Selection for increased host resistance and increased pathogen specificity in the Meloidogyne-Pasteuria penetrans interaction

Abstract

Africa (PP3), the progeny of those nematodes which escaped infection were less susceptible to spore attachment than the original nematode population. M. graminicola and M. naasi were initially poor hosts of PP3. Exposure of M. graminicola to large numbers of spores resulted in multiplication of the isola te, and the spore population thus produced gave significantly greater attachment than the original PP3 population to M. naasi, but nat to M. graminicola. Attachment by the new PP3 population to M. incognita (ex Bangladesh) was significantly reduced. Out of four populations of M. incognita and M. javanica, one, M. incognita ex Barbados, was also initially a poor host of PP3. Exposure of M. incognita(ex Barbados) to large numbers of spores resulted in the multiplication of a P. penetrans isolate which gave significantly grearer attachment to M. incognita ex Barbados than the original PP3 population. However this isolate gave significantly reduced attaclunent to the other three Meloidogyne populations. When isolares of P. penetrans from several sources were blended, the consistency of spore attachment between and within a range of Meloidogyne populations was increased. Ir is concluded that populations of P. penetrans and Meloidogyne can be genetically heterogeneous with respect to specificity and susceptibility respectively. Thus biological control is unlikely to be consistent or durable unless populations of P. penetrans with a broad spectrum of host specificity can be deployed.