Perithecia of Gibberella fujikuroi were found on old maize (Zea mays) stalks in northern Vietnam. Single ascospores from these perithecia produced cultures of the anamorph Fusarium moniliforme but perithecia were not produced in single spored cultures. Eleven single ascospore cultures originating from 3 perithecia were crossed with known tester strains and were shown to belong to mating population A of G. fujikuroi. Three strains were identified as A+, six as A- and two strains that did not produce perithecia when crossed with the testers. Some combinations when crossed with each other produced fertile perithecia of G. fujikuroi, confirming the potential for perithecial production by these strains in the field. Samples of maize kernels were collected from markets and F. moniliforme was isolated from these sources. These isolates also belonged to the A population and contained both + and - strains. Perithecia produced by compatible crosses and sclerotial-like structures produced by incompatible crosses were sectioned and their morphology examined. Only perithecia produced by compatible strains produced a layer of mother cells capable of producing asci.
