Resistant Host Responses to Ten California Populations of Meloidogyne incognita

Resistant and susceptible cultivars of tomato, lima beans, cotton, and alfalfa were tested with 10 populations of Meloidogyne incognita from different California locations. Nine of the populations differed in aggressiveness on the nine cultivars tested. Two populations were especially aggressive toward resistant tomato cultivars.     

The Development and Influence of Meloidogyne incognita and M. javanica on Wheat

The effects of soil temperature and initial inoculum density (Pi) of Meloidogyne incognito and M. javanica on growth of wheat (Triticum aestivum cv. Anza) and nematode reproduction were studied in controlled temperature baths in the glasshouse. Nematode reproduction was directly proportional to temperature between 14 and 30 C for M. incognita and between 18 and 26 C for M. javanica. Reproduction rates (Pf/Pi, where Pf = final number of eggs) for Pi''s of 3,000, 9,000, and 30,000 eggs/plant were greatest at each temperature when Pi = 3,000. Maximum M. incognita reproduction rate (Pf/Pi = 51.12) was at 30 C. At 26 C, M. javanica reproduction (Pf/Pi = 14.82, 9.02, and 4.23 for Pi = 3,000, 9,000, and 30,000, respectively) was about half that of M. incognita when Pi = 3,000 or 9,000 but similar when Pi = 30,000. Reproduction of both species was depressed between 14 and 18 C. Shoot and root growth and head numbers were inversely related to soil temperature between 14 and 30 C but were not affected by the Pi of M. incognita when 7 d old seedlings were inoculated. When newly germinated seedlings were inoculated with M. incognita or M. javanica, the Pi did not affect shoot and root fresh weights, shoot/root ratio, and tillering, but it did reduce root dry weight (M. javanica at 26 C) and increase shoot dry weight (M. incognita at 18-22 C). The optimum temperature range is lower for wheat growth than for nematode reproduction. Wheat cv. Anza is a good host for M. incognita and M. javanica, but it is tolerant to both species.     

Effect of Temperature on Growth, Development and Reproduction of Meloidogyne hapla in Lettuce

Temperature was an important factor in growth, development and reproduction of Meloidogyne hapla in lettuce. Growth, as measured by increase in diameter of females, was not appreciably different at the intermediate (21.1 C night and 26.7 C day) and high (26.7 C night and 32.2 C day) temperature regimes, but was considerably less at the low temperature regime (15.5 C night and 21.1 C day) than at the two higher temperature regimes. Second-stage female larvae developed into adults 14 days after inoculation at the high, 18 days at the intermediate and 34 days at the low temperature regime. Eggs were observed 20 days after inoculation at the high, 26 days at the intermediate and 54 days at the low temperature regime. Number of eggs and larvae after 6 weeks was greater at the high than at the intermediate temperature regime and no eggs or larvae occurred at the low temperature regime during the observed 6 weeks.     

Nematicidal Principles from Two Species of Lamiaceae

Aqueous extracts of Ocimum sanctum and O. basilicum leaves contained compounds that killed Meloidogyne incognita larvae in 160 min. Thin layer and gas-liquid chromatography, and infrared spectrophotometry indicated that the essential oils eugenol and linalool were the active nematicidal compounds.     

Pathogenicity of Two Populations of Meloidogyne hapla Chitwood on Alfalfa and Sainfoin

The pathogenicity of two populations of the northern root-knot nematode, Meloidogyne hapla Chitwood, population 1 (P1) from alfalfa and population 2 (P2) from sainfoin, was studied on both alfalfa and sainfoin for 25 weeks. Alfalfa and sainfoin plants inoculated with P2 had significantly (P ≤ 0.05) higher mortality than plants inoculated with P1. Plant stands over all weeks for the uninoculated control, P1, and P2 were 90.5, 78.5, and 64.0% for alfalfa and 84.5, 51.0, and 41.0% for sainfoin, respectively. The increased virulence of P2 was again shown when means of plant species were combined (inoculation × week of count interaction). Plants inoculated with P2 had significantly higher mortality than either those inoculated with P1 or the uninoculated control beginning at week 7 and continuing through week 25. Plant stands over species at 25 weeks for the uninoculated control, P1, and P2 were 82.5, 29.0, and 18.0%, respectively. Sainfoin was significantly more susceptible to either population than alfalfa (plant species × week of count interaction). Separation between species first occurred after week 7 and continued until week 25. Percentages of plants remaining for alfalfa and sainfoin were 61.5 and 25.0 after 25 weeks. Significantly higher reproduction occurred in the alfalfa plants remaining after 25 weeks in P2 than in P1. Mean number of eggs per root system were 60,371 for P1 and 104,438 for P2, a difference of 42%. The results of this study indicate a need for breeders to adequately sample nematode populations present in the intended area of cultivar use and to design screening procedures to account for population pathogenicity variability.     

Evaluation of Cultivars,Experimental Lines and Plant Introduction Collection of Sainfoin for Resistance to Meloidogyne hapla Chitwood

Stands of several cultivars and experimental lines of sainfoin (Onobrychis viciifolia) were severely reduced (92% average loss) in a field naturally infested with Meloidogyne hapla. Stands of two alfalfa cultivars included in the test were unaffected. In studies conducted in the greenhouse with plants inoculated at the time of seeding, average mortality was 55% for sainfoin entries and 7% for Ladak alfalfa. Little mortality occurred when plants were inoculated after establishment. Three months after inoculation, all sainfoin entries were heavily galled (range of 3.3-3.7 on a scale of 1-4) while roots of Ladak were only slightly galled (rating of 1.6). Intermating of plants selected in the field plots for resistance to M. hapla showed a slight increase in resistance. Of the 147 plant introduction lines tested in the greenhouse, none were resistant to M. hapla.     

Influence of Meloidogyne hapla Chitwood, 1949 on Development and Establishment of Heterodera schachtii Schmidt, 1871 on Beta vulgaris L

Influence of Meloidogyne hapla on estahlishnrent and maturity of Heterodera schachtii in sugarbeet was studied. Results indicated that when the majority of M. hapla were in second, third, or fourth larval stages within plants prior to H. schachtii inoculation, growth and development of the latter was retarded. However, when M. hapla reached the young female stage prior to inoculation of H. schachtii, establishment and development of the latter was greatly enhanced. As M. hapla reached maturity before and after egg production prior to H. schachtii inoculation, establishment and growth of the latter was progressively decreased. In each instance, M. hapla developed independently and matured at the same rate as in plants inoculated with only M. hapla. Usually ratios of total soluble carbohydrates to reducing carbohydrates were lower, but not significantly different, in plants receiving both nematodes as compared to other treatments.     

Vertical Migration of Meloidogyne chitwoodi and M. hapla under Controlled Temperature

Migratory ability of second-stage juveniles (J2) of two Meloidogyne chitwoodi races and a M. hapla population were compared in soil-filled columns at 12, 18, and 24 C. J2 of all populations migrated farthest at 18 C and least at 12 C. Nematode survival was significantly reduced (P = 0.05) at 24 C.M. chitwoodi J2 migrated further and in greater numbers than M. hapla J2 at all temperatures. A comparison with and without a host plant demonstrated no preferential migration toward the plant. Water percolation through the migration columns stimulated upward migration.     

Variability in Reproduction of Four Races of Meloidogyne incognita on Two Cultivars of Soybean

Variability in the reproduction of the four races ofMeloidogyne incognita on the soybean cuhivars Pickett 71 and Centennial was studied in growth chamber experiments. Analysis of variance in the number of eggs produced by the races 6 weeks after the plants had been inoculated with 5,000 eggs of each race revealed that the nematode race by soybean cultivar interaction was highly significant (P = 0.001). Races 1, 3, and 4 produced from about 5,000 to 15,000 eggs per root system on Pickett 71 and only from about 300 to 600 eggs per root system on Centennial. In contrast, race 2 produced about 8,000 eggs per root system on Centennial and about 1,200 eggs per root system on Pickett 71. In a second experiment, in which the plants were inoculated with 2,000 second-stage juveniles, race 1 and race 2 produced about 13,000 and 3,000 eggs per root system, respectively, on Pickett 71 and about 600 and 10,000 eggs per root system, respectively, on Centennial. The results suggest that M. incognita resistance in soybean is race-specific.     

Optimum Initial Inoculum Levels for Evaluation of Resistance in Tomato to Meloidogyne spp. at Two Different Soil Temperatures

The effects of Meloidogyne incognita or M. javanica at five initial inoculum levels of 20, 100, 200, 1,000, and 2,000 eggs and infective juveniles per seedling on ''Floradade,'' ''Nemarex,'' ''Patriot,'' and ''PI 129149-2(sib)-5'' tomatoes maintained at 25 or 32.5 C were studied. The number of egg masses on roots of the susceptible cultivar Floradade was similar for both species of root-knot nematodes at either 2.5 or 32.5 C soil temperatures. At 25 C, very low numbers of egg masses were produced by both species of root-knot nematodes on Nematex, Patriot, and Lycopersicon peruvianum PI 129149-2(sib)-5. At 32.5 C, the best inoculum level for assessing resistance in these tomato genotypes was 200 eggs and infective juveniles per seedling. With 28 days of incubation, this temperature and inoculum level produced quantitative differences in resistance for both species of Meloidogyne.     

Effects of Temperature and Root Leachates on Embryogenic Development and Hatching of Meloidogyne chitwoodi and M. hapla

At 20 C the duration of the embryogenic development of Meloiclogyne chitwoodi and M. hapla was about 20 days. At 10 C the embryogenic development was 82-84 days for M. chitwoodi and 95-97 days for M. hapla. The effect of distilled water and root leachates of potato cv. Russet Burbank, tomato cv. Columbian, and wheat cv. Hyslop on the hatching of eggs of the two root-knot nematode species was investigated at 4, 7, 10, 15, 20, and 25 C (± 1 C). Cumulative egg taatch was no greater in root leachates titan in distilled water, but temperature did significantly affect egg hatch (P = 0.05). Less than 1% of the eggs of both nematode species hatched at 4 C. The percent cumulative hatch at 10 C was significantly less (P = 0.05) than at higher temperatures for both nematodes and significantly more (P = 0.05) M. chitwoodi eggs hatched than did M. hapla eggs. At 15 G the percent cumulative hatch of both species was significantly lower (P = 0.05) than that at 20 and 25 C. The percent cumulative egg hatch of two species did not differ at 25 C, but was higher (P = 0.05) at 25 C than at 20 C. At 7 C the emergence of M. chitwoodi juveniles was about seven times (P = 0.01) greater than that of M. hapla in distilled water.     

Nematode Temperature Responses: a Niche Dimension In Populations of Bacterial-Feeding Nematodes

The optimum temperatures for population development were determined for six species of bacterial-feeding nematodes from among eight temperatures, ranging from 5 to 40 C. Four of the species are cohabiting species. The range of temperatures over which population development occurs (temperature niche breadth) is different for the cohabiting species. This difference may be a means of reducing competition between species, thus increasing temperatures over which habitats can be exploited.     

Effects of Fluctuating Temperatures and Different Host Plants on Development of Pasteuria penetrans in Meloidogyne javanica

Greenhouse and growth room experiments were conducted to investigate the effect of host plant in relation to different nematode inoculum levels, and temperature fluctuations on the development of Pasteuria penetrans. Host plant affected the development of P. penetrans indirectly through its effect on nematode development. Endospores collected from Meloidogyne javanica females reared on different hosts did not show any differences in subsequent attachment and infectivity. The numbers of endospores produced per infected female were reduced with increasing numbers of females parasitizing okra and tomato roots. Fluctuating temperatures retarded the development of P. penetrans. The life cycle of the parasite was completed faster at approximately constant temperatures close to 30 °C than when the temperature fluctuated away from 30 °C. The temperature of irrigation water did not affect the duration of life cycle of P. penetrans.     

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.     

Relationship Between Morphology and Parasitism in Two Populations of Meloidogyne incognita

The reliability of morphological characters and host differential plants for distinguishing between two populations of Meloidogyne incognita was studied. Population A (originally from North Carolina) had incognita-type perineal patterns. A single egg mass subpopulation of population A had a mixture of incognita and acrita perineal patterns with 33% of the patterns atypical for either species. Population B (from Georgia) had predominantly acrita-type patterns with only about 5% atypical patterns. The head shapes of males from both populations were mainly M. incognita. On the basis of stylet length, both populations conformed to M. incognita acrita. Both populations were identified as M. incognita race 1 by reaction on the North Carolina differential hosts. Reactions on azalea and pepper gave no clear identification of the populations. We concluded that there is no relation between perineal pattern, male head shape, and parasitism of host differentials with the two populations studied.     

A Theoretical Model of the Winter Survival Dynamics of Meloidogyne spp. Eggs and Juveniles

A theoretical model of the winter survival dynamics of Meloidagyne spp. was developed by considering the roles of egg hatching and juvenile mortality and the initial populations of eggs and juveniles at the onset of winter. Two distinct patterns of juvenile dynamics appear which depend upon the numerical values of the model parameters. The model predicts whether eggs or juveniles are the major component of overwintering nematode populations at any time prior to planting. The model could be elaborated to include egg viability and differential mortality of eggs but at some cost in ease of mathematical analysis. A general procedure for fitting the proposed model to experimental or observational data is outlined.     

Effects of Hirsutella minnesotensis and N-Viro Soil® on populations of Meloidogyne hapla

This study was conducted to determine the effects of Hirsutella minnesotensis (Hm), an endoparasitic fungus, and N-Viro Soil® (NVS), a recycled municipal biosolid, on Meloidogyne hapla greenhouse populations from Rhode Island (RI), Connecticut (CT), Geneva, New York (NYG), Lyndonville, New York (NYL), and Michigan (MI). In a greenhouse experiment, tomato (cv. Rutgers) seedlings were inoculated with 0 or 600 eggs of each nematode population and exposed to Hm mycelium (0 or 0.1 g fresh) and NVS (0 or 1 g 0.1 L^-1 of soil) in a factorial design. Hirsutella minnesotensis reduced nematode densities by 31-83% across nematode populations in one test, but only slightly reduced densities of NYG and CT populations in another test. NVS reduced nematode densities by 33-92% across populations in two repeated tests. The combination of the two agents resulted in greater nematode reduction compared with Hm alone, but not compared with NVS alone. Across all Hm and NVS treatments, reduction of nematode densities were generally greater in NYG, CT, and RI than in MI and NYL populations. This study demonstrated that Hm and NVS may be used to suppress different M. hapla populations.