Abscission chemicals for Valencia oranges in New South Wales

Three abscission chemicals inducing production of ethylene, have been evaluated as aids for mechanical harvesting of Valencia oranges at Horticultural Research Stations at Gosford (coastal) and Dareton (inland) in New South Wales during 1971-75. Ethephon (CEPA) promoted abscission without visible injury to the fruit but leaf drop at concentrations required to give adequate loosening (500 p.p.m.) was excessive. Cycloheximide (CHI) at 20 p.p.m. reduced fruit removal force (FRF) to 3.2 kg at Gosford and to 4.6 kg at Dareton in 1971, and again to 3.7 kg at Gosford in 1972. There was no reduction in FRF at Dareton in 1972. The addition of Polycote (R) (polyethylene emulsion) to CHI at Gosford enhanced theabscission response by reducing FRF an additional 20 per cent. Spraying before or after irrigation at Dareton; or during December, January or February at Gosford had no effect on FRF. Leaf and fruitelt drop caused by CHI were too high for commercial practice. Release (R) (CMNP) was selective for mature fruit only, and at concentrations up to 300 p.p.m. no fruitlet or leaf drop occurred while FRF was reduced to between 2 kg and 4 kg. This chemical was the most promising for incorporation into a mechanical harvesting system, but because of damage to the rind is limited to fruit for processing only.

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Relationships between kernel oil content, fruit removal force and abscission in macadamia.

Australian Journal of Experimental Agriculture ◽

10.1071/ea00004 ◽

2000 ◽

Vol 40 (6) ◽

pp. 859 ◽

Cited By ~ 31

Author(s):

S. J. Trueman ◽

S. Richards ◽

C. A. McConchie ◽

C. G. N. Turnbull

Keyword(s):

Oil Content ◽

New South ◽

New South Wales ◽

Fruit Maturation ◽

Fruit Removal ◽

Oil Accumulation ◽

Fruit Abscission ◽

Kernel Oil ◽

Macadamia Integrifolia ◽

South Wales

Delayed or extended fruit abscission in many cultivars of macadamia, Macadamia integrifolia (Proteaceae), necessitates multiple harvests from the orchard floor. However, it is not known whether there is a link between fruit maturation and timing of abscission. In this study, relationships between kernel oil content, nut size, removal force and abscission were investigated in 2 commercial orchards, one in Queensland (24˚S) and one in New South Wales (29˚S). Abscission lasted 6 months (March–September) at both sites due to differences in timing of abscission between cultivars and extended abscission within cultivars. Abscission was consistently associated with declines in fruit removal force, from more than 2 kgf in early March towards 1 kgf at the peak of abscission. Later abscission in cvv. A16 and 246, compared with cvv. 344 and 741, was correlated with more gradual declines in removal force. Fruits containing small nuts and kernels tended to possess lower removal forces and these fruits were often heavily represented in the population of fruits that abscised earliest. There was little or no difference in kernel oil content between fruits of different removal force or between sample dates for any cultivar, either for samples taken from the tree or from the orchard floor. Attainment of maximal oil content and onset of fruit abscission are therefore independent processes in macadamia. If abscission can be accelerated, it may be possible to advance the harvest of late-abscising cultivars such as A16 and 246 which retain mature nuts on the tree up to several months after maximal oil accumulation.

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