Verticillium-wilt (Verticillium albo-atrum) on Medicago sativa (alfalfa) in Iran

An outbreak of a wilt-like disease of alfalfa (lucerne) in the Markazi Province of Iran was investigated. Field symptoms during early growth stages typically consisted of V-shape orange-pinkish necrotic areas on the leaflets. On severely affected shoots of more mature plants, leaflets were usually desiccated and twisted, forming spirals. Vascular browning could be seen in stem sections. Diseased stems remained erect and did not themselves become chlorotic, until after all the leaves had lost their chlorophyll. New shoots on infected plants appeared normal at first but showed symptoms as they approached physiological maturity. These symptoms are very similar to those reported for Verticillium-wilt in alfalfa (Leath & Pennypacker, 1990). Verticillium albo-atrum was isolated from field collected plant samples by plating surface-sterilised stem tissue onto water agar. V. albo-atrum was confirmed as the causal agent of the disease by inoculating lucerne plants by root dipping into conidial suspensions. Symptoms on inoculated plants were similar to those described above for field infections.

Following amplification by PCR, the sequences of the complete ITS1/5.8S/ITS2 regions of the rRNA gene repeats for three isolates (GenBank Acc. Nos AY536044-6) were identical to that previously reported for the lucerne (L) pathotypes of V. albo-atrum (Barbara & Clewes, 2003). Although generally similar morphologically to V. albo-atrum, the resting mycelium produced in culture was paler than expected and without the torulose cells described previously (Hawksworth & Talboys, 1970). The source of the outbreak is unknown but V. albo-atrum is known to be seed-borne in alfalfa (Leath & Pennypacker, 1990) and may have been introduced to Iran by this means.

As compared to the non-lucerne pathotype, the L pathotype of V. albo-atrum has a restricted host range and geographic distribution and generally causes only mild diseases in hosts other than alfalfa (Leath & Pennypacker, 1990). Verticillium-wilt of alfalfa was first reported in Europe but has since been reported from the Unites States, Canada, New Zealand and Japan (Pegg & Brady, 2002). This is the first reported occurrence of Verticillium-wilt disease of alfalfa in Iran, or indeed anywhere in continental Asia. Verticillium-wilt can be a severe disease in alfalfa and should it become widespread in Iran, it could cause significant crop loss.