Vertical Distribution of Pasteuria penetrans Parasitizing Meloidogyne incognita on Pittosporum tobira in Florida

摘要

Pasteuria penetrans is considered as the primary agent responsible for soil suppressiveness to root-knot nematodes widely distributed in many agricultural ?elds.A preliminary survey on a Pittosporum tobira ?eld where the grower had experienced a continuous decline in productivity caused by Meloidogyne incognita showed that the nematode was infected with Pasteuria penetrans.For effective control of the nematode, the bacterium and the host must coexist in the same root zone.The vertical distribution of Pasteuria penetrans and its relationship with the nematode host in the soil was investigated to identify (i) the vertical distribution of P.penetrans endospores in an irrigated P.tobira ?eld and (ii) the relationship among P.penetrans endospore density, M.incognita J2 populationdensity,and hostplantrootdistributionovertime.Soil bioassaysrevealedthatendosporedensitywasgreaterin theupper 18 cm of the top soil compared with the underlying depths.A correlation analysis showed that the endospore density was positively related to the J2 population density and host plant root distribution.Thus, the vertical distribution of P.penetrans was largely dependent on its nematode host which in turn was determined by the distribution of the host plant roots.The Pasteuria was predominant mostly in the upper layers of the soil where their nematode host and the plant host roots are abundant, a factor which may be a critical consideration when using P.penetrans as a nematode biological control agent.