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

Summary

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.). Forty-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 with fruit harvested at 159 DAFB and placed in a controlled room with a 208C and 90% r.h. After harvest, the fruit firmness decreased dramatically 13 d after harvest (DAH). In 2,4±DP treatment, the levels decreased gradually 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 untreated control. In each treatment, water-soluble polyuronide (WSP) concentrations increased with time and hexametaphosphate-soluble polyuronide (HMP) and HCl-soluble polyuronide (HP) concentrations decreased. WSP concentration increased rapidly 20 DAH in harvested fruit and 194 DAFB in 2,4-DP treatment. Harvested and 2,4-DP treated fruit reached the edible condition on 17 DAH and 194 DAFB, respectively. Pectinesterase (PE) activity increased slightly with time for all treatments, showing no significant difference between treatments. Polygalacturonase (PG) activity increased gradually in all cases, 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 pear 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.