Biannual Peaches in the Tropics

Abstract

The normal growth pattern of high-latitude, temperate zone peaches is such that shortening of daylength in late summer initiates mechanisms that cause the plant to stop growth well before the first killing frosts of autumn. Photoperiod regulates both flower bud formation and cessation of vegetative growth, the latter of which is the first stage of cold acclimation. This early stage of dormancy may be reversible in that trees not induced into deeper dormancy by cold weather may not have built up a full load of growth inhibitors, and thus may not need as much or any cold to overcome the dormancy inhibitors. In fact, observations have shown that peach cultivars induced into deep dormancy require more hours of chilling to break dormancy than those induced only into shallow dormancy. The second stage of acclimation requires low temperatures for induction and is not as reversible unless a certain amount of chilling is accumulated. Temperate zone peach trees have evolved rest period chilling requirements to keep them dormant during winters with temperatures fluctuating between severe freezes and warm periods which might induce growth. In peaches adapted to low latitudes, chilling requirement is not only reduced, but our hypothesis is that response to shortening daylength in late summer is also reduced so that trees tend to grow as long as temperatures and soil moisture are favorable. In addition, flower bud formation continues with vegetative growth.