Comparisons of the growth of Pasteuria penetrans in adult root-knot nematode females infected with P. penetrans dissected from the roots of tomato plants were undertaken using bright-field and scanning electron microscopy. Samples of infected females were nutritionally compromised by maintaining them in sterile saline at 30°C for different periods of time following their removal from the root system. Observations of these females maintained in saline revealed a series of growth stages of Pasteuria hitherto not documented, consisting of rhizoids, rod-like bacilli and granular masses. A new life-cycle for Pasteuria is described consisting of three phases: Phase I: attachment and germination; Phase II: rhizoid production and exponential growth; and Phase III: sporogenesis. These newly observed stages of the life cycle show a high degree of similarity to the developmental stages seen in other Bacillus spp.
Spirotetramat (Movento™, Bayer CropScience) (SPT), an effective insecticide, has also demonstrated potential activity as a nematicide. No significant effects on hatching rates of Caenorhabditis elegans, Meloidogyne incognita or Heterodera glycines were observed when eggs were soaked in a maximum concentration of 105 ppm of technical grade spirotetramat-enol (SPT-enol), the active form in plants. Synchronised first-stage juveniles of C. elegans soaked in SPT-enol concentrations as low as 30 ppm demonstrated arrested juvenile development with calculated EC95 of 44-48 ppm. Single applications of formulated SPT (Movento 240SC) were applied to plant foliage at the labelled insecticidal rate of 87.6 g a.s. ha−1 at 1-week intervals on soybean plants inoculated with H. glycines or tomato plants inoculated with M. incognita in glasshouse tests. SPT consistently inhibited nematode development to reproductive maturity when applied at 1-2 weeks after inoculation. Optimal SPT application timings coincide with early stages of root infection, when nematodes are still in vulnerable juvenile stages.
Here we report the genome sequence of the lesion nematode, Pratylenchus coffeae, a significant pest of banana and other staple crops in tropical and sub-tropical regions worldwide. Initial analysis of the 19.67 Mb genome reveals 6712 protein encoding genes, the smallest number found in a metazoan, although sufficient to make a nematode. Significantly, no developmental or physiological pathways are obviously missing when compared to the model free-living nematode Caenorhabditis elegans, which possesses approximately 21 000 genes. The highly streamlined P. coffeae genome may reveal a remarkable functional plasticity in nematode genomes and may also indicate evolutionary routes to increased specialisation in other nematode genera. In addition, the P. coffeae genome may begin to reveal the core set of genes necessary to make a multicellular animal. Nematodes exhibit striking diversity in the niches they occupy, and the sequence of P. coffeae is a tool to begin to unravel the mechanisms that enable the extraordinary success of this phylum as both free-living and parasitic forms. Unlike the sedentary endoparasitic root-knot nematodes (Meloidogyne spp.), P. coffeae is a root-lesion nematode that does not establish a feeding site within the root. Because the P. coffeae nematode genome encodes fewer than half the number of genes found in the genomes of root-knot nematodes, comparative analysis to determine genes P. coffeae does not carry may help to define development of more sophisticated forms of nematode-plant interactions. The P. coffeae genome sequence may help to define timelines related to evolution of parasitism amongst nematodes. The genome of P. coffeae is a significant new tool to understand not only nematode evolution but animal biology in general.