Various virus, bacterial and fungal diseases of yam have been reported in Nigeria since 1956. A shoestring virus, which is transmitted mechanically and by aphids with particles consisting of flexuous rods 600 nm in length, is known to occur in various species of yam. Pre-harvest and post-harvest tuber rot may result in storage loss of 25%. Pre-harvest rot is induced by the bacteria, Corynebacterium sp., Erwinia sp. and the fungus Botryodiplodia theobromae; whilst the post-harvest rot is caused by B. theobromae, Fusarium moniliforme, Penicillium sclerotigenum and Aspergillus niger. Wilt diseases, which may cause premature death of 45-70% of the crop, are incited by Fusarium oxysporum and Sclerotium rolfsii. Amongst the foliar diseases described anthracnose can depress yield by 67% and 'Appollo' may result in total loss of planting 'seed'. Storage losses have been controlled by careful handling of the tubers and selections for resistant cultivars may help to control the other diseases.
Tijdschrift beschrijving