Showing papers on "Heterodera avenae published in 1990"

The life-cycle, population dynamics and host specificity of a parasite of Heterodera avenae, similar to Pasteuria penetrans.

Abstract: SUMMARY The occurrence of a population of Pasteuria, similar to Pasteuria penetrans, and possibly a new species, parasitic on Heterodera avenue in a cereal-cyst nematode suppressive soil, is reported. The life-cycle was respicted to the H. avenue second-stage juvenile, and prevented such infected juveniles from invadmg plant roots. Between March and July, 38-56 ?h of the juveniles present in the soil had between one and five spores adhering to their cuticles; microcolonies could be seen in the juveniles as early as April, however, mature spores were not recorded until July. Developing females, and cysts extracted from plant roots were not infected by the bacterium. The suppressive soil also contained juveniles and adults of Pratylenchus and Tylenchorhynchus infected with Pasteuria. Although the spores adhering to, and within, al1 three nematode species were approximately the same size, between 4 and 5 Pm, it was not clear whether or not the Pasteuria population was either a single or a mixed population. Host specificity studies with spores extracted from the juveniles of H. avenue showed that it adhered to the cuticles of schachtii, H. glycines, Globodera rostochiensis, G. pallida and Meloidogyne javanica. Attempts to bait soil by adding these nematodes failed to result in the infection of females. It is reported the soil contained approximately 7 x IO3 spores per gram as evaluated using differential centrifugation.

Characterization of soil organisms involved in the degeneration of ammophila-arenaria

Abstract: The degeneration of Ammophila arenaria (marram grass) in stable stages of coastal foredunes may be due to pathogenic or parasitic soil organisms. To test this, and to characterize the organisms involved, biocides were applied to sand collected from the root zone of natural stands of A. arenaria. Seedlings of A. arenaria were grown and biomass production was measured and compared with growth of seedlings in γ-irradiated soil to determine effects of applied biocides. Sand from stable and mobile foredune sections (degenerated and vigorous A. arenaria, respectively) was examined. Improved seedling growth followed fungicide and ncmaticide treatments m sand from stable, as well as from mobile foredunes. On the other hand, bactericides (streptomycin and penicillin) had no effect. The fungicide propamocarb only stimulated growth very weakly, whereas the fungicide benomyl increased growth significantly. However, the effect of benomyl may not be solely due to its fungiddal action, as it also prevented root infection by the nematodes Heterodera (avenae group) and Meloidogyne maritima. The highest increase in yield was obtained with the nematicide oxamyl, which prevented root-infection by endo-parasitic nematodes (Heterodera avenae group, M. maritima and Pratylenchus sp.). Oxamyl also reduced numbers of ecto-parasitic nematodes. It is concluded that plant parasitic nematodes could be important in the degeneration of A. arenaria, but that interactions with other groups of soil organisms, such as soil fungi, cannot be excluded.

Resistance toHeterodera avenue in the rye genome of triticale.

Abstract: The cereal cyst nematode,Heterodera avenue Wollenweber, is a serious pest of cereals in many countries. A high level of resistance to the unique Australian pathotype of the nematode has been demonstrated in a triticale line (T701-4-6), which was originally obtained from CIMMYT. The level of resistance is similar to that in rye cultivar, South Australian, but higher than that in the wheat line (AUS 10894), hitherto reported to have useful resistance to the Australian pathotype. The gene for resistance was located on rye chromosome 6 (6R) after backcrossing the T701-4-6 line to wheat and correlating the resistance with the presence of individual rye chromosomes identified by morphological, cytological, and isozyme markers. Preliminary evidence suggests that the gene is located on the long arm of6R. To transfer the resistance to wheat, double monosomics of6R and6D in aph1bph1b homozygous background were selected from F2 progeny from a cross of disomic6R substitution for6D to theph1b mutant. Selfed seeds from these F2 plants will be screened for wheat-rye chromosome recombinants.

Morphometric Relationships of Some Members of the Heterodera a Venae Complex (Nematoda: Heteroderidae)

Abstract: A detailed morphological and biometrical study was made of eight Spanish, two British and two Swedish populations of the Heterodera avenae complex. Morphometrical data have been statistically evaluated. Monovariate analysis (Student's t test) was applied to measurements of cysts, cone tops, eggs and juveniles, and multivariate analysis (discriminant analysis and two clusters) was applied to measurements of juveniles. Results demonstrated that there are two well differentiated groups within the H. avenae complex. One is represented by British Ha 11, Spanish Sp. 1 and Swedish Sw. 1 populations. This agrees with previous descriptions of H. avenae. The second group, represented by British Ha 23, Spanish Sp. 3 and Swedish Sw. 2, agrees with previous descriptions of British pathotype 3, Gotland race and H. filipjevi. The two groups are well differentiated by size and colour of old cysts and cone top structures. Spanish populations Sp. 1 and Sp. 3 are best differentiated by the measurements, and significant differences have been shown in 25 of the 29 parameters considered, compared with 14 in British and 11 in Swedish populations. The Spanish populations are more similar to the British than to Swedish populations of the same group as shown by the results of Student's t test. The characters useful for differentiating groups in both Spanish and British populations were: length as well as width of cysts, length of body, tail and hyaline region of tail, "c" and hyaline region of tail/stylet length in juveniles. The measurements of vulva slit length and fenestra size which differentiate H. filipjevi from H. avenae may also differentiate Spanish populations but not British populations.

The cereal cyst nematode (Heterodera avenae) on oats. I. Identification of attributes useful in early screening for tolerance to H. avenae

Abstract: Variation in morphology, development, and water relations of four oat cultivars inoculated with a range of densities of Heterodera avenae larvae was assessed during early growth to identify distinguishing traits for tolerance. Experiments were performed under glasshouse conditions on cultivars previously rated for tolerance. Cultivar differences were found in the effects of H. avenae on final leaf length, and on root and shoot mass within 20 to 30 days of planting. These differences corresponded to cultivar differences in tolerance to H, avenae at maturity. Differences between cultivars in their sensitivity to root stunting by H, avenae were also related to their final tolerance ratings. Tiller removal generally enhanced tolerance but had little effect on the overall tolerance ranking of the four cultivars examined. H. avenae infection had the least effect on the water use efficiency (WUE) of the most tolerant cultivar and the greatest effect on the least tolerant cultivar. In the absence of nematodes, intolerant cultivars used water more efficiently than did tolerant cultivars. Results suggest that oats can be screened for tolerance to H. avenae during early plant development.

Inhibition of verticillium suchlasporium and other nematophagous fungi by bacteria colonising heterodera avenae females

Abstract: Summary .Pseudomonas fluorescens and a bacterium with similar characteristics (isolate A) were obtained from females of Heterodera avenae which caused growth-inhibition 'halos' in colonies of Verticillium suchlasporium or Acremonium sp. from naturally infected young females of H. avenae. These bacteria partially inhibited the growth of the egg-parasites Paecilomyces carneus and Acremonium sp. on agar. Isolate A also inhibited the growth of V. suchlasporium while Cladosporium cucumerinum, a fungal plant pathogen, was unaffected indicating a certain degree of specificity in the mycostasis. The percentage of nematodes infected by nematophagous fungi belonging to the genus Verticillium was less in young females than for n~wly formed cysts. The young females may bave been initially protected by mycostasis which gradualIy decreased allowing the Verticilliu~ spp. to infect the newly-formed cysts. The importance of mycostasis in the understanding of the process by which H. avenae is infected by nematophagous fungi under field conditions has stilI to be investigated.

Influence of Heterodera avenae on winter wheat in France: experiments with resistant and susceptible varieties

Abstract: Summary A succession of oat crops resistant or susceptible to Heterodera avenue produced plots lightly or moderately infested with the pest with little risk of interaction with other soil pathogens in succeeding cereal crops. Using these plots, the effects of the nematode on growth and yield of winter wheat were studied. The nematode affected the crop throughout its development, with a marked effect on yield. The effects of H. avenue are similar to those of water stress and are accentuated to a greater or lesser extent by climatic conditions. In the field the efficacy and durability of resistant genes incorporated in wheat and oats were checked. After four-years' cultivation of oats (cv. Panema), no resistance-breaking pathotypes were detected. Some advanced wheat lines with nematode resistance were also tolerant of nematode attack.

Bio-ecological craracteristics of tre cereal cyst nematode heterodera a venae in spain

Abstract: The life cycles of Heterodera avenae populations from three cereal growing areas in Spain with mediterranean continental climate, showed similar biological characteristics to those from other mediterranean countries. Juvenile emergence starts in the autumn. Second stage juveniles undergo a diapause of four months, followed by a period, probably of quiescence in which hatching is possible if moisture is suitable. An increase of emergence was observed at the beginning of spring, and was more evident for populations from areas with the most extreme climatic characteristics. This can be considered as an adaptation of the nematode to climatic conditions that allow it to develop in an area in which spring sowing is a frequent cultured practice.