Genotypic and environmental influences on the host-parasite interaction between meloidogyne arenaria and pasteuria penetrans
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Root-knot nematodes (Meloidogyne spp., RKN) are economically important plant-parasitic nematodes that have a wide distribution. Pasteuria penetrans is gram-positive bacterium that is an obligate parasite of RKN. Numerous field studies have shown the suppression of RKN by P. penetrans, demonstrating the potential to be developed into a biological control product. The endospores of P. penetrans attach to the surface coat of RKN and subsequently sterilize the female. Environmental factors influenced P. penetrans spore attachment. Exposure to root exudates of second-stage juveniles (J2) reduced spore attachment, suggesting the nematode surface coat was influenced by root exudates. Application of P. penetrans spores in furrow reduced egg production more than as a seed treatment. When applied in furrow, spores may have a wider distribution in the soil compared to spores applied to the seed, and J2s migrating through the soil would encounter P. penetrans spores before they were exposed to root exudates and become more resistant to spore attachment. The susceptibility of RKN progeny was shown to be influenced by the maternal environment. Mothers raised under stressed conditions produced more resistant offspring than did mothers raised under favorable conditions. In a 4 year field study, rapid changes in the dominant spore phenotype were observed in each plot in each year, and the changes occurred on the local level. Such findings indicate the occurrence of negative frequency-dependence selection in this field. Single spore lines of a Florida P. penetrans population were used to test the phenotypic and immunological differences among spore lines. No difference in spore attachment phenotype was observed mainly because these single spore lines were obtained from single egg mass line (clonal) of M. arenaria; thus they may be the same spore attachment phenotype. This project provided much needed information on understanding the host-parasite interactions between P. penetrans and Meloidogyne spp, and provides suggestions for better developing P. penetrans into a biological control product.