Nematode Egg Production Research Articles

Immune markers in goats selected for reduced gastrointestinal nematode egg count under artificial infection conditions

This study aimed to further investigate the mechanisms responsible for inhibition of gastrointestinal nematode egg production in a line of Scottish Cashmere Goat selected for low faecal egg count. Animals were chosen as the lowest egg producers from a line selected for low egg output (selected group) with a second group from the wider herd based on high faecal egg count as controls. All animals were artificially infected with Teladorsagia circumcincta and Trichostrongylus vitrinus, then treated with anthelmintic and challenge infected prior to euthanasia and post mortem sampling.There was no effect on body weight between groups at any point in the study. Mean faecal egg count was reduced by 68 % in the selected group when compared with the controls. Circulating eosinophil counts were consistently elevated in the selected group, but this was only marginally significant (P = 0.045). Most of the circulating and tissue antibodies (IgG, IgA and IgE) measured were slightly elevated in the selected group but not significantly. Mucosal mast cells, eosinophils and globule leukocyte levels were higher in the abomasal and intestinal tissues in selected animals. Following challenge infection there was no difference in numbers of parasites, however there were more early stage parasite larvae and fewer late stage larvae in the both the abomasum and duodenum of the selected group compared with the unselected group, indicating some inhibition of parasite development.Overall, the study further demonstrated that selection based on low egg count has resulted in a line of goats producing significantly fewer parasites under identical infection with no effect on bodyweight. This appears to be associated with elevation in antibody and effector cells. Some evidence of host inhibition of parasite development was observed in the selected animals.

Non-fumigant Nematicides are Promising Alternatives to Fumigants for the Management of Meloidogyne Enterolobii in Tobacco.

Experiments were conducted to evaluate the efficacy of three currently available non-fumigant chemical nematicides (oxamyl, fluopyram, and fluensulfone) and a biological nematicide derived from Burkholderia against Meloidogyne enterolobii on tobacco in a growth room environment. The non-fumigant chemical nematicides greatly suppressed nematode egg production compared to the untreated control, the suppression being 99.9% for fluensulfone and oxamyl, and 93% for fluopyram. Similarly, oxamyl-, fluensulfone-, and fluopyram-treated pots, respectively, had 99%, 98%, and 94% less J2/100 cm3 of soil than those in the control. The biological nematicide did not have a significant effect on nematode egg production and the soil abundance of J2. The root biomass of tobacco was significantly reduced by the application of fluensulfone, while the effects of oxamyl, fluopyram, and Burkholderia metabolites were not significant compared to the untreated control. Results from this study suggest that non-fumigant nematicides have a potential to serve as an alternative to fumigant nematicides.

The non-invasive measurement of faecal immunoglobulin in African equids.

Eco-immunological research is encumbered by a lack of basic research in a wild context and by the availability of few non-invasive tools to measure the internal state of wild animals. The recent development of an enzyme-linked immunosorbent assay for measuring immunoglobulins in faecal samples from Soay sheep prompted us to optimize such an assay to measure immunoglobulin A (IgA: an antibody associated with parasitic nematode fecundity) in faecal samples from equids. We measured total IgA in domestic donkeys, wild plains zebras, and wild Grevy's zebras sharing the same landscape in central Kenya over two field seasons. Attempts to measure anti-nematode IgA more specifically, using a homogenized extract from a mixture of excreted nematodes, failed to clear background. However, we found that total IgA positively correlated with strongyle nematode faecal egg counts (FECs) in donkeys sampled during the wetter field season - a time when the donkeys were in good condition. Further, this relationship appeared among donkeys with high body condition but not among those with low body condition. Time lags of 1–4 days introduced between IgA and FEC measurements in repeatedly sampled donkeys did not yield correlations, suggesting that IgA and FEC roughly tracked one another without much delay in the wet field season. Such a direct IgA-FEC relationship did not appear for zebras in either the wet or dry field season, possibly due to higher interindividual variation in body condition among the free-roaming zebras than in the donkeys. However, Grevy's zebras had higher overall levels of IgA than either plains zebras or donkeys, potentially associated with their reportedly lower FECs at the population level. Our results suggest that equids may mount an IgA response to nematode egg production when the host is in good condition and that equid species may differ in baseline levels of mucosal IgA.

Rootstocks for Florida Stone Fruit

Rootstocks have been used in many tree fruit systems to provide growth advantages and/or pest and disease resistance without affecting (or sometimes improving) productivity and fruit quality. In Florida, stone fruit are grown on rootstocks that specifically provide resistance to the peach root-knot nematode, Meloidogyne floridensis (Handoo, et al., 2004; Sherman, et al., 1991). Although several root-knot nematode-resistant rootstocks are available for stone fruit grown in other locations and climates, ‘Flordaguard’ peach rootstock is currently the only rootstock recommended for stone fruit production in Florida.
 
 Root-knot nematodes (M. incognita and M. javanica) have historically been the most important species of root-knot nematodes parasitizing peach in the southeastern United States peach industry. ‘Guardian’, ‘Nemaguard’, ‘Nemared’, and ‘Okinawa’ rootstocks are resistant to these species of nematode. However, in 1966 a new species of root-knot nematode was detected on ‘Nemaguard’ and ‘Okinawa’ peach rootstocks in Gainesville, Florida, and ultimately identified as M. floridensis in 2004 (Han-doo, et al., 2004). This nematode reproduces abundantly on ‘Nemaguard’ and ‘Nemared’ peach rootstocks as well as on other crops (verbena, eggplant, squash, basil, impatiens, tomato, snapdragon, dill, and certain ornamental plants) (Table 1). Consequently, ‘Nemaguard’, ‘Nemared’, and ‘Okinawa’ peach rootstock are no longer recommended for peaches, nectarines, and plums in Florida. ‘Nemaguard’ and ‘Nemared’ rootstocks had been used in north Florida for many years, but continued use may increase nematode populations to damaging levels on these rootstocks.
 
 ‘Flordaguard’ rootstock has better resistance to M. floridensis than ‘Nemaguard’ rootstock. Field evaluation of peach rootstocks to different root-knot nematode species indicated that after 25 months, nematode egg production was greater on ‘Nemaguard’ than on ‘Flordaguard’ rootstock (Nyczepir, et al., 2006). Longer-term observations in Florida also suggest that trees on ‘Nemaguard’ rootstock do not perform well in soils infested with M. floridensis. Accordingly, ‘Flordaguard’ rootstock is the only rootstock the University of Florida currently recommends for commercial peach production. ‘Sharpe’, a clonal plum hybrid rootstock (Beckman, et al., 2008), is only recommended for backyard fruit production because of its reduced yield and smaller fruit size when compared to trees budded onto ‘Flordaguard’ rootstock.

A role for ALF4 during gall and giant cell development in the biotic interaction between Arabidopsis and Meloidogyne spp.

Root-knot nematodes (RKNs; Meloidogyne spp.) are a major pest for the agriculture worldwide. RKNs induce specialized feeding cells (giant cells, GCs) inside galls which are de novo formed pseudo-organs in the roots that share similarities with other developmental processes as lateral root (LR) and callus formation or grafting involving new vascular development or pericycle proliferation. Hence, it is pertinent to study the molecular mechanisms directing the plant-nematode interaction. In this respect, ALF4 is a key gene during LR formation, vascular vessels reconnection in grafting, hormone-induced callus formation or de novo root organogenesis from leaf explants. Our results show that ALF4 is also induced in galls at early infection stages in an auxin-independent way. Furthermore, ALF4 activity is necessary for the formation of proper galls and GCs, as the mutant alf4-1 presents aberrant galls and GCs with severe structural abnormalities leading to a dramatic reduction in the nematode egg production. However, a low-reproduction rate is maintained, that might be explained by the local auxin maximum build by the nematodes in galls, partially rescuing alf4-1 phenotype. This would be similar to the partial rescue described for LR formation with exogenous auxins and also agrees with the LR emergence from alf4-1 galls but not from uninfected roots. In addition, ALF4 is also induced in syncytia formed by cyst nematodes. All these data support a pivotal role for ALF4 during de novo organogenesis processes induced by endoparasitic nematodes, in addition to its role in LR formation, callus development or vessel reconnection during grafting.

Differing interactions between an introduced beetle and a resident root nematode mediated by an invasive plant and its native congener

Interactions between above- and below-ground herbivores play an important role in shaping plant competition and invasion, while the effects of non-native species invasions on above- and below-ground interactions remain unexplored. In this study, we report the interactions between an above-ground introduced beetle and a resident root nematode hosted by an invasive plant or its native congener with a laboratory bioassay and a greenhouse experiment in Wuhan, China. Nematode infections decreased beetle food conversion rates and larval biomass on the native plant, and increased beetle food conversion rates with no detectable impact on the larval biomass on the invasive plant. Beetle defoliation decreased nematode egg production on both the native and invasive plants. The interactions of the introduced beetle and the nematode were different by the invasive and native plants, which suggests that invasive plants and their introduced herbivores have the potential to alter above- and below-ground interactions and affect associated community members, which may in turn affect invasion processes and the safety of classical biocontrol practices.

Effect of Trichoderma spp. and Purpureocillium lilacinum on Meloidogyne javanica in commercial pineapple production in Kenya

Plant-parasitic nematodes, in particular Meloidogyne species, cause significant yield reduction in commercial pineapple, Ananas comosus, worldwide. The efficacy of three Trichoderma isolates (Trichoderma asperellum M2RT4, T. atroviride F5S21, Trichoderma sp. MK4) and two isolates of Purpureocillium lilacinum (KLF2 and MR2) were evaluated against Meloidogyne javanica, using rooted pineapple crowns in a pot experiment under greenhouse conditions. All the three Trichoderma isolates successfully colonized pineapple root endophytically. The application of two isolates of Trichoderma (T. asperellum M2RT4 and Trichoderma sp. MK4) and the two isolates of P. lilacinum significantly reduced nematode egg and egg mass production reducing root galling damage by between 60.8 and 81.8% and increased the plant root mass growth compared to the untreated control. T. asperellum M2RT4 most effectively reduced galls, egg mass and eggs, by 81.8, 78.5 and 88.4% respectively. P. lilacinum MR2 most effectively reduced galls, egg mass and eggs, by 71.6, 73.9 and 82.6% respectively. In contrast Trichoderma atroviride F5S21 application had no significant effect on nematode multiplication or root damage compared with the control. Inoculation with T. asperellum M2RT4 increased root fresh weight by 91.5%, Trichoderma sp. MK4 by 63.8%, T. atroviride F5S21 by 50.0%, P. lilacinum KLF2 by 43.8% and MR2 by 32.3%. Results indicate that local isolates Trichoderma spp. and P. lilacinum directly and indirectly affected nematode reproduction and host response, demonstrating their control potential against M. javanica on pineapple. Such alternative options for managing Meloidogyne spp. would provide more environmentally sensitive options for combining with other management methods towards more sustainable pineapple production systems.

Genetic Mapping of Resistance to Meloidogyne arenaria in Arachis stenosperma: A New Source of Nematode Resistance for Peanut.

Root-knot nematodes (RKN; Meloidogyne sp.) are a major threat to crops in tropical and subtropical regions worldwide. The use of resistant crop varieties is the preferred method of control because nematicides are expensive, and hazardous to humans and the environment. Peanut (Arachis hypogaea) is infected by four species of RKN, the most damaging being M. arenaria, and commercial cultivars rely on a single source of resistance. In this study, we genetically characterize RKN resistance of the wild Arachis species A. stenosperma using a population of 93 recombinant inbred lines developed from a cross between A. duranensis and A. stenosperma. Four quantitative trait loci (QTL) located on linkage groups 02, 04, and 09 strongly influenced nematode root galling and egg production. Drought-related, domestication and agronomically relevant traits were also evaluated, revealing several QTL. Using the newly available Arachis genome sequence, easy-to-use KASP (kompetitive allele specific PCR) markers linked to the newly identified RKN resistance loci were developed and validated in a tetraploid context. Therefore, we consider that A. stenosperma has high potential as a new source of RKN resistance in peanut breeding programs.

Differences between female and castrated male lambs in susceptibility to natural, predominantly Teladorsagia circumcincta infection

The difference between castrated male lambs and entire female lambs in susceptibility to gastrointestinal nematode infection was investigated in a flock of Scottish Blackface sheep. Castrated male lambs had higher faecal egg counts, higher body weights, lower parasite-specific plasma IgA activity and more adult nematodes. There were no detectable differences in the length of adult Teladorsagia circumcincta. Heavier egg shedding by males was associated with greater worm burdens. The difference in plasma IgA activity may have been a consequence of larger numbers of adult nematodes inhibiting the transfer of mucosal IgA to the plasma. At least part of the sex difference in egg production could be a consequence of males ingesting larger amounts of grass and hence numbers of infective larvae because of their larger size. The differences between castrated males and females contribute to the observed variation in nematode egg production in naturally infected lambs.

QTL Analysis for Transgressive Resistance to Root-Knot Nematode in Interspecific Cotton (Gossypium spp.) Progeny Derived from Susceptible Parents

The southern root-knot nematode (RKN, Meloidogyne incognita) is a major soil-inhabiting plant parasite that causes significant yield losses in cotton (Gossypium spp.). Progeny from crosses between cotton genotypes susceptible to RKN produced segregants in subsequent populations which were highly resistant to this parasite. A recombinant inbred line (RIL) population of 138 lines developed from a cross between Upland cotton TM-1 (G. hirsutum L.) and Pima 3–79 (G. barbadense L.), both susceptible to RKN, was used to identify quantitative trait loci (QTLs) determining responses to RKN in greenhouse infection assays with simple sequence repeat (SSR) markers. Compared to both parents, 53.6% and 52.1% of RILs showed less (P<0.05) root-galling index (GI) and had lower (P<0.05) nematode egg production (eggs per gram root, EGR). Highly resistant lines (transgressive segregants) were identified in this RIL population for GI and/or EGR in two greenhouse experiments. QTLs were identified using the single-marker analysis nonparametric mapping Kruskal-Wallis test. Four major QTLs located on chromosomes 3, 4, 11, and 17 were identified to account for 8.0 to 12.3% of the phenotypic variance (R2) in root-galling. Two major QTLs accounting for 9.7% and 10.6% of EGR variance were identified on chromosomes 14 and 23 (P<0.005), respectively. In addition, 19 putative QTLs (P<0.05) accounted for 4.5–7.7% of phenotypic variance (R2) in GI, and 15 QTLs accounted for 4.2–7.3% of phenotypic variance in EGR. In lines with alleles positive for resistance contributed by both parents in combinations of two to four QTLs, dramatic reductions of >50% in both GI and EGR were observed. The transgressive segregants with epistatic effects derived from susceptible parents indicate that high levels of nematode resistance in cotton may be attained by pyramiding positive alleles using a QTL mapping approach.

Genetic Determinants of Differential Resistance to Root‐Knot Nematode Reproduction and Galling in Lima Bean

Root‐knot nematodes (Meloidogyne spp.) are important root parasites that limit lima bean (Phaseolus lunatus L.) production, although genetic resistance is available. In accession L‐136, we investigated the apparent independence of genes controlling nematode reproduction and root galling. Segregation of nematode egg production and root‐galling phenotypes in F1, F2, F2:3, and F2:7‐9 populations from L‐136 × susceptible ‘Henderson Bush’ was determined in growth pouch, greenhouse pot, and field screenings. Three nuclear genes designated mir‐1 (recessive), Mig‐1 (dominant), and Mjg‐1 (dominant) were found to control M. incognita reproduction, M. incognita galling, and M. javanica galling, respectively. Contrast analysis indicated that gene combinations affected nematode egg production and gene combinations provided comprehensive resistance. This independent resistance to root‐knot galling and reproduction, reported for other leguminous crops and cotton (Gossypium spp.), has important implications for breeding broad‐based nematode resistance.

A transgressive segregation factor (RKN2) in Gossypium barbadense for nematode resistance clusters with gene rkn1 in G. hirsutum

Host plant resistance is an important strategy for managing root-knot nematode (Meloidogyne incognita) in cotton (Gossypium L.). Here we report evidence for enhanced resistance in interspecific crosses resulting from transgressive segregation of clustered gene loci. Recently, a major gene, rkn1, on chromosome 11 for resistance to M. incognita in cv. Acala NemX was identified using an intraspecific G. hirsutum cross with susceptible cv. Acala SJ-2. Using interspecific crosses of Acala NemXxsusceptible G. barbadense cv. Pima S-7, F1, F2, F2:3, backcross, and testcross Acala NemXxF1 (Pima S-7xSJ-2), parental entries and populations were inoculated in greenhouse tests with M. incognita. Genetic analyses based on nematode-induced root galling and nematode egg production on roots, and molecular marker analysis of the segregating interspecific populations revealed that gene rkn1 interacted with a gene (designated as RKN2) in susceptible Pima S-7 to produce a highly resistant phenotype. RKN2 did not confer resistance in Pima S-7, but when combined with rkn1 (genotype Aa or aa), high levels of resistance were produced in the F1 and segregating F2, F3, and BC1F1 populations. One SSR marker MUCS088 was identified tightly linked to RKN2 within 4.4 cM in a NemXxF1 (Pima S-7xSJ-2) testcross population. Using mapped SSR markers and interspecific segregating populations, MUCS088 linked to the transgressive gene from the susceptible parent and was located in the vicinity of rkn1 on chromosome 11. Diverse genome analyses among A and D genome diploid and tetraploid cottons revealed that marker MUCS088 (165 and 167 bp) is derived from G. arboreum, A2 diploid genome. These results demonstrated that a highly susceptible parent contributed to nematode resistance via transgressive segregation. Derived highly resistant lines can be used as improved resistance sources in cotton breeding, and MUCS088 can be used to monitor RKN2 introgression in diverse populations. The close genomic location of the transgressive resistance determinants provides an important model system for studying transgressive segregation and epistasis in plants.

Root-Knot Nematode Resistance in Pearl Millet From West and East Africa.

Resistance to Meloidogyne incognita is important to provide stability to pearl millet production and to reduce nematode populations that can damage crops grown in rotation with pearl millet. The objectives of this study were to determine whether resistance to M. incognita exists in pearl millet from West and East Africa, and to determine if heterogeneity for resistance exists within selected cultivars. Resistance was assessed as nematode egg production per gram of root in greenhouse trials. Seventeen pearl millet cultivars of diverse origin were evaluated as bulk (S0) populations. All African cultivars expressed some level of resistance. P3Kollo was among the least resistant of the African cultivars, Zongo and Gwagwa were intermediate, and SoSat-C88 was among the most resistant. Thirty selfed (S1) progeny selections from SoSat-C88, Gwagwa, Zongo, and P3Kollo were evaluated for heterogeneity of resistance within cultivar. Reactions were verified in 13 S2 progeny of each of the four cultivars. In S1 evaluations, each of these cultivars was heterogeneous for resistance. Progeny reaction varied from highly resistant to highly susceptible. Patterns of apparent segregation of resistance varied among the four cultivars. Discreet resistant and susceptible phenotypes were identified in Zongo progeny, and it was estimated that two dominant genes for resistance segregated in this cultivar. Averaged across progenies, egg production on the four cultivars was less (P ≤ 0.001) than on the susceptible hybrid HGM-100, but was not different from resistant hybrid TifGrain 102. Reproduction of M. incognita on the S2 progeny tended to confirm the results from inoculations of S1 progeny. Heritability of nematode reproduction (standardized as the ratio of the value to HGM-100) determined by parent-offspring regression was 0.54. Realized heritability determined by divergent selection was 0.87.

Climatic Conditions and Gastrointestinal Nematode Egg Production: Observations in Breeding Sheep and Goats

Parasitic egg production was studied in sheep and goats affected by parasitic gastroenteritis. The herds studied were located at different altitudes and in different climatic conditions. Samples were taken every month and the number of eggs per grams of feces was calculated. Observation of preliminary data shows that the maximum peak of egg production was during the winter period, whereas in other countries winter is a period of hypobiosis. This study shows that understanding peak time of infection related to different climatic and environmental conditions will help improve anthelminthic treatments and animal health strategies.

Root-knot nematodes affect annual and perennial weed interactions with chile pepper

A field microplot experiment was conducted in 1996 and 1997 to determine the influence of root-knot nematodes on intra- and interspecific interactions between chile pepper (chile) and spurred anoda and between chile and yellow or purple nutsedge (or both) using a substitution design. An additional objective was to determine the influence of London rocket, a winter annual and host plant for root-knot nematodes, on the inter- and intraspecific interactions between chile and spurred anoda. Twelve plant combinations were planted into paired 76-cm-diam microplots at a density of 24 plants per microplot each year. Each pair of microplots had one root-knot nematode–infested and one uninfested plot. One randomly selected plant pair or triplet from each plot was destructively sampled in June, July, August, and September each year. Data included leaf area, plant dry weights (leaf, stem, root or root plus rhizome, chile fruit, and nutsedge tuber), and nematode egg production from the belowground biomass of the different plant species within a 2,355-cm3sampled soil volume. Chile hosted the highest population of root-knot nematodes, followed by spurred anoda, purple nutsedge, and yellow nutsedge. Few root-knot nematode eggs were recovered from London rocket before incorporation into the microplots each spring. Root-knot nematode populations were higher in 1997 and, as a result, more interactions between nematodes and plant combinations were observed for chile. Spurred anoda and root-knot nematodes reduced chile shoot and root weights to levels not significantly different from zero in 1997. Yellow and purple nutsedge shoots, except for those from the original tuber, were removed throughout the season, and these species interfered less with chile. Spurred anoda was not affected by interspecific interference. Few interactions were observed between the spurred anoda plant combinations and root-knot nematodes. In June 1996, low populations of root-knot nematodes (&lt; 4,000 eggs per gram of root) stimulated spurred anoda growth, but higher populations in June 1997 (&gt; 30,000 eggs per gram of root) reduced spurred anoda growth. Prior presence of London rocket had little consistent influence on spurred anoda or chile. Yellow and purple nutsedge growth variables were affected by interference from chile and the other nutsedge species. Tuber number and tuber weight were higher when plants were infected with root-knot nematodes, particularly early in the season. The enhanced tuber production may increase early-season interference from nutsedge species under production conditions. The results suggest that the presence of root-knot nematodes influences plant interference, but the effect is species specific. Annual plants are affected differently compared with perennial nutsedges, possibly because of the continuous association between the perennials and the parasite.

Efficacy of the Fungus Verticillium lecanii for Suppressing Root-knot Nematode Egg Numbers on Cantaloupe Roots

Two strains of the fungus Verticillium lecanii (A. Zimmermann) Viégas were studied as potential biocontrol agents for root-knot nematode (Meloidogyne incognita (Kofoid &amp; White) Chitwood) on cantaloupe (Cucumis melo L.). For the study, pots were filled with soil that had been inoculated with M. incognita (inoculum was applied at two levels: 1000 and 5000 eggs/pot). Each fungus strain was applied individually by pouring an aqueous suspension (made from a wettable granule formulation) into the inoculated soil. Controls received water only. One cantaloupe seedling was then transplanted into each pot. Plants were grown for 55 days in the greenhouse, and then harvested and assessed for root and shoot growth and for nematode egg production. In pots inoculated with 1000 eggs/plant, neither fungus strain affected nematode egg numbers. At the 5000 eggs/plant inoculum level, both strains of the fungus suppressed egg numbers (counts were 28% and 31% less than water controls). Neither strain of V. lecanii affected the number of eggs embedded in root galls; the fungus suppressed nematode population numbers overall solely by affecting the number of eggs located outside of root tissues. Both fungus strains were also autoclaved and then applied to soil, to test for effects of nonviable fungus. In pots inoculated with 5000 eggs, application of one autoclaved strain resulted in a 35% suppression in egg numbers after 55 days, suggesting that the fungus produced a heat-stable substance deleterious to the nematode.

Reduced egg counts in mixed infections with Oestrus ovis and Haemonchus contortus: influence of eosinophils?

In all, 2 groups of lambs were infected either with Oestrus ovis first-instar larvae or with 10,000 third-stage larvae (L3) of Haemonchus contortus. Another group of lambs was infected with both parasites. Fecal nematode egg counts, plasma pepsinogen concentrations, specific O. ovis enzyme-linked immunosorbent assay (ELISA) antibodies, and blood eosinophil counts were monitored and compared to with the values recorded for a control group of uninfected lambs. There was no significant difference between the burden of H. contortus found in mixed and single infections. However, the nematode egg production was significantly depressed in mixed infections. O. ovis affects the population of H. contortus at least by decreasing the parasite egg output. This effect may be mediated through the increase in eosinophil production stimulated by the presence of O. ovis.

Response to root-knot nematodes of a germplasm collection of red clover and related species.

A germplasm collection of red clover (Trifolium pratense L.) and seven related species was evaluated in greenhouse tests for resistance to Meloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood, and M. Javanica (Treub) Chitwood. Plants were rated for root galling severity and nematode egg production at eight weeks after inoculation with 1500 nematode eggs. A resistance index, RI = √(gall2; + egg2;), was generated to assess the plants' reaction to nematode infection as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, or highly susceptible. More than 98% of red clover accessions were intermediately to highly susceptible to all four root-knot nematode species. Only one accession, PI 271627 introduced from India, had a moderate resistance level to the four nematodes tested. About one third of the T. medium accessions were resistant or highly resistant to M. arenaria, M. incognita, and M. javanica whereas more than 50% of the T. alpestre accessions were highly resistant or immune to all four nematodes species. Genetic factors for resistance to root-knot nematode could be introduced into T. pratense through interspecific hybridization with T. medium and/or T. alpestre

Evaluation ofAlysicarpusGerm Plasm for Resistance to Root-Knot Nematodes

Root-knot nematodes reproduce freely on alyceclover (Alysicarpus vaginalis) cv. Florida Common, limiting alyceclover establishment, forage production, and utility as a component of crop rotations. This study was conducted to identify alyceclover germ plasm with resistance to Meloidogyne hapla and M. incognita. Individual alyceclover seedlings planted in Cone-Tainers were infested with at least 2,300 eggs of M. hapla or M. incognita and grown for 77 days under glasshouse conditions at Overton, TX. Root systems were scored for galling on a 0 to 5 scale (0 = no galls, 1 = 1 to 2, 2 = 3 to 10, 3 = 11 to 30, 4 = 31 to 100, and 5 = more than 100 galls). Nematode egg production on selected alyceclover entries was evaluated and expressed as eggs per g of fresh root weight. Twenty-six alyceclover lines were evaluated in 1990, and five lines were reevaluated in 1991. Four alyceclover germ plasm groups were identified according to relative galling responses to M. hapla and M. incognita. Two groups were heavily galled by both nematodes, one group was not galled by M. incognita and was variable in response to M. hapla, and one group was galled by M. incognita and variable in galling response to M. hapla. Nematode egg production was often not related to gall response. M. hapla produced up to 62,000 eggs per g of fresh root weight on plants of breeding line FL-3 with no visible galls. Breeding lines of alyceclover were identified that contained individual plants resistant to either nematode species, but no single alyceclover line had resistance to both nematodes.

Third generation progress in breeding white clover for resistance to root-knot nematode

Root-knot nematode (Meloidogyne sp.) reduces growth and nutrition of white clover (Trifolium repens L.) in New Zealand, and breeding resistant cultivars (with low galls per gram of root) is the preferred control method. Resistant and susceptible selections were bred from a wide range of white clover lines for three generations. In the third generation there were significant differences between seed lines from the selections for number of galls, root dry weight, visual growth score and galls/gram of root dry weight. Resistant selections had 43% of the susceptible selections' galls per gram, and 50% of the number of galls. Germplasm showing resistance to Meloidogyne spp. in the USA showed partial resistance to the local Meloidogyne sp. Two resistant and two susceptible genotypes were also compared for nematode egg production; resistant genotypes had a mean of 3,460 eggs/plant, compared to 25,030 for susceptible genotypes. Keywords: breeding, Meloidogyne sp., resistance, rootknot nematode, screening, selection, Trifolium repens, white clover