First report of Albugo trianthemae on Delosperma and Lampranthus in the UK

Aizoaceae is the largest family of succulent plants containing 127 genera and about 2500 species of which most are endemic to arid or semi-arid parts of southern Africa, with a few occurring in Australasia and the Americas. South African Aizoaceae have long been cultivated in British gardens since they were introduced in the second half of the 17^th Century. Some, notably Carpobrotus edulis, have become naturalised by the coast in south west England and compete with native species. In summer 2007 and 2008, diseased samples of Delosperma cooperi, Lampranthus ‘Tresco Orange’, L. roseus and Lampranthus sp., both genera belonging to the Aizoaceae,were received at the Royal Horticultural Society, Wisley and at the Royal Botanic Gardens at Kew. These samples originated from private gardens in East Sussex, West Sussex and Devon.Infected plants were covered with chalky blister-like pustules typical of white blister (Albugo spp.) (Fig. 1). For samples of both genera, microscopic examination revealed oospores in the leaf tissue that were spherical, 50-61 x 53-61 μm (average 56 x 57 μm), with a two-layered wall, 4-8 μm thick. The outer layer was reticulated, the alveoli angular and irregular, 3-6 μm wide (Fig. 2). Conidiophores were cylindrical (50 x 21 μm). Conidia were cubical, globose or elliptical, 16-23 x 13-23 μm (average 19 x 16 μm) (Fig. 3). The morphological characteristics fit the description of Albugo trianthemae (Wilson 1908; Waterhouse 1975). Material from East Sussex on L. roseus was deposited in Kew (Accession No. K(M) 159430). The ITS region of the isolate infecting Delosperma was amplified following Bonants et al. (1997), cloned and sequenced (GenBank Accession No. FJ234425) but with no ITS sequences of Albugo trianthemae available in GenBank, results of the sequence search came back as unique.

Albugo trianthemae causes yellowing and poor development, and may lead to shrivelling of shoots and death of the host. It has been recorded on various genera belonging to the Aizoaceae in New Zealand, Australia, Ghana, Sudan and southwestern United States (Waterhouse, 1975; Farr et al., 2008). However, it has not previously been recorded on Delosperma before but has been found on Lampranthus in Australia and New Zealand (Farr et al., 2008). This is the first report of Albugo trianthemae in the UK and indeed Europe. A second species on this host family, A. austroafricana occurs on Aizoon in South Africa. It is distinguished from A. trianthemae in having warted rather than reticulate oospores (Waterhouse, 1975).