Effect of environmental conditions on spore production by Fusarium verticillioides, the causal agent of maize ear rot

Abstract

Silk infection by Fusarium verticillioides is caused by conidia produced on maize crop residues and results in kernel infection and consequent accumulation of fumonisins. Studies were carried out in both controlled and field conditions to understand the dynamics of sporulation on maize residues. The effect of temperature (5°C to 45°C) and incubation time (3 to 41 days) on spore production on maize meal agar was described by a logistic model that accounted for 85% of variability. The rate parameter depended on the length of incubation and the asymptote on temperature. Maximum sporulation occurred at 27°C, with a progressive increase between 5°C and 27°C and then a rapid decline, with no sporulation at 45°C. Fusarium verticillioides strains from different geographic origins showed different sporulation capabilities, with similar optimum temperatures. Pieces of stalk residues inoculated with F. verticillioides and placed above the soil between rows of maize crops, in 2003 to 2005, produced conidia continuously and abundantly for some weeks, particularly during the period after silk emergence, with an average of 1.59×107 conidia g-1 of stalk, over a wide range of environmental conditions. Sixty-seven percent of variability of the spore numbers found on stalks was accounted for by a multiple regression model. Precipitation (rain or overhead irrigation) in the 14 days before stalk sampling decreased the number of spores, whilst the number of days with conducive conditions of moisture (i.e. days with rainfall, average relative humidity >85% or vapour pressure deficit <4 hPa) and greater degree-days (base 0°C) in the 14 and 3 days before sampling, respectively, increased sporulation. © 2008 KNPV.