Hormone profiling in artificially induced 'crumbly' fruit in raspberry (Rubus idaeus L.) at two different development stages

In red raspberry, a condition known as 'crumbly' fruit causes the formation of misshapen fruits with drupelets reduced in number but enlarged in size. Complex fruits such as those of raspberry, formed by the aggregation of many fertilised ovaries, require a regulating mechanism to coordinate and synchronise their growth and development. The receptacle was hypothesised as the leading hub that, by means of hormonal crosstalk with the fertilised ovaries, regulates the fruit growth process. Experiments were designed to perturb the regulating system by damaging the receptacle of hand pollinated flowers of the floricane-fruiting variety Glen Ample to produce artificially crumbly fruits. Hormone profiling was performed in control and artificially induced crumbly fruit samples at two stages of development green developing fruit and red ripe fruit. Of the hormones that could be adequately detected and quantified, abscisic acid (ABA) was elevated in the receptacle of crumbly samples at both developmental stages while SA was higher only in green fruit receptacles. In the druplets, trans-zeatin (tZ) concentration was greater in green than red fruit but the crumbly treatment did not influence content. The data highlight a potential role for these three phytohormones in the development of misshapen 'crumbly-like' fruits.