Embryo Development and Germination of Cycas Seeds

Abstract

Germination of Cycas revoluta seed is slow and erratic when planted immediately after collection, and most lose viability in a few months. In a 2 × 4 × 4 factorial experiment, seeds were stored at 5° and 22°C for 24 weeks and subsequently treated with H 2 SO 4 (18 M) for 0, 1, 2, or 3 hr followed by GA 3 (1000 ppm) for 0, 24, 48, or 72 hr. Morphophysiological complex dormancy contributes to the lengthy germination process. Removal of the fleshy, water-repellant sarcotesta (containing inhibitors), scarification of the thick water-impermeable sclerotesta, and maturation of the embryo, which is in very early stages of development at the time of seed abscission, all enhance germination. At 5°, 92% of the seeds survived, but only 42% of the seeds stored at 22° were viable after 24 weeks, the result of desiccation. Under all but 72 hr of GA 3 exposure time, response surface shapes lead to the expectation that germination will be better without H 2 SO 4 or with higher levels of H 2 SO 4 than with intermediate levels. The response to GA 3 at any given exposure to H 2 SO 4 is similar in both cold- and warm-stored seeds: for a given GA, level, one optimum H 2 SO 4 exposure gives the best germination percentage, peak value (PV), or germination value (GV). Optimal GV results when seeds are stored at 5° for 24 weeks to allow embryo maturation followed by removal of the sarcotesta, 1 hr of H 2 SO 4 exposure, and 36 hr of GA 3 exposure.