Morphophysiological dormancy and germination in seeds of the Azorean tree Picconia azorica

Abstract

Picconia azorica (Oleaceae) is an Azorean tree with high ecological value. We investigated possible causes for P. azorica seed dormancy and the germination conditions to break it, using acid scarification (scarified stones) or complete removal of the endocarp (seeds), in conjunction with different stratification and incubation temperature regimes and gibberellic acid (GA3) treatments. Embryos in ripe drupes were subspatulate, axile and occupied 60% of the endosperm length. Water imbibition was verified for both acid scarified stones and seeds. The highest total phenolic compounds content occurred in the seed coat (36.4 ± 1.51 mg GAE g-1 FW). Germination was significantly affected by the type of endocarp treatment (acid scarification, 23%; removal of the endocarp, 46%), and by temperature (62% at 10/5°C and 15/10°C; 8% at 20/15°C and 4% 25/20°C), but not by concentration of GA3. Under the two best temperature regimes, only acid scarified stones were significantly affected by the stratification regime, with the highest germination (ca. 60%) after 60 days cold or 30 days warm followed by 30 days cold stratification regimes, although always lower than those obtained for seeds (> 80%). Epicotyl development required low temperature and three months to cotyledon leaf expansion. Germination requirements and embryo characteristics suggest a non-deep simple epicotyl morphophysiological dormancy including the occurrence of a possible chemical inhibition mechanism. For P. azorica propagation we recommend using naked seeds incubated at a temperature of 10/5 or 15/10°C.