Carbon storage in banana – a key trait under stress?

Banana (Musa sp.) is the most important fruit worldwide, as well as a major food crop. It is a semi-perennial herb that reproduces vegetatively through suckers. After bunch formation, the main banana plant senesces and the sucker forms the start of the next cycle. The belowground corm and the aboveground pseudostem are hypothesized to function as carbon storage organs supplying energy for fruit and sucker growth, particularly under stress. However, neither the existence of such reserves nor their role under stress has been experimentally confirmed. Accordingly, a field experiment was initiated in Guadeloupe (Caribbean) with a twofold objective: to quantify carbon storage and remobilization throughout the banana growth cycle and to assess its potential role under stress. More specifically, we evaluated the impact of stress caused by Black Sigatoka disease, one of the most important biotic limitations to banana production worldwide and the number one constraint in the region. The disease, as well as its management (sanitary leaf removal) causes a substantial reduction in source strength. We hypothesize that carbon reserves become particularly important under stress causing carbon depletion, as can be deducted indirectly from research on drought stress. Two banana varieties (Cavendish (AAA) and Big Ebanga (AAB)) were subjected to two contrasting leaf removal treatments (minimal and severe de-leafing). De-leafing, as well as leaf surface measurements were carried out on a weekly basis. Corm samples were taken at six predetermined times during the plant cycle, using a tree increment borer. During the vegetative phase and during fruit filling, four plants per treatment were furthermore destroyed for pseudostem sampling and in order to assess biomass allocation between leaves, pseudostem, corm, sucker and fruit. NSC (non-structural carbon) content of corm and pseudostem samples were determined through alcohol and enzymatic extraction, followed by spectrophotometric quantification. This is the first study focusing on carbon storage in banana and its potential role under stress. As climate change is expected to exacerbate a wide range of biotic (Black Sigatoka, Fusarium wilt) and abiotic (drought, heat) stresses, it is critical we gain insight into the role of carbon reserves in the banana plants' stress response.