Effect of exogenous pH on development and growth of Colletotrichum musae and development of anthracnose in different banana cultivars in Sri Lanka

Abstract

In the present study, the relationship between the
observed inter-cultivar variation of anthracnose development
in banana by Colletotrichum musae and fruit peel pH was
investigated. The results of a survey showed that anthracnose
does not develop on Mondan (ABB), a cooking-type cultivar.
In contrast, the highest susceptibility to anthracnose was
reported by the dessert cultivars Anamalu and Embon (AAA).
Variations of the pH of fruit peel exudates (FPE) of different
banana cultivars were monitored during the ripening stages.
The effects of FPE, collected from different banana cultivars at
two maturity stages, on germ tube formation and elongation and
appressoria development of C. musae were also determined.
Furthermore, the effects of culture medium pH on the growth
of C. musae, anthracnose development and the expression of a
virulence-related gene, pelB were determined. With ripening
the pH of FPE and fruit pulp decreased. The highest pH of FPE
was shown by cultivars Seenikehel, Alukehel and Mondan with
pH values greater than 6.0 at mature-unripe stage. At the ripe
stage, pulp of all cultivars had pH values less than 4.5 with
the lowest being 3.9 in Embul. When grown in culture media
at a pH range from 4.0 – 8.0, the highest mycelial growth of
C. musae was observed at 4.5, indicating that an exogenous pH
of 4.5 can favour colonization by C. musae. The expression of
pelB gene was detected by RT-PCR only in C. musae grown
in a culture medium having a pH of 4.5. In addition, soluble
solid content of the fruit peel was quantified as a possible
factor responsible for the variation in anthracnose development
among different banana cultivars, and its effects on germ tube
formation, elongation and appressoria formation are discussed.