EFFECT OF RACEME THINNING AND GIRDLING ON FRUIT SET OF MACADAMIA NUT

Abstract

Premature fruit drop of Macadamia integrifolia is a major limitation to yield. This study investigated the effects of raceme thinning and branch girding on find fruit set of macadamia nut 'Ikaika' and 'Keaau'. Eleven-year old grafted trees grown near Hilo, Hawaii were used. Racemes were thinned to 1, 2, or 4 racemes per branch two weeks after anthesis. The base of half these branches was girdled when the racemes were thinned.Premature fruit drop occurred during the 97 and 151 days following anthesis for `Keaau' and `Ikaika', respectively. Peak fruit drop occurred within 70 days after anthesis for both cultivars. Raceme thinning and girdling had no effect on final fruit set (nuts/branch) of `Ikaika' 151 days after anthesis. There was a significant interaction between raceme thinning and girdling on final fruit set of `Keaau'. Branches with four racemes set more fruit than branches with one or two racemes. Raceme thinning and girdling had no effect on fruit retention (% of initial fruit set retained through final fruit set per branch) of `Ikaika'. There was a significant interaction between girdling and raceme thinning on fruit retention of `Keaau'. Branches with four racemes had greater fruit retention than branches with one or two racemes. Premature fruit drop may be altered on individual branches by altering raceme load and limiting phloem transport of assimilates into the girdled branch.