Alleviation of Postharvest Skin Dimpling of MN55 Apple Fruit and a Possible Association with Apple stem pitting virus

MN55 is an apple (Malus ×domestica Borkh.) cultivar recently released by the University of Minnesota apple breeding program, with fruit marketed in the U.S. as Rave®. When stored for 4 months at 0 to 4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested 1 week later than those harvested earlier. Dimpling was not alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine or by holding fruit at room temperature for 1 day before long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6 to 7 °C. Because viruses have been implicated in other fruit dimpling disorders, the presence of viruses in MN55 leaves and fruit was studied. Apple stem pitting virus (ASPV) was detected by microscopy, reverse transcriptase polymerase chain reaction (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of storage at 0 to 1 °C. ASPV was also detected in supermarket-purchased fruit of other cultivars with noticeable skin dimpling. Although ASPV was not conclusively demonstrated to cause skin dimpling in our work, its prevalence indicates that further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.

Loquat (Eriobotrya japonica) Is a New Natural Host of Apple Stem Pitting Virus

Loquat (Eriobotrya japonica) is a minor but important woody crop cultivated in Asia and Europe. High-throughput sequencing (HTS) analysis of an asymptomatic loquat plant using RNAseq Illumina technology has allowed the detection for the first time of apple stem pitting virus (ASPV), the type species of the genus Foveavirus in the family Betaflexiviridae, infecting this crop. A nearly complete genome of 9303 nts (ASPV-SL61) reconstructed bioinformatically shows the typical genomic structure of this viral species and a highest nucleotide identity (85.9%) with the Chinese ASPV isolate YLX from pear. A close phylogenetic relationship between ASPV-SL61 and ASPV-YLX has been confirmed by the sequence analysis of full-length ASPV genomic sequences available in the databases. In fact, a phylogenetic study based on a partial CP N-terminal sequence previously proposed to be involved in host adaptation has shown that ASPV-SL61 loquat isolate is more closely related to ASPV pear isolates. The presence of ASPV in loquat has been further confirmed by RT-PCR and Sanger sequencing and DAS-ELISA. An incidence of 15% was determined in one of the loquat Spanish growing areas. The sequence analysis of the partial CP sequences amplified by RT-PCR has shown a high level of variability between loquat isolates. To our knowledge, this is the first record of loquat as a natural host of ASPV.

Evolving by deleting: patterns of molecular evolution of Apple stem pitting virus isolates from Poland

In this study, 267 coat protein gene (CP) sequences from 48 Polish isolates of Apple stem pitting virus (ASPV) were determined. The genetic structure of the virus population was analysed and possible mechanisms of molecular evolution explored. We found evidence of recombination within the ASPV population and the presence of 17 ASPV molecular variants that differ in the length, number and arrangement of deletions in the CP. Population genetic analyses showed significant variation among isolates from pear and apple trees, between isolates from the same host species and, more interestingly, within isolates, supporting the existence of significant levels of variability within individual hosts, as expected by a quasispecies population structure. In addition, different tests support that selection might have been an important force driving diversification within isolates: positive selection was found acting upon certain amino acids. Phylogenetic analyses also showed that isolates did not classify according to the host species (pear or apple trees) but according to the pattern of deletions, suggesting a possible role for deletions during clade diversification.

Gospodarski važni virusi jezgričavog voća

Virusi jabuke, kruške ili dunje relativno su slabo poznati stručnjacima i voćarima. Najvažnijim virusima koji se javljaju na jezgričavim voćnim vrstama smatraju se virus mozaika jabuke (Apple mosaic virus, ApMV), virus klorotične pjegavosti lista jabuke (Apple chlorotic leaf spot virus, ACLSV), virus brazdavosti debla jabuke (Apple stem grooving virus, ASGV) i virus jamičavosti debla jabuke (Apple stem pitting virus,ASPV). U radu je ukratko opisana njihova važnost, biologija i regulativni status, kao i osnovne mjere zaštite.