A supernumerary chromosome called a conditionally dispensable chromosome (CDC) is essential for pathogenicity of Nectria haematococca on pea. Among several CDCs discovered in N. haematococca, the PDA1 CDC that harbors the pisatin demethylation gene PDA1 is one of the best-studied CDCs and serves as a model for plant-pathogenic fungi. Although the presence of multiple copies is usual for supernumerary chromosomes in other eukaryotes, this possibility has not been examined well for any CDCs in N. haematococca. In this study, we produced strains with multiple copies of the PDA1 CDC by protoplast fusion and analyzed dosage effects of this chromosome. Using multiple methods, including cytological chromosome counting and fluorescence in situ hybridization, the fusion products between two transformants derived from the same strain that bears a single PDA1 CDC were shown to contain two PDA1 CDCs from both transformants and estimated to be haploid resulting from the deletion of an extra set or sets of A chromosomes in the fused nuclei. In phenotype assays, dosage effects of PDA1 CDC in the fusion products were evident as increased virulence and homoserine-utilizing ability compared with the parents. In a separate fusion experiment, PDA1 CDC accumulated up to four copies in a haploid genome.

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High genetic diversity increases the chances of obtaining varieties resistant to abiotic stress in breeding programs. Plum rootstocks that are resistant to disease can be used for the propagation of various Prunus species. This research was conducted to evaluate different myrobalan plum genotypes and their resistance to three pathogenic bacteria, i.e. Rosellinia necatrix, Verticillium dahlia, Phytophthora cactorum. It was also endeavored to identify resistant genotypes, their degree of resistance to disease, and the correlation between their morphological traits. The experiment spanned from 2016 to 2018. In the first phase of the experiment, the morphological traits of 5 superior genotypes of myrobalan plum were evaluated. These genotypes were, namely, Ahmad-beigloo, Anar-1, 4835, 4813 and G14. In the second phase of the experiment, the genotypes were examined for their degree of resistance to the three mentioned pathogenic fungi. This was performed in two separate groups of complete randomized designs, with five treatments (genotypes) and nine repetitions. According to the results, the seedlings showed a high level of diversity with respect to morphological traits and features relating to the seed. Furthermore, under the influence of the Rosellinia fungi, as the length of the shoot and root increased, the length and percentage of the necrosis decreased. The Anar-1 genotype exhibited the longest necrosis and the highest percentage of necrosis which makes it the most susceptible genotype to the fungus in one group. The genotype Ahmad-beigloo exhibited the shortest necrosis and the lowest percentage of necrosis, making it the most resistant genotype to the Rosellinia fungus, and was placed in a separate group. With respect to the degree of seedling resistance to Phytophthora and Verticillium, there were no significant differences among the genotypes.