay hatch.     

Sensitive PCR Detection of Meloidogyne arenaria, M. incognita, and M. javanica Extracted from Soil

We have developed a simple PCR assay protocol for detection of the root-knot nematode (RKN) species Meloidogyne arenaria, M. incognita, and M. javanica extracted from soil. Nematodes are extracted from soil using Baermann funnels and centrifugal flotation. The nematode-containing fraction is then digested with proteinase K, and a PCR assay is carried out with primers specific for this group of RKN and with universal primers spanning the ITS of rRNA genes. The presence of RKN J2 can be detected among large numbers of other plant-parasitic and free-living nematodes. The procedure was tested with several soil types and crops from different locations and was found to be sensitive and accurate. Analysis of unknowns and spiked soil samples indicated that detection sensitivity was the same as or higher than by microscopic examination.     

Interaction of Meloidogyne javanica with Different Races of Meloidogyne incognita

The interspecific interactions of Meloidogyne javanica with races 1, 2, 3, and 4 of M. incognita on tomato were determined. Impacts of the interactions on fecundity and morphometrics of females were also examined. Mutually inhibitory interactions occurred between M. javanica and the races of M. incognita, but the negative interactions did not reflect in plant growth. Numbers of root galls, egg masses, mature females, total population, fecundity, and reproduction factor declined in concomitant treatments, but the morphometrics of the females remained unaltered. In general, mutual suppressive effects in all parameters were smaller for M. javanica than M. incognita, but some variations occurred among the races of M. incognita. Race 2 appeared to be more competitive than other races. The interaction between the species was not intense; therefore, the species coexist in mixed populations in agricultural fields.     

Pepper Rootstock Graft Compatibility and Response to Meloidogyne javanica and M. incognita

Resistance of pepper species (Capsicum annuum, C. baccatum, C. chinense, C. chacoense, and C. frutescens), cultivars and accessions to the root-knot nematodes Meloidogyne incognita race 2 and M. javanica, and their graft compatibility with commercial pepper varieties as rootstocks were evaluated in growth chamber and greenhouse experiments. Most of the plants tested were highly resistant to M. javanica but susceptible to M. incognita. Capsicum annuum AR-96023 and C. frutescens accessions as rootstocks showed moderate and relatively high resistance to M. incognita, respectively. In M. incognita-infested soil in a greenhouse, AR-96023 supported approximately 6-fold less nematode eggs per gram root and produced about 2-fold greater yield compared to a nongrafted commercial variety. The commercial variety grafted on AR-96023 produced a yield as great as the non-grafted variety in the root-knot nematode-free greenhouse. Some resistant varieties and accessions used as rootstocks produced lower yields (P < 0.01) than that of the non-grafted variety in the noninfested greenhouse. Use of rootstocks with nematode-resistance and graft compatibility may be effective for control of root-knot nematodes on susceptible pepper.     

Control of Meloidogyne javanica by Formulations of Inula viscosa Leaf Extracts

Inula viscosa is a perennial plant that is widely distributed in Mediterranean countries. Formulations of I. viscosa extracts were tested for their effectiveness in control of Meloidogyne javanica in laboratory, growth chamber, microplot, and field experiments. Oily pastes were obtained by extraction of dry leaves with a mixture of acetone and n-hexane or n-hexane alone, followed by evaporation of the solvents. Emulsifiable concentrate formulations of the pastes killed M. javanica juveniles in sand at a concentration of 0.01% (paste, w/w) or greater and reduced the galling index of cucumber seedlings as well as the galling index and numbers of nematode eggs on tomato plants in growth chamber experiments. In microplot experiments, the hexane-extract formulation at 26 g paste/m² reduced nematode infection on tomato plants in one of two experiments. In a field experiment, a reduction of 40% in root galling index by one of two formulations was observed on lettuce plants. The plant extracts have potential as a natural nematicide, although the formulations need improvement.     

Carbon Partitioning in Soybean Infected with Meloidogyne incognita and M. javanica

Seven-day-old seedlings of two cultivars (Cristalina and UFV ITM1) of Glycine max were inoculated with 0, 3,000, 9,000, or 27,000 eggs of Meloidogyne incognita race 3 or M. javanica and maintained in a greenhouse. Thirty days later, plants were exposed to ¹⁴CO₂ for 4 hours. Twenty hours after ¹⁴CO₂ exposure, the root fresh weight, leaf dry weight, nematode eggs per gram of root, total and specific radioactivity of carbohydrates in roots, and root carbohydrate content were evaluated. Meloidogyne javanica produced more eggs than M. incognita on both varieties. A general increase in root weight and a decrease in leaf weight with increased inoculum levels were observed. Gall tissue appeared to account for most of the root mass increase in seedlings infected with M. javanica. For both nematodes there was an increase of total radioactivity in the root system with increased levels of nematodes, and this was positively related to the number of eggs per gram fresh weight and to the root fresh weight, but negatively related to leaf dry weight. In most cases, specific radioactivities of sucrose and reducing sugars were also increased with increased inoculum levels. Highest specific radioactivities were observed with reducing sugars. Although significant changes were not observed in endogenous levels of carbohydrates, sucrose content was higher than reducing sugars. The data show that nematodes are strong metabolic sinks and significantly change the carbon distribution pattern in infected soybean plants. Carbon partitioning in plants infected with nematodes may vary with the nematode genotype.     

Reproduction of Belonolaimus longicaudatus,Meloidogyne javanica,Paratrichodorus minor,and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum)

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid ''TifGrain 102'' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet (''HGM-100'' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.     

Evidence for a Dosage Effect of the Mi gene on Partially Virulent Isolates of Meloidogyne javanica

The reproduction of single egg-mass isolates of Meloidogyne javanica from Crete that differed in virulence were compared on tomato (Lycopersicon esculentum) genotypes homozygous or heterozygous for the Mi gene. The reproduction of three isolates with partial virulence was much greater on tomato genotypes heterozygous for the Mi gene (cultivars Scala, Bermuda, and 7353) than on two homozygous genotypes (F8 inbred lines derived from Scala). The reproduction of a highly virulent isolate on the homozygous and heterozygous genotypes was similar to that on a susceptible cultivar. These results pose questions regarding the nature of partial virulence and indicate a quantitative effect of the Mi gene in relation to such virulence.     

Relative Virulence of Meloidogyne incognita Host Races on Soybean

Sensitivity and host efficiency of susceptible (''Lee 68'', ''Coker 156'') and resistant (''Bragg'', ''Centennial'', ''Forrest'', ''Lee 74'') soybean (Glycine max (L.) Merr.) cultivars for races of Meloidogyne incognita (Mi) were determined in greenhouse experiments. Eight Mi populations collected from the southeastern United States were utilized. All Mi races reproduced readily on Lee 68 and Lee 74 and moderately on Forrest and Bragg. Coker 156 exhibited resistance to races 1 and 2, and some race 3 populations, but was very susceptible to certain race 3 and 4 populations. Reproduction of all races was lowest on Centennial. Forrest and Centennial shoot growth was not significantly suppressed by any race. There were no distinct differences in virulence between races except for a race 3 population which reproduced readily on all cultivars, stunting their growth. Considerable variation in reproduction existed within races 1 and 3.     

Induced Resistance to Meloidogyne hapla by other Meloidogyne species on Tomato and Pyrethrum Plants

Advance inoculation of the tomato cv. Celebrity or the pyrethrum clone 223 with host-incompatible Meloidogyne incognita or M. javanica elicited induced resistance to host-compatible M. hapla in pot and field experiments. Induced resistance increased with the length of the time between inoculations and with the population density of the induction inoculum. Optimum interval before challenge inoculation, or population density of inoculum for inducing resistance, was 10 days, or 5,000 infective nematodes per 500-cm³ pot. The induced resistance suppressed population increase of M. hapla by 84% on potted tomato, 72% on potted pyrethrum, and 55% on field-grown pyrethrum seedlings, relative to unprotected treatments. Pyrethrum seedlings inoculated with M. javanica 10 days before infection with M. hapla were not stunted, whereas those that did not receive the advance inoculum were stunted 33% in pots and 36% in field plots. The results indicated that advance infection of plants with incompatible or mildly virulent nematode species induced resistance to normally compatible nematodes and that the induced resistance response may have potential as a biological control method for plant nematodes.     

Effects of Etomopathiogenic Nematodes on Meloidogyne javanica on Tomatoes and Soybeans

Two Hawaiian isolates of Steinernema feltiae MG-14 and Heterohabditis indica MG-13, a French isolate of S. feltiae SN, and a Texan isolate of S. riobrave TX were tested for their efficacy against the root-knot nematode, Meloidogyne javanica, in the laboratory and greenhouse. Experiments were conducted to investigate the effects of treatment application time and dose on M. javanica penetration in soybean, and egg production and plant development in tomato. Two experiments conducted to assess the effects of entomopathogenic nematode application time on M. javanica penetration demonstrated that a single application of 10⁴ S. feltiae MG-14 or SN infective juveniles per 100 cm³ of sterile soil, together with 500 (MG-14) or 1,500 (SN) second-stage juveniles of M. javanica, reduced root penetration 3 days after M. javanica inoculation compared to that of a water treatment. Entomopathogenic nematode infective juveniles applied to assess the effects on M. javanica egg production did not demonstrate a significant reduction compared to that of the water control treatment. There was no dose response effect by Steinernema spp. On M. javanica root penetration or egg production. Steinernema spp. did not affect the growth or development of M. javanica-infected plants, but H. indica MG-13-treated plants had lower biomass than untreated plants infected with M. javanica. Infective juveniles of S. riobrave TX, S. feltiae SN, and MG-14 but not those of H. indica MG-13 were found inside root cortical tissues of M. javanica-infected plants. Entomopathogenic nematode antagonism to M. javanica on soybean or tomato was insufficient in the present study to provide a consistent level of nematode suppression at the concentrations of infective juveniles applied.