Aetiology of dryberry disease of boysenberry in New Zealand

Abstract

Studies indicated that Peronospora sparsa (Synonym P. rub'), causal agent of dryberry disease of boysenberry and other brambles, overwintered primarily as a 'systemic' cortex infection of canes, crowns, roots, and buds. The disease cycle started each spring with the production of internally infected shoots from infected root ~ow~,. ,and cane buds. . Abundant sporangi~ ( comdla) were observed m the field on these diseased shoots, predominantly on the undersides of the first few leaves formed. By contrast sporulation on overwintered cane surfaces was sparse. 'Systemic' infection was confined to the outer cortex parenchyma and appeared to keep pace with cell division at apical meristems. Unfolding leaves were invaded during warm wet conditions causing typical leaf symptoms, including distortion. Systemic cane infection was often indicated by a red streaking of stems and petioles linking successively diseased leaves on a shoot. Secondary infections of flowers and developing berries during wet warm weather were initiated from flowering onwards primarily by conidia produced on diseased shoots and producing the dryberry phase. Diseased berries then became an important source of inoculum for new cycles of berry infection. Spores were produced on the protected pith surfaces in split berries, on the inner calyx surfaces, and on the lower druplets protected by the calyx. Heavy sporulation often occurred befo~e disease symptoms were obvious on green bernes. After harvest, infection of developing primocanes lying on the ground continued by internal mycelial growth and spore infection. Oospores were only found on the root surfaces in dead cortex cells.

Quantification of downy mildew (Peronospora sparsa) in Rubus species using real-time PCR

“…P. rubi) causes downy mildew disease in Rubus and Rosa species (Hall, 1989;Breese et al, 1994), resulting in the ÔdryberryÕ disease and severe yield losses in Rubus plants such as blackberry (Rubus fruticosus), boysenberry (Rubus spp. hybrid) and arctic bramble (Rubus arcticus subspecies arcticus) (Tate, 1981;McKeown, 1988;Hall, 1989;Lindqvist et al, 1998).…”

Downy mildew of boysenberry and tummelberry in the UK

“…la is associated with infection by spores. Oospores, produced in the outer dead cortex of all underground parts ofthe plant, are considered to have little importance in the disease cycle; they may, however, survive to infect healthy plants when a previously diseased site is replanted (Tate, 1981b).…”

Occurrence of Peronospora sparsa (P. rubi) on cultivated and wild Rubus species in Finland and Sweden

“…In 1995, P. sparsa was observed in several cultivations in Finland (Koponen & Valkonen, 1996) that were affected by 'dryberry symptoms' that reduced yields substantially, and in some cases no yield was obtained. The symptoms resembled those of the dryberry disease of boysenberry caused by P. sparsa (Tate, 1981). In 1995 and 1996, hundreds of samples of cultivated arctic bramble from eastern and western parts of Finland were examined and a high incidence of infections with P. sparsa was detected .…”

“…Sampling from the field Leaf samples were collected from plants of Rubus spp. selectively, giving preference to leaves showing symptoms typical of those caused by P. sparsa, such as small carmine-red leaf spots randomly distributed over the leaf surface or angular purple blotches delineated by or running along the veins (Tate, 1981;Breese et al, 1994;Lindqvist et al, 1998). A few samples were collected also from symptomless plants of R. saxatilis, wild and cultivated raspbeny (R. idaeus) and cultivated roses in Finland.…”