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Effect of mode of ripening on ethylene biosynthesis during ripening of on diploid banana (Musa spp.) fruit

Hubert O., Chillet M., Julianus P., Fils-Lycaon B., Mbéguié-A-Mbéguié D.. 2010. In : Dubois T. (ed.), Hauser S. (ed.), Staver Charles (ed.), Coyne D. (ed.). Proceedings of the International Conference on banana and plantain in Africa : harnessing international partnerships to increase research impact, Mombasa, Kenya, October 5-9, 2008. Louvain : ISHS [Belgique], p. 385-392. (Acta Horticulturae, 879). International Conference on Banana and Plantain in Africa: Harnessing international partnerships to increase research impact, 2008-10-05/2008-10-09, Mombasa (Kenya).

Ripening is the main physiological process affecting banana (Musa spp.) fruit quality traits. The progress of banana ripening process differs for fruit ripened on the plant versus green harvested bunches and depends on the treatment of the fruit after harvest. We investigated the effect of the mode of ripening on ethylene biosynthesis of 'IDN 110' (Musa acuminata, AA genome) banana fruit ripened (a) in planta (On-Plant); (b) ex planta in air (Air-Fruit); or (c) after acetylene treatment (Ace-Fruit). The levels of ethylene production of the whole fruit and, those of 1-aminocyclopropane-1-carboxylic acid (ACC) in pulp, and ACC oxidase (MA-ACO1 and MA-ACO2) and ACC synthase (MA-ACS1) mRNA in both peel and pulp tissues were examined. From harvesting at mature-green stage, the ripening speed of fruit was not correlated with ethylene production. Ace-Fruit took 10 days to reach overripe stage with a maximum of 22.6 µl kg-1 h-1 of ethylene production, whereas Air-Fruit and On-Plant fruit took 27 and 33 days to reach overripe stage, respectively, and produced 11.5 and 29.6 µl kg-1 h-1 of ethylene, respectively. During ripening, ACC accumulated differentially; except for On-Plant fruit, ACC level increased during ripening and concomitantly with ethylene production and MA-ACS1 mRNA level. Whatever the mode of ripening, the level of MA-ACO1 mRNA was 100-fold higher than that of MA-ACO2. The mRNA level of MA-ACO1 and MA-ACO2 were accumulated sequentially during fruit development and ripening. MA-ACO1 gene was transiently induced between mature green and ripe stages while that of MA-ACO2 increased mainly at the overripe stage. The pattern of MA-ACO2 gene expression was correlated with that of ethylene production whatever the mode of ripening while this correlation was observed with MA-ACO1 only On-Plant fruit. These results suggest that: (a) the level of ripening-ethylene production of the whole fruit is not the sole factor controlling the speed of fruit ripening in planta; (b) this level is regulated at the downstream step of ACC biosynthesis mediated by the MA-ACS1 gene; and (c) the product of MA-ACO2 might be involved in this regulation in pulp tissue. These findings are also discussed in regard with improvement of banana quality traits project throughout breeding programs. (Résumé d'auteur)
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