The objective of this study was to determine the different morphotypes of Fusarium oxysporum present in the root of Xanthosoma sagittifolium and evaluate the effect of alcoholic extracts of Psidium guajava on their in vitro inhibition. Strains of Fusarium oxysporum were collected in eight localities where X. sagittifolium is grown. Fusarium strains isolated from roots of X. sagittifolium harvested in each locality were grown on PDA medium. The antifungal test was evaluated using ethanol extracts from P. guajava leaves at 30 and 60%. The virulence test of each strain on young plants of X. sagittifolium aged three months were realized. Eight strain of Fusarium oxysporum were successfully isolated. After maximum growth, five morphological types were observed (pionnotal, sclerotic, clowny, cottony and ras senescent). The cottony strain was abundant and present in all the locality. Histological analysis of the different strains obtained revealed the presence of septate or siphoned hyphae and three types of conidia (microconidia, macroconidia and sporangiospores or chlamidospores). The inhibition tests were very high with 60% of ethanol extract of P. guajava, and 83.33% of inhibitory effect were observed after eight days of growth, in the strains collected in X. sagittifolium roots, in L3 (Loum) and L4 (Bangoua) localities. After infection of X. sagittifolium plants with each strain of F. oxysporum isolated, symptoms observed were yellowing and wilting of leaves. However, plants inoculated with the L3 (Loum) strain showed both yellowing and wilting of leaves. The application of ethanol extracts from P. guajava leaves reduced the severity of the disease in the inoculated plants after 14 days. These results obtained showed that F. oxysporum is not only saprophytic fungi, it’s also able to induce yellowing and wilting of leaves in X. sagittifolium.
Le manioc (Manihot esculenta Crantz) est une plante pluriannuelle cultivée dans les régions tropicales de la plupart des pays d’Afrique, d’Asie et d’Amérique Latine. Il contribue fortement à la sécurité alimentaire. L’objectif de cette étude est d’analyser le comportement des polyphénoloxydases (PPO), de la peroxydase (POX) et des composés phénoliques chez trois variétés de manioc au cours de leur induction au Benzo (1,2,3) thiadiazol-7-carbothionic acid-s-methyl ester (BTH) vis-à-vis de C. gloeosporioides. L’induction de résistance a été évaluée par des PPO , de la POX et de la teneur en composés phénoliques totaux solubles accumulés avant et après l’inoculation (I) par C. gloeosporioides, la stimulation (St) par BTH et de la stimulation suivie de l’inoculation (St+I). Avec les différents traitements, on note une augmentation progressive et significative (p<0,05) de l’activité de ces enzymes et des teneurs en phénols dans les feuilles et les tiges chez les trois variétés. Ces résultats montrent bien que le BTH stimule les mécanismes de défenses des plantes de manioc, bien que ces mécanismes diffèrent en fonction des variétés. English title: Evaluation of polyphenoloxidase and peroxidase activities and accumulation of phenolic compounds in the resistance of stimulated cassava to Benzo (1,2,3) thiadiazol-7-carbothionic acid-s-methyl ester against Colletotrichum gloeosporioides Penz. Cassava (Manihot esculenta Crantz) is a perennia plant cultivated in the tropical regions of most countries in Africa, Asia and Latin America. It contributes strongly to food security. The aim of this study was to analyze the behavior of polyphenoloxidases (PPO), peroxidase (POX) and phenolic compounds in three cassava varieties during their induction to Benzo (1,2,3) thiadiazol-7-carbothionic acid-s-methyl ester (BTH) against C. gloeosporioides. Resistance induction was evaluated by PPO, POX and total soluble phenolic compounds content accumulated before and after inoculation (I) with C. gloeosporioides, stimulation (St) with BTH and stimulation followed by inoculation (St+I). With the different treatments, there was a progressive and significant (p<0.05) increase in the activity of these enzymes and in the phenol contents in the leaves and stems of the three varieties. These results show that BTH stimulates the defense mechanisms of cassava plants, although these mechanisms differ according to the varieties.
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