Collar Rot on Italian Alder Trees in California Caused by Phytophthora siskiyouensis

Abstract

In November 2006, trees of Italian alder (Alnus cordata) were observed declining in association with bleeding trunk cankers in a commercial landscape in Foster City, CA. A species of Phytophthora was isolated on PARP selective medium from the leading edge of the cankers. The Phytophthora species was homothallic with primarily paragynous antheridia and had oospores that were mostly globose and aplerotic. Sporangia were produced from mycelia on plugs of carrot piece agar in soil extraction solution and were semi-papillate and ovoid to ellipsoid in shape. The intergenic transcribed spacer region of rDNA from an alder isolate matched with 100% identity to isolates in GenBank of Phytophthora siskiyouensis, a recently described species associated with tanoak and found in the soil and waterways of coastal Oregon. Pathogenicity was tested on young alder trees growing in pots. Pathogenicity was confirmed on Italian alder trees and potential pathogenicity was demonstrated on red and white alder trees. Accepted for publication 11 March 2009. Published 13 April 2009.

Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands

“…4i, j ) might pose an additional threat to alder stands in Europe. Phytophthora siskiyouensis was previously reported causing collar rot lesions on planted trees of A. glutinosa and A. cordata in Victoria, Australia, and in California, respectively, and from A. rhombifolia and A. rubra in riparian forests in Oregon ( Smith et al 2006 , Rooney-Latham et al 2009 , Sims et al 2015a ). In underbark inoculation tests, P. siskiyouensis caused similar lesion lengths on A. rubra as P. uniformis ( Navarro et al 2015 ).…”

Diversity and Pathogenicity of Phytophthora Species Associated with Declining Alder Trees in Italy and Description of Phytophthora alpina sp. nov

“…In North America Phytophthora chlamydospora, P. gonapodyides and P. siskiyouensis are considered the most important species involved in the aetiology of root and stem alder diseases [9] and the pathogenicity of these species was demonstrated on Italian, red and white alder [17,18]. At the same time, P. uniformis was reported in Alaskan soils around thin-leaf alder but not in association with declining trees [7].…”

Alder Canopy Dieback and Damage in Western Oregon Riparian Ecosystems

“…in Melbourne, Australia (Smith et al 2006) and planted Italian alder (Alnus cordata (Loisel.) Duby) in California (Rooney-Latham et al 2009 (Reeser et al 2007). …”