Preliminary evaluation of Prunus spp. germplasm for resistance to white root rot (Rosellinia necatrix) disease

Rosellinia necatrix (Prill.) is one of the most important soil-borne pathogens affecting fruit trees in Iran. A preliminary selection of open-pollinated seedlings of 13 Prunus spp. genotypes, including ‘Early Golden’, ‘Obilnaja’, ‘Mirabolano’, ‘Blue Free’, ‘Tanasgol’, ‘Mandchurica’, ‘Saint Julien’, ‘Greengage’, ‘Cadaman’, GF-677, K-R.T-02, K-R.T-01, and K-R.T-41, for resistance to white root rot disease was carried out through artificial inoculation in the greenhouse as part of plum and prune rootstocks breeding programme. In the first experiment, among 559 seedlings belonging to the Prunus population, 282 plants survived 120 days after inoculation. The survivors were exposed to twofold higher concentration of inoculum. The successful establishment of the pathogen on roots of ‘Early Golden’, ‘Obilnaja’, ‘Greengage, K-R.T-41, ‘Blue Free’, and ‘Tanasgol’ led to the destruction of almost all plants. The resistance level of ‘Mirabolano’, ‘Saint Julien’, ‘Blue Free’, and K-R.T-02 did not change with the amount of inoculum, and they were defined as moderately resistant in both experiments. Among all studied Prunus s pp. germplasm, the resistance level of the seedlings of K-R.T-01 was determined as resistant regardless of inoculum density. Although a large number of hybrid GF-677 seedlings died with exposure to a low level of inoculum, the remaining plants were able to survive even at high fungal density. Similarly, the plants of ‘Mandchurica’ and ‘Cadaman’ showed resistant responses with a high level of inoculum. It was a preliminary test for the screening of Prunus spp. population against R. necatrix . The selected seedlings that survived after two fungal inoculation trials are currently being evaluated for reproductive performance and will be screened for precise resistance to white root rot disease in the near future.