First Report of Colletotrichum gloeosporioides as a Foliar and Die-back Pathogen of Prunus africana in Kenya

Abstract

During tree disease surveys between February 1996 and March 1998 in highland forests of Kenya, leaves of Prunus africana (Hook f.) Kalkman collected from regeneration wildings in natural forests and seedlings raised in nurseries were found to be consistently heavily infected with a leaf spot and shot-hole disease caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz., anamorph of Glomerella cingulata (Stoneman) Spauld. & H. Schrenk. The pathogen was identified by sectioning sub-epidermal acervuli on the leaf and also by plating infected tissue segments on 2% malt extract agar. The cultural and conidial morphologies were characteristic of C. gloeosporioides. The isolate is maintained at Kenya Forestry Research Institute (KEFRI) culture collection (No. 069-63) and identity ascertained by the International Mycological Institute (IMI) (ref. W5794). To confirm pathogenicity, leaves of 3-month-old seedlings of P. africana were sprayed to run-off with a conidial suspension adjusted to 105 conidia per ml or sterile water as a control. Following inoculation, the seedlings were covered with transparent plastic bags for 48 h and kept in a glasshouse at 23 ± 3°C under natural light conditions and relative humidity of 80%. Leafspot symptoms similar to those found on leaves of wildings in natural forests and nursery seedlings were evident on the inoculated leaves within 3 weeks. Five weeks later the necrotic spots on the leaves measured 2 to 6 mm in diameter. The spots were circular or irregular usually surrounded by a zone paler than the healthy tissue. Later the centers of the spots fell, leaving clean shotholes. C. gloeosporioides was consistently reisolated from all inoculated plants. When infection was severe, the pathogen caused premature leaf fall and die-back of the leader shoot. P. africana, formerly known as Pygeum africanum, is a widespread tree species in moist tropical Africa and produces durable timber; extracts from its bark are used for the treatment of prostrate gland disorders. This is the first report of which we are aware of C. gloeosporioides emerging as an important pathogen of P. africana.