Aw. Whiley et al., CHANGING SINK STRENGTHS INFLUENCE TRANSLOCATION OF PHOSPHONATE IN AVOCADO (PERSEA-AMERICANA MILL) TREES, Australian Journal of Agricultural Research, 46(5), 1995, pp. 1079-1090
Translocation of phosphonic acid (H3PO3) in cv. Hass avocado trees was
studied after trunk injection with 20% H3PO3, formulated as potassium
phosphonate, at three stages of tree phenology during the growing sea
son. Initially, translocation was solely acropetal in the xylem, and H
3PO3 was detected in the leaves 24 h after treatment. Several days aft
er injection, H3PO3 concentration in the bark of trunks and in roots i
ncreased, indicating basipetal phloem transport of H3PO3 from leaves.
The rate of accumulation and the final concentration of H3PO3 in the r
oots were directly related to the sink strength of the shoot at the ti
me of injection. For example, trunk injection at the beginning of spri
ng growth flush, when renewal shoots were strong sinks, resulted in lo
w H3PO3 root concentrations (<9 mu g g(fw)(-1)) which peaked about 45
days after treatment. When potassium phosphonate was injected after th
e transition of spring-grown shoots from sinks to sources, or at summe
r shoot maturity, root concentrations of H3PO3 increased to greater th
an or equal to 25 mu g g(fw)(-1) by 30 days after treatment. These res
ults suggest that strategic timing of injections according to phenolog
ical events may greatly improve fungicide efficacy when targeting spec
ific organs for protection.