Seed dormancy in vetch (Vicia species)

The aims of this study were to develop appropriate methods for screening Vicia species for dormancy and dormancy mechanisms and determine factors responsible for the development of seed impermeability and how impermeability can be overcome. The materials recommended by the International Seed Testing Association (ISTA 1993 and 1996) for the germination of seeds were evaluated. Loamy sand, paper towel and Petri dishes were all suitable for germination of Vicia seeds. The three types of material have their advantages and disadvantages but the advantages outweighed the disadvantages in the different type of media. The towel method was chosen for this study because it was easier to germinate many seeds (100 seeds per towel) at a time and the towels could be reused until the end of the study. Also, there was no need for regular watering during the tests because towels held enough water for two weeks. The optimum temperature for Vicia seed germination was identified to be between constant 15 and 20C. These results agree with recommendations by ISTA of germinating most Vicia seeds at 20C. A fluctuating temperature of 22/11C also had good germination but the germination rate was reduced. Ten Vicia species and subspecies were assessed for dormancy. Vicia sativa, V. benghalensis, V. ervilia and V. articulata had no impermeable seeds. Almost all the V. villosa accessions had a high level of impermeable seeds ranging from as low as 10% to a high of 60%. Breeding against this trait has been successfully achieved by SEEDCO, a seed company based in South Australia and cultivars with reduced levels of impermeable seeds have been released. The remaining species; V. sativa ssp nigra, V. sativa ssp sativa, V. serratifolia, V. amphicarpa and V. lutea all had higher levels of impermeable seeds ranging from 50 to 95%. These studies concentrated on overcoming impermeable seed coat by mechanical and chemical scarification. Scratching the seed coat with a pin was enough to enhance germination. Commercial scarifier was not as effective as scratching the seed coat with a pin. This could partly explain the need to penetrate the seed coat as achieved by a pin as compared to rubbing off part of the seed coat with sand-paper. The use of sulphuric acid was effective in enhancing germination in Vicia seeds with high proportion of impermeable seeds. Exposure of the seeds to the acid for 30 minutes was effective. Low temperature storage (5C) reduced the level of impermeable seeds in most species. The seed moisture was increased under low temperature storage and this resulted in higher germination. This type of storage is not suitable for long term storage but can be used if the relative humidity is reduced to about 0%. High temperature storage reduced seed moisture and encouraged seed impermeability. Fluctuating temperature of 22/11C reduced the proportion of impermeable seeds. Storage environment also played an important role in the development of impermeable seeds in Vicia. Dry conditions imitated by desiccator reduced seed moisture and resulted in higher levels of impermeable seeds. Seed storage under laboratory conditions had no effect on the proportion of impermeable seed