Methyl jasmonate and CMN-pyrazole applied alone and in combination can cause mature orange abscission

Methyl jasmonate (MJ) and CMN-pyrazole alone and in combination were applie d to 'Hamlin' and 'Valencia' orange trees (Citrus sinensis (L,) Osbeck) in seven separate experiments in the 1998/ 1999 and 1999/2000 growing seasons to induce abscission of mature fruit for mechanical harvesting. MJ alone si gnificantly reduced fruit detachment force (FDF) of 'Hamlin' oranges at con centrations of 10 mM and higher. However, MJ at 20 and 100 mM caused signif icant defoliation. For 'Hamlin' oranges, the most effective treatments were those combining 10 mM MJ and 50 mg l(-1) CMN-pyrazole, and 20 mM MJ and 25 mg l(-1) CMN-pyrazole. 'Valencia' oranges did not respond to 10 mM MJ trea tments alone or in combination with CMN-pyrazole, and required MJ at 20 mM in combination with CMN-pyrazole to loosen this late-maturing variety to be low 50 N, but excessive defoliation occurred. (C) 2001 Elsevier Science B.V . All rights reserved.