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To reduce economic losses caused by viruses and phytoplasmas, one of the main preventive measures is to use 'certified' plant material. A nuclear-stock plum collection under insect-proof house is conserved at FRDS Bistrița and consists in twenty-one varieties and one rootstock used for stone fruits propagation. A widening of Romanian plum varieties at Pre-basic category is required to create the opportunity to establish a larger national valuable nuclear-stock collection and to secure the prerequisite for a good transfer of Romanian plum breeding results to the practical application. Plants belonging to other six Romanian plum varieties (Diana, Silvia, Tita, Pescăruș, Gras românesc and Tuleu dulce) were monitored in the field along two consecutive years for potential viral symptoms and tested by serological and molecular tools according EPPO standards. Selected trees of each variety were grafted onto virus-free Saint Julien rootstocks, into insect-proof house, and retested. Three grafted plants from each of the six varieties were chosen to become Candidate Pre-basic material and they were biological indexed onto virus free plants of GF 305. Thus, candidate Pre-basic material, the precursor for Pre-basic category, was established to other six valuable Romanian plum varieties.

Scab resistance through the Rvi6 gene was largely used in Romanian breeding programs including those from Fruit Research & Development Station (FRDS) Bistrita. The aim of the study was to verify the efficacy of the resistance due to the Vf gene under the current conditions in the Bistrita area. Three scab resistant apple cultivars bred at FRDS Bistrita were monitored in the field, in comparison with the Rvi6 ‘Florina’ and ‘Prima’ cvs., and the sensitive ‘Idared’ and ‘Golden Delicious’ cvs. Molecular markers (AM-19, U1₄₀₀ and AL07) were used in PCR to check the presence of the Rvi6 gene in the genome of the three Romanian varieties. During the years 2019-2021, scab lesions appeared on all the resistant cultivars studied. PCR results showed the presence of Rvi6 gene on ‘Bistritean’, ‘Salva’, ‘Aura’, ‘Prima’ and ‘Florina’ genoms. The results suggest a possible breakdown of the resistance given by the Rvi6 gene in the current ecological conditions in this area. Scab symptoms occurring on cultivars that have the Rvi6 gene could lead to the hypothesis that different scab races are now present in our area or that some genetic variations occurred on the existing races so that they overcome Rvi6 gene.

Apple scab, caused by Venturia inaequalis is one of the most damaging pathogens that affects apple species. Cross combinations were made between Auriu de Bistrița cv. (female genitor) - a valuable local variety in terms of fruit quality but only tolerant to scab, and Florina cv. (male genitor) used as a donor of Vf resistance gene. It was first detected in Malus floribunda Clone 821, which was later transferred to commercial varieties by different breeding programs. To confirm the presence of Vf gene, progenies resulting from the mentioned combination were tested with MAS (Marker Assited Selection), using two dominant primers pairs (AM19, U1400), and another one codominant (AL07) used to distinguish homozygous and heterozygous genotypes. After the crossing combination, a number of twenty-six hybrids were obtained, of which 50% (13 hybrids) were clasified as resistant (heterozygous), respectively 50% (13 hybrids) as susceptible (recessive homozygotes), so the Mendelian ratio was confirmed.

To assess the durability of resistance to PPV of HoneySweet transgenic plum harbouring plum pox virus (PPV) capsid gene, a new field trial was recently established in Romania at Fruit Research & Development Station Bistrita. Stanley and Reine Claude d’Althan cvs. are used as control. PPV inoculum source is secured within the experimental plot. PPV monitoring was made by visual observation of symptoms development on leaves and by serological (DAS-ELISA) and molecular (IC/-RT-PCR) testings. Three years after planting PPV was observed and detected only on Stanley. 'HoneySweet' and Reine Claude d’Althan cultivars remained PPV free.