New white button mushroom (Agricus bisporus) 'Seolgang' was developed by crossing two monokaryons 'CM020913-27' and SSU423-31. Because of the secondarily homothallism, only a small percentage of the basidia produce 3 or 4 spores, which are mostly haploid (n) and do not fruit. Single spore cultures derived from these types of spores produce a vegetative mycelium that also contain a variable number of genetically identical nuclei per cell called monokaryon. Because of the lack of clamp connections between mono- and dikaryons, a series of mycelial culture and fruiting test were progressed. After crossing, hybrids were cultivated on a small scale and on a commercial scale at a farm. For this, the spawn was made by a commercial spawn producer and the spawned compost by a commercial compost producer. Mycelial growth of 'Seolgang' on CDA was better at 20℃ and 25℃ when it was compared with that of No. 505. The mature cap shape of new strain 'Seolgang' is oblate spheroid and the immature cap shape is round to oblate spheroid. The cap diameter was 41.2 mm on average. In comparison with white strain 505 Ho, the strain had a yield that was 9% higher. It produced fruiting bodies which had a higher weight on average per fruiting body and were 19% firmer with a good shelf life. Days of fruiting body were 3~4 days later than that of No. 505. The physical characteristics such as elasticity, chewiness, adhesiveness were better than that of No. 505. Genetic analysis of the new strain 'Seolgang' showed different profiles compared to No. 505, CM02913-27, SSU413-31, when RAPD primers A02 and O04 were used.

The purpose of this study was to breed new white strains of Agaricus bisporus with high yield and high quality by single spore crossbreeding program. In Agaricus bisporus the compatibility of strains is controlled by one mating type factor and different alleles are needed for fertility in . Fertile vegetative mycelium called heterokaryon consists of a network cells, each of which has a variable number of two genetically distinct nuclei with opposite mating type. In the basidia, specialized cells on the lamellae, a normal meiosis takes place after nuclear fusion and produces two spores, each containing two non-sister nuclei (n+n). Fruiting tests show that these single spore cultures can produce mushrooms, i.e. that they contain both mating types. Because of this secondarily homothallism, only a small percentage of the basidia produce 3 or 4 spores, which are mostly haploid (n) and do not fruit. Single spore cultures derived from these types of spores produce a vegetative mycelium that also contain a variable number of genetically identical nuclei per cell called homokaryon. Other characteristics of A. bisporus is the lack of clamp connections in heterokaryons. The typical life cycle and the lack of differences between homo- and heterokaryons are a serious drawback in breeding. Therefore, the availability of uninucleate self-sterile homokaryons is a pre-requisite for producing hybrids in crossbreeding program. Two homokaryons were isolated from two parental strains, SSU413 and CM0299021. They were crossed and cultivated on a small scale and on a commercial scale at a farm. For this, the spawn was made by a commercial spawn producer and the spawned compost by a commercial compost producer. The mature cap shape of new strain CM021002 is oblate spheroid and the immature cap shape is round to oblate spheroid. The cap diameter ranged from 30-43mm, with an average of 39mm. In comparison with white strain 505 Ho, the strain had a yield that was on average 9% higher. It produced fruiting bodies which had a higher weight on average per fruiting body and were 19% firmer with a good shelf life.

Single basidiospores were isolated from a Pleurotus ostreatus strain collected in Boryeong, Korea showing gray and semispherical in color and shape of pileus. Mycelial growth and several other characters were good to be a breeding material. Mating experiments were performed using 23 monokaryons to provide mating compatibility data. Pairings were performed in 90 mm petri dishes on PDA. They were allowed to grow at 25℃ until two fronts of the advancing mycelia met and developed a conspicuous contact zone. The contact zone and the outer edges of paired colonies on each plate were examined for clamp connections and the crosses were considered positive when clamp connections were found at the growing margin of either side of the interacting monokaryons. The collected strain resulted in tetrapolar incompatibility system in intrastrain crosses. Compatible matings could be visibly distinguished from incompatible ones by the rapid growth and gross morphology. The dikaryotic colony was also confirmed microscopically by the presence of clamp connections from incompatible pairings. The four classes of tester strains representing the four incompatibility types were chosen from intrastrain mating tests as expected. The mating tests with the tester strain were performed for the determination of the rest monokaryons. As a result of these tests it was found that the strain share the same A and B incompatibility factors showing tetrapolar incompatibility system.

Agaricus bisporus is a nutritious edible fungus that is cultivated worldwide. Because of its secondarily homothallic life cycle, 90% or more of the basidia lining the gills at fruit bodies are predominantly two-spored, with each spore receiving two of the four meiotic nuclei. Such homothallic system results in scarcity of monokaryotic basidiospores in its progeny but the availability of uninucleate self-sterile homokaryons is a pre-requisite for producing hybrids in breeding program. This experiment screened 64 single spore isolates collected from CN0210-021, which is white button mushroom cultivated in Chungnam area. They were germinated on PAD meduium at 25℃. After 30 days of incubation colony diameter and morphology type of each isolates was determined. Based on growth rate, 5 strains showing very slow growing morphology than that of parental heterokaryotic strain were selected. Out of 5 slow growing isolates, 2 of them fruited and the rest 3 isolates did not fruit, which were considered as putative homokaryons. These data will provide the outcrossing sources that could be used in commercial breeding programs later. However, in the identification of homokaryotic strains, there is no direct morphological distinguishing features such as a clamp connection that would permit the reliable sorting between homokaryons and heterokaryons. Traditional method to verify a homokaryon thorough the fruiting trial is also time-consuming and not perfect. Therefore, to accelerate the breeding of Agaricus bisporus, quick and reliable methods such as molecular markers to identify the infrequent homokaryons from heterokaryons are needed to be carried out.