The interaction between Meloidogyne arenaria and Cylindrocladium parasiticum in runner peanut

Cylindrocladium black rot (CBR), caused by Cylindrocladium parasiticum , and root-knot nematode, Meloidogyne arenaria , both infect and cause damage to the roots of peanut. Greenhouse and microplot experiments were conducted with the runner type peanut genotypes C724-19-15, C724-19-25 and Georgia-02C with different levels of resistance to nematode and CBR to better understand the interactions between the two pathogens. In the greenhouse, inoculation of 500–3000 eggs per plant of M. arenaria did not affect the level of root rot induced by 1·0 to 5·0 microsclerotia of C. parasiticum per g soil. In microplots, the root rot ratings from Georgia-02C and C724-19-25 were higher in plots infested with M. arenaria (0·4–2·0 eggs per cm³ soil) and C. parasiticum than in plots with C. parasiticum alone; however, M. arenaria did not increase the root rot ratings on the nematode resistant C724-19-15. This was inconsistent with results in the greenhouse. Gall indices were not affected by C. parasiticum inoculations in the greenhouse or microplots. In both 2006 and 2007, a significant interaction between C. parasiticum inoculum densities and nematode level was observed on plant mortality. CBR inoculum greatly increased mortality on C724-19-25 and Georgia-02C, but not on C724-19-15, in the presence of M. arenaria . The mortality increase was more apparent at lower inoculum levels of both pathogens, but on the nematode-susceptible cultivars plant mortality was more with co-inoculations of the two pathogens than from either alone. Simultaneous inoculation with the two pathogens decreased yield of C724-19-25 and Georgia-02C as C. parasiticum inoculum levels increased, but even the largest inoculum of M. arenaria (2·0 eggs per cm³ soil) did not decrease yield of C724-19-15.