Indirect effects of transgenes on resistance to northern leaf blight of maize under chemical and manual management practices of weeds

Abstract

The effects of transgenes on plant resistance to non-target diseases caused by foliar fungi are still poorly studied. This study aimed to evaluate the indirect effects of the TC1507 event, isolated and in combination with NK603, on the maize genetic resistance to northern leaf blight, in the presence and absence of chemical control of weeds. Three isogenic hybrids were used as treatments in this study: the non-genetically modified conventional hybrid BG7060 (NGM); the genetically modified hybrid BG7060H (Hx), carrying transgenes cry1F and pat (TC1507 event); and the genetically modified hybrid BG7060HR (Hxrr), carrying transgene cp4epsps (NK603 event) combined with the TC1507 event. To evaluate the resistance of the three isogenic hybrids to that pathogen, three experiments were carried out in Florianópolis, southern Brazil, in complete randomized blocks with three replications in experiment 1 (2012/2013 harvest) and four replications in experiments 2 and 3 (2016/2017 harvest). The control of weeds was done by manual weeding, in experiments 1 and 2, and with the application of the herbicide Finale in a single dose, in experiment 3. The severity of northern leaf blight was evaluated under natural conditions of disease occurrence, in experiment 1, and from inoculation of the pathogen, in experiments 2 and 3. The isogenic hybrid Hxrr showed higher incidence and shorter incubation and latency periods than the Hx and conventional isogenic hybrids in the two management environments of weeds. Pathogen resistance, measured from these three variables, tended to be lower in the genetically modified hybrid Hxrr, which contains two events (TC1507 and NK603), followed by the hybrids Hx and NGM, in increasing order of resistance. The addition of the herbicide for the control of weeds increased the susceptibility of the genetically modified hybrids Hx and Hxrr, as well as the conventional hybrid not submitted to this control, but cultivated close to the hybrids Hx and Hxrr managed with the use of the herbicide.