Seasonal pattern of seed dormancy in Parthenium hysterophorus L

Earlier non-conclusive results have been reported on the initial dormancy status of parthenium (parthenium hysterophorus l.) seeds. the present study reports the seasonal dormancy pattern of parthenium in lahore,pakistan where there are four distinct seasons viz. summer,autumn,winter and spring in a year. mature parthenium seeds were collected on the last day of each month from january to december 2006 and investigations for their germination percentage and rate of germination were started on the next day. parthenium seeds collected during coldest months of january and december showed highest germination of 100% with germination rate of 33.3% per day. conversely,seeds collected in summer months of april to september exhibited lowest germination of 0-7% and germination rate of 0-1.75% per day. seeds collected in rest of the months showed variable final germination percentage and germination rate ranging from 30-97% and 3.8-17.4%,respectively. both the final germination and germination rate showed a highly significant negative correlation with the solar radiation and environmental temperature during the seed development period. the present study concludes that dormancy in parthenium seeds depends upon the temperature and solar radiation during the seed development period.