Infection of two endosperm mutants of sweet corn by Fusarium moniliforme and its effect on seedling vigor.
Kernels of hybrid sweet corn [maize] plants with the recessive shrunken-2 (sh2) gene became heavily infected with F. moniliforme [Gibberella fujikuroi] in the field earlier than kernels of hybrid plants with the standard sugary (su) gene. Mature ears of both mutants inoculated 10 days postpollination (DPP) had higher levels of rot and seed infection than those inoculated later in development. In sh2 seeds, the pathogen appeared to enter through small cracks in the pericarp or by appressoria. It spread throughout pocketlike areas between the pericarp and aleurone layer, and eventually moved into the endosperm and embryo. Infection increased the number of abnormal su seedlings and reduced seedling growth of sh2 seeds germinated under opt. conditions. Germination of infected sh2 seeds was lower in a cold soil test and growth rates were reduced compared to those observed under opt. conditions. Poor seed and seedling vigour of sh2 was due, in part, to infection with G. fujikuroi but this did not appear to be the primary factor involved in the loss of vigour. Under stress conditions, uninfected sh2 seeds had less germination and vigour than uninfected su seeds.