Colonization of Wild Blackberry Plants in California by Fusarium oxysporum f. sp. mori

Fusarium oxysporum f. sp. mori, the causal agent of Fusarium wilt of blackberry, was first reported in California and Mexico in 2016. A limited survey of the population revealed this pathogen to be one of the most diverse formae speciales of F. oxysporum. We explored the possibility that strains of F. oxysporum pathogenic to commercial blackberry could also be recovered from wild blackberry (Rubus spp.) in California. For this purpose, wild Rubus species in blackberry nurseries, fruit production fields, and nearby areas were collected between 2017 and 2019. Thirty-four isolates of F. oxysporum were recovered from asymptomatic Rubus armeniacus and Rubus ursinus plants. Based on sequence of the translation elongation factor 1-α, somatic compatibility, and pathogenicity to blackberry, 16 isolates were confirmed as F. oxysporum f. sp. mori. These isolates were associated with three somatic compatibility groups, one of which was first identified in this study. Recovery of the pathogen confirmed that wild blackberry plants can act as a reservoir of inoculum of F. oxysporum f. sp. mori and that it can move from wild blackberry plants to commercial cultivars or vice versa.

New Records of Vascular Plant Distribution in the Polish Part of the Lithuanian Lakeland, North-Eastern Poland

The paper presents new localities of 15 vascular plants recorded in the Polish part of the Lithuanian Lakeland, north-eastern Poland in 2017–2018, using the ATPOL cartogram method. Crepis capillaris, Diplotaxis tenuifolia, Eragrostis albensis, Matthiola longipetala, Oenothera fruticosa, Oenothera glazioviana and Rubus armeniacus are listed as new species for the regional flora.

Invasive Blackberry Species in Oregon: Their Identity and Susceptibility to Rust Disease and the Implications for Biological Control

Two of the five species of European blackberry (Rubus fruticosus L. aggregate) along the West Coast of the United States are considered invasive. They are also similar in appearance. Biological control of invasive blackberry by Phragmidium violaceum, causal agent of a rust disease, had been under consideration when rust-diseased blackberry was discovered in Oregon in 2005. An investigation was initiated to determine whether this disease would be an important factor affecting population density of these blackberries. Surveys were made over a 5-yr period at more than 30 field sites in the Willamette Valley and along the Pacific coast of Oregon. Diseased and nondiseased blackberry specimens were collected for artificial greenhouse inoculations and for identification. The two blackberry species, Rubus armeniacus and R. praecox, were identified as the most invasive. They were readily distinguished morphologically on the basis of inflorescence and flower characteristics and to a certain extent by differences in primocane leaf and leaflet shape. Artificial greenhouse inoculation studies revealed that R. praecox was susceptible to the rust disease and that R. armeniacus was not. These results were confirmed during a field survey. Results of this investigation revealed that the rust disease will not be effective for biological control of R. armeniacus and other approaches to management of this particular species will be required.

Nest-site preference and reproductive performance of Song Sparrows (Melospiza melodia) in historically extant and colonist shrub species

Many studies report mixed results on the influence of invasive plants on native animals, partly due to uncertainties about habitat preference and reproductive performance in native animals before and after plant invasion. We used vegetation surveys 20 years apart and 18 years of breeding data from Song Sparrows (Melospiza melodia (A. Wilson, 1810)) to compare nest-site preference and reproductive performance during the colonization of Mandarte Island, British Columbia, by one shrub species native to the region but historically absent from the island (red elderberry, Sambucus racemosa L.) and another species that is exotic to North America (Himalayan blackberry, Rubus armeniacus Focke = Rubus bifrons Vest). Nest-site preference declined where red elderberry increased but was unrelated to change in the cover of Himalayan blackberry. Song Sparrows nested in trailing blackberry (Rubus ursinus Cham. and Schltdl.) and its exotic congener Himalayan blackberry in preference to two common shrubs native to Mandarte Island (Nootka rose, Rosa nutkana C. Presl; snowberry, Symphoricarpos albus (L.) S.F. Blake) and built just 1 of 1051 nests in red elderberry. In contrast, reproductive performance was similar in all shrub species used regularly as nest substrates. Our results show that Song Sparrow nest-site preference and reproductive performance were independent of plant species origin.

An Evaluation of the Flora Adjacent to Wine Grape Vineyards for the Presence of Alternative Host Plants of Grapevine red blotch-associated virus

Grapevine red blotch-associated virus (GRBaV) is a recently discovered virus of concern to wine grape production in North America. While the vector of this virus is unknown, other elements of virus epidemiology are essential to develop guidelines for the management of the virus as well as to assist in the search for its vector. The objective of this study was to evaluate vegetation within and surrounding GRBaV-infected vineyards to identify potential virus reservoirs that may serve as sources of inoculum. In this study, 13 plant species were sampled throughout the year and were tested for the presence of GRBaV. Of the 13 species tested, two species, Rubus armeniacus and wild grapes (Vitis californica × V. vinifera), tested positive by quantitative PCR. Of these two species, only wild grapes were determined to be a true host. This study documents the first time GRBaV has been confirmed in an alternative host or in a species outside of a commercial vineyard and suggests that a mechanism exists by which GRBaV moves between plant species that is not human-mediated. The precise role that wild grapes play in the epidemiology of GRBaV remains unknown.

Rates of Epiphytic Growth of Erwinia amylovora on Flowers Common in the Landscape

We evaluated epiphytic growth of the fire blight bacterium, Erwinia amylovora, on flowers of plant species common to landscapes where pears and apples are grown. The plants were from genera regarded as important nectar and pollen sources for pollinating insects: Acer, Amelanchier, Brassica, Cytisus, Populus, Prunus, Rubus, Salix, Taraxacum, Trifolium, and Symphoricarpos. Floral bouquets were inoculated with E. amylovora and incubated in growth chambers at 15°C for 96 h. Regardless of their susceptibility to fire blight, all species from the rose family except Prunus domestica (European plum) supported epiphytic populations of E. amylovora that exceeded 1 × 106 CFU/flower with relative growth rates for the populations that averaged 7% per hour. Nonrosaceous plants were generally poor supporters of epiphytic growth of the fire blight pathogen with relative growth rates averaging <4% per hour. In two seasons of field inoculations, the rosaceous non-disease-host plants, Prunus avium (sweet cherry) and Rubus armeniacus (Himalayan blackberry), yielded mean population sizes of E. amylovora that exceeded 1 × 106 CFU/flower; in contrast, at 8 days after inoculation, mean population sizes of the pathogen were in the range of 5 × 103 to 5 × 104 CFU/flower on Cytisus scoparius (Scotch broom) and <1 × 102 CFU on Acer macrophylum (big leaf maple). Because vectors of E. amylovora, principally bees, visit many kinds of flowers in landscape areas between pear and apple orchards, flowers of rosaceous, non-disease-host species could serve as potential sites of inoculum increase during their periods of bloom.