K. Evans

Distribution of Species of Potato Cyst-Nematodes in South America

Twenty six populations of potato cyst-nematodes from Colombia, Ecuador, Peru and Bolivia were examined and identified as Heterodera rostochiensis Woll. or H. pallida Stone. North of 15.6°S only H. pallida was found, but south of this latitude most populations examined were H. rostochiensis or a mixture of the two species. Possible reasons for the distribution of the two species being dependent on latitude are discussed, particularly the influence of daylength.

Tolerance To Cyst-Nematode Attack in Commercial Potato Cultivars and Some Possible Mechanisms for Its Operation

Ten commercial potato cultivars, one resistant to Globodera rostochiensis Ro1 and the others susceptible, were grown on two sites, one heavily infested with G. rostochiensis Ro1 and the other uninfested. The only resistant cultivar, Maris Piper, suffered least yield loss; of the susceptible cultivars Pentland Crown suffered least loss and the early maturing Maris Peer most. The degree of tolerance to nematode attack was related to the amount of calcium accumulated in the dry matter of plants growing on the uninfested site and this relationship may have been due to the efficiency with which different cultivars used water. Other mechanisms which might lead to tolerance include reduced ability to stimulate hatching, reduced root invasion by juveniles and the formation of fewer adult females.

A fluidising column for extracting nematodes from soil

An apparatus which uses a controlled water current passing through a sintered plate to separate nematodes from soil particles is described. Nematodes of all types and sizes can be extracted, and the apparatus is particularly useful for extracting white Heterodera females. Construction is simple, so the apparatus is cheap, robust and valuable where only limited facilities are available. It may prove useful for extracting other small soil invertebrates, or their eggs.

Inter and intra-specific genomic variability of the potato cyst nematodes Globodera pallida and G. rostochiensis from Europe and South America using RAPD-PCR

Eleven populations of the potato cyst nematode Globodera pallida from the UK and Peru were analyzed and compared using RAPD-PCR with four 10-mer primers. In addition, seven populations of G. rostochiensis from the UK and single populations from Germany, the Netherlands and Bolivia were included for comparison. Genomic variability was found both between and within species, with more variability in G. pallida than G. rostochiensis. The genomic pool of British G. pallida populations showed considerably less variation than the Peruvian populations, with 73% and 41% similarity between populations respectively. The genomic similarity among populations of G. rostochiensis was 89% for UK populations and 82% when the two continental European populations were included. Nevertheless, between populations within each species and from the same locality, genomic differences were still found.

Plant and nematode surfaces : Their structure and importance in host-parasite interactions

The surface of animal parasitic nematodes has been well studied with respect to its immunological role in host-parasite interactions. However, very little information is available concerning plant parasitic nematode surfaces as primary sites of response to the host environment, and the way that they interact with plant cell wall components is not fully understood. This review examines the surfaces of both the plant cell and the nematode, specifically their composition, and how this changes during parasitism, and their functional roles, which are relevant to the understanding of both compatible and incompatible interactions. Finally, the methods that have been used to study both the plant extracellular matrix and the nematode cuticle are described and their various advantages and disadvantages are analysed.

Morphological Variation in Some Populations of Potato Cyst-Nematodes From Europe and South America

A hundred and thirty one populations of potato cyst-nematodes from South America and sixteen populations from elsewhere were examined and several methods of assessing their variability are described, including hierarchical analyses of variance and canonical variate analyses. A simple method of determining the minimum number of observations of a given character required to differentiate between given populations is also described. Some effects of changes of environment on nematode morphology are reported and standard procedures for comparative morphological studies are recommended. Populations collected in South America north of 15.6° S were Globodera pallida except for one or two populations which seemed to be mixtures of G. pallida and G. rostocbiensis and two populations of G. rostocbiensis in Venezuela which may have been introduced from Europe.

Longevity of males and fertilisation of females of Heterodera rostochiensis.

After emerging from roots, H. rostochiensis males remained active for 9 or 10 days whether females were present or not. Females modified male behaviour by secreting a sex attractant powerful enough to attract males up to at least 15 cm away. Isolated females remained fertilisable for at least 40 days beyond the time when they would normally be fertilised. When allowed to mate on plants, some females were fertilised as soon as 24 days after the roots were invaded by the larvae. Very young females seemed able to store enough sperm to fertilise all their eggs. Most females were mated soon after they ruptured the root cortex and within a few days of males beginning to emerge. All females were mated within 50 days of roots being invaded.

Effects of Daylength On the Multiplication of Potato Cyst-Nematode (Globodera Spp.) Populations

The effects of different daylengths (12 and 16 hr) on hatching, invasion of the host, and reproduction of different populations of potato cyst-nematodes on European potato plants, Solanum tuberosum ssp. tuberosum, were studied. Invasion and root weight were greater in plants grown in 16- than in 12-hr days. The ratio of male to female larvae of G. pallida hardly changed but the ratio of male to female G. rostochiensis larvae was greater in 16- than in 12-hr days. Populations of both species from Europe tended to produce more cysts on plants grown in 16-hr days, but G. rostochiensis from Peru produced more on plants grown in 12-hr days. Hatching from cysts produced in 16-hr days was also greater than from those produced in 12-hr days but no significant differences between activities of root diffusates produced in different daylengths were found.

Serological identification and quantification of Heterodera avenae from processed soil samples

Monoclonal antibodies (MAbs) and polyclonal antibodies (PCs) were produced to antigens of an Australian population of cereal cyst nematode (CCN), Heterodera avenae. MAb IACR CCNj-49.2 recognised an antigen with a molecular weight of approximately 200 kDa, which was immunolocalised apparently in granules in the nematode gut. A procedure to extract CCN antigens from soil samples, under laboratory conditions was devised, and 50 g samples of soil containing 5 CCN cysts were processed by two sets of flotation techniques to recover the nematodes. Milling using Ballotini glass beads was then used to release the antigens from the CCN cysts recovered in the float. A double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA) was the better ELISA format used to identify and quantify the CCN population from the processed soil samples containing up to 20% of organic matter. The threshold limit of detection was estimated by serial dilutions of the soil extracts. It was approximately equivalent to 0.5 eggs or 3.6 eggs per g of soil in a DAS-ELISA, when using respectively the PC or the MAb as the trapping antibody. The assay could be made more sensitive in soils with lower contents of organic matter.

Effects of Amino Acids On the Reproduction of Heterodera Rostochiensis

Of several racemic mixtures of amino acids tested, the most toxic to H. rostochiensis and the least toxic to potato plants growing in pots was DL methionine. The D and L forms were equally toxic to the nematodes which became less sensitive as they aged. Methionine did not act directly by contact with the nematode: it had first to be taken up by the host plant and was presumably ingested in sap extracted from giant cells. Although methionine affected populations of H. rostochiensis in field plots, even large amounts did not control it adequately.