Fungal associations and improving micropropagation of native Rhododendron spp.

Abstract

Rhododendron is the most abundant genus in the Ericaceae family, consisting of over 1000 species that are native to North America, Western Europe, and Northern Asia. With certain Rhododendron varieties being desirable due to flower color or bloom time, propagation of these shrubs is of increased interest. Micropropagation is a technique of multiplying small plant explants, or cultures, in a sterile environment. The overall goal of this study was to improve established micropropagation protocols to increase explant survivability and shoot growth of native deciduous Rhododendron in vitro. The specific objectives were: 1) to evaluate fungicide media amendments to increase shoot survivability; 2) to investigate fungal contamination found in micropropagation systems for endophytic associations; and 3) to investigate alternative hormones and container sizes for increasing shoot production. For the first objective, five native deciduous Rhododendron nicknamed varieties were established in fungicide amended media. Shoot survival and bud production in each variety was recorded for all fungicide-amendments over 31 days in culture. Thiophanate-methyl-amended media was shown to significantly increase survivability and bud production in four of these varieties. To address the second objective, 20 fungal isolates were identified and analyzed for potential endophytic associations. Of the 20, two isolates were identified from genera Alternaria and Trichoderma, both known for endophytic activity within Rhododendron. For the third objective, Thidiazuron hormone ratios and container sizes were tested in five Rhododendron varieties. Change in explant weight, shoot proliferation, and shoot elongation was evaluated over a 4 week culture period. Shoot performance was significantly improved with the addition of 4.4-8.8 ppm of TDZ stock solution and larger test tube sizes compared to the control.