First Report of Phomopsis Fruit Rot of Strawberry in Ohio

Molecular reassessment of diaporthalean fungi associated with strawberry, including the leaf blight fungus, Paraphomopsis obscurans gen. et comb. nov. (Melanconiellaceae)

Phytopathogenic fungi in the order Diaporthales (Sordariomycetes) cause diseases on numerous economically important crops worldwide. In this study, we reassessed the diaporthalean species associated with prominent diseases of strawberry, namely leaf blight, leaf blotch, root rot and petiole blight, based on molecular data and morphological characters using fresh and herbarium collections. Combined analyses of four nuclear loci, 28S ribosomal DNA/large subunit rDNA (LSU), ribosomal internal transcribed spacers 1 and 2 with 5.8S ribosomal DNA (ITS), partial sequences of second largest subunit of RNA polymerase II (RPB2) and translation elongation factor 1-α (TEF1), were used to reconstruct a phylogeny for these pathogens. Results confirmed that the leaf blight pathogen formerly known as Phomopsis obscurans belongs in the family Melanconiellaceae and not with Diaporthe (syn. Phomopsis) or any other known genus in the order. A new genus Paraphomopsis is introduced herein with a new combination, Paraphomopsis obscurans, to accommodate the leaf blight fungus. Gnomoniopsis fragariae comb. nov. (Gnomoniaceae), is introduced to accommodate Gnomoniopsis fructicola, the cause of leaf blotch of strawberry. Both of the fungi causing leaf blight and leaf blotch were epitypified. Fresh collections and new molecular data were incorporated for Paragnomonia fragariae (Sydowiellaceae), which causes petiole blight and root rot of strawberry and is distinct from the above taxa. An updated multilocus phylogeny for the Diaporthales is provided with representatives of currently known families.

The nuclear small subunit ribosomal genes of Sphaeronaemella helvellae, Sphaeronaemella fimicola, Gabarnaudia betae, and Cornuvesica falcata: phylogenetic implications

Sequences were obtained from the nuclear small subunit ribosomal RNA genes for representatives of four ophiostomatoid genera (Ceratocystis, Gondwanamyces, Cornuvesica, and Sphaeronaemella) to resolve their phylogenetic position within the Ascomycota. Phylogenetic analysis suggests that these genera are monophyletic and share common ancestry with members of the Microascales. Based on sequence data, strains representing the mitotic species Gabarnaudia betae (Delacr.) Samson & W. Gams were shown clearly to be derived from Sphaeronaemella species. Sequences were also obtained from strains representing the syntype of Sphaeronaemella fragariae, the exholotype of Sphaeronaemella humicola, and the extype of Gabarnaudia tholispora. The results suggest that putative extype cultures for S. humicola and G. tholispora no longer represent the original material deposited. Our data also support the exclusion of S. fragariae from Sphaeronaemella. Key words: Cornuvesica, Gabarnaudia, Gondwanamyces, Sphaeronaemalla fragariae, ophiostomatoid fungi, ribosomal DNA.

Reliability and accuracy of visual estimation of phomopsis leaf blight of strawberry

ABSTRACT Six different individuals (raters) assessed the severity of Phomopsis leaf blight on strawberry leaflets in five experimental repetitions over 2 years by making a direct visual estimation of the percentage of diseased area of each leaflet or by using the Horsfall-Barratt (H-B) disease scale. Intra-rater and inter-rater reliability and accuracy were determined, and then the relationship between visually estimated severity values and actual severity values was evaluated. Agreement in estimated disease severity values between assessment times by the same raters (i.e., intra-rater reliability), and agreement in disease severity values among raters at a single assessment time (i.e., inter-rater reliability), were both high, with most correlation coefficients being greater than 0.85. The intra-class correlation for overall agreement among raters ranged from 0.80 to 0.96 for the five repetitions. Based on the concordance coefficient calculated for each rater in each repetition, agreement between estimated and actual severity (i.e., accuracy) was somewhat lower than reliability. The relationship between estimated and actual severity was linear, and there was a slight trend to overestimate disease severity. The H-B scale was not more reliable or accurate than direct estimation of severity, and the linear relationship between estimated and actual severity did not support the principles underling the H-B scale. Both size of leaflets and number of lesions per leaflet slightly affected the error in estimate of disease severity.