First Report of Five Sooty Blotch and Flyspeck Fungi on Prunus americana in the United States

Abstract

The sooty blotch and flyspeck (SBFS) complex includes more than 30 fungi that blemish the cuticle of apple fruit, causing economic losses in humid regions worldwide (1). In August 2005, we sampled SBFS-infested wild plum (Prunus americana) fruit growing in hedgerows in Iowa. Colonies were categorized according to mycelial type (1), and isolates were made from representative colonies onto acidified water agar (AWA). Plum skins with SBFS signs were excised, pressed, and photographed. DNA was obtained from purified isolates and also from mycelium and fruiting bodies scraped directly from plum fruit skins. Extracted DNA was amplified using primer pair ITS1-F/Myc1-R (ACTCGTCGAAGGAGCTACG) and PCR products were sequenced using primer pair ITS-1F/ITS4. Six sequences were obtained from pure cultures and seven from colonies on plum fruit skin. BLAST analysis of the 470-bp sequences showed 100% homology to five known species in the SBFS complex: Zygophiala cryptogama, Zygophiala wisconsinensis, Pseudocercosporella sp. RH1, and Stomiopeltis spp. RS1 and RS2 (GenBank Accession Nos. AY598854, AY598853, AY5988645, AY598882, and AY598883, respectively). Observations of colony and fruiting structure morphology from cultures on potato dextrose agar (PDA) and colonies on plums confirmed species identity. A modified version of Koch's postulates was conducted to verify that these fungi caused the signs observed on plum and could also infest apple fruit. In June 2006, 1-month-old cultures on PDA were pulverized in a blender with sterile distilled water, passed through four layers of sterile cheesecloth, and transferred to sterile jars. Each isolate was inoculated onto 20 fruit on plum trees (P. americana) on the Iowa State University (ISU) campus and 20 fruit on cv. Golden Delicious apple trees at the ISU Research Station, Gilbert, IA. Each fruit was disinfested with 70% ethanol, air dried, swabbed with inoculum, and covered with a Fuji bag. At harvest, fungal colonies on fruit were reisolated onto AWA. DNA was extracted from pure cultures; when isolations on agar were unsuccessful, DNA was extracted directly from colonies on fruit. PCR was conducted using ITS1-F/Myc1-R, and PCR products were sequenced using ITS1-F/ITS4. All five species were reisolated and sequenced from apple. Pseudocercosporella sp. RH1 and Stomiopeltis sp. RS1 were sequenced from inoculated plums. Although flyspeck, presumably caused by Schizothyrium pomi, was reported on Japanese plum (P. salicina) in Japan (2) and black cherry (P. serotina) in the United States (3), to our knowledge this is the first report of SBFS fungi on plum in the United States and the first confirmation that fungi from plum can produce SBFS signs on apple fruit. Wild plum may therefore act as a reservoir host, providing inoculum for SBFS infestations on apple. References: (1) J. Batzer et al. Mycologia 97:1268, 2005. (2) H. Nasu and H. Kunoh. Plant Dis. 71:361, 1987. (3) T. B. Sutton. Plant Dis. 72:801, 1988.

A New View of Sooty Blotch and Flyspeck

“…For example, some of the same SBFS species that infest apple also produce signs on fruit of other crop species such as persimmon (36,59), pawpaw (28), winter squash (D. Mayfield, Iowa State University, unpublished data), avocado, grape (45), banana, carambola (star fruit), and mango (47). Recent surveys in China revealed SBFS species colonizing the stem surfaces of two species of bamboo (74) and two species of Chinese medicinal plants (75).…”

Molecular and Morphological Analysis Reveals Five New Species of Zygophiala Associated with Flyspeck Signs on Plant Hosts from China

“…This species was firstly described in the USA on apple fruit and it was also reported on wild plum ( Prunus americana ) in Iowa [36] and apple ( M. × domestica ) in northern China [13] .…”

“…This species has a far-ranging geographic distribution and multiple hosts. It has been reported on apple fruit in the US [9] , China [20] , [36] and northeastern Turkey [11] . It also has been found on sweet persimmon fruit in Korea [37] .…”

“…“ Z. jamaicensis ” was reported on a very wide range of hosts, including 120 species in 44 families of seed plants [8] , [16] – [18] . Recently, taxonomic classification and biogeographic research on the genus Zygophiala were conducted, focusing primarily on apple and its reservoir hosts [1] , [3] , [9] , [11] , [13] , [14] , [36] , [38] . In this study, we investigated Zygophiala species in a wide range of hosts and regions in China.…”

“…In recent literatures, host plants of newly described species only included apple, wild plum and sweet persimmon [9] , [13] , [14] , [36] , [38] . In this paper, the host range of Zygophiala was expanded to pear, hawthorn, persimmon, pawpaw and banana.…”