Abstract
In the meristem culture of Cattleya alliance, both explants and culture media usually turn reddish brown by enzymatic browning in the presence of phenolic compounds that are produced by explanted tissues. Under such conditions, cultures eventually die because of toxic effects of phenolic compounds. Thus, some factors which influence the survival of explants in connection with phenolic compounds produced by new pseudobulb tissues were examined in this study.
1. Lateral buds with bracts were cut off from new pseudobulbs and then explanted in the liquid RM medium which was renewed once every week for 3 weeks. After that, bracts and leaf primordia were removed to get apical domes of explants exposed, and then transferred to the solid RM medium. Such an explanting technique seemed superior to the current method in both growth and survival rates of explants.
2. When tissues were incubated in sterilized water, fully mature lateral buds of new pseudobulbs that had grown 9 to 12cm in length were better than those of younger pseudobulbs in both survival rate and adventitious bud formation in vitro. The former was revealed to produce less amount of phenolic compounds than the latter.
3. When cultures were incubated in sterilized water, phenolic compounds produced in tissue pieces of pseudobulbs were less in amount at 15-20°C than above 25°C. Excellent growth and survival rates of explants were achieved when the temperature was kept at 15-20°C during the first 4 weeks from explanting (during the first 3 weeks in a liquid medium and subsequent 1 week on a solid medium), and thereafter 25°C.
4. Though medium pH had no direct effects on the growth of Cattleya plantlets within a range from 4.2 to 6.0, maximum survival rate was obtained when medium pH was adjusted to 5.5. Tissue pieces of new pseudobulbs produced less amount of phenolic compounds when incubated in sterilized water of pH 5.5 than in media of the other pH range and compositions.
