Population Development of Heterodera glycines and Soybean Yield in Soybean-maize Rotations Following Introduction into a Noninfested Field

An 11-year field study was initiated in 1979 to monitor population development of Heterodera glycines. Fifty cysts of a race 5 population were introduced into plots in a field with no history of soybean production and that had been in sod for 20 years. Soybean cultivars either susceptible or resistant to H. glycines were grown either in monoculture or rotated with maize in a 2-year rotation. During the first 5 years, resistant cultivars with the Peking source of resistance were planted. After year 5, monocuhure of Peking resistance resulted in 18 cysts/250 cm³ of soil, whereas populations resulting from the continuous cropping of susceptible soybean resulted in 45 cysts/250 cm³. Some plots in all treatments, including control plots, were contaminated at the end of year 5. Crop rotation delayed population development of H. glycines. During years 6 through 11 cv. Fayette (PI88.788 source of resistance) was planted. In year 6 numbers of cysts declined to 1/250 cm³ of soil in the treatment consisting of monocultured Fayette. At the end of year 10, cysts were below the detection level in all treatments in which Fayette was planted. Yield of susceptible soybean in monoculture with or without H. glycines infestation was lower beginning in year 6 when compared to yield of soybean grown in rotation and remained lower throughout the duration of the experiment except for 1987 (year 9). Yields of susceptible and resistant soybean were different each year except for drought years in 1980 and 1988. From 1979 to 1982 differences in yield were due to lower yield potential of resistant cultivars. Except for the drought year, yield of cv. Fayette was greater than susceptible Williams 82 during years 6 through 11.     

Soybean and Maize Cropping Models for the Management of Meloidogyne incognita in the Coastal Plain

Models are presented to describe the influence of rotations of Meloidogyne incognita-susceptible cultivars, resistant cultivars, and maize on postharvest abundance of M. incognita juveniles in the soil. Depending on initial densities of juveniles, monocultured regimes reached equilibrium densities after a few years of 287, 40, and 10 juveniles per 10 cm³ soil for susceptible soybean, resistant soybean, and maize, respectively. Yearly changes in the population density of juveniles due to rotation of these crops were simulated by iterative substitution of the model equations for each crop. A maximum density of 319 per 10 cm³ soil was reached following a susceptible cultivar in a susceptible-resistant soybean rotation. Soybean yield loss estimates are presented for monocultured regimes and for various rotations with maize.     

Effect of Within-field Variation in Soil Texture on Heterodera glycines and Soybean Yield

The influence of soil texture on Soybean yield in the presence of Heterodera glycines was investigated by comparing yields of susceptible cultivars with a resistant cultivar for 2 years. Soybean yield was negatively correlated with increasing sand content (P = 0.05). Yields of susceptible cultivars were suppressed with increasing sand content. Final nematode population densities were lowest in plots with greatest sand content. Soybean infection by SCN, as determined by the number of cysts 30 days after planting, was not consistently related to soil texture over 2 years. Initial nematode population density was positively related to soybean yield the first year and negatively related to soybean yield the second, probably a result of greater yield suppression by H. glycines in plots with greater sand content.     

Effects of Potato-Cotton Cropping Systems and Nematicides on Plant-Parasitic Nematodes and Crop Yields

Belonolaimus longicaudatus has been reported as damaging both potato (Solanum tuberosum) and cotton (Gossypium hirsutum). These crops are not normally grown in cropping systems together in areas where the soil is infested with B. longicaudatus. During the 1990s cotton was grown in a potato production region that was a suitable habitat for B. longicaudatus. It was not known how integrating the production of these two crops by rotation or double-cropping would affect the population densities of B. longicaudatus, other plant-parasitic nematodes common in the region, or crop yields. A 3-year field study evaluated the viability of both crops in monocropping, rotation, and double-cropping systems. Viability was evaluated using effects on population densities of plant-parasitic nematodes and yields. Rotation of cotton with potato was found to decrease population densities of B. longicaudatus and Meloidogyne incognita in comparison with continuous potato. Population densities of B. longicaudatus following double-cropping were greater than following continuous cotton. Yields of both potato and cotton in rotation were equivalent to either crop in monocropping. Yields of both crops were lower following double-cropping when nematicides were not used.     

Effects of Initial Nematode Density on Population Dynamics of Globodera rostochiensis on Resistant and Susceptible Potatoes

The influence of resistant and susceptible potato cultivars on Globodera rostochiensis population density changes was studied at different nematode inoculum levels (Pi) in the greenhouse and field. Soil in which one susceptible and two resistant cultivars were grown and fallow soil in pots was infested with cysts to result in densities of 0.04-75 eggs/cm³ soil. A resistant cultivar was grown in an infested field with Pi of 0.7-16.7 eggs/cm³ soil. Pi was positively correlated with decline of soil population densities due to hatch where resistant potatoes were grown in the greenhouse and in the field but not in fallow soil. However, Pi was not correlated with in vitro hatch of G. rostochiensis cysts in water or potato root diffusate. Under continuous culture o f a resistant cultivar, viable eggs per cyst declined 60-90% per plant growth cycle (4 weeks) and the number of cysts containing viable eggs had decreased by 77% after five cycles. The rate of G. rostochiensis reproduction on both resistant and susceptible cultivars was negatively correlated with Pi. These data were used to predict the effect of resistant and susceptible potato cultivars on G. rostochiensis soil population dynamics.     

Evaluation of NemX,a New Cultivar of Cotton with High Resistance to Meloidogyne incognita

The level of resistance to root-knot nematode, Meloidogyne incognita, in NemX, a new cultivar of the Acala-type upland cotton, was evaluated in relation to four resistant breeding lines (N6072, N8577, N901, and N903) and four susceptible cultivars (Maxxa, SJ2, Royale, and Prema). In growth pouch tests, an average of only 4 nematode egg masses was produced on roots of NemX or the resistant lines, compared to a significantly higher average of 21 on the susceptible cultivars. In pot tests, the nematode reproduction factor (RF = Pf/Pi) in NemX and the resistant lines averaged 0.7, compared to a significantly higher average of 10 on the susceptible cultivars. Root galling in NemX or other resistant cotton averaged 15%, compared to 74% on the susceptible cultivars, in either pot or field tests. In plots with low levels of nematode infestation (Pi ≤ 150 second-stage juveniles [J2]/500 g soil), lint yield of NemX averaged 1,370 kg/ha and was less than the yield of susceptible Maxxa (1,450 k g /h a ). However, in plots with medium or high levels of nematode infestation (Pi = 151-300 or >300 J2/500 g soil, respectively), yields of NemX decreased only slightly and averaged 1,300 or 1,050 kg/ha, respectively, whereas yields of Maxxa were severely reduced to 590 or 503 kg/ha, respectively. Fusarium wih symptoms were observed on both NemX and Maxxa, and percent occurrence increased with increasing preplant nematode density. In plots with the highest nematode densities, 22% of NemX and 65% of Maxxa plants were wilted. NemX was highly effective against five M. incognita isolates and moderately effective against a sixth isolate that had been exposed to resistant cotton over several seasons. These results showed that NemX is as resistant to M. incognita as the four breeding lines, and much more resistant than the tested susceptible cultivars of cotton.     

Response of Resistant and Susceptible Bell Pepper (Capsicum annuum) to a Southern California Meloidogyne incognita Population from a Commercial Bell Pepper Field

To determine the presence and level of root-knot nematode (Meloidogyne spp.) infestation in Southern California bell pepper (Capsicum annuum) fields, soil and root samples were collected in April and May 2012 and analyzed for the presence of root-knot nematodes. The earlier samples were virtually free of root-knot nematodes, but the later samples all contained, sometimes very high numbers, of root-knot nematodes. Nematodes were all identified as M. incognita. A nematode population from one of these fields was multiplied in a greenhouse and used as inoculum for two repeated pot experiments with three susceptible and two resistant bell pepper varieties. Fruit yields of the resistant peppers were not affected by the nematodes, whereas yields of two of the three susceptible pepper cultivars decreased as a result of nematode inoculation. Nematode-induced root galling and nematode multiplication was low but different between the two resistant cultivars. Root galling and nematode reproduction was much higher on the three susceptible cultivars. One of these susceptible cultivars exhibited tolerance, as yields were not affected by the nematodes, but nematode multiplication was high. It is concluded that M. incognita is common in Southern California bell pepper production, and that resistant cultivars may provide a useful tool in a nonchemical management strategy.     

Population Dynamics of Plant Nematodes in Cultivated Soil: Length of Rotation in Newly Cleared and Old Agricultural Land

During a 6-year study of 1-, 2-, and 3-year crop rotations, population densities of Pratylenchus brachyurus, Trichodorus christiei, and Meloidogyne incognita were significantly affected by the choice of crops but not by length of crop rotation. The density of P. brachyurus and T. christiei increased rapidly on milo (Sorghum vulgate). In addition, populations of P. brachyurus increased significantly in cropping systems that involved crotalaria (C. rnucronata), millet (Setaria italica), and sudangrass (Sorghum sudanense). Lowest numbers of P. brachyurus occurred where okra (Hibiscus esculentus) was grown or where land was fallow. The largest increase in populations of T. christiei occurred in cropping systems that involved millet, sudangrass, and okra whereas the smallest increase occurred in cropping systems that involved crotalaria or fallow. A winter cover of rye (Secale cereale) had no distinguishable effect on population densities of P. brachyurus or T. christiei. Meloidogyne incognita was detected during the fourth year in both newly cleared and old agricultural land when okra was included in the cropping system. Detectable populations of M. incognita did not develop in any of the other cropping systems. Yields of tomato transplants were higher on the newly cleared land than on the old land. Highest yields were obtained when crotalaria was included in the cropping system. Lowest yields were obtained when milo, or fallow were included in the cropping system. Length of rotation had no distinguishable effect on yields of tomato transplants.     

Host Suitability of Soybean Cultivars and Breeding Lines to Reniform Nematode in Tests Conducted in 2001

Reproduction of reniform nematode Rotylenchulus reniformis on 139 soybean lines was evaluated in a greenhouse in the summer of 2001. Cultivars and lines (119 total) were new in the Arkansas and Mississippi Soybean Testing Programs, and an additional 20 were submitted by C. Overstreet, Louisiana State Extension Nematologist. A second test of 32 breeding lines and 2 cultivars from the Clemson University soybean breeding program was performed at the same time under the same conditions. Controls were the resistant cultivars Forrest and Hartwig, susceptible Braxton, and fallow infested soil. Five treatment replications were planted in sandy loam soil infested with 1,744 eggs and vermiform reniform nematodes, grown for 10 weeks in 10 cm-diam.- pots. Total reniform nematodes extracted from soil and roots was determined, and a reproductive factor (final population (Pf)/ initial inoculum level (Pi)) was calculated for each genotype. Reproduction on each genotype was compared to the reproduction on the resistant cultivar Forrest (RF), and the log ratio [log₁₀(RF + 1) is reported. Cultivars with reproduction not significantly different from Forrest (log ratio) were not suitable hosts, whereas those with greater reproductive indices were considered suitable hosts. These data will be useful in the selection of soybean cultivars to use in rotation with cotton or other susceptible crops to help control the reniform nematode and to select useful breeding lines as parent material for future development of reniform nematode resistant cultivars and lines.     

Interactions between Heterodera avenae and Pratylenchus neglectus on Wheat

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (cv. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars were equally good hosts of Pratylenchus neglectus in a glass house experiment with field soil. On wheat crops grown after oats in field experiments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infestations (40 H. avenae eggs/g soil). The field observations indicated that the reduction in population densities of P. neglectus coincided with the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alternation of H. avenae resistant and susceptible cultivars is a possible way of exploiting the inverse relationship between these nematodes, whilst controlling cyst nematode -populations in intensive cereal production systems.     

Effects of Crop Rotation and Nonfumigant Nematicides on Peanut and Corn Yields in Fields Infested with Criconemella Species

The effects of nematicide treatments and corn-peanut cropping sequences on the population development of Criconemella ornata, and C. sphaerocephala and the related impact on crop yields were investigated at two North Carolina locations. Criconemella ornata and C. sphaerocephala were present at the Norman Perry farm, Bertie County (BERTIE); however, only C. ornata was found at the Central Crops Research Station, Johnston County (CCRS). An untreated control was compared to aldicarb 15G, carbofuran 15G, ethoprop 10G, and terbufos 15G granular formulations applied at a rate of 2.2 kg a.i./ha. The cropping sequences were monocuhured corn (C-C-C); monocultured peanut (P-P-P); and two corn-peanut (C-P-C; P-C-P) rotations. Nematicides were inconsistent in controlling C. sphaerocephala and C. ornata. Nematicide treatments enhanced corn yields in the monoculture-cropping cycle in the final year of the experiment at CCRS. Peanut yields were greater in the rotated cropping sequence than under monoculture at BERTIE, but rotation had less effect on peanut yields at CCRS. Declining yields were correlated with an increase in numbers of nematodes. Corn was an intermediate host for C. sphaerocephala and a moderate to poor host for C. ornata. Peanut was an excellent host for C. ornata and a poor host for C. sphaerocephala.     

Influence of Meloidogyne incognita on the Content of Amino Acids and Nicotine in Tobacco Grown Under Gnotobiotic Conditions

Seedlings of Meloidogyne incognita-resistant (N.C. 95) and -susceptible (McNair 30) tobacco cultivars were grown aseptically for 55 days inside isolator chambers in autoclaved soil infested with 0 or 3,000 axenized eggs of M. im ognita per 500 cc of soil. Healthy and infected plants were compared. Dry root weights of infected plants of resistant and susceptible cultivars were 16% and 84%, respectively, less than the controls. Sixteen amino acids, including those precursors for nicotine, and nicotine, increased significantly in infected roots of both cultivars. Increases in amino acids in infected roots ranged from 28% for valine to 103% for tyrosine in the resistant N.C. 95, and from 30% for leucine to 148% for tyrosine in lhe susceptible McNair 30. Nicotine content (dry weight basis) increased 42% and 62% in infected roots of resistant and susceptible cultivars, respectively. Nematode infection increased nicotine by 112% in leaves of N.C. 95, and decreased it by 56% in leaves of McNair 30. Root damage by M. incognita probably decreased nicotine movement into leaves of McNair 30. In N.C. 95, nicotine movement into leaves apparently was not adversel b affected due to lack of significant root damage.     

Meloidogyne incognita Resistance Characteristics in Tomato Genotypes Developed for Processing

Nine resistant processing tomato (Lycopersicon esculentum) cultivars and advanced lines were compared with four susceptible cultivars in 1,3-dichloropropene-fumigated and nontreated plots on Meloidogyne incognita-infested sites over 3 years. Yield of all resistant genotypes grown in nontreated and nematicide-treated plots did not differ and was greater than yield of susceptible genotypes. M. incognita initial soil population densities caused 39.3-56.5% significant (P = 0.05) yield suppressions of susceptible genotypes. Nematode injury to susceptible plants usually caused both fruit soluble solids content and pH to increase significantly (P = 0.05). Only trace nematode reproduction occurred on resistant genotypes in nontreated plots, whereas large population density increases occurred on susceptible genotypes. Slightly greater nematode reproduction occurred on resistant genotypes at the southern desert location, where soil temperature exceeded 30 C, than at other locations. At two locations resistant MOX 3076 supported greater reproduction than other resistant genotypes.     

Effects of One and Two Applications of Nematicides on Nematode Populations and Soybean Yields

Yields of ''McNair 800'' soybeans, Glycine max (L.) Merr., were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied at-planting and with phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Meloidogyne incognita (Kofoid and White) Chitwood. Yields of ''GaSoy 17'' were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied, preplant and with DBCP, carbofuran, phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Hoplolaimus columbus Sher. In several instances, preplant or at-planting treatments plus postplant treatments with the same or different chemicals were more effective than either treatment alone. Generally, the fumigants were more effective than the nonfumigants when they were applied at-planting to M. incognita-infested soil and preplant to H. columbus-infested soil. Phenamiphos, aldicarb, and DBCP were about equally effective when they were applied postplant in M. incognita-infested soil, but DBCP was more effective than carbofuran. Carbofuran, phenamiphos, aldicarb, and DBCP were about equally effective when applied postplant to H. columbus-infested soil.     

Bahiagrass,Corn, Cotton Rotations,and Pesticides for Managing Nematodes,Diseases, and Insects on Peanut

Florunner peanut was grown after 1 and 2 years of Tifton 9 bahiagrass, corn, cotton, and continuous peanut as whole-plots. Pesticide treatments aldicarb (3.4 kg a.i./ha), flutolanil (1.7 kg a.i./ha), aldicarb + flutolanil, and untreated (control) were sub-plots. Numbers of Meloidogyne arenaria second-stage juveniles in the soil and root-gall indices of peanut at harvest were consistently lower in plots treated with aldicarb and aldicarb + flutolanil than in flutolanil-treated and untreated plots. Percentages of peanut leaflets damaged by thrips and leafhoppers were consistently greater in flutolaniltreated and untreated plots than in plots treated with aldicarb or aldicarb + flutolanil but not affected by cropping sequences. Incidence of southern stem rot was moderate to high for all chemical treatments except those that included flutolanil. Stem rot loci were low in peanut following 2 years of bahiagrass, intermediate following 2 years of corn or cotton, and highest in continuous peanut. Rhizoctonia limb rot was more severe in the peanut monoculture than in peanut following 2 years of bahiagrass, corn, or cotton. Flutolanil alone or combined with aldicarb suppressed limb rot compared with aldicarb-treated and untreated plots. Peanut pod yields were 4,186 kg/ha from aldicarb + flutolanil-treated plots, 3,627 kg/ha from aldicarb-treated plots, 3,426 kg/ha from flutolanil-treated plots, and 3,056 kg/ha from untreated plots. Yields of peanut following 2 years of bahiagrass, corn, and cotton were 29% to 33% higher than yield of monocultured peanut.     

Relationship Between Time of Infection with Heterodera glycines and Soybean Yield

Experiments were conducted to determine the relationship between time of infection by Heterodera glycines and soybean growth in the greenhouse and yield of plants grown in the field. Soybean cultivar Essex seedlings growing in the greenhouse were inoculated with H. glycines at 2, 4, or 6 weeks after planting. Seedling growth was inhibited by H. glycines infection at 2 or 4 weeks after planting but not at 6 weeks. Infection of Essex by H. glycines in the field was delayed 2-6 weeks by nematicides. Yields were significantly increased when H. glycines infection was delayed 2 weeks by nematicide treatment. Essex yields were highest when infection was delayed 6 weeks, equalling the yield of the H. glycines-resistant cultivar Asgrow 5474. The effect of H. glycines on soybean growth in the greenhouse and yields in the field declined when infection was delayed 6 weeks. Thus, soybean sensitivity to H. glycines seemed to diminish with age of the soybean plants.     

A Nematicide Seed Treatment to Control Ditylenchus dipsaci on Seedling Alfalfa

Three nematicides were evaluated as seed treatments to control the alfalfa stem nematode (Ditylenchus dipsaci) on seedling alfalfa. Alfalfa seeds were soaked for 10 hours in a 0.5% (formulated by weight) concentration of either carbofuran, phenamiphos or oxamyl in acetone with no adverse effect on seed germination. All three treatments decreased nematode damage and increased survival of ''Ranger'' (susceptible) and ''Lahontan'' (resistant) alfalfa plants, when seeds were planted in soil infested with D. dipsaci. Mean live plant counts after 6 weeks in the untreated control, acetone alone, carbofuran, phenamiphos, and oxamyl treatments, respectively, were 4.3, 6.3, 19.0, 19.8, and 19.0 for Lahontan and 4.5, 1.5, 18.5, 19.3, and 18.0 for Ranger from 20 seeds/pot. Nematicide seed treatments resulted in significantly healthier Ranger alfalfa plants 4 months after planting. The combination of seed treatment and host resistance may provide a means of establishing alfalfa in an alfalfa monocropped system where soil populations of D. dipsaci are high.     

Interaction of Vesicular-Arbuscular Mycorrhizae and Cultivars of Alfalfa Susceptible and Resistant to Meloidogyne hapla

The interaction between vesicular-arbuscular mycorrhizal (VAM) fungi and the root-knot nematode (Meloidogyne hapla) was investigated using both nematode-susceptible (Grasslands Wairau) and nematode-resistant (Nevada Synthetic XX) cultivars of alfalfa (Medicago sativa) at four levels of applied phosphate. Mycorrhizal inoculation improved plant growth and reduced nematode numbers and adult development in roots in dually infected cultures of the susceptible cultivar. The tolerance of plants to nematode infection and development when preinfected with mycorrhizal fungi was no greater than when they were inoculated with nematodes and mycorrhizal fungi simultaneously. Growth of plants of the resistant cultivar was unaffected by nematode inoculation but was improved by mycorrhizal inoculation. Numbers of nematode juveniles were lower in the roots of the resistant than of the susceptible cultivar and were further reduced by mycorrhizal inoculation, although no adult nematodes developed in any resistant cultivar treatment. Inoculation of alfalfa with VAM fungi increased the tolerance and resistance of a cultivar susceptible to M. hapla and improved the resistance of a resistant cultivar.     

Effect of Initial Nematode Density on Managing Globodera rostochiensis with Resistant Cultivars and Nonhosts

Cropping systems in which resistant potato cultivars were grown at different frequencies in rotation with susceptible cultivars and a nonhost (oats) were evaluated at four initial nematode population densities (Pi) for their ability to maintain Globodera rostochiensis at a target level of <0.2 egg/cm³ of soil. At a Pi of 0.1 to 1 egg/cm³ of soil, cropping systems with 2 successive years of a resistant cultivar every 3 years of potato production reduced and maintained G. rostochiensis at <0.2 egg/cm³ of soil. At a Pi of 1 to 4 eggs/cm³ of soil, 2 successive years of a resistant cultivar followed by 1 year of oats for every 4 years of production were necessary to reduce and maintain G. rostochiensis populations at <0.2 egg/cm³ of soil. At a Pi greater than 4 eggs/cm³ of soil, 2 successive years of a resistant cultivar plus 1 year of oats reduced G. rostochiensis densities to <0.2 egg/cm³ of soil, but the population increased above that density after cropping 1 year to a susceptible cultivar. The numbers of cysts and eggs per cyst in the final population (Pf) of G. rostochiensis were influenced by initial density and the frequency of growing a susceptible cultivar in a cropping system. The lowest number of cysts and eggs per cyst in the final G. rostochiensis population occurred with a cropping system consisting of 2 successive years of a resistant cultivar followed by oats with a susceptible cultivar grown the fourth year of production.     

Effects of Host Resistance on Second-stage Juveniles and Adult Males of Globodera rostochiensis

Potato cultivars Katahdin (susceptible) and Rosa (resistant) were exposed to infective second-stage juveniles (J2) of Globodera rostochiensis for varying periods of time, after which root systems were washed and plants were placed in Hoagland''s solution to assess J2 egression and male emergence. After transfer to liquid culture, many J2 egressed from both cultivars, but significantly more egressed from the resistant Rosa than from Katahdin. Juveniles that egressed from Rosa invaded a second host, resistant or susceptible, in significantly fewer numbers than did juveniles that egressed from Katahdin. Also, significantly fewer males developed in and emerged from resistant host roots, relative to susceptible ones. These effects of resistance may be an important component of the tolerance to invasion by G. rostochiensis exhibited by Rosa.