PHASE-CHANGE IN CITRUS - GROWTH AND FLOWERING OF CITRUS SEEDLINGS FROM 13 GENETICALLY DIVERSE SEEDLING FAMILIES

Seedlings of 13 families belonging to the citrus group were grown unde r greenhouse and natural conditions at Camden, Australia and at Palmer ston North, New Zealand. Lateral branches were removed for 24 months s o that the seedlings had a single main stem. After 24 months, the plan ts pregrown under greenhouse conditions were transferred to natural ou tside conditions. Seedlings were subsequently allowed to form lateral branches from axillary buds, some of which eventually bore flowers. Fl oral branches were found predominantly in the apical region of seedlin gs, indicating a relationship between large plant size and the end of the juvenile phase. Only populations that had previously been grown in the greenhouse environments flowered. Within 30 months of germination some seedlings of some families formed flowers (e.g. 'West Indian' li me, 'Eureka' lemon, 'Rangpur lime', 'Palestine' citron and 'Cleopatra' mandarin). Within 48 months, some seedlings of all families had forme d flowers, but the proportion of plants that flowered, the intensity o f flowering, and the minimum height of flowering branches on the main axis varied between seedling families. Seedlings of lime, lemon and ma ndarin parentage flowered sooner than those of sweet orange, grapefrui t and trifoliate orange parentage.