RESOURCES FOR IMPROVING THE ASSORTMENT OF SWEET CHERRY VARIETIES IN BELARUS

The sweet cherry genetic collection of RUE "Institute of Fruit Growing" is including 273 accessions, which have been studied for the main economic and biological traits. The main features for selection are large-fruited combined with winter hardiness and resistance to cherry leaf spot. After an evaluation of the collection, three large-fruited accessions with tough pulp of the fruit were selected. The Ukrainian early fruit ripening variety ‘Annushka’ was selected among the introduced cherry varieties. This variety has large fruits of excellent taste and is characterized by high winter hardiness. Two Belarusian promising selections ‘84-10/98’ (‘Narodnaya’ o.p.) and ‘94-30/41’ (‘Vityaz’ × ‘Aelita’) were selected on these grounds. Selection ‘84-10/98’ has a medium and ‘94-30/41’ has late fruit ripening terms.

Resistance to Boscalid, Fluopyram and Fluxapyroxad in Blumeriella jaapii from Michigan (U.S.A.): Molecular Characterization and Assessment of Practical Resistance in Commercial Cherry Orchards

Management of cherry leaf spot disease, caused by the fungus Blumeriella jaapii, with succinate dehydrogenase inhibitor (SDHI) fungicides has been ongoing in Michigan tart cherry orchards for the past 17 years. After boscalid-resistant B. jaapii were first isolated from commercial orchards in 2010, premixes of SDHI fungicides fluopyram or fluxapyroxad with a quinone outside inhibitor were registered in 2012. Here, we report widespread resistance to fluopyram (FluoR), fluxapyroxad (FluxR), and boscalid (BoscR) in commercial orchard populations of B. jaapii in Michigan from surveys conducted between 2016 and 2019. A total of 26% of 1610 isolates from the 2016–2017 surveys exhibited the fully-resistant BoscR FluoR FluxR phenotype and only 7% were sensitive to all three SDHIs. Practical resistance to fluopyram and fluxapyroxad was detected in 29 of 35 and 14 of 35 commercial tart cherry orchards, respectively, in surveys conducted in 2018 and 2019. Sequencing of the SdhB, SdhC, and SdhD target genes from 22 isolates with varying resistance phenotypes showed that BoscS FluoR FluxS isolates harbored either an I262V substitution in SdhB or an S84L substitution in SdhC. BoscR FluoR FluxR isolates harbored an N86S substitution in SdhC, or contained the N86S substitution with the additional I262V substitution in SdhB. One BoscR FluoR FluxR isolate contained both the I262V substitution in SdhB and the S84L substitution in SdhC. These mutational analyses suggest that BoscR FluoR FluxR isolates evolved from fully sensitive BoscS, FluoS, FluxS isolates in the population and not from boscalid-resistant isolates that were prevalent in the 2010–2012 time period.

Draft Genome Sequence Resource for Blumeriella jaapii, the Cherry Leaf Spot Pathogen

Blumeriella jaapii is the causal agent of cherry leaf spot (CLS), the most important disease of tart cherry in the Midwestern United States. Infection of leaves by B. jaapii leads to premature defoliation, which places trees at heightened risk of winter injury and death. Current management of CLS relies primarily on the application of three important fungicide classes, quinone outside inhibitors, sterol demethylation inhibitors, and succinate dehydrogenase inhibitors. Here, we present the first high-quality genome of B. jaapii through a hybrid assembly of PacBio long reads and Illumina short reads. The assembled draft genome of B. jaapii is 47.4 Mb and consists of 95 contigs with a N50 value of 1.5 Mb. The genomic information of B. jaapii, representing the most complete sequenced genome of the family Dermateaceae (Ascomycota) to date, provides a valuable resource for identifying fungicide resistance mechanisms of this pathogen and expands our knowledge of the phytopathogenic fungi in this family.

Identification of sources of winter hardiness, resistance to coccomycosis, large-fruited of sweet cherry

The results of the evaluation of the genetic cherry collection of the Republican Unitary Enterprise “Institute for Fruit Growing” for winter hardiness, resistance to coccomycosis and large-fruited are presented. Among the studied 213 cherry accessions 6 highly winter resistant, 105 resistant to cherry leaf spot, three genotypes with very large fruits (varieties Krupnoplodnaya, Lyubava Donetskaya, Legenda Mliyeva, the fruit weight of which exceeds 8.3 g) and 11 accessions with a fruit weight exceeding 7.0 g (varieties Krasavitsa, Dar Mlieva, Donetskaya Krasavitsa, Donchanka, Sashenka, Ugolek, Yaroslavna, Lambert Compact, hybrids 10/98, D-7-87, № 5) were identifi ed. Two sources (varieties of sweet cherries of the Belarusian breeding Severnaya and Syubarovskaya), combining high winter hardiness and resistance to coccomycosis, were revealed. On the base of the identified genotypes a characteristic collection of sources of winter hardiness, large-fruited and resistance to coccomycosis has been formed for use in the new sweet cherry breeding program.

Disease threshold for cherry leaf spot incidence on commercial sweet cherry cultivars

The aim of this study was to demonstrate the 10% threshold level for cherry leaf spot incidence on 23 commercial sweet cherry cultivars in two training systems. Twenty three cherry cultivars were evaluated in the two training systems with a spacing of 4 x 1 m and with a spacing of 2 x 5 m. Results showed that leaves of many cultivars were heavily infected, e.g. cultivars (cvs) ’Biggareau Burlat’, ’Sunburst’, while others showed low disease incidence e.g. cvs ’Celeste’ and ’Blaze Star’. According to the 10 % threshold level, cv ’Celeste’ proved to be the most resistant cultivar to leaf infection, while cv ’Münchebergi korai’ exceeded extremely the 10% threshold level. Leaf spot incidence was affected by training system on most cultivars. Thirteen cultivars had less than 10% infection in the 4 x 1 m spacing (i.e. they did not reach the 10% disease threshold level). At the same time, only 3 cultivars showed less than 10% infection in the 5 x 2 m spacing.

Boscalid Resistance in Blumeriella jaapii: Distribution, Effect on Field Efficacy, and Molecular Characterization

Cherry leaf spot (CLS), caused by the fungus Blumeriella jaapii, is a major disease of tart cherry (Prunus cerasus L.) trees, leading to early defoliation that results in uneven ripening and poor fruit quality in the current season, reduced fruit set in the following season, and increased potential for winter injury and tree death. Pristine (BASF Corporation, Research Triangle Park, NC), a commonly used fungicide for CLS management in Michigan, is a premix of boscalid, a succinate dehydrogenase inhibitor, and pyraclostrobin, a quinone outside inhibitor. Reduced efficacy of Pristine for CLS control was observed in field trials and commercial orchards and highlights the importance of fungicide resistance monitoring. A total of 1,189 isolates from 31 commercial orchards in Michigan, 111 isolates from nontreated trees (four locations in Michigan and two locations in Ohio), and 133 isolates from a research orchard were collected during 2010, 2011, and 2012 and assayed on boscalid-amended media at concentrations ranging from 0 to 25 μg ml−1. Because of the very slow growth rate of B. jaapii in culture, we determined the minimum inhibitory concentration (MIC) of boscalid as opposed to the effective concentration that inhibits mycelial growth to 50% of the control. Isolates from nontreated trees had MIC values ranging from 0.1 to 0.5 μg ml−1; the MIC of isolates from commercial orchards ranged from 0.1 to >25 μg ml−1, and isolates from the research orchard ranged from 2.5 to >25 μg ml−1. Isolates with MIC values ≥25 μg ml−1 were considered boscalid resistant and comprised 0% of the nontreated isolates, 30.4% of the commercial isolates, and 42.1% of the research orchard isolates. Sequencing of the sdhB gene of resistant isolates led to the detection of the amino acid mutation H260R, which is known to confer boscalid resistance in other phytopathogenic fungi. Our results indicate that the occurrence of the H260R mutation in Michigan populations of B. jaapii is correlated with the reduction in sensitivity to boscalid observed in commercial orchards.