2019 ASHS Annual Conference

Nursery citrus trees in California must be grown in insect exclusion facilities to be protected against Huanglongbing (HLB), a deadly disease spread by the Asian Citrus Psyllid. Although faster year-round propagation is critical for citrus nurseries to offset the investment in new exclusion facilities, nurseries currently face serious problems of poor bud push and slow scion growth in fall-budded container grown trees. Therefore, the purpose of this study was to explore the effect of supplemental LED lighting technique on improving container citrus tree growth and propagation efficiency. In this experiment, 144 trees of the common ‘Carrizo’ citrange rootstock with and without ‘Clementine Mandarin’ scion were placed in growth chambers under six photoperiod treatments. The treatments were: T1:10 h LED, T2: 10 h LED with low-intensity supplemental night interruption (NI), T3: 10 h LED with high-intensity NI, T4: 10 h LED with high-intensity supplemental light extension of Day length (EoD), T5: 10 h LED with Low-intensity EoD, and T6: 10 h Fluorescent with NI. Light quality of LEDs were adjusted to 80:20 Red:Blue ratio and the trees were maintained in the growth chambers at 28/21 °C day/night temperatures and 65% RH for 12 weeks. The preliminary results of this study showed that there were higher number of leaves and average shoot growth (shoot length, fresh and dry weights) in the LED treatments than the florescent light treatment. Moreover, trees with low-intensity EoD and NI treatments exhibited higher shoot and root growth and chlorophyll contents than high-intensity EoD and NI treatments. Also, it was found that non-budded trees had higher shoot and root fresh and dry weights and lower shoot length than budded trees.