Abstract

Some experiences on « Tarocco» and « Washington Navel » sweet oranges and clementine mandarin concerning the effects of gibberellic acid on fruit rind senescence are here reported. The following treatments were compared: I - one treatment at start of fruit colouring; 2 - one treatment about 40 days later; 3 - one treatment about 80 days later; 4 - two treatment; at start of fruit colouring and 40 days later; 5 - two treatments: at start of fruit colouring and 80 days later; 6 - control. All the treatments were made with 1O p.p.m. of gibberellic acido Rind samples were made from fruits collected at two different period of harvest season: as untreated fruits were ripen and two months later. Histological observations were made on cell size of flavedo and middle albedo and intercellular spaces percentage of inner albedo were evaluted. Results showed no effect of gibberellic acid on clementine mandarin, probably because of typical rind structure of this species, in wich no compact tissues can be observed once during first ripening phases. In «Tarocco» and « Washington Navel» on the contrary, gibberellic acid proved to be effective in reducing rind senescence; infact rind tissues of treated fruits appeared more compact, with smaller celles, and minor intercellular spaces in inner albedo, also in fruits collected two months later. More effective treatments resulted those made at the start of fruit colouring.

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