First Report of a Leaf Spot caused by Sphaerulina tirolensis on Rubus phoenicolasius

Authors: Bruckart, William; Eskandari, Farivar

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2015
Publication Date: 8/24/2015
Citation: Bruckart, W.L., Eskandari, F. 2015. First Report of a Leaf Spot caused by Sphaerulina tirolensis on Rubus phoenicolasius. Plant Disease. Volume 99, Number 9, Page 1275.

Interpretive Summary: Wineberry is a raspberry that came from Asia. The wineberry fruit is very good, and birds spread the plant by eating the fruit, which has seeds in it. This plant is also an important weed. It is invasive and spreads rapidly into many new places; it needs to be controlled. Presently, there is nothing to control it, except by spraying and pulling. Biological control by use of diseases is a possibility, but only a few pathogens are known in the world and they all occur in Asia. Recently, wineberry plants were found in Maryland that had a leaf spot disease. This is the first time any disease has been found on winebery in the United States. The fungus was identified and tested. It causes the disease and it is clear that this fungus has not been reported on wineberry in the United States. It may be a new disease wherever wineberry occurs in the world. This is important to know, for several reasons. It may be useful for biological control. Knowing about the disease and knowing the name of the fungus is the first of many steps needed to develop a disease for this use. It is also possible that this fungus occurs in Asia where wineberry grows naturally but scientists haven’t identified it in Asia. If someone goes to Asia to find wineberry diseases for biological control, they would know that this leaf spot disease is already present in the US and would not need to collect it for research. Samples of the sick plants have been sent to special labs (museums, herbaria) so that other scientists can study this disease, too.

Technical Abstract: Diseased leaves of Rubus phoenicolasius (wineberry) were discovered on October 11, 2013 in a small, 3x3 m, infestation at a sunny location along Indian Springs Rd., Frederick, MD (N 39.467634, W 77.461362). Although the proportion of diseased plants was estimated to be less than10 per cent of the population, several leaves had numerous, angular, discrete necrotic spots, as large as 1 mm diam., characterized by white or light gray, necrotic centers containing pycnidia and distinct, thin, dark red margins. Isolation from surface-sterilized leaf tissue on acidified potato dextrose agar resulted in recovery of a Septoria-like fungus (FDWSRU 13-028). Koch’s postulates were satisfied after two separate inoculations of five healthy cut canes each of R. phoenicolasius from greenhouse-propagated plants; the same fungus was reisolated after each inoculation. The isolate was characterized by narrow, tubular, long, hyaline, and straight, curved or flexuous conidia having 4–6(–8) septations and measuring (mean [c.i.], P = 0.05; w x l) 2.25 [0.12] x 54.5 [ 4.6] microns. DNA was extracted from the isolate using DNEasy and sequenced for ITS1, 5.8S, and ITS2 (GenBank No. KM408152). Using the BLAST option in GenBank, two accessions from raspberry, Rubus idaeus (GenBank Nos. KF251638 and KF251637), listed as “living cultures ex-type CBS 109017, 109018” by Verkley et al (2013), were 99 per cent similar, having only one nucleotide difference from the FDWSRU 13-028 sequence. The pathogen is tentatively identified as Sphaerulina cf. tirolensis Verkley, Quaedvlieg & Crous, on the basis of similar conidium morphological (Ellis et al. 1991, Verkley et al. 2013) and molecular characteristics (Verkley et al. 2013). Specimens have been submitted to the USDA, ARS, SMML and to the CBS Fungal Biodiversity Centre in Utrecht, The Netherlands. Wineberry is a raspberry that was introduced from Asia and is now an invasive species in the eastern USA. This is the first report of S. tirolensis, a raspberry pathogen, on R. phoenicolasius. Characterization of diseases at new locations for plant introductions is fundamental to understanding ecological events and interactions where the host is introduced. This disease is likely established in the USA, because symptomatic plants were found at a new site near the original patch on August 15, 2014, and observations of significant increase in incidence have been made in September, 2014. At the present level of disease and the fact that symptoms appear after fruiting, it seems unlikely that this leaf spot is affecting population density to any significant level.