Increase in final fruit size of tangor (Citrus reticulata × C. sinensis) cv W. Murcott by application of benzyladenine to flowers

•Benziladenine applied to W Murcott flowers at 90 ppm increases final fruit size.•Application increases size and cell number of fruit during the first growth phase.•Hormone promotes not only pericarp growth, but also locule and central axis growth.•Stimulating ovary growth with benzyladenine improves fruit retention.

Fruit development involves the phenomena of cell division and cell elongation. The process is signalled and regulated by the combined action of hormonal substances such as gibberellins, cytokinins and auxins. Benzyladenine (BA) in the presence of adequate internal auxin concentrations is able to stimulate cell division. When BA is applied to mandarins immediately after flowering, initial fruit development can increase, coinciding with endogenous cytokinin content behaviours. Different BA concentrations were therefore applied through immersion of flowers of tangor cv. W. Murcott during anthesis: 30 ppm (BA30); 60 ppm (BA60), 90 ppm (BA90) and an untreated control. BA effects were first determined on the development of different tissues during early fruit growth stages and final fruit size. In the first growth stage, BA90 led to an increase in the number and size of pericarp cells, with size increases also seen in locules and the central axis. This effect led to larger fruit size at the end of development. There was also an increase in the fruit number retained when treated with BA. No effect was seen on internal quality parameters. The effect of application of different BA concentrations on W. Murcott tangor trees is yet to be determined.