Influence of Photoperiod and Temperature on Migrations of Meloidogyne Juveniles

Photoperiod influences the migration of M. incognita juveniles toward tomato roots. Approximately 33% migrated vertically 20 cm in 7 days to roots when 12 h dark were alternated with 12 h light. Only 7% migrated when light was constant for 24 h. Vertical migration of M. incognita juveniles was studied at 14, 16, 18, 20, and 22 C. The migration of M. incognita juveniles begins at about 18 C and reaches its maximum at 22 C. The migration of M. hapla and M. incognita juveniles were compared at 14, 18, and 22 C. Juveniles of M. hapla were able to migrate at a lower temperature than those of M. incognita. With M. hapla, there was no significant difference in migration between 18 and 22 C.     

Influence of Chilling and Freezing Temperatures on Infectivity of Meloidogyne incognita and M. hapla

Egg masses and second-stage larvae of Meloidogyne incognita and M. hapla in soil were exposed to temperatures ranging from 20 to -8 C. Temperature was lowered in 2-day intervals to 16, 12, 8, 4, 0, -4, and -8 C, and the nematodes remained at 4, 0, -4, or -8 C for 18, 14, 10, or 6 days, respectively. Unhatched larvae of both species were more resistant to low temperatures than were embryonic stages. Within the eggs of M. incognita, 7.5% of embryos and 48% of larval stages survived 14 days at 0 C, whereas 9% of embryos and 90% of larval stages in the eggs of M. hapla survived 10 days at -4 C. Second-stage larvae of both species remained infective in sol.1 at 4 or 0 C, but were injured at -4 and -8 C. Infectivily of these larvae was lower in saturated soil than in soil at 51 cm moisture tension at all temperatures.     

Influence of Low Temperature on Development of Meloidogyne incognita and M. hapla Eggs in Egg Masses

Egg masses of Meloidogyne incognita and M. hapla were placed in soil at 10, 12, 16, and 20 C. At regular intervals, eggs from samples of egg masses were released from the gelatinous matrices and their developmental stages recorded. The number of days necessary to complete each stage from gastrulation to hatch is given for each temperature. The minimal temperature threshold for the development of eggs was computed by linear regression to be 8.26 C for M. incognita and 6.74 C for M. hapla.     

Relationships of Initial Population Densities of Meloidogyne incognita and M. hapla to Yield of Tomato

Microplots 80 × 100 cm, infested with varying initial population densities (P_i) of Meloidogyne incognita or M. hapla, were planted to tomato at two locations. Experiments were conducted in a sandy loam soil at Fletcher, N. C. (mountains) where the mean temperature for May to September is ca 20.7 C, and in a loamy saml at Clayton, N. C. (coastal plain) where the mean temperature for May to Septemher is ca 24.8 C. In these experimentally infested plots, M. incognita and M. hapla caused maximunt yield losses of 20-30%, at lhe mountain site with Pi of 0-12,500 eggs and larvae/500 cm³ of soil. In the coaslal plain, M. incognita suppressed yields up to 85%, and M. hapla suppressed yields up to 50% in comparison with the noninfested control. A part of the high losses at this site apparently was due to M. incognita predisposing tomato to the early blight fungus. In a second experintent, in which a nematicide was used to obtain a range of P_is (with P_i as high as 25,000/50 cm³ of soil) at Fletcher, losses due to M. incognita were as great as 50%, but similar densities of M. hapla suppressed yields by only 10-25%. Approximate threshold densities for both species ranged from 500 to 1,000 larvae and eggs (higher for surviving larvae) for the mountain site, whereas nutnbers as low as 20 larvae/500 cm³ of soil of either species caused signiticant damage in the coastal plain. Chemical soil treatments proved useful in obtaining various initial population densities; however, problems were encountered in measuring effective inoculum after such treatments, especially in the heavier soil.     

Interaction of Meloidogyne hapla and M. javanica Infecting Tomato

A soil temperature of 20 C was equally suitable for the invasion and development of M. hapla and M. javanica. However, M. javanica predominated in a mixed species infection at this temperature. Predominance increased with increasing mixed-species inoculum levels. Invasion by M. hapla was more density-dependent than M. javanica. M. hapla produced a greater incidence of terminal galls and lateral roots.     

Effects of Meloidogyne spp. and Rhizoctonia solani on the Growth of Grapevine Rootings

A disease complex involving Meloidogyne incognita and Rhizoctonia solani was associated with stunting of grapevines in a field nursery. Nematode reproduction was occurring on both susceptible and resistant cultivars, and pot experiments were conducted to determine the virulence of this M. incognita population, and of M. javanica and M. hapla populations, to V. vinifera cv. Colombard (susceptible) and to V. champinii cv. Ramsey (regarded locally as highly resistant). The virulence of R. solani isolates obtained from roots of diseased grapevines also was determined both alone and in combination with M. incognita. Ramsey was susceptible to M. incognita (reproduction ratio 9.8 to 18.4 in a shadehouse and heated glasshouse, respectively) but was resistant to M. javanica and M. hapla. Colombard was susceptible to M. incognita (reproduction ratio 24.3 and 41.3, respectively) and M. javanica. Shoot growth was suppressed (by 35%) by M. incognita and, to a lesser extent, by M. hapla. Colombard roots were more severely galled than Ramsey roots by all three species, and nematode reproduction was higher on Colombard. Isolates of R. solani assigned to putative anastomosis groups 2-1 and 4, and an unidentified isolate, colonized and induced rotting of grapevine roots. Ramsey was more susceptible to root rotting than Colombard. Shoot growth was inhibited by up to 15% by several AG 4 isolates and by 20% by the AG 2-1 isolate. AG 4 isolates varied in their virulence. Root rotting was higher when grapevines were inoculated with both M. incognita and R. solani and was highest when nematode inoculation preceded the fungus. Shoot weights were lower when vines were inoculated with the nematode 13 days before the fungus compared with inoculation with both the nematode and the fungus on the same day. It was concluded that both the M. incognita population and some R. solani isolates were virulent against both Colombard and Ramsey, and that measures to prevent spread in nursery stock were therefore important.     

Nature of Sweet Potato Resistance to Meloidogyne incognita and the Effects of Temperature on Parasitism

Penetration, rate of development, and total population of Meloidogyne incognita in roots of susceptible ''Allgold'' and resistant ''Nemagold'' sweet potatoes increased with temperature 24-32 C. Rate of larval penetration in ''Allgold'' was significantly higher than in ''Nemagold'' after 48 hr of root exposure at 24, 28, and 32 C. At 24, 28, and 32 C (16 hr) day and 20 C (8 hr) night temperature the life cycle of M. incognita required 42, 32, and 28 days in ''Allgold'', and 44, 33, and 31 days in ''Nemagold''; mature females in the first generation were 40, 40, 40, and 10, 22, 20 respectively. The correlation between the length of time roots were allowed to grow in the soil prior to inoculation and number of larvae recovered from the roots after inoculation was positive for ''Allgold'' and negative for ''Nemagold''. Therefore, a root exudate repellent to M. incognita larvae is proposed as a hypothetical basis for resistance to M. incognita in sweet potatoes.     

Effect of Soil Temperature on the Pathogenicity and Reproduction of Meloidogyne chitwoodi and M. hapla on Russet Burbank potato

Meloidogyne chitwoodi and M. hapla were pathogenic to both roots and tubers of Russet Burbank potato. Both species affected root growth at 15, 20, and 25 C, but not 30 C. Meloidogyne chitwoodi reprotluced best at 15, 20, and 25 C and M. hapla at 25 and 30 C. Reproduction of M. chitwoodi was reduced at 30 C; reproduction of M. hapla was reduced at 15 C and less at 20 C. The reproductive potential of M. chitwoodi was higher than that of M. hapla at 15, 20, and 25 C. M. hapla reproduced better at 30 C than did M. chitwoodi. M. chitwoodi infected potato tubers in higher numbers than did M. hapla.     

Interrelationship of Heterodera schachtii and Meloidogyne hapla on Tomato

Invasion of tomato (Lycopersicon esculentum L.) roots by combined and sequential inoculations of Meloidogyne hapla and a tomato population of Heterodera schachtii was affected more by soil temperature than by nematode competition. Maximum invasion of tomato roots, by M. hapla and H. schachtii occurred at 30 and 26 C, respectively. Female development and nematode reproduction (eggs per plant) of M. hapla was adversely affected by H. schachtii in combined inoculations of the two nematode species. Inhibition of M. hapla development and reproduction on tomato roots from combined nematode inoculations was more pronounced as soil temperature was increased over a range of 18-30 C and with prior inoculation of tomato with H. schachtii. M. hapla minimally affected H. schachtii female development, but there was significant reduction in the buildup of H. schachtii when M. hapla inoculation preceded that of H. schachtii by 20 days.     

Interrelationships of Meloidogyne Species with Flue-cured Tobacco

Microplot and field experiments were conducted to determine relationships of population densities of Meloidogyne spp. to performance of flue-cured tobacco. A 3-yr microplot study of these interactions involved varying initial nematode numbers (P_i).and use of ethoprop to re-establish ranges of nematode densities. Field experiments included various nematicides at different locations. Regression analyses of microplot data from a loamy sand showed that cured-leaf yield losses on ''Coker 319'' for each 10-fold increase in P_i were as follows: M. javanica and M. arenaria—-13-19%; M. incognita—5-10%; M. hapla—3.4-5%; and 3% for M. incognita on resistant ''Speight G-28'' tobacco. A P_i of 750 eggs and larvae/500 cm³ of soil of all species except M. hapla caused a significant yield loss; only large numbers of M. hapla effected a loss. M. arenaria was the most tolerant species to ethoprop. Root-gall indices for microplot and most field-nematicide tests also were correlated negatively with yield. Relationships of P_i(s) and necrosis indices to yield were best characterized by linear regression models, whereas midseason numbers of eggs plus larvae (P_m) and sometimes gall indices vs. yield were better characterized by quadratic models. The relation of field P_m and yield was also adequately described by the Seinhorst model. Degrees of root galling, root necrosis, yield losses, and basic rates of reproduction on tobacco generally increased from M. hapla to M. incognita to M. arenaria to M. javanica.     

Effects of oximecarbamate, organophosphate and benzimidazole nematicides on life cycle stages of root-knot nematodes, Meloidogyne spp.

A study was made of the effects of concentrations of 2 to 32 ppm of oximecarbamate, organophosphate and benzimidazole nematicides on the hatch, larval viability and migration of Meloidogyne javanica, M. incognita and M. hapla and on development of M. javanica in roots. Aldicarb at less than 8 ppm had little effect on hatch and methomyl markedly affected only the hatch of M. hapla. As little as 2 ppm of fenamiphos or thionazin markedly reduced hatch of all three species but less than 8 ppm ethoprophos significantly reduced only the hatch of M. incognita and phorate had little effect on hatch. Benomyl and thiabendazole had no significant effects on hatch. When egg masses of M. incognita were transferred from nematicides which suppressed hatch to water, hatching occurred, but aldicarb, fenamiphos, ethoprophos and thionazin significantly reduced total hatch. None of the nematicides killed larvae of the three species immersed in 16 and 32 ppm solutions of them for 3 days. Aldicarb at 2 ppm reduced migrations of all three species; the effects of methomyl, fenamiphos or thionazin on migration varied according to species, while phorate, ethoprophos, benomyl or thiabendazole had little or no effect on migration. Aldicarb or thionazin at 2 ppm stopped development of M. javanica in roots of tomato seedlings while methomyl, ethoprophos or fenamiphos at 4 ppm reduced development by 60% and at 8 ppm of ethoprophos or fenamiphos or 16 ppm of methomyl, development was stopped. Phorate had little effect on development and benomyl or thiabendazole had no effect. Nematicide concentrations which reduced development prevented the normal orientation of larvae in the roots and reduced or prevented giant cell formation.     

Penetration and Development of Meloidogyne hapla in Resistant and Susceptible Alfalfa Under Differing Temperatures

Studies were conducted to examine under differing temperatures (12, 16, 20, 24, 28, and 32 C) the penetration anti development of Meloidogyne hapla in resistant lines ''298'' and ''Nev. Syn XX'', and susceptible ''Lahontan'' and ''Ranger'' hardy-type alfalfas. The results indicated that resistance to M. hapla was similar to that previously described for M. incognita in nonhardy alfalfa. Although initial penetration in resistant seedlings was similar to that of susceptible seedlings, nematode larvae failed to establish and develop in root tissues and nematode numbers subsequently declined. In susceptible seedlings, nematode development proceeded rapidly, and egg production began after 5 weeks. Temperature had little influence on the nematode development except to slow the response at the lower temperatures. Other studies were conducted to verify a previously reported immune (no penetration) reaction to M. hapla by the ''Vernal'' selection ''M-4''. When compared to the resistant (penetration without nematode development) Vernal selection ''M-9'' under differing temperatures (20, 24, 28, and 32 C), each selection was equally penetrated by M. hapla but at a lower level than in susceptible Ranger cuttings. Generally, no root galling was observed in either M-4 or M-9; however, very slight galling was found 35 days after inoculation on about 50% of these cuttings when grown at 32 C.     

Application of Isoelectric Focusing to the Taxonomic Identification of Meloidogyne spp.

Meloidogyne incognita, M. arenaria, M. hapla, and M. javanica were distinguishable from each other by isoelectric focusing (IEF) of nematode egg proteins. Proteins extracted from larvae and adults of Hoplolaimus columbus and from eggs of Heterodera glycines had distinctive profiles, also. Protein profiles from eggs, preparasitic larvae and egg-laying adults of M. incognita showed differences. It was necessary to compare samples run at the same time to ensure reliability.     

Interactions between Meloidogyne incognita,M. hapla,and Pratylenchus brachyurus in Tobacco

In a greenhouse pot experiment on the pathogenicity and interactions of Meloidogyne incognita, M. hapla and Pratylenchus brachyurus on four cultivars o f tobacco the cultivars ''Hicks'' and ''NC 2326'' were susceptible to each nematode and "NC 95'' and ''NC 2512'' resistant only to M. incognita.Mean heights of susceptible plants were depressed but fresh weight of tops did not differ significantly. Meloidogyne spp. increased fresh weight of susceptible (but not the resistant) roots.Reproduction of M. incognita was decreased in the presence of P. brachyurus in one case. M. hapla reproduction was less with either of the other nematodes in five out of eight cases. In 12 combinations involving P. brachyurus, reproduction of this species was depressed in seven, not affected in four and increased in one.Mechanisms involved in associative interactions were not identified but appeared to be indirect and to involve individual host-nematode responses.     

Effect of Plant Age on Resistance of Alfalfa to Meloidogyne hapla

Meloidogyne hapla-resistant plants grown from cuttings and inoculated with M. hapla larvae were free of galls. However, 35 to 48% of the seedling intercross progeny of resistant genotypes that were inoculated in the germinated seed stage were galled. There was an inverse relationship between the age of plants grown from seed and the percentage of plants galled by M. hapla; the older the plants at inoculation, the greater the percentage of gall-free plants. The per cent of galled plants was significantly reduced when galled roots were removed and plants reinoculated. Reproduction of M. hapla on galled progeny of resistant plants was significantly less than that on susceptible plants. There were no differences in nematode reproduction on galled progeny of resistant plants, regardless of age at time of inoculation. An in,ease in inoculum levels from 100 to 10,000 M. hapla larvae did not affect resistance or susceptility. There was a direct correlation between galling of inoculated seedlings of resistant progeny and temperature; inoculated 8-week-old cuttings of resistant plants were galled only at 32 C.     

Antioxidant Enzymes in Phytoparasitic Nematodes

Presence of different antioxidant enzymes, such as superoxide dismutase (SOD), catalase, and ascorbate, p-phenilendiamine-pyrocathecol (PPD-PC), o-dianisidine, and guaiacol isoperoxidases, was shown in the phytoparasific nematode species Meloidogyne incognita, M. hapla, Globodera rostochiensis, G. pallida, Heterodera schachtii, H. carotae, and Xiphinema index. The activity of the enzymes tested differed among the life stages examined. SOD was present in cysts but was not detected in Meloidogyne egg masses. Catalase activity of Meloidogyne females was higher than that of preparasitic stages and cyst-nematode females. For the first time, ascorbate peroxidase was found to occur commonly in phytoparasitic nematodes, with the highest activity in the invading life-stages. In all the life stages examined, the antioxidant enzyme activities of M. hapla were markedly higher than those of M. incognita. Glutathione peroxidase was not found in the species examined.     

Comparative Studies on Root Invasion,Root Galling,and Fecundity of Three Meloidogyne spp. on a Susceptible Tobacco Cultivar

Root invasion, root galling, and fecundity of Meloidogyne javanica, M. arenaria, and M. incognita on tobacco was compared in greenhouse and controlled environment experiments. Significantly more M. javanica than M. arenaria or M. incognita larvae were found in tobacco roots at 2, 4, and 6 d after inoculation. Eight days after inoculation there were significantly more M. arenaria and M. javanica than M. incognita larvae. Ten days after inoculation no significant differences were found among the three Meloidogyne species inside the roots. Galls induced by a single larva or several larvae of M. javanica were significantly larger than galls induced by M. incognita: M. arenaria galls were intermediate in size. Only slight differences in numbers of egg masses or numbers of eggs produced by the three Meloidogyne species were observed up to 35 d after inoculation.     

Morphological Comparison of Second-Stage Juveniles of Six Populations of Meloidogyne hapla by SEM

External morphology of second-stage juveniles of six populations of Meloidogyne hapla, hclonging to two cytological races (A and B), and one population each of M. arenaria, M. incognita, and M. javanica was compared by scanning electron microscopy (SEM). Race A of M. hapla included three facultatively parthenogenetic populations with haploid chromosome numbers of 15. 16, and 17; race B consisted of three mitotically parthenogenetic populations with somalic chromosome numhers of 45, 45, and 48. The mitotically parthenogenetic populations of M. arenaria, M. incognita, and M. javanica had 54, 41-43, and 44 chromosomes, respectively. Observations were made on head structures, lateral field, excretory pore, anal opening, and tail. Head morphology, including shape and proportion of labial disc and lips, expression of labial and cephalic sensilla, and markings on head region, was distinctly different for each species. M. hapla populations of race A were distinct from each other but showed much intrapopulatiou variation in head morphology. Populations of race B were different from those of race A and were very stable and quite similar in head morphology. Considerable inter- and intrapopulatiou variation made the structure of the lateral field, excretory pore, anal opening, and tail of little value in distinguishing species or populations. The results are discussed in relation to earlier SEM observations on the genus Helerodera.     

Morphological Comparison of Meloidogyne Males by Scanning Electron Microscopy

Males of five populations of Meloidogyne hapla were compared by scanning electron microscopy (SEM). Three populations of race A had haploid chromosome numbers of 15, 16, and 17 and reproduced by facultative parthenogenesis. Race B consisted of two mitotically parthenogenetic populations with somatic chromosome numbers of 45 and 48. Males of one population each of M. arenaria, M. incognita, and M. javanica were also examined to delineate species differences. The populations of M. arenaria, M. incognita, and M. javanica had 54, 41-43, and 44 chromosomes, respectively, and reproduction was by mitotic parthenogenesis. Observations were made on head structures, lateral field, excretory pore, and tail. The expression of labial and cephalic sensilla, shape and proportion of labial disc and lips, and markings on the head region were distinctly different for each species. The head morphology of the two cytological races of M. hapla was dissimilar. Populations of race A were different from each other and showed intrapopulation variation. Populations of race B were morphologically similar and stable in head morphology. The structure of the lateral field, excretory pore, and tail was of little value in distinguishing species or populations because of inter- and intrapopulation variation. The results are discussed in relation to earlier SEM observations of second-stage juveniles of the same populations.     

Effect of Soil Temperature on Reproduction of Meloidogyne chitwoodi and M. hapla Alone and in Combination on Potato and M. chitwoodi on Rotation Plants

Meloidogyne chitwoodi developed and reproduced more rapidly than M. hapla in potato roots at 15, 20, or 25 C when both species of nematodes were inoculated simultaneously at 250 or 1,000 juveniles of each. At 30 C significantly more M. hapla than M. chitwoodi females were found at the lower inoculum level after 41 days. More M. chitwoodi than M. hapla juveniles were extracted from soil at 15, 20, and 25 C, but only at the lower inoculum level at 30 C. Potato was considered a more suitable host for M. chitwoodi than M. hapla because of M. chitwoodi''s greater reproduction at 15, 20, and 25 C. Corn and wheat cultivars tested supported M. chitwoodi reproduction at temperatures of 10, 15, 20, and 25 C, but fewest eggs were produced on these plants at 20 C. Temperatures of 10 to 25 C had little influence on the low reproduction of M. chitwoodi on four alfalfa cultivars. M. chitwoodi reproduced on the alfalfa entry Mn PL9HF.