Pollen source in Prasophyllum affects seed quantity and quality
Marc Freestone, Celeste C. Linde, Noushka ReiterContext
Prasophyllum (Orchidaceae) contains 40 nationally threatened species in Australia, and the collection of viable seed is key to their conservation. However, knowledge of mating systems in Prasophyllum is limited, and the effects of pollen source (self, outcross, and natural) on seed quality and quantity are not well understood.
Aims
To investigate whether pollen source in three Prasophyllum species affects seed quantity and quality, and, therefore, optimum methods for seed collection.
Methods
For three Prasophyllum species we compared seed viability from asymbiotic germination and 2,3,5-triphenyltetrazolium chloride (TTC) staining and seed weight (mg per fruit) from hand-pollinated (emasculated, selfed, and crossed within and between populations), naturally pollinated, and pollinator-excluded inflorescences.
Key results
Prasophyllum lindleyanum produced seed in all treatments, including fruits of emasculated flowers that did not receive any pollen, whereas P. tadgellianum and P. frenchii produced seed only in pollinated flowers (both hand-pollinated and naturally pollinated). Prasophyllum tadgellianum seed viability was lowest in fruits of hand-selfed inflorescences and highest in fruits of artificially hand-outcrossed inflorescences. For Prasophyllum frenchii, seed viability was lowest in fruits of hand-selfed inflorescences and equally high in fruits of hand-crossed and naturally pollinated inflorescences. There was no correlation between viability estimates obtained with TTC staining or asymbiotic germination.
Conclusions
Prasophyllum lindleyanum produces seed even when emasculated (in the absence of pollination) and is likely to be apomictic. Seed viability of Prasophyllum tadgellianum is reflective of a mixed mating system, with evidence of outcross pollen limitation, whereas P. frenchii also appears to have a predominantly outcrossing mating system.
Implications
Conservation actions need to be tailored to individual species, as Prasophyllum species differ in their mating and pollination systems.