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KITANI, Y., L. S. OLIVE, and ARiF S. EL-ANI. (Columbia U., New York City.) Genetics of Sordaria fimicola. V. Aberrant segregation at the g locus. Amer. Jour. Bot. 49(7): 697-706. Illus. 1962.-Aberrant segregation of the gray-spore color locus in Sordaria fim cola was studied with the aid of closely linked markers. It was found that 6:2 and 5:3 asci occur with about the same frequency, but asci with an excess of wild-type spores occur with a frequency 5.5 times that of asci with an excess of gray spores. Also, the frequency of related crossing over (occurring close to the miscopied locus and involving the miscopying strand) was much higher than the expected value, and in 5:3 asci it appears to be at least twice that found in 6:2 asci. Nine aberrant 4:4 asci, each with 2 spore pairs heterogeneous for color, were found. These are believed to have resulted from reciprocal double transreplication. The rarest aberrant type was represented by a single 7 :1 ascus, which is difficult to explain on the basis of a single meiotic process. Miscopying is discussed with relation to an 8-strand model of paired homologues and the occurrence of localized chromosome pairing during prezygotene DNA synthesis. Several possible explanations for the occurrence of aberrant tetrads are considered. Miscopying has also been found to involve several spore-color loci not previously studied; whereas, several other such mutant loci fail to show evidence of it. One locus (m) shows abnormal segregation of the 6:2 but not the 5:3 type. Asci showing aberrant segregation for sporecolor loci in Sordaria fimicola were reported earlier by Olive (1956, 1959) and Kitani, Olive, and El-Ani (1961). Similar aberrant segregation has been described for various markers by Mitchell (1955a, b; 1959), Case and Giles (1958), and Stadler (1959a, b) in Neurospora crassa; by Strickland (1958) in Aspergillus nidulans; by Lindegren (1953) and Roman (1956) in Saccharomyces cereviseae. While these authors have demonstrated the occurrence of 3:1 or 6:2 segregation for a particular locus, both 6:2 and 5:3 asci have been reported by us in S. fimicola and essentially the same types were found by Rizet, Lissouba, and Mousseau (in press) in Ascobolus immersus. Certain aberrant asci of Neurospora crassa classified by Mitchell (1959) as "artificial" may have represented 5:3 segregations. After markers closely linked to the gray-spore locus were obtained in S. fimicola (El-Ani, Olive, and Kitani, 1961), the present study of aberrant segregation of the g locus was undertaken, especially for the purpose of determining whether there is a relationship between miscopying or transreplication of the locus and crossing over in its vicinity, and whether 6:2 and 5:3 asci have a similar explanation. The terms miscopying and transreplication are here used interchangeably as a convenient means of description with no intention of describing the precise mechanism involved, 1 Received for publication December 1, 1961. This research was supported by grants NSF G-14236, NIH E-2326, and NIH 2G-216 (ClS1). 2Present address: 211 Sakuragoaka, Mino, Osaka, Japan. 3 A record of the progeny of all asci analyzed is retained by the second author. since the details of the mechanism remain unknown. MATERIALS AND METHODS-The characteristics of the g mutant have been previously reported (Olive, 1956). In the crosses studied here, the following linked markers were used: Spotty (sp): growth and perithecial distribution in a spotty pattern; fertile. Milky (mi): thin, milky-colored mycelium; fertile; nonautonomous spore-color mutant with grayish-brown spores. Mat (mat): slow-growing, thick mycelium; fertile. Corona (cor): distinctive ring developing around inoculum; partially fertile. Sterile no. 22 (st-22): scattered small protoperithecia; self-sterile. The positions of these mutant loCi are shown in Fig. 1. In most cases doubleand multiple-mutant progeny were distinguishable from wild-type and single-gene mutants, as well as from each other, on culture media, except for a few combinations with mi in their genotypes. The latter were identified in confirming crosses. Any cluster of asci found to contain an aberrant ascus was transferred to a plate of cornmealdextrose agar containing 0.7% sodium acetate to stimulate germination, and all 8 spores of the desired ascus were isolated in order.4 Crosses and analysis of progeny were made on Difco cornmealdextrose agar with 0.1%o yeast extract added. I Aberrant ascospores of both mutant and wild phenotype from 31 asci were tested in back crosses and all were found to agree in genotype. Further transreplications occurred in the back crosses.

A B S T RA C T Ten mutant sites have been located in linkage group II of Sordaria fimicola, nine of them affecting fertility. Two different regions of the chromosome are marked with allelic mutations or mutant sites in closely linked loci involved in sexual reproduction. Mutants of one of these two regions also have an arginine deficiency. Crosses between the self-sterile mutants of each region yield hybrid perithecia containing asci with four spores of each parental genotype and few or no asci with recombinant spores. The bearing that these findings have upon the evolution of heterothallism is discussed. THIS SERIES of genetic investigations on the homothallic ascomycete Sordaria fimicala was initiated after the isolation of three ascospore color markers that made possible the visible distinction between selfed and hybrid asci (Olive, 1956). The wild type produces perithecia containing 8-spored asci with dark ascospores. It is a remarkably stable fungus in the laboratory; very few spontaneous mutants have been detected during 16 years of investigation. Most of the mutants have been obtained by irradiating ascospores with xrays. Recently, both auxotrophic and self-sterile mutants have been isolated after treatment with nitrosoguanadine (Jha and Olive, unpublished data). Eleven morphological mutants differing from wild type in ascospore color, loss of fertility, rate of growth, or mycelial characteristics have been mapped in linkage group I (El-Ani, Olive, and Kitani, 1961). The present paper contains a study of 10 additional mutants constituting linkage group II (Fig. 1). The haploid chromosome complement in S. fimicola is seven (Carr and Olive, 1958).

CERATOSTOMELLA RADICICOLA, the perfect stage of Chalaropsis, is a heterothallic pyrenomycete with long-necked perithecia and hyaline single-celled ascospores. Asexual reproduction is accomplished by means of two types of conidia, the microconidia (fig. 6) produced endogenously, and the macroconidia (fig. 2, 3) borne on sympodially branched macroconidiophores. Previous studies (Bliss, 1941; El-Ani et al., 1957) have revealed the occurrence of two distinct strains on roots of the date palm, the black strain (fig. 1) producing dark macroconidia (fig. 3) and black perithecia (fig. 5b), and the brown strain (fig. 1) in which both macroconidia (fig. 2) and perithecia (fig. 5a) are brown. The ascospores are uninucleate (fig. 7), and single-ascospore cultures are hermaphroditic, selfsterile, and of two compatibility types (A and a), which must be brought together before perithecia can be produced. When black and brown strains are mated, the progeny has been found to consist of black and brown thalli in a 1:1 ratio. Thus the two strains differ genotypically from each other by black to brown has been observed in vitro. Recently two mutants (fig. 1), gray and tan, which arose spontaneously in vitro were used with the other strains for further genetic investigation, the results of which are described in the present paper. MATERIALS AND METHODS. Cultures of C. radicicola derived from single ascospores were grown on two media, potato-dextrose-yeast agar (2g. yeast extract/I.) on which rapid vegetative growvth at temperatures of 27-30?C. ensures morphological distinction of each strain; and Bacto prune agar (48 g./l.) used mainly for perithecial production. In crosses between two thalli, conidia suspended in distilled sterile water were transferred from one thallus to another of different compatibility. Perithecia with mature ascospores were formed within four days. Single-ascospore cultures grown on the potato-dextrose-yeast agar medium were assorted according to their morphological characters within a week. In order to determine the mating type and perithecial color of each single-ascospore culture, a small conidial inoculum was transferred from the unknown thallus to each of two tester thalli of the same perithecial color but differing in compatibility factors. Tester thalli with perithecial color presumably different from that of the tested culture were chosen. For example, if the single-ascospore a single gene. As yet, however, no mutation from

A B S T R A C T The cytology of ascus development in Nectria cinnabarina was investigated with the orceinsmear technique, from crozier formation to ascospore maturation. At prophase I synapsis occurs while the chromosomes are still contracted, and the nucleus passes through dictyotene, a diffuse stage rarely seen in plants. A haploid complement of five chromosomes has been precisely determined. The first two divisions in the ascus constitute meiosis, and the third (mitotic) is followed by ascospore delimitation. A fourth division takes place in the ascospore, which is subsequently divided by a septum into two uninucleate cells. Of all species of Nectria thus far investigated N. cinnabarina is the only species in which additional nuclear divisions in the ascus do occur, accounting for the multinucleate condition in the ascospore cells. The bearing that this distinctive nuclear condition has on phylogeny and evolution in the Hypocreales is discussed. IN THE WAKE of a controversy related to sex determination and chromosome numbers in the ascomycete Hypomyces solani2 Rke. et. Berth. emend. Snyd. et Hans. (Hirsch, 1949; El-Ani, 1954), a series of cytological studies was undertaken for three main purposes. First, to determine the haploid chromosome number(s) in wild-type and mutant strains of H. solani f. cucurbitae Snyd. et Hans. Second, to find out whether a polyploid relationship does exist between homothallic and heterothallic strains as reported by Hirsch (1949).