The 2012 ASHS Annual Conference

Orchidaceae is one of the largest and most evolved families of flowering plants found especially in tropical and sub-tropical regions. Orchids are undoubtedly the ornamental elite because of their perplexingly complex flowers of exquisite beauty. Polyploidy induction is a common technique utilized to obtain plants with enhanced characteristics.  Polyploid orchids might present larger flowers, larger number of flowers per inflorescence, enhanced vigor, and intensified coloration. The traditional polyploidy inductor used worldwide is colchicine, but this alkaloid is extremely toxic to human manipulation due to its high affinity to microtubules of animal cells. Oryzalin and trifluralin are herbicides recognized for their antimitotic activity and suitable plant polyploidy induction ability. They can be effective in very low quantities, present more affinity for plant tubulin dimers and consequently have reduced human toxicity. The objective of this study was to evaluate the effects of oryzalin and trifluralin in the induction of polyploidy in in vitro Cattleya walkeriana orchids. Seeds from C. walkeriana were germinated in vitro and 90-day old protocorms were treated with different concentrations (0, 15, 30, 50, and 100 µM) of both antimitotic agents for 3 and 6 days. After that they were transferred to 180-mL flasks containing 50 mL of semi-solid ½ strength MS culture medium. The experimental design consisted of 20 treatments, 5 flasks per treatment and 10 protocorms per flask, with a total of 1,000 explants. The evaluation included biometrical responses (protocorm survival and number of shoots recorded at 8 weeks), and cytogenetic and flow cytometry analyses 22 weeks after the experiment establishment. Data were subjected to analysis of variance (ANOVA), and means compared using Tukey test (α = 0.05). Treatments for both antimitotic agents decreased rooting and dramatically increased the number of shoots compared with controls. Trifluralin was significantly more toxic than oryzalin, particularly when protocorms were exposed to it for 6 days, and showed lower survival rates and high callus formation. The cytogenetic and flow cytometry analyses of regenerated plantlets confirmed the level of polyploidy induction.  This study demonstrated that oryzalin showed more promising results and it was more effective in polyploidy induction as compared to trifluralin.  Renegerated plants of C. walkeriana will be further evaluated for growth ex vitro and subsequently for floral characteristics.