Evaluation of Fusarium graminearum inoculation methods in maize ears and hybrid reaction to Gibberella ear rot under southern Brazilian environmental conditions

Abstract

Natural infection of Gibberella ear rot (GER) of maize, caused by Fusarium graminearum, is not consistent from year to year in southern Brazil, thus an effective approach to identifying resistance to GER is to use artificial inoculation methods to test germplasm, however not widely implemented in Brazil where no maize hybrids are known with resistance to GER. A GER index, Fusarium-damaged kernels (FDK), and Fusarium-infected kernels (FIK) were used to evaluate the inoculation methods and hybrids resistance. Four different inoculation methods were tested on four hybrids in three environments during the 2011/12 growing season. Silk-channel, silk-channel-spray, pin and collar-deposition method were tested. For all hybrids, the pin method consistently showed the highest GER index values followed by the silk-channel method. Collar-deposition method was also able to infect the ears, suggesting attention to this point of infection. These two best methods were used to screen the 20 hybrids for GER in two environments during the 2012/13. The pin method showed 2-fold more GER index, FDK, and FIK (P < 0.05) than the silk-channel method. Silk-channel and pin method showed a significant positive GER index correlation (r = 0.646; P = 0.001). The hybrids appeared to have a form of silk resistance rather than kernel resistance, since the majority (95 %) of hybrids tested were either moderately susceptible (MS) or susceptible (S) to F. graminearum when pin method was used. However, 65 % of the hybrids were classified as MS or S in the silk-channel method.