Symptomless Resistance of Alfalfa to Meloidogyne incognita acrita

Penetration, development and migration of the cotton root-knot nematode, Meloidogyne incognita acrita, in resistant and susceptible alfalfa varieties was compared. Larvae entered both resistant and susceptible plants in approximately the same numbers. After 3 to 4 days, the number of larvae in resistant roots decreased sharply until at 7 days fewer than 5 larvae/seedling and no nematode development could be found. In susceptible roots, larvae became sedentary and developed normally; egg production began as early as 18 days after penetration of the host.     

Meloidogyne incognita wartellei n. subsp. (Meloidogynidae), a Root-knot Nematode on Resistant Soybeans in Louisiana

Meloidogyne incognita wartellei n. subsp, is described and illustrated from roots of soybean (Glycine max L.) near Washington, Louisiana. It is rather limited in distribution in that state, being known at five locations comprising about 60,000 acres. It not only attacks commonly susceptihle soybeans but is a destructive pest on other commercial soybean varieties that are resistant to other forms of the M. incognita group in the area. This new subspecies is related most closely to M. i. incognita and M. i. acrita, but differs especially in the females having a delicate stylet with small, rounded knobs sloping posteriorly; dorsal esophageal gland orific further back (5 μm) from base of stylet; and excretory pore often two to three stylet lengths (sometimes more) from the anterior end. Also, males are often without detectable head annules and with an average stylet length of 22.4 μm. Comments and morphometric data are given on M. i. incognita and M. i. acrita.     

Identification of the Chromosome Carrying the Factor for Resistance to Meloidogyne incognita in Tobacco

To identify the chromosome carrying the factor for resistance to Meloidogyne incognita in tobacco, crosses were made between resistant tobacco ''NC95'' as pollen parent and each of the 12 tobacco monosomics (A-L) representative of the Tomentosae half of the Nicotiana tabacum chromosome complement. Of the F₁ seedlings, 927 plants were grown for observation. From these, 223 plants were selected as possible monosomics on the basis of morphological characteristics. These plants were self-pollinated, and the resulting F₂ plants were inoculated with both M. incognita acrita and M. incognita incognita. Sixteen F₂ populations, derived from the haplo-G monosome, were completely resistant. All of the F₂ populations derived from the other 11 monosomic crosses segregated into a 3:1 (resistant:susceptible) ratio. These results indicate that the factor for resistance to M. incognita is located on the G chromosome of N. tabacum. This is the first report establishing the N. tabacum chromosome that carries the factor for root-knot resistance. The results are consistant with our earlier evidence that M. incognita resistance in tobacco is derived from N. tomentosa, a species in the section Tomentosae of the subgenus Tabacum, genus Nicotiana. The other 12 chromosomes of N. tabacum have affinities with N. sylvestris, section Alatae, subgenus Petunoides, genus Nicotiana.     

Field evaluation of starter N and delayed inoculation ofLespedeza cuneata grown in minesoil

A field study was conducted on freshly reclaimed surface-mined area to determine response of sericea lespedeza (Lespedeza cuneata [Dumont] G. Don.) to delayed rhizobial inoculation. Soybeans (Glycine max L.) were used as a control legume. Plots were inoculated with spray applications of rhizobial suspensions at seeding, cotyledon stage or second trifoliate leaf stage, or not inoculated. Starter N at 0, 10 or 20 kg ha^?1 was applied preplant in a factorial arrangement with inoculation timings.G. max. was grown for 92 days andL. cuneata for 121 days. Starter N increased plant growth and total shoot N in both species. However, % shoot N was found to increase only inL. cuneata. Delaying inoculation had no significant effect upon total shoot N or % shoot N accumulation inL. cuneata. Inoculation ofG. max at planting produced greater plant growth and N accumulation than delayed inoculation treatments. Application of inoculum as a surface spray appeared to be an effective method for delayed inoculation as evidenced by nodule formation. Lack of increased plant growth, regardless of time of inoculation, suggests that delayed inoculation does not improve establishment and growth ofL. cuneata in minesoil.     

Relationships Between Tolerance and Resistance to Meloidogyne incognita in Cotton

The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the United States, and both resistance and tolerance to M. incognita could be valuable management approaches. Our objectives were to evaluate advanced cotton breeding lines for resistance and tolerance to M. incognita and to determine if a relationship between resistance and tolerance exists. Reproduction of M. incognita was evaluated on 17 breeding lines, a susceptible control (Delta and Pine Land DP5415), and a resistant control (M-120) in two greenhouse trials with six replications in a randomized complete block design. Two-week-old seedlings were inoculated with 8,000 M. incognita eggs and assessed for egg production 8 weeks later. Reproduction on the resistant control was only 10% of that on the susceptible control. Eight breeding lines supported 45% to 57% less (P <= 0.05) nematode reproduction than the susceptible control, and none of them were as resistant as M-120. Yield was determined in 2001 and 2002 in fumigated (1,3-dichloropropene at 56 liters/ha) and nonfumigated plots in a strip-plot design with three replications in a field naturally infested with M. incognita. Yield suppression caused by nematode infection differed among genotypes (P ≤ 0.05 for genotype × fumigation interaction). Six genotypes in 2001 and nine in 2002 were tolerant to M. incognita based on no difference in yield between the fumigated and nonfumigated plots (P ≥ 0.10). However, only three genotypes had no significant yield suppression in both years, of which two also were resistant to M. incognita. Regression analysis indicated that yield suppression decreased linearly as nematode resistance increased.     

Influence of olfactory stimulants on resistance/susceptibility of pearl millet, Pennisetum americanum to the rice weevil, Sitophilus oryzae

The orientation responses of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) as influenced by the olfactory stimulants emanating from either resistant or susceptible pearl millet, Pennisetum americanum, kernels were studied using a Y-tube olfactometer. The rice weevils were more attracted towards odours from millet grains than to blank controls and to susceptible entries more than to resistant entries, in general. However, there were exceptions. Odours from some resistant entries caused statistically the same, or even more positive orientations than those from some susceptible entries, and this suggests that the relative resistance of an entry and its olfactory attractiveness may not be strongly related, or that the resistance to infestation might be influenced by factors other than attractiveness. The partial damage of the millet kernel pericarp by abrasion slightly increased the orientational response of the weevils to odours from some susceptible and some resistant entries alike.     

The Relationship of Meloidogyne incognita acrita to the Incidence of Cabbage Yellows

Three inoculum level combinations of Meloidogyne incognita acrita and Fusariurn oxysporurn f. conglutinans did not affect the incidence of cabbage yellows in the moderately-resistant ''Greenback'' or the highly-resistant ''Marion Market'' varieties. The susceptible ''Early Round Dutch'' variety was more susceptible to low levels of fungus inoculum in the presence of the nematode.     

Resistance of Cucumis spp. to the Root-knot Nematode,Meloidogyne incognita acrita

The nature of resistance in Cucumis ficifolius and C. metuliferus to the root-knot nematode, Meloidogyne incognita acrita, was studied under greenhouse conditions. Although as many larvae penetrated the roots of these species as those of the susceptible C. melo, few developed to the adult female stage. Resistance in C. ficifolius and C. metuliferus was associated with hindrance of larval development beyond the second stage, delayed development of larvae to adults and stimulation toward maleness. Tissue necrosis or hypersensitivity was not associated with larval penetration. Comparisons of the histopathology of 26-day-old infections of C. melo and C. metuliferus roots showed no observable differences in the type of giant cell development in regions of roots associated with adult females. However, in C. rnetuliferus immature nematodes were associated with small giant cells which were limited to a few cells near the head of the nematode.     

Identification of resistance source in wheat germplasm against spot blotch disease caused by Bipolaris sorokiniana

Four hundred and twenty-two spring wheat germplasm (Triticum aestivum L.) lines belonging to Indian, CIMMYT and Chinese wheat programme were evaluated for their tolerance against natural epiphytotic conditions of spot blotch caused by Bipolaris sorokiniana at the hot spot location, Pusa, Bihar, India. Of the 422 entries screened, none of the genotype showed immunity to the disease, whereas 52 were resistant, 180 moderately susceptible, 171 susceptible and 19 highly susceptible. Indian germplasm lines tended to be more susceptible than lines originated from CIMMYT and China. Chirya 3, Chirya 7 and Mayoor from CIMMYT showed high degree of resistance to the disease both under field and polyhouse conditions. On the basis of the disease severity under field conditions, 20 promising resistant genotypes and 10 highly susceptible lines were isolated for further testing under artificial epiphytotic conditions in polyhouse for genetic analysis and their potential for spot blotch resistance breeding.     

Retention of Resistance to Meloidogyne incognita in Lycopersicon Genotypes at High Soil Temperature

Lycopersicon glandulosum and L. peruvianum clones and L. esculentum cultivars ''VFN8'' (resistant) and ''Rutgers'' (susceptible) were tested for their resistance to Meloidogyne incognita (race l) at soil temperatures of 25 and 32 C. L. esculentum cv. VFN8 and L. peruvianum Acc. No. 128657, both of which possess the Mi gene, were resistant at 25 C but were susceptible at 32 C. L. glandulosum Acc. No. 126443 and L. peruvianum Acc. No. 270435, with combined resistance to M. hapla and M. incognita, and L. peruvianum Acc. Nos. 129152 and LA2157, with resistance to M. incognita, were highly resistant at both temperatures. In a second experiment three of these accessions under heat stress simulated by 32 C ambient and soil temperature retained a high level of resistance. Two clones of L. glandulosum Acc. No. 126440, with resistance to M. hapla, were moderately susceptible to M. incognita at 25 and highly susceptible at 32 C. M. incognita produced significantly (P = 0.01) more eggs on L. esculentum cv. Rutgers at 32 than at 25 C. This study supports the existence of genes other than the Mi gene that confer resistance to M. incognita and are functional at high soil temperatures.     

Hatching Response of Meloidogyne incognita acrita to Electric Shock

The influence of electric shock on hatch of Meloidogyne incognita acrita from egg masses taken from roots of ''Acala SJ-I'' cotton (Gossypium hirsutum L.) was studied. Egg masses in tap water were individually placed between the tips of needle electrodes 1 mm apart and exposed to potentials of l, 10, 20, and 60 vdc/mm at 1, 1, 1, and 86 milliamperes dc, respectively, for periods of 2 and 60 seconds. Hatched larvae were counted at five-day intervals for 60 days. Of the eight treatment combinations used, six gave a greater egg hatch than the control. The largest hatch, 520 percent greater than the control, resulted from exposure to 1 vdc/mm for 60 seconds; 60 vdc/mm for 2 and 60 sec decreased egg hatch 11 and 94 percent of the untreated control. Hatched larvae from all treatments except the 60 vdc/mm, 60-second exposure were infective and reproduced on young cotton plants in a glasshouse.     

Control of Meloidogyne javanica and M. arenaria on kenaf and roselle with genetic resistance and nematicides

Kenaf (Hibiscus cannabinus) and roselle (H. sabdarifla) were evaluated in nematicide-treated and untreated field soil naturally infested with either Meloidogyne javanica or M. arenaria. Root-knot indices indicated that the kenaf breeding line j-l-113 had moderate resistance to M. javanica and low resistance to M. arenaria. Kenaf cv Everglades 71 was highly susceptible to both M. javanica and M. arenaria, and roselle breeding line A59-56 was highly resistant. Both nematode species reproduced on all plant entries, but more larvae were recovered from the soil in plots planted to Everglades 71 than in plots planted to j-l-l13 or A59-56. In untreated soil infested with M. javanica, dry-matter yields were greater (P = 0.05) for j-l-l13 and A59-56 than for Everglades 71. The percentages of live plants at harvest were: j-l-l13, 88; A59-56, 93; and Everglades 71, 9. Ethylene dibromide (1,2-dibromoethane) at 73.9 kg a.i./ha and DBCP (1,2-dibromo-3-chloropropane) at 17.6 kg a.i./ha increased dry-matter yields significantly for all entries planted in soil infested with M. arenaria. Carbofuran (2.3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) at 5.9 kg a.i./ha did not increase the dry-matter yields of any entry. None of the nematicides increased the growth of any entry significantly in soil infested with M. javanica.     

Yield Response and Injury Levels of Meloidogyne incognita and M. javanica on the Susceptible Tobacco 'McNair 944'

The effects of Meloidogyne incognita and M. javanica on a susceptible tobacco (Nicotiana tabacum L.) cv. McNair 944 were investigated in field microplots during 1978 and 1979. Three initial inoculum levels—4, 16, and 64 nematode eggs and/or second-stage larvae per 100 cm³ of soil—were used for each nematode species. Data obtained from the experiments included plant yield and the amount of reproduction of the two nematode species. At comparative inoculum levels, M. javanica was more aggressive than M. incognita on tobacco and caused approximately twofold more yield suppression than M. incognita. The calculated initial population of M. incognita, derived from the average for 2 yr, which produced a 7% suppression in plant yield was four eggs and/or second-stage larvae per 100 cm³ of soil; whereas less than one M. javanica egg and/or second-stage larvae per 100 cm³ of soil was needed to achieve similar suppression. Nematode reproduction varied in the 1978 and 1979 tests, but similar trends were observed. Early season M. javanica populations were greater than those of M. incognita, but late season populations of M. incognita were twice anti three times those of M. javanica.     

Effect of molecular weight of condensed tannins from warm-season perennial legumes on ruminal methane production in vitro

The objectives of the present study were to determine if the molecular weight of condensed tannins (CT) from warm-season perennial legumes affects the biological activity of CT relative to suppression of methane (CH₄) production by ruminants, and to identify potential North American native forage plants to use for mitigation of enteric CH₄ emission. Eight North American native warm-season perennial legumes were evaluated: Leucaena retusa Benth. (littleleaf leadtree), Desmanthus illinoensis (Michx.) MacMill. Ex B.L. Rob. & Fernald (Illinois bundleflower), Lespedeza stuevei Nutt. (tall lespedeza), Mimosa strigillosa Torr. & A. Gray (powderpuff), Neptunia lutea (Leavenworth) Benth. (yellow puff), two ecotypes of Acacia angustissima var. hirta (Nutt.) B.L. Rob (prairie acacia), and Desmodium paniculatum (L.) DC. var. paniculatum (panicledleaf ticktrefoil). Two introduced legumes were also included: Arachis glabrata Benth. (rhizoma peanut) and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza). Forages were fermented with cattle rumen fluid for 48 h anaerobically using an in vitro gas production technique. D. paniculatum, L. stuevei, and M. strigillosa were high in CT, ranging from 11.7 to 12.5%. D. illinoensis, L. cuneata, N. lutea, and two ecotypes of A. angustissima var. hirta had less CT (P < 0.05), ranging from 8.1 to 8.9%, whereas L. retusa and A. glabrata had the least CT (P < 0.05), measuring 3.2 and 0.5%, respectively. Weight-average molecular weight (M_W) of CT ranged from 1483 Da for L. cuneata to 552 Da for L. stuevei. In vitro CH₄ production was greatest for L. retusa and A. glabrata at 40.7 mg/g DM and 38.2 mg/g DM, respectively. The least amount of in vitro CH₄ was produced by fermentation of two ecotypes of A. angustissima var. hirta, which measured 0.8 and 0.6 mg/g DM, respectively. In vitro CH₄ production regressed on CT M_W resulted in a R² of 0.0009 (P = 0.80), strongly suggesting that CT M_W does not explain the biological activity of in vitro CH₄ production by the forage legumes surveyed. Five of the seven North American native warm-season perennial legumes have promise for use in ruminant diets for the purpose of CH₄ emission mitigation.     

Virulence of Meloidogyne incognita to expression of N gene in pepper

Four pepper genotypes classified as resistant and four pepper genotypes classified as susceptible to several avirulent populations of M. incognita were compared for their reactions against a population of Meloidogyne incognita (Chitwood) Kofoid and White which had been shown to be virulent to resistant bell pepper (Capsicum annuum) in preliminary tests. The virulent population of M. incognita originated from a commercial bell pepper field in California. The resistant pepper genotypes used in all experiments were the Capsicum annuum cultivars Charleston Belle, Carolina Wonder, and Carolina Cayenne, and the C. chinense cultigen PA-426. The susceptible pepper genotypes used in the experiments were the C. annuum cultivars Keystone Resistant Giant, Yolo Wonder B, California Wonder, and the C. chinense cultigen PA-350. Root gall indices (GI) were ≥ 3.0 for all genotypes in both tests except for PA-426 (GI=2.57) in test 1 and 'Carolina Cayenne' (GI=2.83) in test 2. Numbers of eggs per gram fresh root weight ranged from 20,635 to 141,319 and reproductive indices ranged from 1.20 to 27.2 for the pepper genotypes in both tests, indicating that all eight pepper genotypes tested were susceptible to the M. incognita population used in these tests. The M. incognita population used in these studies overcame resistance conferred by the N gene in all resistant genotypes of both C. annuum and C. chinense.     

Evaluation of Perennial Glycine Species for Response to Meloidogyne Incognita,Rotylenchulus Reniformis,and Pratylenchus Penetrans

Root-knot (Meloidogyne incognita (Kofoid & White) Chitwood), reniform (Rotylenchulus reniformis Lindford & Oliveira), and lesion nematodes (Pratylenchus penetrans (Cobb) Filipjev & Schuurmans Stekhoven) are plant-parasitic nematodes that feed on soybean (Glycine max (L.) Merr.) roots, limiting seed production. The availability of resistance in soybeans to these nematodes is limited. However, new sources of resistance can be discovered in wild relatives of agronomic crops. Perennial Glycine species, wild relatives to soybean, are a source of valuable genetic resources with the potential to improve disease resistance in soybean. To determine if these perennials have resistance against nematodes, 18 accessions of 10 perennial Glycine species were evaluated for their response to M. incognita and R. reniformis, and eight accessions of six perennial Glycine species were evaluated for their response to P. penetrans. Pot experiments were conducted for M. incognita and R. reniformis in a growth chamber and in vitro experiments were conducted for P. penetrans. We found both shared and distinct interactions along the resistance-susceptible continuum in response to the three plant-parasitic nematode species. Ten and 15 accessions were classified as resistant to M. incognita based on eggs per gram of root and gall index, respectively. Among them, G. tomentella plant introductions (PIs) 446983 and 339655 had a significantly lower gall index than the resistant soybean check cv. Forrest. Of three R. reniformis resistant accessions identified in this study, G. tomentella PI 441001 showed significantly greater resistance to R. reniformis than the resistant check cv. Forrest based on nematodes per gram of root. In contrast, no resistance to P. penetrans was recorded in any perennial Glycine species.     

Reproductive Variability of Field Populations of Meloidogyne spp. on Grape Rootstocks

Variability in penetration, development, and reproduction of two resistance-breaking field pathotypes (pt.) of Meloidogyne arenaria, M. incognita, and a population of mixed Meloidogyne spp. virulent to grape hosts were compared on two resistant Vitis rootstocks ''Freedom'' and ''Harmony'' in separate tests. ''Cabernet Sauvignon'' was included as a susceptible host to all four nematode populations. Secondstage juveniles (J2) of the mixed population failed to penetrate Freedom roots. By contrast, 6% of J2 in the M. incognita population penetrated Freedom roots but did not develop beyond the swollen J2 stage. The two resistance-breaking populations of M. arenaria differed in their virulence except on susceptible roots of Cabernet Sauvignon. More J2 of M. arenaria pt. Freedom penetrated Freedom roots and reached adult stage than did M. arenaria pt. Harmony. Later life stages of M. arenaria pt. Freedom occurred earlier and in greater numbers in Harmony roots than did M. arenaria pt. Harmony. Reproduction of M. arenaria pt. Freedom was greater in Freedom and Harmony roots than M. arenaria pt. Harmony. Thus, one population of M. arenaria is highly virulent and the other is moderately virulent.     

Identification of Sources of Resistance to Four Species of Root-knot Nematodes in Tobacco

Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.     

Attraction of Ditylenchus dipsaci and Meloidogyne hapla by Resistant and Susceptible Alfalfa Seedlings

Ditylenchus dipsaci Kühn were equally attracted to and equally invaded resistant (''Lahontan'') and susceptible (''Ranger'') germinating alfalfa (Medicago sativa L.) seedlings exposed singly in moist sand except at a distance of 12.5 mm at 20 C when the susceptibles proved more attractive than the resistants. Larvae hatching from egg-masses of Meloidogyne hapla Chitwood were also attracted equally to germinating seedlings of resistant (''M-9'') and susceptible (''Lahontan'') alfalfa offered singly. When hatched midway between resistant and susceptible, however, more larvae were attracted to the susceptibles. M. hapla larvae were attracted equally to the root and stem apices, region of elongation, and upper hypocotyl of resistant and susceptible plants.     

Characterization of Root-Knot Nematode Resistance in Medicago truncatula

Root knot (Meloidogyne spp.) and cyst (Heterodera and Globodera spp.) nematodes infect all important crop species, and the annual economic loss due to these pathogens exceeds $90 billion. We screened the worldwide accession collection with the root-knot nematodes Meloidogyne incognita, M. arenaria and M. hapla, soybean cyst nematode (SCN-Heterodera glycines), sugar beet cyst nematode (SBCN-Heterodera schachtii) and clover cyst nematode (CLCN-Heterodera trifolii), revealing resistant and susceptible accessions. In the over 100 accessions evaluated, we observed a range of responses to the root-knot nematode species, and a non-host response was observed for SCN and SBCN infection. However, variation was observed with respect to infection by CLCN. While many cultivars including Jemalong A17 were resistant to H. trifolii, cultivar Paraggio was highly susceptible. Identification of M. truncatula as a host for root-knot nematodes and H. trifolii and the differential host response to both RKN and CLCN provide the opportunity to genetically and molecularly characterize genes involved in plant-nematode interaction. Accession DZA045, obtained from an Algerian population, was resistant to all three root-knot nematode species and was used for further studies. The mechanism of resistance in DZA045 appears different from Mi-mediated root-knot nematode resistance in tomato. Temporal analysis of nematode infection showed that there is no difference in nematode penetration between the resistant and susceptible accessions, and no hypersensitive response was observed in the resistant accession even several days after infection. However, less than 5% of the nematode population completed the life cycle as females in the resistant accession. The remainder emigrated from the roots, developed as males, or died inside the roots as undeveloped larvae. Genetic analyses carried out by crossing DZA045 with a susceptible French accession, {"type":"entrez-protein","attrs":{"text":"F83005","term_id":"11352626","term_text":"pir||F83005"}}F83005, suggest that one gene controls resistance in DZA045.