Cell wall metabolism of pear fruit on the tree after 2,4-DP treatment

The effect of 2,4-dichlorophenoxy-propionic acid (2,4-DP) on fruit ripening on the tree was investigated in 'La France' pears (Pyrus communis L.). For ty-five ppm. 2,4-DP solution was applied at 159 d after full bloom (DAFB), which was optimum harvest date for 'La France' pears. They were compared wi th fruit harvested at 159 DAFB and placed in a controlled room with a 20 de grees C and 90% r.h. After harvest, the fruit firmness decreased dramatical ly 13 d after harvest (DAH). In 2,4-DP treatment, the levels decreased grad ually 13 d after treatment (172 DAFB). In the untreated control, the levels also showed a slight decrease with time. Final ethylene concentration was almost the same in harvested and 2,4-DP treated fruit, but lower in the unt reated control. In each treatment, water-soluble polyuronide (WSP) concentr ations increased with time and hexametaphosphate-soluble polyuronide (HMP) and HCl-soluble polyuronide (HP) concentrations decreased. WSP concentratio n increased rapidly 20 DAH in harvested fruit and 194 DAFB in 2,4-DP treatm ent. Harvested and 2,4-DP treated fruit reached the edible condition on 17 DAH and 193 DAFB, respectively. Pectinesterase (PE) activity increased slig htly with time for all treatments, showing no significant difference betwee n treatments. Polygalacturonase (PG) activity increased gradually in all ca ses, being higher in 2,4-DP treated fruit than in control fruit left on the tree. These results suggest that 2,4-DP treatment before harvest induces p ear fruit softening. This implies that 2,4-DP may be used as a replacement for low-temperature storage to promote the ripening, and good quality ripe fruit with buttery and juicy texture may be harvested on the tree.