Studies on fungi associated with root rot and vine decline of melons in California (US)
Melons (Cucumis melo) are important crops in California (US), in 1999 they were planted on approximately 37,500 ha representing 68 % of the US production. The occurrence of fungi associated with root rot and vine decline has been surveyed in commercial melon fields from 1995 to 1997. The most commonly found fungi species, isolated from diseased roots, were the following: Acremonium cucurbitacearum (EPPO Alert list – recovered from plants in 32 % of surveyed fields), Rhizopycnis vagum (a recently described species, implicated in vine decline in Rio Grande Valley in Texas – 31%), Pythium spp. (23 %), Macrophomina phaseolina (23;%), Verticillium dahliae (25 %), Fusarium solani (21 %), Monosporascus cannonballus (EPPO Alert list – 15 %) and Rhizoctonia solani (7 %). According to the species found, symptomatology varied, but with some overlap of symptoms. In many cases more than one species was isolated. For example, A. cucurbitacearum and R. vagum were often found together. The frequency of isolation of a given fungus also varied with geographical location. M. cannonballus was only present in the southern production areas, whereas A. cucubitacearum and R. vagum were most common in the northern production areas. Pathogenicity tests were carried out in field microplots and in glasshouses. M. cannonballus caused vine collapse and severe root rot of melon in field microplot tests. R. vagum and A. cucurbitacearum were weakly pathogenic in field microplots, but caused root discoloration and reduced vine growth in glasshouse tests. The authors pointed out that the colonization of melon roots by A. cucurbitacearum, R. vagum and M. cannonballus may contribute to plant decline, but other environmental factors are likely to be involved in the disease and need to be determined.
Aegerter, B.J.; Gordon, T.R.; Davis, R.M.; (2000) Occurrence and pathogenicity of fungi associated with melon root rot and vine decline in California.
Plant Disease, 84(3), 224-230.