In vitro and transplantation experiments with germination of date embryos

In vitro experiments with date palm embryos were designed to determine (i) which carbon sources support growth and (ii) what culture conditions promote haustorial growth and development. Date palm embryos were also transplanted into Washington filifera seeds to deterine whether any developmental characteristics were determined by the seed or endosperm. Date embryos did not grow on media containing starch or galactomannan any better than they do on medium lacking a carbon source. Good growth occurred on medium containing mannose, glucose, or sucrose as the carbon source. Embryos imbibed in the seed for 6 days grew better and produced larger haustoria than those imbibed 2 days, imbibed in water, imbibed in 3% mannose, or unimbibed. Date embryos imbibed in Washington seeds grew as well as those imbibed in date seeds. Optimum seedling and haustorium weights occurred at pH 7. The transembryonic seedlings germinated and grew normally but the shape of the haustorium was altered. Haustoria produced by in vitro grown seedlings exhibited many normal anatomical features, but haustoria from transembryonic seedlings exhibited more normal histological features. Results support the hypotheses that (i) date embryos do not possess the enzymes necessary to digest mannans and (ii) haustorium development is controlled by at least two steps, an initial inductive step that occurs by 6 days of imbibition and a further step that occurs later. We hypothesize that diffusable substances from the endosperm are responsible for controlling haustorium initiation and development. Key words: germination, embryo culture, palms, palm tissue culture, Arecaceae, haustorium.