Micro-tubers are important propagules in potato breeding and potato production, and they are also dormant and easily transported and therefore good targets for mutation induction in potato mutation breeding. A prerequisite for mutation breeding is to determine optimal mutation treatments. Therefore, radio-sensitivity tests of a tetraploid and a diploid potato to gamma irradiation were undertaken. Effects of different gamma sources on radioactivity were also studied. In vitro potato cuttings were gamma irradiated using a wide dose range (0, 3, 6, 9, 12, 15 and 20 Gy). The irradiated cuttings were then cultured to induce micro-tubers directly in vitro. Microtuber morphotypes were assessed after irradiation of cuttings using three gamma sources with emission activities of 1.8, 7.07 and 139 Gy/min. The diploid species (Solanum verrucosum) was more radio-sensitive than the tetraploid cultivar Desirée (Solanum tuberosum). Gamma dose rates had significant influences on subsequent micro-tuber production at various mutant generations. Effects included reductions in the number, size and weight of micro-tubers produced. Gamma dose was more lethal for the diploid potato genotype and micro-tubers produced were small compared to those produced by the tetraploid genotype after irradiation. Different treatments are recommended for diploid and tetraploid potato irradiation in producing large mutant micro-tuber populations.

In the present study, 20 fungal strains were isolated from tomato rhizosphere of Senegal. Of 20 strains, five showed the chitinolytic activity on chitin agar medium. Of the five strains, NG4 showed the maximum solubilization zone. This strain was identified by preliminary biochemical and 18S rRNA sequencing analysis. Enzyme production started after 3 days of incubation and maximum was observed after 5 days of incubation. Culture filtrate amended with 0.1% colloidal chitin was used in the production medium. The optimum conditions for maximum chitinase activity are -6 days of growth and temperature of 30°C at pH 6.0. The chitinase activity was also influenced by the addition of carbon and nitrogen sources in the production medium.

Influence in vitro de divers facteurs abiotiques (température, pH, salinité) sur la croissance mycélienne de trois souches locales de Trichoderma sp. RESUMELes Trichoderma sont des champignons imparfaits saprophytes que l'on retrouve dans divers milieux comme le sol, le bois mort, les débris des végétaux et les organes aériens des plantes. Ils ont un rôle phytoprotecteur et stimulateur du développement des plantes associées. L'effet de différents facteurs abiotiques (température, pH, salinité) sur la croissance mycélienne de trois souches locales de Trichoderma a été évalué. Ces souches ont été isolées à partir de la rhizosphère de la tomate. Une étude préliminaire a été effectuée sur quatre milieux de culture (PDA, MEA, SB et DOX) pour la sélection du milieu d'étude. Les résultats obtenus montrent que le milieu PDA permet une meilleure croissance des souches de Trichoderma. La température optimale de croissance des différentes souches est de 29 °C et le pH 5 se révèle être le plus adéquat pour la culture des Trichoderma. Cette étude montre également que les souches de Trichoderma résistent à des concentrations de sel (NaCl) allant jusqu'à 3%. © 2016 International Formulae Group. All rights reserved. Mots clés:Trichoderma, facteurs limitant, température, pH, salinité, milieu de culture.In vitro influence of various abiotic factors (température, pH, salinity) on mycelium growth of three local strains of Trichoderma sp. ABSTRACTTrichoderma are saprophytic imperfect fungi that are found in various environments such as soil, dead wood, vegetable fragments and plant aerial organs. They protect and stimulate development of related plants. Effects of various abiotic factors (temperature, pH, salinity) on mycelium growth of three local Trichoderma strains were investigated. These strains were isolated from tomato rhizosphere. A preliminary study was performed on four culture media (PDA, MEA, SB and DOX) for the selection of the best media. The results N. GUEYE et al. / Int. J. Biol. Chem. Sci. 10(2): 769-778, 2016 770 showed that PDA medium was highly growth of Trichoderma strains. The optimum temperature for growth of different strains is 29 °C and pH 5 was found to be most suitable for Trichoderma culture. Indeed, Trichoderma strains resistant to salt concentrations (NaCl) up to 3%.