Pea plants (Pisum sativum L. cv. Alaska) were grown from seeds for eleven days at different irradiances. Cuttings were then excised and rooted at 16 W × m−2. Gibberellic acid (GA3, 10−11 to 10−3M) was applied to the cuttings immediately after excision.

Cuttings from stock plants grown at the highest level of irradiance (38 W × m−2) formed the lowest number of roots. An increasing number of roots per cutting was obtained by decreasing the irradiance to the stock plants. In cuttings from stock plants grown at low irradiances, low concentrations of GA3 (10−8 and 10−7M) promoted root formation further. No effect on rooting by these GA3 concentrations was observed when applied to cuttings originating from stock plants grown at the high irradiances. Root formation in all cuttings was inhibited by GA3 at concentrations higher than 10−6M. The degree of inhibition by GA3 was influenced by the irradiance pretreatment and was increased with an increase in the irradiance during the stock plant growth.

Seeds from different years produced cuttings with different response patterns regarding the irradiance and GA3 effects on rooting.