Secretory proteins encoded by parasitism genes expressed in the esophageal gland cells of plant-parasitic nematodes play key roles in nematode-plant interactions. A fourth ß-1,4-endoglucanase full-length cDNA (designated Hg-eng-4) was isolated from a Heterodera glycines esophageal gland-cell long-distance polymerase chain reaction cDNA library. The cDNA hybridized to genomic DNA of H. glycines in Southern blots. The Hg-eng-4 cDNA contained an open reading frame encoding 352 amino acids, with the first 18 amino acids being a putative secretion signal. Hg-ENG-4 contained a family 5 endoglucanase catalytic domain and a peptide linker of repeat amino acids, but no cellulose binding domain. In-situ hybridization analyses showed that transcripts of Hg-eng-4 accumulated specifically in the subventral gland cells of pre-parasitic and parasitic second-stage juveniles of H. glycines.
cDNA; cellulase; cyst nematode; esophageal gland cell; Heterodera glycines; parasitism gene
We report the cloning of a Heterodera glycines cDNA that has 72% identity at the amino acid level to a pectate lyase from Globodera rostochiensis. In situ hybridizations showed that the corresponding gene (Hg-pel-1) is expressed in the subventral esophageal gland cells of second-stage juveniles. The deduced amino acid sequence of the H. glycines cDNA shows homology to class III pectate lyases of bacterial and fungal origin.
esophageal gland; molecular nematology; nematode; pectate lyase gene
Penetration, post-infectional development, reproduction, and fecundity of Meloidogyne arenaria races 1 and 2 were studied on susceptible (CNS), partially resistant (Jackson), and highly resistant (PI 200538 and PI 230977) soybean genotypes in the greenhouse. The ability to locate and invade roots was similar between races, but more juveniles penetrated roots of susceptible CNS than the resistant genotypes. At 10 days after inoculation, 56% and 99% to 100% of race 1 second-stage juveniles were vermiform or sexually undifferentiated in CNS and the resistant genotypes, respectively. In contrast, only 2%, 42%, 44%, and 62% of race 2 juveniles had not initiated development in CNS, Jackson, PI 200538, and PI 230977, respectively. By 20 days after inoculation, 88% to 100% of race 2 nematodes in roots of all genotypes were females, whereas only 25% and 1% of race 1 were females in CNS and the resistant genotypes, respectively. For all four genotypes, race 1 produce 85% to 96% fewer eggs per root system 45 days after inoculation than race 2. At 45 days after inoculation race 2 produced more eggs on CNS than the other genotypes.
Glycine max; Meloidogyne arenaria; pathogenicity; plant introduction; race; resistance; root-knot nematode; soybean
The cellular responses induced by Meloidogyne arenaria races 1 and 2 in three soybean genotypes, susceptible CNS, resistant Jackson, and resistant PI 200538, were examined by light microscopy 20 days after inoculation. Differences in giant-cell development were greater between races than among the soybean genotypes. M. arenaria race 1 stimulated small, poorly formed giant-cells in contrast with M. arenaria race 2, which induced well-developed, thick-walled, multinucleate giant-cells. The number of nuclei per giant-celt was variable, but fewer nuclei were usually present in giant-cells induced by race 1 (mean 16 nuclei) than in giant-cells induced by race 2 (mean 41 nuclei). Differences observed in giant-cell development were related to differences in growth and maturation of M. arenaria races 1 and 2 and host suitability of the soybean genotypes.
histopathology; giant-cell; Glycine max; Meloidogyne arenaria; nuclei; pathogenicity; plant introduction; resistance; root-knot nematode; soybean
Three monodonal antibodies (MAbs) that bound to secretory granules within the subventral esophageal glands of second-stage juveniles (J2) of the soybean cyst nematode (SCN), Heterodera glycines, were developed from intrasplenic immunizations of a mouse with homogenates of SCN J2. Two MAbs to the secretory granules within subventral glands and one MAb to granules within the dorsal esophageal gland of SCN J2 were developed by intrasplenic immunizations with J2 stylet secretions. Stylet secretions, produced in vitro by incubating SCN J2 in 5-methoxy DMT oxalate, were solubilized with a high pH buffer and concentrated for use as antigen. Three of the five MAbs specific to the subventral esophageal glands bound to stylet secretions from SCN J2 in immunofluorescence and ELISA assays. Two of these three MAbs also bound to secretory granules within both the dorsal and subventral esophageal glands of young SCN females. All five of the subventral gland MAbs bound to the subventral glands of Heterodera schachtii and one bound to the subventral glands of Globodera tabacum, but none bound to any structures in Meloidogyne incognita or Caenorhabditis elegans.
Caenorhabditis elegans; esophageal gland; Heterodera glycines; Heterodera schachtii; immunoassay; Meloidogyne incognita; monoclonal antibody; nematode; plant parasite; soybean; stylet secretions
Plant and soil nematodes significandy impact our lives. Therefore, we must understand and manage these complex organisms so that we may continue to develop and sustain our food production systems, our natural resources, our environment, and our quality of life. This publication looks specifically at soil and plant nematology. First, the societal impact of nematodes and benefits of nematology research are briefly presented. Next, the opportunities facing nematology in the next decade are outlined, as well as the resources needed to address these priorities. The safety and sustainability of U.S. food and fiber production depends on public and administrative understanding of the importance of nematodes, the drastic effects of nematodes on many agricultural and horticultural crops, and the current research priorities of nematology.
alternative management tactics; behavior; benefit to society; beneficial nematodes; biochemistry; biological control; constraints in nematology; control; crop rotation; cultural practice; ecology; education; environment; extension; diagnostics; funding; genetics; host-parasite interaction; information transfer; molecular genetics; nematicide; nematode; nematology; nematode management; nutrient cycling; pesticide; plant parasites; research goals; research priorities; resistance; resource; science of nematology; society; spread; sustainable agriculture; systematics
Resistant plant introductions, PI 230977 and PI 200538, and partially resistant Jackson and susceptible CNS were evaluated for seed yield in response to races 1 and 2 of Meloidogyne arenaria. Initial soil population densities (Pi) of the nematode were 0, 31, 125, and 500 eggs/100 cm³ soil. At the highest Pi, yield suppressions of CNS, Jackson, PI 230977, and PI 200538 were 55, 28, 31, and 29%, and 99, 86, 66, and 58% for races 1 and 2 compared with uninfested controls. Numbers of second-stage juveniles (J2) present in roots 14 days after planting increased as Pi increased, but did not differ between the two races. At the highest Pi, fewer race 1 (40-57%) and race 2 (53-68%) J2 were present in roots of the plant introductions than in roots of Jackson. Soil population densities of race 1 J2 at 135 days after planting were 83-89% lower on the resistant genotypes than on CNS. These numbers did not differ for race 2. Reproductive factors were considerably higher for race 2 compared to race 1 for all genotype by Pi combinations, except for CNS at the highest Pi.
aggressiveness; Glycine max; Meloidogyne arenaria; microplots; nematode; plant introduction; resistance; root-knot nematode; soybean; yield response
One hundred thirty-nine cultivars of soybean (Glycine max) in Maturity Groups V, VI, VII, and VIII were evaluated in a greenhouse for resistance to Heterodera glycines races 3 and 14 and Meloidogyne incognita, M. arenaria, and M. javanica. Of the cultivars tested, 37% had resistance to H. glycines race 3 alone, 12% had resistance to both races 3 and 14, and 69% exhibited a moderate or high level of resistance to one or more of the Meloidogyne spp. However, 24% were susceptible to each race of H. glycines and to all Meloidogyne spp. Whereas 40% of the cultivars were moderately resistant to M. javanica, only 23% were moderately resistant to M. incognita and 24% to M. arenaria. Although 28% of the cultivars had a high level of resistance to M. incognita, only 6 and 3% had this level of resistance to M. javanica and M. arenaria, respectively. Seventeen percent of the cultivars possessed a moderate or high level of resistance to all three Meloidogyne spp., and 37 % had resistance to H. glycines race 3 and M. incognita. With the exception of resistance to H. glycines race 14, resistance in soybean to these nematodes was fairly uniformly distributed across maturity groups.
Heterodera glycines; Glycine max; Meloidogyne incognita; Meloidogyne arenaria; Meloidogyne javanica; nematode resistance; soybean; susceptibility
Meloidogyne incognita penetration and development were studied in roots of highly resistant (PI 96354, PI 417444), resistant (Forrest), and susceptible (Bossier) soybean genotypes. Although more second-stage juveniles (J2) had penetrated roots of PI 96354 and PI 417444 than roots of Forrest and Bossier by 2 days after inoculation, fewer J2 were present in roots of PI 96354 at 4 days after inoculation. Juvenile development in all genotypes was evident by 6 days after inoculation, with the highest number of swollen J2 present in roots of Bossier. At 16 days after inoculation, roots of PI 96354 had 87%, 74%, and 53% fewer J2 than were present in roots of Bossier, Forrest, and PI 417444, respectively. Differential emigration of J2, not fewer invasion sites, was responsible for the low number of nematodes in roots of the highly resistant PI 96354. Some 72% of the J2 penetrating the roots of this genotype emerged within 5 days after inoculation, whereas 4%, 54%, and 83% emerged from roots of Bossier, Forrest, and PI 417444, respectively. Penetration of roots of PI 96354 decreased the ability of J2 emerging from these roots to infect other soybean roots.
emigration; Glycine max; infectivity; Meloidogyne incognita; plant introduction; root penetration; soybean
Effects of vesicular-arbuscular mycorrhizal (VAM) fungi and soil phosphorus (P) fertility on parasitism of soybean cultivars Bragg and Wright by soybean cyst nematode (SCN) were investigated in field micropiot and greenhouse experiments. VAM fungi increased height of both cultivars and yield of Wright in microplot studies in 1986 and 1987. Conversely, yield of mycorrhizal and nonmycorrhizal plants of both cultivars was suppressed by SCN. Soil population densities of SCN were unaffected by VAM fungi in 1986 but were greater in microplots infested with VAM fungi than in control microplots in 1987. Growth of Wright soybean was stimulated by VAM fungi and suppressed by SCN in greenhouse experiments. The effect of VAM fungi on SCN varied with time. Numbers of SCN in roots and soil were decreased by VAM fungi by as much as 73% at the highest SCN inoculum level through 49 days after planting. Later, however, SCN numbers were usually comparable on mycorrhizal and nonmycorrhizal plants. Soil P fertility generally had no effect on SCN. Results of a split-root experiment indicated that VAM fungal suppression of SCN was not systemic.
endomycorrhizae; Glycine max; Heterodera glycines; interaction; microplot; phosphorus; soybean; soybean cyst nematode; vesicular-arbuscnlar mycorrhizal fungi
The response of two soybean plant introductions, PI 96354 and PI 417444, highly resistant to Meloidogyne incognita, to increasing initial soil population densities (Pi) (0, 31, 125, and 500 eggs/100 cm³ soil) of M. incognita was studied in field microplots for 2 years. The plant introductions were compared to the cultivars Forrest, moderately resistant, and Bossier, susceptible to M. incognita. Averaged across years, the yield suppressions of Bossier, Forrest, PI 417444, and PI 96354 were 97, 12, 18, and < 1%, respectively, at the highest Pi when compared with uninfested control plots. Penetration of roots by second-stage juveniles (J2) increased linearly with increasing Pi at 14 days after planting. At the highest Pi, 62% fewer J2 were present in roots of PI 96354 than in roots of the other resistant genotypes. Soil population densities of M. incognita were lower on both plant introductions than on Forrest. At 75 and 140 days after planting, PI 96354 had the lowest number of J2 in the soil, with 49% and 56% fewer than Forrest at the highest Pi. The resistance genes in PI 96354 should be useful in a breeding program to improve the level of resistance to M. incognita in soybean cultivars.
Glycine max; Meloidogyne incognita; population density; resistance; root-knot nematode; root penetration; soybean; yield response
Twenty-six susceptible and resistant soybean, Glycine max, cultivars in Maturity Groups V, VI, VII, and VIII were compared with Coker 156, Wright, and PI97100 for tolerance to Heterodera glycines races 3 and 14. Seed yields were compared in nematicide-treated (EDB, fenamiphos) and untreated plots at two H. glycines-infested locations over 3 years. Coker 488, DP 417, and NK S72-60 had the highest average tolerance indices ([yield in untreated plot + yield in nematicide-treated plot] x 100) of the race 3-susceptible cultivars to races 3 and 14. Plant height and seed weight of untreated soybean plants were suppressed in race 3-infested soil, but only plant height was suppressed at the race 14-infested location. Several race 3-resistant and race 14-susceptible cultivars were moderately tolerant to race 14.
Heterodera glycines; soybean cyst nematode; Glycine max; susceptibility; resistance; tolerance; yield; soybean
Monoclonal antibodies to secretory granules in the dorsal or subventral esophageal glands were generated by injecting BALB/c mice with immunogens from preparasitic second-stage juveniles (J2) of Meloidogyne incognita. Antibodies specific for secretory granules in the J2 subventral esophageal glands or the dorsal gland were identified by indirect immunofluorescence microscopy. Only antibodies that reacted with granules in the J2 dorsal gland reacted with the esophageal gland lobe ofM. incognita adult females. The antibodies also reacted with secretory granules in both types of esophageal glands in M. javanica and M. arenaria J2 but not with granules in esophageal glands of Heterodera glycines J2.
esophageal gland; immunocytochemistry; immunofluorescence; Meloidogyne incognita; monoclonal antibody; root-knot nematode; secretion; secretory granule
Interactions among Meloidogyne incognita, Pratylenchus brachyurus, and soybean genotype on plant growth and nematode reproduction were studied in a greenhouse. Coker 317 (susceptible to both nematodes) and Gordon (resistant to M. incognita, susceptible to P. brachyurus) were inoculated with increasing initial population densities (Pi) of both nematodes individually and combined. M. incognita and P. brachyurus individually usually suppressed shoot growth of both cultivars, but only root growth on Coker 317 was influenced by a M. incognita × P. brachyurus interaction. Reproduction of both nematodes, although dependent on Pi, was mutually suppressed on Coker 317. P. brachyurus reproduced better on Gordon than on Coker 317 but did not affect resistance to M. incognita. Root systems of Coker 317 were split and inoculated with M. incognita or P. brachyurus or both to determine the nature of the interaction. M. incognita suppressed reproduction of P. brachyurus either when coinhabiting a half-root system or infecting opposing half-root systems; however, P. brachyurus affected M. incognita only if both nematodes infected the same half-root system.
Glycine max; antagonism; concomitant infection; population density; root-knot nematode; lesion nematode
Secretions from amphids, phasmids, and excretory system were stained by incubating nematodes in 0.1% coomassie brilliant blue G-250 in 40% aqueous methanol containing 10% acetic acid on slides with coverslips sealed with nail polish or Zut. Nematodes incubated in this staining solution usually produced copious amounts of secretions from their amphids and excretory pore. Phasmids also stained dark blue, enabling them to be easily observed. Other biological dyes stained these secretions or were useful for differentiating specific morphological features of nematodes.
secretion; amphid; phasmid; excretory system; stain; coomassie brilliant blue; exudate
Ultrastructural cytochemical tests for several enzymes, proteins, carbohydrates, and nucleic acids were conducted on secretory granules o£ dorsal and subventral esophageal glands of preparasitic second-stage juveniles and the dorsal gland of adult females of Meloidogyne incognita. Secretory granules in the subventral glands of juveniles stained positive for acid phosphatase. Peroxidase, DNase, RNase, cellulase, and nucleic acids were not detected in these granules. Secretory granules in the dorsal gland of adult females stained positive for peroxidase (pH 7.6) in < 50% of the tests, Acid phosphatase, β-glucuronidase, DNase, RNase, polyphenoloxidase, cellulase, and carbohydrates were not detected in dorsal gland granules in adult females. Positive staining with cobalt thiocyanate, a stain for amino groups of basic proteins, occurred in secretory granules in the dorsal gland, ribosomes, and chromatin in adult females. Ribosomes, nuclei, and secretory granules of the dorsal gland of adult females intensely stained when incubated in three reagents specific for nucleic acid.
cytochemistry; Meloidogyne incognita; secretory granule; esophageal gland; enzyme; root-knot nematode; electron microscopy
The effects of host genotype and initial nematode population densities (Pi) on yield of soybean and soil population densities of Heterodera glycines (Hg) race 3 and Meloidogyne incognita (Mi) race 3 were studied in a greenhouse and field microplots in 1983 and 1984. Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were planted in soil infested with 0, 31, or 124 eggs of Hg and Mi, individually and in all combinations, per 100 cm³ soil. Yield responses of the soybean cultivars to individual and combined infestations of Hg and Mi were primarily dependent on soybean resistance or susceptibility to each species separately. Yield of Centennial was stimulated or unaffected by nematode treatments, yield of Braxton was suppressed by Hg only, and yield suppressions caused by Hg and Mi were additive and dependent on Pi for Coker 237. Other plant responses to nematodes were also dependent on host resistance or susceptibility. Population densities of Mi second-stage juveniles (J2) in soil were related to Mi Pi and remained constant in the presence of Hg for all three cultivars. Population densities of Hg J2 on the two Hg-susceptible Cultivars, Braxton and Coker 237, were suppressed in the presence of Mi at low Hg Pi.
soybean cyst nematode; root-knot nematode; Glycine max; interaction; microplot; Heterodera glycines; Meloidogyne incognita
The influence of the vesicular-arbuscular mycorrhizal fungus Glomus intraradices (Gi) and superphosphate (P) on penetration, development, and reproduction of Meloidogyne incognita (Mi) was studied on the Mi-susceptible cotton cultivar Stoneville 213 in an environmental chamber at 28 C. Plants were inoculated with Mi eggs at planting or after 28 days and destructively sampled 7, 14, 21, and 28 days after nematode inoculation. Mi penetration after 7 days was similar in all treatments at either inoculation interval. At 28 days, however, nematode numbers were least in mycorrhizal root systems and greatest in root systems grown with supplemental P. The rate of development of second-stage juveniles to ovipositing females was unaffected by Gi or P when Mi was added at planting, but was delayed in mycorrhizal root systems when Mi was added 28 days after planting. Nematode reproduction was lower in mycorrhizal than in nonmycorrhizal root systems at both Mi inoculation intervals. Nematode reproduction was stimulated by P when Mi was added at planting, but was similar to reproduction in the low P nonmycorrhizal treatment when Mi was added 28 days after planting. Eggs per female were increased by P fertility when Mi was added at planting.
endomycorrhizae; Gossypium hirsutum; Meloidogyne incognita; root-knot nematode; phosphorus; cotton
Greenhouse and field microplot studies were conducted to compare soybean shoot and root growth responses to root penetration by Heterodera glycines (Hg) and Meloidogyne incognita (Mi) individually and in combination. Soybean cultivars Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were selected for study. In the greenhouse, pot size and number of plants per pot had no effect on Hg or Mi penetration of Coker 237 roots; root weight was higher in the presence of either nematode species compared with the noninoculated controls. In greenhouse studies using a sand or soil medium, and in field microplot studies, each cultivar was grown with increasing initial population densities (Pi) of Hg or Mi. Interactions between Hg and Mi did not affect early plant growth or number of nematodes penetrating roots. Root penetration was the only response related to Pi. Mi penetration was higher in sand than in soil, and higher in the greenhouse than in the field, whereas Hg penetration was similar under all conditions. At 14 days after planting, more second-stage juveniles were present in roots of susceptible than in roots of resistant plants. Roots continued to lengthen in the greenhouse in the presence of either Mi or Hg regardless of host genotype, but only in the presence of Mi in microplots; otherwise, responses in field and greenhouse studies were similar and differed only in magnitude and variability.
soybean cyst nematode; root-knot nematode; Glycine max; root penetration; root length; microplots; Heterodera glycines; Meloidogyne incognita
Cuticles isolated from second-stage juveniles and adult females of Meloidogyne incognita were purified by treatment with 1% sodium dodecyl sulfate (SDS). The juvenile cuticle was composed of three zones differing in their solubility in β-mercaptoethanol (BME). Proteins in the cortical and median zones were partially soluble in BME, whereas the basal zone was the least soluble. The BME-soluble proteins from the juvenile cuticle were separated into 12 bands by SDS-polyacrylamide gel electrophoresis and characterized as collagenous proteins based on their sensitivity to collagenase and amino acid composition. The adult cuticle consisted of two zones which were dissolved extensively by BME. The basal zone was completely solubilized, leaving behind a network of fibers corresponding to the cortical zone. The BME-soluble proteins from the adult cuticle were separated by electrophoresis into nine bands one of which constituted > 55% of the total BME-soluble proteins. All bands were characterized as collagenous proteins. Collagenous proteins from juvenile cuticles also contained glycoproteins which were absent from the adult cuticles.
biochemistry; collagens; cuticle; electrophoresis; Meloidogyne incognita; root-knot nematode
Five soybean cultivars (Braxton, Gordon, Jeff, Bragg, and Wright) resistant to Meloidogyne incognita (Mi) and three susceptible cultivars (Coker 156, GaSoy 17, and Coker 237) were grown at two locations for four seasons in microplots with increasing initial soil population densities (Pi) of Mi. The resistant cultivars and Coker 156 yielded better than GaSoy 17 and Coker 237 at all Pi. Yield response was dependent on environmental conditions and at one location was stimulated on Braxton, Gordon, Jeff, and Bragg by low Pi. Although Mi reproduced well on all cultivars, the pattern of reproduction differed. Population densities of Mi leveled off after 90 days on GaSoy 17 and Coker 237 but were still increasing after 120 days on the resistant cultivars; population densities were lower on resistant than on the susceptible cultivars. The population density of Mi on Coker 156 after 120 days was intermediate between those on the other susceptible and on the resistant cultivars. Mi population densities followed the same pattern under varying environmental conditions.
resistant cultivars; nematode reproduction; yield loss; population dynamics; nematode x environment interaction
Microplot and field experiments were conducted to determine the effects of two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices (Gi) and Gigaspora margarita (Gm), and dicalcium phosphate (P) on Meloidogyne incognita (Mi) reproduction and seed cotton yield of the Mi-susceptible cotton cultivar, Stoneville 213. In 1983 population densities of Mi juveniles were significantly lower 60 and 90 days after planting in microplots receiving Gi. Mycorrhizal fungi reduced the severity of yield losses to Mi, whereas P fertilization increased yield losses to Mi. In 1984 microplot yields were reduced linearly as nematode inoculum densities increased in treatments of Mi alone, Gm, or P, but the response was curvilinear with Gi. Yield suppressions in the 1984 field experiment occurred only in plots infested with Mi alone. In the 1984 microplots, numbers of Mi juveniles penetrating seedling roots increased Iinearly with increasing nematode inoculum densities and was favored when mycorrhizal fungi or superphosphate were added. Juvenile penetration of roots was negatively correlated with yields in all treatments (r = -0.54 to -0.81) except Gm and with number of bolls in Mi alone (r = -0.85) and P (r = -0.81) treatments. Mycorrhizal fungi can increase host tolerance to M. incognita in field conditions and may function as important biological control agents in soils infested with high population densities of efficient VAM species.
biocontrol; endomycorrhizae; interaction; Meloidogyne incognita; root-knot nematode; microplots
Fifty-four susceptible soybean, Glycine max, cultivars or plant introductions were evaluated for tolerance to H. glycines, the soybean cyst nematode (SCN). Seed yields of genotypes were compared in nematicide-treated (1,2-dibromo-3-chloropropane, 58 kg a.i./ha) and nontreated plots at two SCN-infested locations over 3 years. Distinct and consistent levels of tolerance to SCN were observed among soybean genotypes. PI 97100, an introduction from Korea, exhibited the highest level of tolerance with an average tolerance index ([yield in nontreated plot ÷ yield in nematicide-treated plot] × 100) of 96 over 2 years. Coker 156 and Wright had moderate levels of tolerance (range in index values 68 to 95) compared to the intolerant cuhivars Bragg and Coker 237 (range in index values 33 to 68). Most of the soybean genotypes evaluated were intolerant to SCN. The rankings of five genotypes for tolerance to SCN and Hoplolaimus columbus were similar. Tolerance for seed yield was more consistently correlated with tolerance for plant height (r = 0.55 to 0.64) than for seed weight (r = 0.23 to 0.65) among genotypes.
soybean cyst nematode; Glycine max; seed yield; Hoplolaimus columbus
The influence of two vesicular-arbuscular mycorrhizal fungi and phosphorus (P) nutrition on penetration, development, and reproduction by Meloidogyne incognita on Walter tomato was studied in the greenhouse. Inoculation with either Gigaspora margarita or Glomus mosseae 2 wk prior to nematode inoculation did not alter infection by M. incognita compared with nonmycorrhizal plants, regardless of soil P level (either 3 μg [low P] or 30 μg [high P] available P/g soil). At a given soil P level, nematode penetration and reproduction did not differ in mycorrhizal and nonmycorrhizal plants. However, plants grown in high P soil had greater root weights, increased nematode penetration and egg production per plant, and decreased colonization by mycorrhizal fungi, compared with plants grown in low P soil. The number of eggs per female nematode on mycorrhizal and nonmycorrhizal plants was not influenced by P treatment. Tomato plants with split root systems grown in double-compartment containers which had either low P soil in both sides or high P in one side and low P in the other, were inoculated at transplanting with G. margarita and 2 wk later one-half of the split root system of each plant was inoculated with M. incognita larvae. Although the mycoorhizal fungus increased the inorganic P content of the root to a level comparable to that in plants grown in high P soil, nematode penetration and reproduction were not altered. In a third series of experiments, the rate of nematode development was not influenced by either the presence of G. margarita or high soil P, compared with control plants grown in low P soil. These data indicate that supplemental P (30 μ/g soil) alters root-knot nematode infection of tomato more than G. mosseae and G. margarita.
Glomus mosseae; Gigaspora margarita; root-knot nematode
Bragg soybeans were planted in nematicide-treated and nontreated plots on 15 May, 15 June, 1 July, and 15 July in 1980 and 1981 to determine the influence of planting date on damage caused by H. glycines. Although earlier studies showed the nematode was sensitive to high soil temperatures (> 34 C), late planting did not reduce damage caused by the nematode. Yields from plots treated with 1, 2-dibromo-3-chloropropane (57.5 kg a.i./ha) were 48, 118, 395, and 403% higher than yields from nontreated plots with planting dates of 15 May, 15 June, 1 July, and 15 July, respectively, when data were averaged over the 2 years. Increase in both seed size and number accounted for the yield increases in treated plots. Soil temperatures were highest during July in 1980, averaging 8.9 and 6.5 hours per day above 34 C at 10- and 20-cm depths, respectively. Larvae populations of H. glycines were reduced by the nematicide but not by late planting. These results indicate that damage caused by H. glycines may actually increase with later planting and that nematicides may be more beneficial when soybeans are planted late in a double-cropped production system.
cyst nematode; soil temperature