Simulation of southern corn rust damage in maize

Predictions of the extent of reduction in yield of maize, <u>Zea mays</u> L., by diseases are extremely useful in determining such matters as whether a crop will be an economic failure, the advisability of fungicide application, and so forth. This researcher's effort is an attempt to provide such a predictive mechanism, first by modeling non-diseased development and then by incorporating disease damage into the model.

Using measures of kernel dry weight on various days after silking, a generalized formula was determined which describes daily increases in kernel weight through the development of the maize kernel until maximum dry weight occurs fifty-one days after silking. Utilization of this formula allows description of the distribution of the photosynthate (above maintenance requirements) produced daily. Assuming that during early kernel development excess photosynthate is temporarily stored in the plant for later transport into the kernel, a model has been developed for healthy kernel development on the plant.

Southern corn rust, caused by <u>Puccinia polysora</u>, prematurely kills the leaf tissue of the maize plant. Based upon the healthy photosynthate distribution model, an analysis was made of the effects of southern corn rust upon kernel development. A routine was designed to show that the reduced photosynthate due to the disease, including premature killing of the leaves, reflects the reduction in yield caused by this disease.

The project includes routines developed in SPSS and FORTRAN IV and processed on an UNIVAC 1106.

Southern corn rust prematurely kills the leaf tissue of the maize plant. It has not yet been determined if the leaves are killed by a toxic chemical or merely by the large numbers of pustules which cover the leaves. These nearly round, orange-red pustules erupt, releasing the wind-borne spores of the fungus. Although Southern corn rust can be evidenced at almost every stage of maize development, it is believed that the plants become progressively more susceptible after silking (4).

Due to the increasing prevelance of Southern corn rust, it is essential that some predictive mechanism be provided via which visual estimates of the amount of pustules may be used to determine damage to corn populations. This author's effort is an attempt to provide such a predictive mechanism, first by modeling non-diseased development and then by incorporating disease damage into the model.