EFFECT OF STOCK PLANT ENVIRONMENT ON LATERAL BRANCHING AND ROOTING

Increasing stock plant irradiance can have a positive, negative or no effect on rooting. The difference in response to irradiance can be attributed to interaction between genotype and irradiance or other environmental factors such as photoperiod, temperature, CO₂ and relative humidity. Supplementary lighting and CO₂ enrichment of many greenhouse plants during winter with low natural daylight is beneficial for cutting production, rooting, lateral branching and subsequent growth of cuttings, and can significantly reduce propagation time. Optimal stock plant irradiance level for rooting varies widely with genotype. Stock plants grown under light with high red (R): far-red (FR) ratio or enriched with CO₂ exhibit increased lateral branching and higher cutting yields. Different light quality effects on subsequent rooting is controversial. Seasonal variation in rooting may be related to changes in irradiance level, light quality and photoperiod. Short days which induce dormancy in many species and flowering in SDP generally inhibit rooting and lateral branching. Long days which induce flowering in LDP inhibit rooting and lateral branching. Temperature can modify the effect of photoperiod and/or irradiance on lateral branching and rooting.