Neurospora discreta, a new heterothallic species defined by its crossing behavior

Abstract

The species is described and named Neurospora discreta sp. nov. because of its stringent reproductive isolation. Isolates collected from burned vegetation at a single site near Kirbyville, Texas, include both mating types (Aanda). Experimental criteria based on cross-fertility were used for assigning species status. Crosses between isolates of opposite mating type are highly fertile, producing abundant eightspored asci. In contrast, when the Kirbyville strains are crossed to sexually compatible speciestester strains representing N. crassa, N. intermedia, N. sitophila, and N. tetrasperma, perithecia are rudimentary and no ascospores are produced. The haploid chromosome number is 7. Chromosomes at pachytene resemble those of other Neurospora species. Biotin is required. Linear growth is slower than for other heterothallic species. When A and a strains from Kirbyville grow toward one another and intersect on crossing medium, there is no barrage. A single homogeneous band of perithecia is formed where they meet, indicating that opposite mating types are vegetatively compatible. The Kirbyville population differs from other heterothallic Neurospora species in ascospore morphology and vegetative traits. Ascospores from Kirbyville parents are larger, and the ribs between confluent parallel grooves are ornamented with dot-like pits. Vegetative cultures from Kirbyville are yellowish rather than orange, and large empty barren protoperithecia or false perithecia are produced abundantly in unfertilized haploid cultures. Isolates from two other N. discreta populations resemble other Neurospora species more closely with respect to these morphological traits but are clearly conspecific with the Kirbyville strains on the basis of fertility in crosses.