INDUCTION OF INSECT RESISTANCE IN DENDROBIUM MIRBELIANUM USING ION BEAM IRRADIATION

Dendrobium orchids have been the major orchid cut-flower export for Malaysia as well as for other Southeast Asian countries like Thailand and Philippines. Although new orchid hybrids are consistently released every year to meet the current demand by customers, the only problem that remains unsolved in this industry until today is the problem of insect infestations. Insect infestations in the orchid flowers have caused a lot of losses not only to growers but also exporters due to strict quarantine regulations. The objective of this project was to produce new orchid mutants of Dendrobium mirbelianum that are resistant or tolerant to insect infestation, especially to mites and thrips. Tissue culture orchid materials (protocorm-like-bodies or PLBs) were irradiated with ion beams at doses of 0.4, 0.8, 1.0 and 2.0 Gy for mutation induction. Following irradiation, regenerated plantlets were randomly selected from each dose and subjected to in vitro infestation with mites and thrips, to analyze their resistance towards these pests. Potential insect resistant orchid mutants were then selected and subsequently planted in the glasshouse. Secondary screenings were carried out at flowering stage by challenge-infestation with the target insects. The obtained results show that in vitro mite infestation study on regenerated D. mirbelianum orchids has led to an increase in resistance towards mite infestation on ion beam irradiated plantlets. The percentages of mite resistant mutant plantlets gradually increased with increasing radiation doses. Through the in vitro mite infestation study, a total of 50 potential mite tolerant plantlets were identified. Of these 50 plants, one plant was tolerant to thrips when a secondary screening was carried out at flowering stage (in vivo). All identified mutants were propagated to achieve large numbers of clones, and some samples were transferred to a private collaborator for pre-commercialization studies.