An evaluation of the interaction between interstocks and rootstocks on the yield and tree size of ‘Valencia’ orange

Abstract The trend towards high-density citrus plantings to maximise returns has created the need for grove management changes to minimise competition and light-penetration effects. The use of interstocks to produce less vigorous trees of high fruitfulness, as opposed to mechanical means of limiting vigorous tree size, has the potential to satisfy this spacial requirement. The performances of 3 interstocks, ‘Trifoliate’ orange ( Poncirus trifoliata ), ‘Microcitrus’ ( Microcitrus australasica ), and ‘Troyer’ citrange ( Citrus sinensis × P. trifoliata ), were assessed in combination with ‘Sweet Orange’ ( C. sinensis ) and citrange rootstocks, and ‘Valencia’ orange ( C. sinensis ) scion over 15 years. ‘Microcitrus’ interstock reduced tree size and yield too much, whereas the tendency of ‘Trifoliate’ orange to moderately influence smaller tree width whilst not reducing yield resulted in a predicted yield greater than its control. Although ‘Troyer’ citrange interstock did not reduce tree size, it enhanced yield with one rootstock combination. The trial indicates that rootstock/interstock combinations of average fruitfulness, and of a size resulting in between 440 and 615 trees per hectare (on 6.5-m rows), could produce more than conventional plantings of larger trees at around 409 trees per hectare.