Germination behaviour in beach spinifex (Spinifex hirsutus Labill.)

Abstract

This paper deals with threshing and seed germination studies on hand-harvested beach spinifex (Spinifex hirsutus Labill.). This work was carried out as part of a detailed study of the autecology of beach spinifex, an important pioneer sand stabilizer on beaches and dunes along the coast of eastern Australia. Hammer-milling was suitable for threshing out caryopses from beach spinifex inflorescences, but in the process the caryopses were excessively damaged. A barley de-awning machine produced spikelets (caryopses enclosed in lemma, palea, and glumes plus the base of the associated spine) which were free flowing and therefore suitable for mechanical planting.

Laboratory germination experiments disclosed that the caryopses were negatively photoblastic when germinated alone, or enclosed within the spikelet. Alternating thermoperiods (10-25, 15-25, 20-25 ; 10-35, 15-35, 20-35°C) were generally superior to constant thermoperiods (25, 30, 35") in the induction of germination. The germination of caryopses from inflorescences harvested 2 months previously agreed with an estimate of viability made by using tetrazolium chloride. This indicated that beach spinifex seed has no pronounced after-ripening requirements.

The rate of germination of caryopses and their germinative capacity were markedly increased when the caryopses were removed from the spikelets. It is likely that germination in the spikelet is inhibited by a slow rate of gaseous exchange between the embryo and the atmosphere. A sensitivity to anaerobic conditions was demonstrated by soaking spikelets for varying periods up to 48 hr in distilled and sea water. Such treatments led to a decrease in germination. Pot trials showed that in waterlogged sand, no appreciable germination occurred below 3.75 cm. In sand held at field capacity, some germination occurred down to the maximum depth tried (8.75 cm), but the best germination was from 2.5 to 3 .75 cm. Soaking spikelets in distilled water for 48 hr and testing the leachate on germinating lettuce seed failed to disclose the presence of water-soluble chemical inhibitors in the spikelets.