ISSN 2375-0979
African Journal of Wood Science and Forestry ISSN 2375-0979 Vol. 8 (4), pp. 001-009, April, 2020. © International Scholars Journals
Full Length Research Paper
A canker and dieback disease threatening the cultivation of Grevillea robusta on small-scale farms in Kenya
Jane W. Njuguna1,2*, Pia Barklund1, Katarina Ihrmark1 and Jan Stenlid1
1Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, Box 7026 SE-75007 Uppsala, Sweden.
2Kenya Forestry Research Institute, P. O. Box 20412, City Square 00200 Nairobi, Kenya.
Accepted 14 October, 2019
Abstract
A canker and dieback disease was recently reported on Grevillea robusta in east Africa but little was known about its magnitude, distribution and associated pathogens. In our survey of the disease approximately 36% of 17,994 G. robusta trees assessed showed canker and dieback symptoms. Disease index increased from the humid zone (18%) and to the semi-arid zones (67%). Tree mortality increased from 0.3 to 20% respectively on the same scale and was highest in trees less than 7 years old in all zones. Disease index and tree mortality showed positive correlations with drought period which increased from an average of 0.7 months (humid) to 7 months (semi-arid zones). Both variables showed negative correlations with farm altitude. Disease index was higher in the woodlots compared to other types of tree planting in all zones. Two Botryosphaeriaceae species, Neofusicoccum parvum and Lasiodiplodia theobromae known to be pathogenic on G. robusta were highly abundant in severely diseased stems and branches and their occurrence also showed positive correlations with disease severity. From the results of this study, it was recommended that G. robusta should not be planted in the semi arid zones of Kenya, due to its susceptibility to the canker and dieback disease.
Key words: Agro-ecological zones, agroforestry, Botryosphaeriaceae, canker and dieback disease, disease index, Grevillea robusta.