Medicinal and aromatic plants
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Item Acute Die-back of Clove Trees in the Zanzibar Protectorate(Annals of Applied Biology, 1952) Nutman, F. J.; Roberts, F. M.; Clove Research Scheme, ZanzibarThe most widespread die-back of clove trees (Eugenia aromatica) in the Zanzibar Protectorate is caused by Cryptosporella eugeniae sp.nov. The most noticeable symptom is the death of a branch or a portion of a branch, or, in young saplings, of the entire tree; in mature trees infection eventually leads to the semi-moribund trees now common in almost every clove plantation. The fungus invariably enters through a wound, most often one resulting from harvest damage. Pycnidia, and later perithecia, develop near the point of entry. Internally the infected wood is clearly distinguishable from the healthy by a dark red-brown stain.Item Quarterly Report Report (March to June 1998): Floriculture Project Crop Protection Programs(Kenya Agricultural Research Institiute, 1998) Anyango, J. J.; Mwaniki S. W.The floriculture research unit in KARI funded by US AID is in its sixth year of existence with various research outputs. The introduction and evaluation of flower varieties imported to Kenya are among the outputs. The recommended new varieties not covered by breeders' rights are also multiplied and then supplied to the growers. Crop protection issues on flowers gained prominence in 1995, necessitating the incorporation of crop protection programs in the research unit. Research input into the program is based at KARI-NARL. Funding for the crop protection input has been provided by both the DFID and USAID. A number of research programs both on station (Tigoni/Thika/NARL) and on-farm (Limuru, Thika, Naivasha, and Athi River) have been conducted under the following broad objectives:Item Studies of the Clove Tree Histology: With Special Reference to Sudden Death Disease(The Annals of Applied Biology , 1950) Sheffield, F. M. L.; Clove Research Scheme, ZanzibarA detailed study was made of the histology of apparently healthy clove trees and of trees expected to die from sudden death disease, in an attempt to find either a diagnostic character of the disease or some indication of a possible pathogen.The apparently healthy clove tree differs from a typical dicotyledon in a number of ways. This is especially true of the vascular system where, not only are the bundles bicollateral, but, in the stem, secondary thickening occurs in the internal phloem, necrosis of the first formed cells keeping pace with the production of new cells. A definite cambium is found only to the exterior of the xylem and this is exceptionally narrow and the cells have very delicate walls. Phloem necrosis may occur in any part of the tree. The development and lignification of the xylem is very uneven, but this seems to bear no relation to the season. Tyloses are formed in the vessels of the root and, to a less extent, in those of the stem. Starch reserves are usually small, but large quantities of tannins, oils and calcium oxalate are secreted in all tissues. The oil may be contained in special schizogenous glands which are abundant in the aerial parts of the tree. Much mechanical tissue, consisting of fibres and stone cells, is formed in the pith and cortex of the stem and in the phloem in all parts of the tree, but lignification of this tissue is very uneven. Occasional dead cells are found in all tissues, even in the primary meristem. In the leaf, the plastids develop very unevenly; this is followed by retarded development of the pigment in some parts, resulting in a flecked appearance. Stomata are exceptionally numerous; in the leaf, they are confined to the lower surface and always communicate with very small cavities. Air spaces in the mesophyll are very small and are almost non-existent in other tissues. Bodies, morphologically similar to the amorphous intracellular inclusions due to some viruses but differing chemically from them, are abundant in the leaves.Some of these characters are usually associated with a diseased condition, but they occur in both healthy and diseased cloves in the Zanzibar Protectorate. In the sudden death suspect, some may occur earlier or be more accentuated than in the healthy tree. This evidence alone might suggest that sudden death is merely the culmination of a long period of adverse conditions, but other evidence suggests very strongly that the disease is due to a pathogen. Of the groups of organisms which may cause disease, only fungi were found. These occurred in the absorbing roots but are unlikely to be the pathogens causing sudden death, for, until the tree has actually wilted, very few hyphae are present, and no more than are found in healthy trees. Nothing incompatible with the suggestion that sudden death is caused by a virus was foundItem Studies of the Clove Tree, the Effect of the Sudden Death Disease on Water Relations(East African Forestry Research Organization, 1950) East African Forestry Research Organization; NUTMAN,F. J.; East African Forestry Research OrganizationExtensive root disorganization is associated with all recognizable stages of the suddendeath disease of cloves, the final symptoms being those of a rapid wilt. In the early stages of the disease, however, the water status of an affected plant is more favourable than that of a healthy one, in spite of the root disorganization. In the diseased plant, the transpiring power and assimilation rate of the leaves are greatly lowered, probably because of partial closing of the stomata. The consequent reduction in transpiration appears to account for the smaller water deficit found in the earlier stages of the disease. These results are considered to furnish additional evidence in favour of the hypothesis that the disease is caused by a pathogen.
