Potencies of the resistant maize genotypes against biotic stresses and understanding their strategies
AdvisorWilliams, W. Paul
Luthe, S. Dawn
Maize is an important food crop in most parts of the world including the United States. The plants growing in the field are constantly challenged with various biotic stresses like insect herbivores and fungal pathogens. The physical wounds produced on the growing crops by the insects render the plants more vulnerable to the fungal pathogens. Hence developing both insect and fungal resistant maize varieties is crucial to benefit more from the harvest. Several studies have been in advance in this direction and as a consequence insect, in particular lepidopteran larve resistant maize genotype Mp708 and Aspergillus flavus resistant genotype Mp313E were developed. This study particularly focuses on understanding the functional involvement of the major phytohormones in the signal transduction and expression of the unique defense protein, Maize insect resistance 1-cysteine protease (Mir1-CP) shown to accumulate in response to herbivory by lepidopteran larvae, Spodoptera frugiperda (Fall armyworm, FAW) as a defense mechanism. Using a pharmacological approach involving exogenous hormone and hormone inhibitor treatments and analyzing the expression and accumulation of Mir1-CP protein and mir1 transcript by immunoblot and qRT-PCR analysis respectively, both JA and ET were found to be involved in mediating Mir1-CP accumulation with JA acting upstream of ET. Results also indicate that Mir1-CP accumulation involves both transcriptional and post-transcriptional (or post-translational) regulations. A different part of the study involved in understanding and evaluating the performance of Aspergillus flavus on the resistant and susceptible maize genotypes during infection. As of part of this study I also analyzed and compared the defense response offered by the resistant maize genotype, Mp313E and the susceptible genotype, Va35 by looking at the expression levels of the various defense related genes. The potency of the resistant maize genotype in sustaining the fungal infection in the field was of particular focus. Resistant maize genotype Mp313E was found to potentially oppose A.flavus proliferation and colonization and also delay aflatoxin biosynthesis unlike Va35. The up regulation of the maize defense genes during the early time points of infection, in Mp313E, indicate the potential role of these genes in conferring resistance against fungal pathogens.