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sur le développement des zones arides et semi-arides

Titre : SOME RHIZOCTONIA SOLANI (KUEHN)-ALFALFA (MEDICAGO SATIVA L.) RELATIONSHIPS

Auteur : El-Khash, Mohammed Najib,

Université de soutenance : University of Arizona

Grade : Master of Science (MS) 1969

Résumé
Rhizoctonia solani (Kuehn) persisted as a pathogen in alfalfa for about one year, and progressed from the plant roots to the shoots. Four cultivars of alfalfa were found equally susceptible to the fungus. Growth studies showed that minimum growth of 6 isolates occurred at 20 C, and optimal growth of most of them occurred at 26 C. Of the combinations of 18 nitrogen and 11 carbon sources used, maximum growth of the fungus occurred on fructose/L-asparagine, and minimum growth occurred on C/N combinations containing DL-aspartic acid, L-glutamic acid, L-histidine HC1, and DL-tryptophane as nitrogen sources. The virulence of Rhizoctonia was not influenced by pre-culturing it on various C/N concentrations. Rhizoctonia grew in various directions over the surface of alfalfa roots. Penetration of roots occurred more commonly from branches arising from single hyphae, and was effected on the same host by either normal hyphal branches or infection pegs. Invaded epidermis and cortical tissues collapsed at later stages in disease development, but the fungus did not advance to the central cylinder. Five Streptomyces spp. reduced severity of lesions caused by Rhizoctonia. No significant difference was found between seed inoculation or soil infestation with the antibiotic producers.

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