University of Khartoum

Some Bacterial Diseases Of Sudan Crop: Bacterial Leaf Blight Of Castor Bean (Ricinus Communis) And Related Species.

Some Bacterial Diseases Of Sudan Crop: Bacterial Leaf Blight Of Castor Bean (Ricinus Communis) And Related Species.

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Title: Some Bacterial Diseases Of Sudan Crop: Bacterial Leaf Blight Of Castor Bean (Ricinus Communis) And Related Species.
Author: Ahmed, Osman Khalil
Abstract: The present investigation confirms Sabet`s finding that the leaf blight of castor bean in the Sudan in caused by a white strain of Xanthomonas ricini (Yoshi and Takimoto) Dowson (Sabet, 1959a). The yellow strain of X. cassavae (Hansford) Wiehe and Dowson from Manihot esculenta and X. poinsettiaecola patel et al from Euphorbia acalyphorides and from Phyllanthus niruri were used in the present study. The strains from E. acalyphorides and P. niruri are reported form the Sudan for the first time. Infection of E. acalyphorides and P. niruri has not been previously reported outside this country. These pathogens agree in most of their characters except for X. cassavae which is different in many respects from the others. Most of these pathogens are restricted to their original hosts. However the bacterium from E. acalyphoides infects R. communis and E. pulcherrima and that from E. pulcherrima infects M. esculenta. Due to the diversity in opinion on speciation in the genus Xanthomonas two alternative proposals are advanced. In the first, Xanthomonas is considered as a monotypic genus with X. campestries as the sole species. X. ricini, X. cassavae and X. poinsettiaecola are reduced to formae speciales proved to differ in pathogenicity from established ones are considered formae speciales of X. compestris. These are X. compestris f. sp. Phyllanthii from Phyllanthus niruri. The other proposal is to lump together pathogens with overlapping host ranges in a single species that comprises a number of formae speciales differing in pathogenicity. Thus the pathogens affecting the members of the family Euphorbiaceae are considered to belong to X. ricini on priority grounds. X. cassavae and X. poinsettiaecola are reduced to formae speciales of this species. New formae speciales are created for the organisms from E. acalyphoides viz X. ricini f. sp. euphoribiae n.f. sp. and from P. niruri viz X. ricini f. sp. phyllanthii n.f. sp. It is probable that weeds of the Euphoriaceae may have some affinity with the survival of the castor bean pathogen. The organism from the weed E. acalyphoides has been found to infect castor bean plants. In the present investigation two methods (immersion of cotyledons and spraying of aerial parts) have been used in assessing the degree of susceptibility of four castor bean varieties and have produced similar results. N-145-4 and Pacific 6 varieties are very susceptible to the bacterial blight while Cimarron and hole varieties are quite resistant. X. ricini may survive for a long period in press-dried leaves. Survival of the pathogen in pure culture or in leaf trash buried in the soil is governed by i) action of micro-flora and ii) soil aeration. The organism survives for a long period in the dry soil while succumbs rapidly in the water saturated soil. Disappearance of the organism from water saturated soil is attributed to prevailing anaerobic conditions. Disappearance of bacteria from moistened soil is largely due to action of competitive saprophytes. X. ricini can be carried by seeds when young capsules (1-2 cm long) become infected. Microscopic examination of infected young capsules reveals that the bacteria advance through the pericarp to the seed integument. Failure of infected seeds produce infected seedling has been discussed. The leaf blights of castor bean can be transmitted from infected to healthy plants by whiteflies (mainly Bemisia tabaci Genn.). Successful transmission requires high level of infestation of the plants by the insects.
URI: http://khartoumspace.uofk.edu/handle/123456789/14306
Date: 2015-06-23


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