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- Author or Editor: R.G. Evans x
- HortScience x
Prohexadione-Ca (BAS 125 W) is currently developed as an inhibitor of excessive vegetative growth in apple. In addition to the control of shoot growth, pronounced effects on the incidence of scab (Venturia inaequalis) and fire blight (Erwinia amylovora) are observed that are not due to any fungicidal or bactericidal effect of the compound. Prohexadione-Ca induces marked changes in the metabolism of phenylpropanoids most likely by inhibiting distinct dioxygenases, such as flavanone 3-hydroxylase, which require 2-oxoglutarate as a co-substrate. The content of flavonoids such as luteoliflavan (which does not normally occur in apple tissue) and eriodyctiol is drastically increased reaching levels in the range of 50 mg per gram of dried young shoot tissue. Simple phenols, the identity of which is still unknown, also undergo intense changes. Since phenylpropanoids have often been found to be involved in defense mechanisms of higher plants, further studies on their role in pathogen resistance in apple are justified from these results.
Prohexadione-Ca (BAS 12511W or Apogee™ Plant Growth Regulator) acts within a plant by blocking the biosynthesis of growth-active gibberellin. The result is decreased cell and shoot elongation; thus, vegetative growth in apple trees can be reduced. Air blast applications of prohexadione calcium were made in the Spring 1998 in commercial orchards. Application rate was 125 ppm a.i. applied twice beginning at 5 to 12 cm of new shoot growth. Reduction of shoot growth averaged 45% across locations. As a result of reduced vegetative growth, dormant pruning was reduced. In total, significant benefits to the grower included reduced pruning costs in addition to other positive effects such as improved light penetration and enhanced resistance to some pathogens. Research will continue with the effect of prohexadione-Ca on pruning in multiple year studies.