Effet du nitrate d'argent sur les potentialités embryogènes des cals issus des embryons immatures de 17 cultivars de blé (Triticum aestivum L. et Triticum durum L.)

L'incorporation du nitrate d'argent (5mg/l) dans le milieu de culture des embryons zygotiques immatures de 17 cultivars de blé (Triticum durum L. et T. aestivum L.), a amélioré significativement les pourcentages d'induction de cals embryogènes et de régénération de plantules par cal. Le rendement en cals embryogènes a été multiplié par trois pour le cultivar «Cocorit» en présence de nitrate d'argent. La régénération de plantes à partir des cals initiés en présence d'AgN03 a été également 7 fois plus importante pour le cultivar <<1765>>. Cette régénération a, néanmoins, montré des variations importantes selon les génotypes testés. L'étude de la réponse in vitro des embryons immatures après quatre semaines de culture dans le milieu d'induction a permis de distinguer trois types de cals. Placés dans le milieu de différenciation, un type n'a régénéré que des racines alors que les deux autres ont régénéré des tiges et des racines

Effect of salicylic acid on phenolic compounds related to date palm resistance to Fusarium oxysporum f.sp. albedinis

Salicylic acid (SA) plays a key role in establishing resistance to pathogens in many plants. To study the possible involvement of SA in the resistance of date palm (Phoenix dactylifera L.) to Fusarium oxysporum f. sp. albedinis (FOA), we investigated levels of phenolic compounds, known as indicators of resistance in the date palm/ Fusarium pathosystem. After treatment with SA the content of root soluble phenolics in F. oxysporum inoculated date palm seedlings was about 4 times higher in cv. Bousthami noir and 6 times higher in cv. Jihel than that in untreated plants showing disease symptoms. The largest increase was at a SA concentration of 50 µM. SA treatment also enhanced the content of cell wall phenolics. In addition, inoculation of SA-treated roots of date palm with FOA (strain ZAG) resulted in a greater number of plants showing only limited hypersensitive reaction-like necrotic lesions. In contrast, SA-untreated plants normally showed spreading necrosis in response to fungus inoculation

Chitosan, Antifungal Product against Fusarium oxysporum f. sp. albedinis and Elicitor of Defence Reactions in Date Palm Roots

The effect of chitosan on the growth and morphology of Fusarium oxysporum f. sp. albedinis (Foa), the causal agent of Bayoud disease, and its ability to elicit a defence reaction against this fungus in date palm roots were investigated. Chitosan at 1 mg ml-1 reduced the growth of Foa on potato dextrose agar medium by an average of 75%, while mycelial growth was totally inhibited in a liquid medium. When added to a solid medium, chitosan caused morphological changes in Foa mycelium. In addition, when injected into roots at three concentrations (0.1, 0.5 and 1 mg ml-1), chitosan elicited peroxidase (PO) and polyphenoloxidase (PPO) activity and, particularly at the concentration of 1 mg ml-1, increased the level of phenolic compounds. Concerning phenolics, chitosan led to an accumulation of non-constitutive hydroxycinnamic acid derivatives, known to be of great importance in date palm resistance to Bayoud. The accumulation of hydroxycinnamic acid derivatives was greater in cv. BSTN than in cv. JHL. Chitosan could be used to protect date palm against this vascular disease