# Nematoidal Properties of Wild Strains of _Pleurotus ostreatus_
## 4 Discussion  
The results of our experiments allowed us to select the mycelia of _P. ostreatus_, which presented the higher speed of growth, especially in the most important temperature ranges, which were 10-15 and 20-25 \({}^{\circ}\)C. The lower temperature range corresponds to spring or autumn conditions, and the higher range corresponds to summer temperatures. The isolates that were well adapted to these temperatures were the Po4 MixMon group (Po4 progenies), and they generally presented better growing parameters than the maternal Po4 strain. Our tested strains were the result of crosses performed according to the Buller phenomenon. Figure 21: Percent reduction in the _H. schachtti_ population by _P. ostreatus_ Po4 in the field experiment (in breeding tents). Figure 22: The influence of _P. ostreatus_ Po4 mycelium on the population _H. schachtti_ in the field conditions (in breeding tents) given in Pf/Pi coefficient; data followed by the same letter do not differ significantly (\(p=0.05\)). The phenomenon was documented for the first time by [PERSON] in 1931 [11], and it relies on the fusion of monokaryotic mycelial hyphae with heterokaryotic hyphae, resulting in new heterokaryotic hyphae varieties. This reaction was first called the \"Buller phenomenon\" by [PERSON] in 1937 [11; 17]. The fusion of homokaryotic and heterokaryotic hyphae generates a hybrid heterokaryon that inherits one homokaryon nucleus and one heterokaryon derived nucleus. The nucleus that has been transferred from heterokaryon (donor) to homokaryon (acceptor) must exhibit sexual compatibility with the acceptor hyphae nucleus. This process allows the creation of new types of heterokaryons, and if this is preferred by natural processes, it is possible that a new type of progeny would present better properties than both parental hyphae. The process occurs naturally between heterokaryotic and homokaryotic hyphae. On the other hand, some basidisospores are binu-cleate, which means that hyphae created from them will give a heterokaryotic mycelium. In our experiments, these binucleate basidisospores were produced by all three maternal strains at the level of \(\sim\)3.0-3.3%. The mycelia obtained from them easily crossed with monokaryons. The Buller phenomenon seems to be a normal process in nature because, in our tests, its frequency was observed at the level of \(\sim\)30% between monokaryons and dikaryons of the same origin (developed from basidisospores from the same wild maternal strain). Crosses between monokaryons achieved 22.5% in Po1 progenies, 27.6% in Po2, and 35.5% for crosses of monokaryons Po1 \(\times\) Po2 (Supplementary Figure S8). Thus, the Buller phenomenon seems to be as desirable as mating between unrelated hyphae [18]. The tested mycelia presented low diversity based on the ISSR markers comparison. Most of them were grouped in two clusters of identical strains and only a few of them, the maternal strains and five progeny strains, were outside of that cluster. This result was surprising because the previously obtained crosses among monokaryons of Po1 and Po2 resulted in a higher ISSR diversity in progenies [12]. The explanation for these results may be that \"Buller crosses\" led to new genetic arrangements in \"Buller offspring\". Some level of diversity among the tested strains was observed based on the morphological and physiological features, but the strains also presented low diversity compared to the typical monokaryotic crosses obtained by [PERSON] et al. [12]. [PERSON] et al. [19] demonstrated that, among the European _P. ostreatus_ varieties, the genetic variation is reduced, which is in agreement with our study. Differences in tested strains were also observed in toxic properties against nematodes. We tested two nematode species--_C. elegans_, which is a model organism in that group of animals, and the plant parasitic _H. schachtii_, which infects sugar beets and many other plants, including weeds [1; 20]. While our strains were able to capture, kill, and digest _C. elegans_, the _H.