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University of Khartoum (2016)

Etiology and Incidence of Bacterial Blight of Guar in Some Irrigated and Rain-fed Production Areas in Sudan

Yousif, Isam Eldin Omer Abdalla

Titre : Etiology and Incidence of Bacterial Blight of Guar in Some Irrigated and Rain-fed Production Areas in Sudan

Auteur : Yousif, Isam Eldin Omer Abdalla

Université de soutenance : University of Khartoum

Grade : Master of Science (MS) 2016

Résumé
The rational to conduct this study was an outbreak of a devastating wilt disease of guar (Cyamopsis tetragonoloba L.) in its commercial production areas in Blue Nile and Gadaref states in year 2013. Preliminary studies indicated that the wilt disease was caused by a bacterium related to Xanthomonas sp. The present study concerns survey for incidence and symptomatology of the disease, in addition to isolation, characterization and verification pathogenicity testes of the suscept to establish the identity of the pathogen. Two field surveys were carried out in irrigated (Khartoum and northern Gezira) and rain-fed (Blue Nile and Sennar) guar production areas in years 2013 and 2014, where close visual inspection of symptoms were made and samples of stem lesions and cankers were collected. Laboratory investigations and pathogenicity tests were performed at the Faculty of Agriculture, University of Khartoum. The disease incidence was greatest under rain-fed conditions, where 100% infection was recorded in the Blue Nile State, followed by 74% disease incidence at ʻGennibʼ (northern Gezira). At the latter location, although guar was produced under artificial irrigation, but it witnessed several rain showers. However, in Sennar area and at ʻAelaphonʼ (Khartoum State) the disease was very meager (0.02% and 0.5%) respectively due to late sowing in September in the former area and to dry conditions at the latter location .The affected guar plants developed leaf spots, stem lesions, stem canker and under severe infection iv wilting and defoliation were also evident. Three bacterial isolates were ʻrecoveredʼ according to type of symptoms (either stem lesions or stem cankers) and locality of infected plants (ʻAelaphonʼ or ʻGennibʼ). The three isolates were apparently undistinguishable with regard to cultural, morphological and biochemical tests. They were Gram negative, motile, had the ability to grow in NA and YDC agar culture media, even at 36 °C and tolerant to 3% salt. They were also found to have the capability to grow aerobically, hydrolyse starch and gelatin and they were oxidase positive. The pathogenicity test availed that the original symptoms were reproduced on healthy guar seedlings verifying that the detected and identified bacterium was Xanthomonas axonopodis pv. Cyamopsidis. In conclusion, some significant perspectives emerging from the thesis were summarized and few future prospectives along these lines of research work were suggested. It is recommended that an integrated disease management programe taking into account provision of clean certified seed stock, efficient weed control (particularly Cassia senna), disease evasion in terms of production site and sowing dates, in addition to screening guar varieties for resistance should be sought to alleviate the impact of such destructive disease.

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