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Dormancy in dimorphic seeds: maternal influence and sibling rivalry.
Dyer, Andrew1,2, 1 2
ABSTRACT- Seed germination in many annual plant species is often well below the potential for the population even under optimal environmental conditions. In germination trials of barbed goatgrass, Aegilops triuncialis, conducted on paper and in soil, larger seeds in dimorphic pairs were not dormant under any of the conditions tested. Germination of the smaller seeds was 100 percent on paper, but was conditional in soil and ranged from zero (in the spikelet) to about 50 percent (bare seed). The non-deep dormancy seen in small seeds was induced both by maternal and sibling influences. The maternal influence in A. triuncalis acted on the smaller of the two dimorphic seeds in a pair, but did not affect the larger seeds. The effect was weakened by washing the spikelet, though not in proportion to the number of washes, suggesting a chemical basis for this influence. A weaker influence on germination of the smaller seed was the presence of the seedling from the larger seed. The effect was stronger when seeds were in the spikelet (both influences present) and persisted after the death of the seedling even in the absence of the spikelet. This study found both the expected maternal influence on dormancy and an unexpected sibling influence. Evidence for a strong maternal influence supports both bet-hedging and competition avoidance strategies for increasing fitness. The weaker sibling influence suggests avoidance of intraspecific competition.
KEY WORDS: seed dormancy, annual grass, competition, germination