Effect of plant density on toxigenic fungal infection and mycotoxin contamination of maize kernels

Field experiments were set up from 2001 to 2004 in North West Italy to determine the effects of plant density on the susceptibility of medium and medium-late maturity maize hybrids to ear rot and to mycotoxin contamination in natural infection conditions. The ears were rated for the incidence and severity of disease symptoms at harvest and the harvested kernels were analysed for mycotoxin fumonisin B1, zearalenone, deoxynivalenol, aflatoxin B1 and ochratoxin A.The plant density significantly influenced the percentage of kernels infected by Fusarium and the fungal ear rot severity. Plots with the highest plant populations had higher values of kernel Fusarium infection (+24%) and higher fungal ear rot severity (+43%) than plots with lower plant densities.The plant density did not influence the type of mycotoxin found in the kernel, which only depended on the climatic conditions during the season and their influence on the infection and the development of different fungal genera and species. It has been confirmed that fumonisins are generally the main mycotoxin contaminant in North Italy, while zearalenone, deoxynivalenol and ochratoxin are only found in cooler and wetter years. No contaminations of aflatoxin B1 were observed for any of the years. The natural occurrence of the mycotoxins found each year was always significantly higher in crops with a higher plant density. No difference for mycotoxin occurrence was observed between the plant density treatments in 2003, as a consequence of a warm and dry climatic trend, with less vegetative crop growth.The use of a medium-late maturity hybrid instead of a medium maturity hybrid could lead to higher contamination of mycotoxins.Maize crops cultivated in temperate areas at high plant populations exhibit a significant increase of mycotoxin contamination risk in the kernels. This study is the first to report the effects of plant density on several mycotoxin contaminations in non-inoculated conditions.