Growth, yield and fruit composition of Washington Navel and Late Valencia orange trees, as affected by rootstock and root temperature

Abstract

Wahington Navel and Late Valencia scions were budded onto three clonal rootstocks (rough lemon, sweet orange and Poncirus trifoliata) mist propagated and grown in sand. The six scion/rootstock combinations were grown in containers in a glasshouse with three root temperature treatments (19¦C, 25¦C, 30¦C). Juvenile characteristics, evident for 5-6 years when scions are budded onto seedling rootstocks, were less marked when clonal rootstocks were used. Highest yield of fruit was produced by Late Valencia/sweet orange. This yield was 30 per cent better than previously obtained with Late Valencia grown from rooted cuttings under similar conditions. The yield from Washington Navel/sweet orange was about 30 per cent less than from Late Valencia/sweet orange; and the yields from the other scion/rootstock combinations were about 50 per cent of that from Washington Navel/ sweet orange. For most combinations more total dry matter was produced at a root temperature of 25¦C than at 19¦C, but there was little benefit from increasing temperature to 30¦C. With either scion on rough lemon, fruit abscission was marked if root temperature treatments were imposed early (in late August). The effect was particularly severe at 25¦ and 30¦C. Root temperature treatments for the other rootstocks were not imposed until mid-October when fruitlets were about 15 mm in diameter; under these conditions there was negligible fruit drop.