Abstract
The germination performances of fresh seed lots were determined for 5 tropical forage species: Mulato II hybrid brachiaria [ Urochloa ruziziensis (syn. Brachiaria ruziziensis ) x U. decumbens (syn. B. decumbens ) x U. brizantha (syn. B. brizantha )], Mombasa guinea [ Megathyrsus maximus (syn. Panicum maximum )], Tanzania guinea [ M. maximus (syn. P. maximum )], Ubon paspalum ( Paspalum atratum ) and Ubon stylo ( Stylosanthes guianensis ), stored under ambient conditions in Thailand (mean monthly temperatures 23‒34 oC; mean monthly relative humidity 40‒92%) or in a cool room (18‒20 oC and 50% relative humidity) for up to 6 years. The first paper of this study showed all seeds, except unscarified Ubon stylo seed, were dead after a single year of storage in ambient conditions. This second paper shows that cool-room storage extended seed viability, but performance varied considerably between species. Germination percentage under laboratory conditions declined to below 50%, after 3 years storage for Mombasa guinea seed and Tanzania guinea seed, 4 years for Ubon paspalum seed and 4‒5 years for Mulato II seed. Ubon stylo seed maintained high germination for 5 years, in both cool-room storage (96%) and ambient-room storage (84%). Apparent embryo dormancy in acid-scarified Mulato II seed steadily increased with time in cool-storage and this seed had to be acid-scarified again each year at the time of germination testing to overcome dormancy. Physical dormancy of Mulato II seeds, imposed by the tightly bound lemma and palea in unscarified seed, was not overcome by length of time in cool-storage and these seeds had to be acid-scarified to induce germination. Hardseeded percentage in Ubon stylo seed remained high throughout the study and could be overcome only by acid-scarification. The difficulties of maintaining acceptable seed germination percentages when storing forage seeds in the humid tropics are discussed. Keywords : Embryo dormancy, hardseededness, humid tropics, seed storage, seed viability. DOI: 10.17138/TGFT(6)26-33
Highlights
Many tropical forage seeds produced and sold in Thailand are stored under ambient conditions in store rooms and shops where there is no control over temperature and humidity
Embryo dormancy in Mombasa and Tanzania guinea grasses was overcome within 6 months in cool-room storage (Hare et al 2014)
Germination percentages of forage grass seeds stored in a cool-room in this study varied substantially after 3 years of storage with many below 50%
Summary
Many tropical forage seeds produced and sold in Thailand are stored under ambient conditions in store rooms and shops where there is no control over temperature and humidity. The seeds are stored in conditions similar to those used to keep other grains for animal feed but which are not required to germinate. Forage seeds are sometimes carried over between years. There have been increasing concerns and reports about the declining germination quality of these forage seeds. Stored tropical grass seeds in a cool-room Relative humidity, RH) and found that germination rates of seeds initially with high viability remained high after 6 years cool-room storage. It was important for us to find the ideal storage conditions in Thailand that would maintain seed germination of our commercial forage seeds at acceptable levels for more than 1 year
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