Hand position on the bunch and source-sink ratio influence the banana fruit susceptibility to crown rot disease

The postharvest development of crown rot of bananas depends notably on
the fruit susceptibility to this disease at harvest. It has been shown that fruit
susceptibility to crown rot is variable and it was suggested that this depends
on environmental preharvest factors. However, little is known about the
preharvest factors influencing this susceptibility. The aim of this work was to
evaluate the extent to which fruit filling characteristics during growth and the
fruit development stage influence the banana susceptibility to crown rot. This
involved evaluating the influence of (a) the fruit position at different levels of
the banana bunch (hands) and (b) changing the source–sink ratio (So–Si ratio),
on the fruit susceptibility to crown rot. The fruit susceptibility was determined
by measuring the internal necrotic surface (INS) after artificial inoculation
of Colletotrichum musae. A linear correlation (r = −0.95) was found between
the hand position on the bunch and the INS. The So–Si ratio was found to
influence the pomological characteristics of the fruits and their susceptibility
to crown rot. Fruits of bunches from which six hands were removed (two
hands remaining on the bunch) proved to be significantly less susceptible
to crown rot (INS = 138.3 mm2) than those from bunches with eight hands
(INS = 237.9 mm2). The banana susceptibility to crown rot is thus likely to
be influenced by the fruit development stage and filling characteristics. The
present results highlight the importance of standardising hand sampling on
a bunch when testing fruit susceptibility to crown rot. They also show that
hand removal in the field has advantages in the context of integrated pest
management, making it possible to reduce fruit susceptibility to crown rot
while increasing fruit size.