SHOOT REGENERATION FROM PETUNIA LEAF-DISKS AS A FUNCTION OF EXPLANT SIZE, CONFIGURATION AND BENZYLADENINE EXPOSURE

The effect of explant size, configuration, and duration of benzyladenine exposure on shoot organogenesis in Petunia x hybrida 'Ultra Salmon' leaf discs was determined. Leaf discs of 13, 10, 8, 5, and 3 mm diameter, and 10 mm with a 5 or 3 mm hole and 13 mm with an 8 or 5 mm hole were tested. The smallest size and configuration for maximum shoot production and consistency of regeneration was a 10 mm whole disc. This was followed by the 8, 10 with a 3 mm hole, 5, 10 with a 5 mm hole and 3 mm disc respectively. Of all configurations tested, the 13 mm disc and the 13 mm disc with a 5 mm hole produced the most shoots. Exposure of leaf discs to benzyladenine-containing medium for 4 days or less resulted in no shoots being formed. Exposure for 10 days or more induced shoot regeneration on all discs tested. A delay of more than 2 days after excision, before plating on benzyladenine-containing medium, decreased shoot regeneration significantly. The explant configurations tested showed that: the area to cut edge ratio was a good predictor of shoot number for either of the two configurations when considered separately; and there are factors other than area to cut edge ratio involved in relating shoot production to explant configuration and size.