Interactions of Pectobacterium carotovorum pv. carotovorum, Xanthomonas campestris pv. carotae, and Meloidogyne javanica on the Disease Complex of Carrot

Abstract

Pectobacterium carotovorum pv. carotovorum (Jones 1901) Hauben et al., Xanthomonas campestris pv. carotae (Pammel) Dowson, and Meloidogyne javanica (Treub) Chitwood are often associated with roots of carrot (Daucus carota L.) under field conditions. This study was undertaken to determine relationships between M. javanica, P. carotovorum pv. carotovorum, and X. campestris pv. carotae in the wilt and spot disease complex of carrot and how the order of inoculation of these pathogens affects disease and plant development. Inoculation of M. javanica alone caused a greater reduction in plant dry weight than did P. carotovorum pv. carotovorum and X. campestris pv. carotae. Inoculation of P. carotovorum pv. carotovorum or X. campestris pv. carotae with M. javanica caused a greater reduction in plant dry weight than inoculation of both bacteria together. Inoculation of M. javanica 15 days prior to either bacterial pathogen caused a higher reduction in plant dry weight compared to inoculation of a bacterial pathogen prior to inoculation with nematodes. P. carotovorum pv. carotovorum and X. campestris pv. carotae adversely affected nematode multiplication and galling; the effect of P. carotovorum pv. carotovorum alone was greater than that of X. campestris pv. carotae alone. The greatest reduction in nematode multiplication and galling was when P. carotovorum pv. carotovorum plus X. campestris pv. carotae were inoculated prior to inoculation with M. javanica. Wilting index was 3, on a 5 scale, when P. carotovorum pv. carotovorum was inoculated alone. Bacterial spot index was also 3, on a 5 scale, when X. campestris pv. carotae was inoculated alone. When P. carotovorum pv. carotovorum and X. campestris pv. carotae were inoculated together or inoculated with M. javanica, the indices were 5. Inoculation of M. javanica prior to bacterial pathogens predisposes carrot plants and aggravates the severity of disease.