lower-bud formation in pome fruits as affected by fruit thinning

Abstract

Fruit thinning is commonly practiced in many fruit bearing woodyperennials to improve fruit quality and to prevent ‘biennial bearing’, thesevere alternation of fruit load in successive ‘on’ and ‘off’ years. Biennialbearing has its origin in the negative effect of the presence of fruits onflower production (return bloom), and, thus, the yield for next year. Forreasons of labour cost, fruit thinning is usually done by using chemicalcompounds such as ethephon and ammonium thiosulphate at the blossomingstage, and for fruit thinning NAA, NAAm, carbaryl, and a few cytokinins.Apart from indirect effects of the various chemicals on return bloom viareduction of fruit load, they may also influence flower formation directly.In view of the supposedly negative relationship between flowering andshoot growth, chemical thinners may even affect bloom via interference withthe vegetative development of the tree. In the present paper, in additionto a short discussion of the essentials of the flower-formation process inpome fruits, the effect of a number of chemical thinners on flower formationis reviewed. It is argued that in most experimental studies the data on theeffect of thinning on return bloom is insufficiently detailed, and a betterunderstanding especially of the early phases of the flower-formationprocess is badly needed.