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SUMMARYSix diploids of Aspergillus parasiticus involving 12 genetic markers were analyzed by means of the parasexual cycle. Heterokaryotic heads consisted of homokaryotic and heterokaryotic conidia...

The recovery of mutants impaired in aflatoxin production and the identification of parasexuality in Aspergillus flavus Link ex Fries now make genetic investigations of aflatoxin biogenesis possible. In wildtype strains, aflatoxin B2, the dihydro derivative of B1, generally accumulates in smaller quantities than B1. Isolates accumulating only aflatoxin B2 were reported by van Walbeek et al. (9) in A. flavus var. columnaris and by Schroeder and Carlton (8) in an A. flavus isolate from black pepper. A relatively stable mutant of A. flavus accumulating high levels of aflatoxin B2 (5,000 jug/g mycelial dry wt) and low levels of aflatoxin B1 (600 tsg/g mycelial dry wt) was recently recovered following treatment of conidia with nitrosoguanidine (6). A parasexual analysis of this mutant revealed a genetic locus involved in aflatoxin biosynthesis (7). Heterozygous diploids exhibited the dominant phenotype of B2 B1. No linkage was detected between this gene locus and selected gene markers of the seven genetically identified linkage groups. The present study is a continuation of our genetic analysis of this mutant, including linkage to the histidine locus and the identification of linkage group VIII.

Strains of Aspergillus flavus were recovered from corn samples from 15 counties in Georgia and placed into 22 different heterokaryon-compatibility (h-c) groups. There was no clear pattern of associ...

Summary: A mutant of Aspergillus flavus accumulating norsolorinic acid and approximately 50% less aflatoxin than the parent strain was recovered after treatment of conidia with N-methyl-N'-nitro-N-nitrosoguanidine. The gene nor controlling this mutant phenotype was recessive and linked to afl-1 and leu on linkage group VII. Diploids homozygous for nor were similar to haploids in norsolorinic acid accumulation. The analysis of recombinant diploids and haploids showed that afl-1 and nor were both distal to leu on the same chromosome arm.

Parasexual crosses involving a mutant of Aspergillus flavus having a high and relatively stable level of aflatoxin B2 relative to aflatoxin B1 have revealed a genetic locus for control of aflatoxin...

Nuclear behavior during conidiogenesis in Aspergillus flavus was studied cytologically and through the analysis of conidial chains in heterokaryons. Many nuclei migrate into the vesicle and one or more are incorporated into phialides. The nuclear constitution of each phialide is independent of all others and, for the most part, all conidia in a chain are identical. The analysis of 105 conidial chains, containing an average of seven conidia each, indicated that each chain was either homokaryotic for one spore-color type or was heterokaryotic. Seven chains, each with one to three deviant spores, were mixed. Occasionally random binucleate conidia were observed within uninucleate chains.

Mutants ofAspergillus flavus were recovered following the irradiation of conidia with ultraviolet light. Analysis of the mutants for aflatoxins B1, B2, G1, and G2 indicated a wide range of variability in aflatoxin levels. None of the isolates produced the G toxins, and four produced little or no aflatoxin B2. Production of B1 and B2 by the mutants ranged from 1.3 µ;g/ml to 967 µg/ml and zero to 30 µg/ml, respectively. The correlation between production of B1 and B2 was statistically significant. There was no apparent correlation between nutritional requirement or conidial color and aflatoxin production.

on the stipe, mentioned in Kauffman's notes, did not appear distinctive even in our collections having a veil. We believe that the layer Kauffman described in his notes is a loosely woven cuticular layer. Kauffman noted the gills as yellowish at first and this feature was included in the description by Hesler and Smith (1963). We were unable to verify his observation, but in view of the general change to yellow, we do not regard this apparent difference as taxonomically significant. In regard to H. pudorinus, the reddish-orange reaction in KOH of the scurf near the apex of the stipe readily distinguishes both color variants from H. amarus.

A dominant mutant of Aspergillus flavus impaired in aflatoxin production, designated afl-1 and linked to leu in linkage group VII, was recovered after treatment of conidia with N-methyl-N'-nitro-N-nitrosoguanidine. Mutant afl-1 failed to complement other non-allelic aflatoxin mutants in diploids and also restricted aflatoxin accumulation when paired with toxigenic strains in diploids. No detectable effect of afl-1 was demonstrated in heterokaryons. This gene locus is apparently not involved in the extracellular degradation of aflatoxin.

Pairings of 5 heterothallic isolates of Pythium sylvaticum in all possible combinations revealed the existence of 2 sexually compatible groups of isolates.Tracings of gametangial hyphae leading to ...

Continuous selection for fast linear growth rate in Neurospora crassa at 18°, 25°, and 35 °C was effective. Crossing plateaued selection lines within the same temperature revealed that different combinations of genes were synthesized in each line. Most of these differences could be attributed to non-additive gene effects. Twelve cycles of selection within progeny from crosses between selected lines were effective, although the growth rate reached previously in the fastest parent was not surpassed.Crossing plateaued selection lines improved at different temperatures generated new genetic variance, thus indicating the fixation of different alleles in different lines with temperature. The difference between lines selected at different temperatures could be explained be the additive effect of two to three genes. Estimates of the average genetic variance were found to be highest among the progeny from crosses involving 35°-selection lines and lowest from crosses involving 18°-selection lines

Part of the polygenic system controlling the response to selection for fast linear growth rate in Neurospora crassa is linked to the aurescent locus on chromosome I. This genotypic material accounts for approximately 18 percent of the total response to selection. There was no evidence of linkage to the yellow locus on chromosome VI.

A mutant of Aspergillus flavus having a high and relatively stable aflatoxin B2/B1 ratio was recovered after treatment with nitrosoguanidine.

Biochemical mutant strains of Cochliobolus carbonum were recovered following irradiation of conidia with ultraviolet light. Because of the multicellular, multinucleate condition of the. spores and the methods of recovery that were employed, low yields of mutants were obtained. Recovery of arginine, methionine, and adenine auxotrophs in highest frequency suggested that the methods of recovery were selective for these classes of mutants. Arginine and methionine mutants were classified into several physiological types, each type representing mutation at a different locus. Pathways for the synthesis of arginine and methionine established in other fungi were demonstrated in C. carbonun. Genetic analyses of auxotrophs were hampered by infertility problems. While crosses between mutants and wild-type isolates were generally fertile, crosses between mutants were generally infertile.

(1973). The Parasexual Cycle in Aspergillus Flavus. Mycologia: Vol. 65, No. 5, pp. 1201-1205.