Protocorm mycobionts of the Federally threatened eastern prairie fringed orchid, Platanthera leucophaea (Nutt.) Lindley, and a technique to prompt leaf elongation in seedlings

Abstract

A yet unresolved question in orchid biology is whether mycorrhizal fungi (= mycobionts) utilized as a carbon source by young seedlings (= protocorms) are different from those utilized by adult plants. This is the first report documenting the protocorm mycobionts of the Federally threatened eastern prairie fringed orchid, Platanthera leucophaea, and the first report describing a technique to culture mycotrophic seedlings to the green leaf stage. Seeds of P. leucophaea placed in retrievable nylon mesh packets were sown at Hildy Prairie (Grundy Co.), Illinois in November, 2000 and recovered in August, 2002. All resulting protocorms yielded mycobionts assignable to Ceratorhiza goodyerae-repentis (Costantin & Dufour) Moore - the same anamorphic fungus recovered from mature P. leucophaea plants in previous studies. Protocorms cultivated in vitro with a Ceratorhiza mycobiont were placed on a substrate of sand, activated charcoal, and modified oats medium and subjected to chilling (6 oC) in darkness, followed by exposure to a 12 h photoperiod (L : D, 12 h : 12 h) at 24 oC. Leaf length accelerated after the second week of incubation in light. Green leaf color became evident during the photoperiod implying that seedlings were capable of photosynthesis. Seedlings also maintained a mycotrophic capability evidenced by the presence of fungal pelotons in root-like organs. This study has significant merit for conservation by providing a protocol for P. leucophaea's cultivation, and by underscoring the importance of C. goodyerae-repentis in the prairie ecosystem.