Stenocarpella (Diplodia)maydis: Influence of nitrogen and inoculation on biochemical components of maize stalk

Mervalin Anderene Morant, Purdue University

Abstract

Two maize hybrids, Pioneer band P3732 and B73 x Mo17 under different N regimes of 0, 67, 201 and 268 Kg N/ha, were inoculated with Stenocarpella maydis at two weeks prior to pollination, midsilk, two and four weeks post-pollination. Stalk rot incidence was rated at eight weeks post-pollination (maturity) as percent of discoloration in the pith tissues, as incidence of lodging at various internodes and also by resistance of internodes to applied pressure. The dry weight of individual internodes of the two and eight weeks post-pollination plants were evaluated. In addition, total structural (nonsoluble), total nonstructural (soluble) components and dry weight of individual internodes in the third internode of plants inoculated at four weeks post-pollination, were evaluated at maturity. When stalk rot incidence was rated as a percentage of pith discoloration, Pioneer 3732 was more severely discolored than B73 x Mo17. Also, in both hybrids receiving 67 Kg N/ha and inoculated at two weeks prior to pollination, plants were more severely discolored than plants inoculated at any other stage of development and any other level of applied N. Discoloration of the pith tissue of the inoculated plants was greater than in the non-inoculated control. In contrast, evaluation of disease incidence based on lodging at specific internodes and resistance of internodes of standing plants to applied pressure, showed that B73 x Mo17 had a higher number of lodged plants than Pioneer 3732. In both hybrids, the incidence of lodging was greater at internode three above ground level. Similarly, internode three in both hybrids was less resistant to applied pressure, although to a greater extent in B73 x Mo17. Further analyses of the structural, nonstructural, dry weight and protein contents of the third internode of the plants showed that cannabalization of these components in the stalk influenced the degree of stalk rot incidence and maize stalk quality. The structural components and protein content in the stalk of B73 x Mo17 were degraded at a greater extent in attempt to replenish the nonstructural components. This was not as pronounced in Pioneer 3732. In all instances, the degree of cannabalization was offset by ensuring that N supply was adequate, since as N level increased, the degree of degradation of these components declined. The results of this study show that B73 x Mo17 is more susceptible to stalk rot pathogens, and more prone to lodging than Pioneer, hence pith discoloration is not an accurate measure of stalk rot incidence. The mechanisms(s) for stalk rot include the dependency of host genotype on N use efficiency which is conditioned by the dynamics of the kernel sink.

Degree

Ph.D.

Advisors

Warren, Purdue University.

Subject Area

Plant pathology

COinS