O.P. Damasco

Gibberellic acid detection of dwarf offtypes in micropropagated Cavendish bananas

Detection of dwarf offtypes produced by micropropagation of Cavendish bananas (Musa spp.) cultivars New Guinea Cavendish and Williams was achieved by spraying gibberellic acid (GA3) solution (289 pmol/L) onto deflasked plants and measuring various plantlet responses. The most useful identification criterion was elongation of the sheath of the first leaf to form after GA3 application. Elongation of this structure was about 2-fold greater in normal plants than observed in dwarfs. Similar measurements taken earlier during in vitro culture or later during plant establishment in soil were not as useful in discriminating between normals and dwarfs as the measurements made at deflasking. The similar GA3-induced elongation response of the dwarf offtype and that of the naturally occurring dwarf cultivar Dwarf Parfitt suggests that the mechanism for dwarfism could be the same in the 2 cases.

Micropropagated dwarf off-type Cavendish bananas (Musa spp., AAA) show improved tolerance to suboptimal temperatures

The responses of micropropagated normal plants and dwarf off-types of Cavendish (Musa spp. AAA) bananas to suboptimal temperatures were evaluated under field and controlled environmental conditions. Compared with bananas grown at 30/25 degrees C (day/night), leaf production at 18/14 degrees C was inhibited by 51% in normal plants and 18% in dwarf off-types. The emergence of the first leaf that developed at low temperature was delayed by 11 days for normal plants and 5 days for the dwarf off-types. Photoinhibition of lamina, measured by decrease in the chlorophyll fluorescence variable Fv/Fm, occurred in all banana plants growing in the field during the winter months. The extent to which the plants were photoinhibited was significantly greater for the normal plants than dwarf off-types. Under controlled environmental conditions, photoinhibition was similarly greater in normal plants than dwarf off-types. After 153 h at 18/14 degrees C and a 9-h photoperiod of photon flux density (PFD) of 380 mu mol/m(2).s, Fv/Fm was reduced by 22 and 13% for normal and dwarf off-types, respectively. When plants were exposed to 18 degrees C and a continuous PFD of 380 mu mol/m(2).s for 20 h, Fv/Fm was reduced by 50% for normal plants and 36% for dwarf off-types. The results of the study indicate that dwarf off-types generated from banana micropropagation showed improved tolerance to low temperature and light, showing better growth and lower susceptibility to low-temperature induced photoinhibition than normal plants.