Occurrence of Black Spot Disease of Brassicas Caused by Alternaria Species in Kenya
Keywords:
Alternaria species, black spot, cabbage, incidence, kale, KenyaAbstract
Brassicas are important vegetable crops in Kenya for domestic economy. They are cultivated by over 90% of the smallholder farmers each with approximately 1 to 2.5 ha of land. Black spot disease of brassicas caused by Alternaria spp. is one of the major constraints to increased yield in Kenya. There is very little information available on Alternaria spp. affecting brassicas in Kenya. The objective of the present study was to establish the pathogenic Alternaria spp. affecting brassicas in Kenya and to determine the distribution and incidence of the disease in farmer’s fields. This was done by carrying out a field survey in 13 selected districts in Kenya with varying agro-ecological zones. The correlation of environmental variables with incidence and Brassica cultivars was analyzed by Analysis of Variance using SAS Computer package release 6.12 and means separation by least significance difference and student Newman-Keuls test. Out of 89 farms surveyed, 46 (51.7%) had black spot. The farms with cabbage were 52 with 28 (53.8%) having black spot, while farms with kale were 37 with 18 (48.6%) having the disease. The disease incidence on cabbage and kale farms was 30.3% and 8.7%, respectively. Alternaria species identified from black spot infected cabbage and kale were A. brassicicola and A. japonica with the former predominant (64.4%) of cabbage and the later predominant (66.7%) of kale. Both pathogens appeared in 17.8% and 11.1% of infected cabbage and kale farms, respectively. The present findings are useful in the development of Brassica cultivars resistant to Kenyan isolates of Alternaria species. This is the first report implicating A. brassicicola and A. japonica as causal agents of black spot disease of brassicas in Kenya.
References
Brayford, D. (1991) Fusarium, Its Relatives and their Teliomorphs. International Course on the Identification of Fungi of Agricultural Importance, 4-15 Nov. 1991, Nairobi, Kenya. International Mycological Institute, UK.
CABI. (2007) Crop Protection Compendium, 2007 Edition, Wallingford UK: CABI International.
Chung, W.C. & Huang, J.W (1993) Effect of mineral elements on disease severity of black spot of Chinese kale. Plant Pathol. Bull. 2:78-87.
Corlett, M. & I.A. MacLatchy (1996) Fungi Canadenses No. 335: Alternaria brassicicola. Canadian J. Plant Pathol. 18: 484-485.
Ellis, M.B. (1971) Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, Surrey, England. Published by Commonwealth Agricultural Bureaux. pages 468 and 473.
Howard, R.J., Garland, J.A. & Seaman, W.L. (1994) Diseases and pests of vegetable crops in Canada: an illustrated compendium. Ottawa, Canada: Entomological Society of Canada & Canadian Phytopathological Society.
Humpherson-Jones, F.M. (1985) The incidence of Alternaria spp. and Leptosphaeria in commercial brassica seed in the United Kingdom. Plant Pathol. 34: 385-390.
Humpherson-Jones, F.M. (1989) Survival of Alternaria brassicae and Alternaria brassicicola on seed debris of oilseed rape and cabbage. An. Appl. Biol. 115: 45-50.
Humpherson-Jones, F.M. (1992) Epidemiology and control of dark leaf spot of Brassicas. In: Chelkowski J, Visconti A, eds. Alternaria-Biology, Plant Diseases and Metabolites. Topics in Secondary metabolism, Vol. 3. Amsterdam, The Netherlands: Elsevier Science Publishers, 267-288.
Jaetzold, R. & Schmidt, H. (1983) Farm Management Handbook of Kenya. Ministry of Agriculture, Vol. II/A, Vol. II/B and Vol. II/C.
Jasalovitch, C.A., Morales, V.M., Pelcher, L.E. & Swartz, S.G. (1995) Comparison of nuclear ribosomal DNA sequences from Alternaria species pathogenic to crucifers. Mycol. Res. 99: 604-614.
Mac Kinon, S.L., Keifer, P. & Ayer, W.A. (1999) Components from the phytotoxic extracts of Alternaria brassicicola, a black spot pathogen of canola. Phytochem. 51: 215-221.
Neergaard, P. (1945) Danish Species of Alternaria and Stemphylium. London, UK: Oxford University Press.
Paul, V.H. & Rawlinson, C.J. (1992) Diseases and Pests of Rape. Gelsenkirchen-Buer, Germany: Verlag Th. Mann.
Poapst, P.A., Ramsoomair, B.A. & Gourley, C.O. (1979) On the promotion of senescence in Brassica oleracea var. capitata by Alternaria brassicicola and by Botrytis cinerea. Canadian J. Bot. 57:2378- 2386.
Rotem, J. (1994) The genus Alternaria: biology, epidemiology, and pathogenicity. St Paul, USA: American Phytopathological Society.
Simmons, E.G. (1992) Alternaria taxonomy: current status, viewpoint, challenge. In: Chelkowski J, Visconti A, eds. Alternaria - Biology, Plant Diseases and Metabolites. Topics in Secondary Metabolism Vol 3. Amsterdam, The Netherlands: Elsevier Science Publishers, 1-35.
Shresta, S.K., Mathur, S.B. & Munk, L. (2000) Alternaria brassicae in seeds of rapseed and mustard, its location, transmission from seed to seedlings and control. Seed Sci. & Technol. 28: 75- 84.
Smith, I.M., Dunez, J., Lelliott, R.A., Phillips, D.H. & Archer, S.A. (1988) European Handbook of Plant Diseases. Blackwell Scientific Publications, Oxford, UK.
Spence, N. J., Lenne, J.M., Pink, D.A.C., Njuki, J., Wanyonyi, C. and Kimani, P.M. (2005) Opportunities and constraints for future economic development of sustainable vegetable seed business in Eastern and Southern Africa. Abstract. International Conference on Agricultural Research for Development: European Responses to Changing Global Needs. 27th –29th April 2005. Swiss Federal Institute of Technology Zurich. Switzerland. p121.
Strandberg, J.O. (1992) Alternaria species that attack vegetable crops: Biology and Options for disease management. In: Alternaria-Biology, Plant Disease and Metabolites, Topics in Secondary Metabolism, Vol. 3. Amsterdam, The Netherlands: Elsevier Science Publishers, 175-208.
Tewari, J.P. (1991) Structural and biochemical bases of the blackspot disease of crucifers. Adv. Struct. Biol. 1, pp. 325-349. In: Beatrice et al., (2003) In vitro fungicide sensitivity of Alternaria brassicicola field isolates highly resistant to both dicarboximides and phenylpyrroles, Crop Protection: Volume 23, issue 6, June 2004, pages 481-488.
Yu, S-H. (1992) Occurrence of Alternaria species in countries of the far east and their taxonomy. In: Cheikowski J, Visconti A, eds. Alternaria - Biology, Plant Diseases and Metabolites. Topics in Secondary Metabolism Vol. 3. Amsterdam, The Netherlands: Elsevier Science Publishers, 37-62.
Verma, P.R. & Saharan, G.S. (1994) Monograph of Alternaria diseases of crucifers. Saskatoon Research Centre Technical Bulletin 1994-6E. Agriculture and Agri-Food Canada, Saskatoon.
Wiltshire, S.P. (1947) Species of Alternaria on Brassicae. Imperial Mycological Institute Papers No. 20. 15 pp.
