Colonization and parasitism of females and eggs of Meloidogyne incognita by fungi

Root-knot nematodes, especially Meloidogyne incognita, are destructive pathogens of commercially grown tomatoes in East Tennessee. The objective of this study was to determine the relationship between females and eggs of M. incognita and nematophagous fungi. Females were either extracted from heavily infested, field-collected tomato roots with no further treatment, rinsed 3x or 20x with sterile water, or surface-sterilized with 1.05% NaOCl. Females were placed on antibiotic-amended water agar for growth of parasitizing fungi. Female viability was determined by observation of stylet thrusting, metacorpus movement, and egg production. Surface colonization of the female cuticle by fungi was examined with the scanning electron microscope (SEM). Eggs were extracted from field-collected egg masses with 1.05% NaOCl and spread on antibiotic-amended water agar for growth and observation of colonizing fungi. Eggs from greenhouse cultures were suspended in agar on slides or in discs and buried in the field to determine the potential for egg parasitism.

In 1987, fungi, primarily Paecilomyces lilacinus, grew from most females (81%) removed from roots and placed on agar. Fungi grew from 37% of the females after sterile water rinses, but were recovered from only 2% of the females treated with NaOCl. All fungal isolates identified from NaOCl-treated females were Paecilomyces spp. Lower percentages of colonization occurred in 1988 but the results were proportionally the same among treatments as those found in 1987. SEM work showed that the cuticular ridges of females, and the hyphae associated with the cuticle, were collapsed by sodium hypochlorite treatment. Parasitism of eggs from egg masses was negligible (<1%), but up to 16% of free eggs buried on agar slides and discs were parasitized. The fungi most commonly isolated from agar discs were Epicoccum purpurascens Ehrenb. ex Schlecht, Humicola grisea Traaen, Paecilomyces lilacinus (Thom) Samson, P. marquandii (Massee) Hughes, several isolates tentatively identified as Phytophthora spp., and two unidentified species.