Clavispora opuntiae, a New Heterothallic Yeast Occurring in Necrotic Tissue of Opuntia Species

We describe Clavispora opuntiae, a new cactophilic species of yeast with a wide distribution in necrotic tissue of Opuntia species. The more than 200 strains recognized thus far come from eastern Australia, Hawaii, Venezuela, Spain, various islands in the Caribbean Sea, Mexico, and southwestern areas of the United States. The new species is heterothallic and occurs in nature exclusively in the haploid state. Upon conjugation of complementary mating types, asci are produced with one or two clavate, warty ascospores (as observed by electron microscopy) that are very rapidly released from the asci. Testing for mating types has indicated that one mating type (arbitrarily designated h+ predominates in Australia, Haiti, Dominican Republic, and Montserrat, whereas in all other areas both mating types are found, sometimes in the same plant. The guanine-plus-cytosine content range for the nuclear deoxyribonucleic acids of 11 strains is 43.0 to 44.1 mol% (average, 43.5 mol%; standard deviation, 0.4 mol%). The type strain of C. opuntiae is strain UCD-FST 77-279 (= ATCC 42172 = CBS 7068), and the complementary mating type is strain UCD-FST 78-540A (= ATCC 42173 = CBS 7069).