Components of cell wall, enzyme activity in pedicel and susceptibility of bananas to finger drop

A major problem in post-harvest handling of bananas is the individual detachment of the fruit from the hands. This study aimed to establishing the relationship between carbohydrate concentration and enzyme activity in the pedicel region of three cultivars of bananas, resistant and susceptible to natural dropping, during post-harvest ripening, and the susceptibility of bananas to finger dropping. Cultivars ‘Terra’ (plantain, AAB group) and ‘Prata’ (banana, AAB group) triploids and the ‘Prata Graúda’ (banana, AAAB group) tetraploid were used. The experiment was distributed in split plots, with three plots (cultivars) and five subplots (peel color stages) in a completely randomized design with three replications and three fruits per sample unit. ‘Terra’ showed resistance to dropping, even though the fruit were ripe, unlike ‘Prata Graúda’, which, starting from the fifth stage (yellow fruit with green tips), exhibited high susceptibility to dropping. At all ripening stages, the ‘Terra’ had the highest dry mass levels. In turn, the ‘Prata Graúda’ always maintained the lowest levels. The ‘Terra’ showed decreasing levels of pectins during ripening, whereas starch remained high even in the ripe fruit. About the enzymes studied, the results confirmed the increased resistance of the ‘Terra’ to dropping, allowing to conclude that polygalacturonase (PG) and pectinametylesterase (PME) are the key enzymes for the solubilization of the cell wall that accompanies ripening, thus playing a critical role in inducing natural dropping. The high susceptibility of the ’Prata Graúda’ to dropping is associated with the high activity of PG and PME and the low levels of dry mass; the greater resistance of the ‘Terra’ to dropping is related to higher accumulation of dry mass and starch in the pedicel.Um dos maiores problemas na comercialização de bananas é o destacamento individual dos frutos das pencas. O presente trabalho teve como objetivo estabelecer a relação entre a concentração de carboidratos e a atividade enzimática na região do pedicelo e a suscetibilidade de bananas ao despencamento natural. Foram utilizadas as cultivares triploides ‘Terra’ (plátano, grupo AAB) e ‘Prata’ (banana, grupo AAB) e a tetraplóide ’Prata Graúda’ (banana, grupo AAAB). O experimento foi conduzido em parcelas subdivididas, com três parcelas (cultivares) e cinco subparcelas (estádios de cor de casca), em um delineamento experimental inteiramente casualizado, com três repetições e três frutos constituindo a unidade amostral. A cultivar Terra mostrou resistência ao despencamento, mesmo estando seus frutos maduros, ao contrário da ‘Prata Graúda’, que, já a partir do estádio 5 (fruto amarelo com pontas verdes), exibiu suscetibilidade à queda. Em todos os estádios de amadurecimento, a cultivar ‘Terra’ teve os maiores teores de matéria seca, apresentando diminuição dos teores de pectinas no decorrer do amadurecimento, enquanto os de amido se mantiveram altos mesmo no fruto maduro. As enzimas pectinametilesterase (PME) e poligalacturonase (PG) são as enzimas-chave na solubilização da parede celular que acompanha o amadurecimento. A alta suscetibilidade da ‘Prata Graúda’ ao despencamento está associada à elevada atividade de PG e PME e ao baixo teor de matéria seca; a maior resistência ao despencamento da cultivar Terra está relacionada com o maior acúmulo de matéria seca e amido no pedicelo