THE ROLE OF LIGHT AND TEMPERATURE IN THE GERMINATION OF 20 HERBACEOUSSPECIES FROM THE HIGHLANDS OF ETHIOPIA

The effects of different light qualities, i.e. white light, darkness a nd light filtered through green leaves, as well as constant (10-30 deg rees C) and diurnally alternating temperatures (20 versus 20/12, 30/12 and 35/12 degrees C) on seed germination of 20 herbaceous species fro m the highlands of Ethiopia were tested in a laboratory and a glasshou se. Species differed considerably with respect to the capacity of fres h seeds to germinate at 20 degrees C in light. Only six of the species showed more than 80% germination whereas in seven of the species germ ination ranged from 1-50%, and in seven of them none of the fresh seed s germinated. In the laboratory test of fresh seeds, 11 of the species had significantly higher percent germination in light than in darknes s. In the glasshouse, percent germination from seeds incubated in dayl ight was significantly higher than those incubated in darkness or unde r leaf shade for 15 out of 17 species tested, indicating the induction of secondary dormancy during incubation in either darkness or leaf sh ade. The species showed diverse responses to the various constant temp erature treatments. For six of the species germination was more than 5 0% at all of the constant temperatures whereas for seven of the specie s germination was less than 50% at the different constant temperatures . Germination was more than 50% at the constant temperatures between 1 5 and 30 degrees C but lower than 43% at 10 degrees C for four of the species. For one of the species, germination was more than 50% at the constant temperatures between 10 and 25 but germination declined to 18 % at 30 degrees C. Of the 16 species tested, 11 showed significantly h igher germination from at least one of the alternating temperatures th an the control. The results provide evidence that germination of almos t all of the species studied is inhibited or greatly suppressed by eit her darkness or leaf shade or both, suggesting that germination and es tablishment of the species would be prevented if the seeds are buried deep into the soil or dispersed under vegetation canopy. The positive germination responses of seeds to alternating temperatures indicates t hat the species require disturbances resulting in the formation of gap s and/or in exposing seeds to the soil surface if they are buried deep into the soil or dispersed under vegetation canopy. The results agree well with the ecology of the species studied, since almost all of the m are known to form persistent soil seed banks in the highlands of Eth iopia.