A root disease of Lupinus angustifolius caused by a new species of binucleate Rhizoctonia

Abstract

A new root disease of narrow-leafed lupins that is common in the northern wheatbelt of Western Australia wa found to be caused by a slow-growing binucleate Rhizoctonia sp. with characteristically narrow hyphae (2–4 µm). The new root disease causes distinct patches of poor growth superficially similar to rhizoctonia bare patch. This root disease of lupins is widespread in the northern lupin-growing areas of Western Australia.

The biological nature of the disorder was established by transfer of soil from a patch to a clean area and by treating patches using a soil fumigant (methyl bromide–chloropicrin).

The thin binucleate Rhizoctonia sp. (TBR) was isolated directly from soil within, but not outside, patches by using a soil immersion plate technique. Lupins grown in pots inoculated with the TBR developed symptoms consistent with those seen on plants in patches in the field, and the fungus was re-isolated from the diseased roots.

Field soil was inoculated with TBR, and in the following year, lupins were sown over the inoculated area and developed patches identical to the stunted patches occurring naturally. The fungus was re-isolated from diseased lupin roots taken from inoculated patches but not from diseased roots from outside patches.