ARS | Publication request: Comparison of different inoculating methods to evaluate the pathogenicity and virulence of Aspergillus niger on two maize hybrids

Submitted to: Phytoparasitica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 2012
Publication Date: January 22, 2012
Citation: Windham, G.L., Williams, W.P. 2012. Comparison of different inoculating methods to evaluate the pathogenicity and virulence of Aspergillus niger on two maize hybrids. Phytoparasitica. DOI 10.1007/s12600-012-0220-x.

Interpretive Summary: Aspergillus niger is a common preharvest contaminant of corn grain. This fungus was not given much attention until researchers discovered that it produced several mycotoxins which are cancer causing. It is not known how aggressive this fungus is in attacking kernels of developing corn ears and if A. flavus resistant corn is also resistant to A. niger. A two-year study was conducted to determine the effect of various inoculation techniques on the infection level of A. niger in grain of A. flavus resistant and susceptible hybrids in the field. Ears were inoculated with A. niger using wounding (pinbar, side needle) and non-wounding techniques (silk channel, spray). The silk-channel, side-needle, and pinbar techniques yielded much higher levels of A. niger infection in grain compared to the spray technique. Also, A. niger infection levels were much lower in the A. flavus resistant hybrid compared to the susceptible hybrid. A. niger was much more aggressive in infecting developing kernels when inoculum was placed inside the corn husks as opposed to spraying the spores on the exposed silks. Kernel infection levels of A. niger were much higher than levels observed for A. flavus in these hybrids in previous studies.

Technical Abstract: A two-year field study was conducted to determine the effects of inoculation techniques on the aggressiveness of Aspergillus niger kernel infection in A. flavus resistant and susceptible maize hybrids. Ears were inoculated with the silk-channel, side-needle, and spray techniques 7 days after midsilk (50% of the plants in a plot had silk emerging). Ears were also inoculated with a modified-pinbar technique 21 days after midsilk. Kernel infection in 2008 in inoculated plants ranged from 2 to 11% and from 3 to 45% in the resistant and susceptible hybrids, respectively. In 2009, kernel infection in inoculated plants ranged from 13 to 32% and from 14 to 67% in the resistant and susceptible, respectively. The silk-channel, side-needle, and modified-pinbar techniques produced significantly higher levels of kernel infection in the susceptible hybrid in both years than the spray technique. When hybrids were compared, the silk-channel, side-needle, and modified-pinbar techniques induced significantly higher levels of infections in the susceptible hybrid than in the resistant hybrid in 2008 and 2009. A. niger infected maize hybrids at a high level when conidia were placed inside the husks of developing ears by wounding (modified-pinbar and side-needle techniques) or non-wounding (silk-channel technique) inoculation methods. Although A. niger kernel infection was significantly lower in the A. flavus resistant hybrid compared to the A. flavus susceptible hybrid, A. niger infection levels were much higher than A. flavus infection levels typically observed in both of these hybrids.