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Title: Observation and identification of wood decay fungi from the heartwood of peach tree limbs in central Georgia, USA

item Chen, Chunxian
item Bock, Clive
item Hotchkiss, Michael - Mike
item GARBELOTTO, MATTEO - University Of California
item Cottrell, Ted

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2015
Publication Date: 3/5/2015
Citation: Chen, C., Bock, C.H., Hotchkiss, M.W., Garbelotto, M.M., Cottrell, T.E. 2015. Observation and identification of wood decay fungi from the heartwood of peach tree limbs in central Georgia, USA. European Journal of Plant Pathology. 143(1):11-23.

Interpretive Summary: Peach is an important fruit crop worldwide. Peach tree health and longevity are affected by many biotic and abiotic stresses. Some peach diseases are well characterized and managed, but it remains unclear what and how ‘white-rot’ lignicolous fungi colonize in peach and affect the long-term health of peach trees. The rot in scion scaffold heartwood may be an additional cause of scaffold limb break and short orchard longevity in the southeastern states (8-10 years compared to 17-20 years in the western states). To remain sustainable and profitable, tree health and orchard longevity must be maximally prolonged. This study is to compare the fungal growth between scion and rootstock cultivars, and to determine the identities of these fungi using sequencing technologies. The results will facilitate further studies on the epidemiology, colonization process, disease progress and management.

Technical Abstract: Peach tree health, longevity, and limb strength can be affected by wood decay fungi, but the extent of the colonization and their identities have not been characterized in Georgia, the United States of America. In an incubation experiment, dense white fungal mycelium grew on the cross-cut faces of asymptomatic limb sections sampled from peach scion cultivars, but no mycelium grew on those from rootstock cultivars. Among the scion cultivars, a Chi-square analysis indicated significant differences in the incidence of colonization. A dissection of 6 broken peach tree scaffold limbs showed symptoms of colonization along the entire length of the limbs. Only 41% of primary branches had symptoms of wood decay, but no secondary branches appeared to have symptoms. Next generation sequencing (NGS) and metagenomic analysis of a combined DNA sample revealed the contigs were aligned to sequences of Trametes versicolor and/or Schizophyllum commune, suggesting these two white-rot fungi were present in the sample tested. Sanger sequencing confirmed two fragments of the same size but distinct nucleotide peak intensities were amplified from the sample used for NGS by two pairs of primers, providing supporting evidence that the two fungi were in the bulk sample but might differ in abundance or incidence. Subsequent multiplexing polymerase chain reaction diagnostics of 10 scion samples confirmed the dominance of Trametes spp. (all 10 samples), although Stereum spp. (5 samples), Schizophyllum spp. (3 samples) and Hericium spp, (1 sample) were sometimes found coexisting with Trametes spp. Future research needs on this peach-fungus association are discussed.