Sequencing Analysis of Wood-decay Fungi Associated with Peach Scaffold Breakage

Breakage of healthy-looking scaffold limbs is commonly seen in peach orchards in central Georgia, in the United States, and may have impact on the health and longevity of peach trees. White fungal mycelia were observed on the broken surface of some newly snapped, but otherwise healthy-looking peach scaffold limbs. Cross-cut limb sections from apparently healthy scion cultivars were collected and incubated under high humidity for 2 weeks. Fungal growth was observed on the cross-cut surface in two repeated experiments. In this study, genomic DNAs were extracted from the fungus growing on surface of the cross-cut sections. Using next-generation sequencing technology and metagenomic analysis, two white-rot fungi, Trametes versicolor and Schizophyllum commune, were deemed to be the most likely fungi colonizing the heartwood in these specimens. The former likely was predominant over the latter partly because there was a much greater number of read alignments onto the sequences from the T. versicolor genome than that from the S. commune genome. The co-existence of the two fungi were confirmed by Sanger sequencing of an internal transcribed spacer (ITS) amplicon and amplicons from new primers designed from selected contigs, as two different fragments of similar sizes were amplified by the ITS and most selected primers from the DNA extracted from the specimens. Possible reasons for the white-rot fungi colonizing and growing within the peach limbs of apparently healthy, living trees are discussed, as are the likely impact of the colonization on the peach tree health. Further research needs are considered.