BARREN PERITHECIA IN NEUROSPORA CRASSA

Abstract

The term Barren is applied to perithecia (sexual fruiting bodies) that produce no or few ascospores. Perithecial number is usually not reduced in barren crosses. The barren condition may result from recessive or dominant mutations, from partial chromosome duplications, and occasionally from balanced chromosome rearrangements. It is characteristic of some but not all of the types of recessive genes that increase radiation sensitivity or the deletion of segmental duplication. Barrenness provides a convenient signal for these genotypes, where meiosis or ascus development is impaired. Duplications are characteristically dominant-barren, and changes from barren to fertile signal that duplicated segments have been deleted. Development has been examined cytologically in perithecia from various crosses where barrenness results from the postfertilization genotype and does not depend on the constitution of maternal tissues. Early development is often normal until it is interrupted at or just before karyogamy. In some genotypes, asci progress into prophase I and a few may reach later stages. Specific defective genotypes show characteristic differences in the time of arrest and in the pattern and details of degeneration. There is considerable overlap, however, so that precise temporal seriation is usually difficult or impractical.