Seed maturation in subterranean clover (Trifolium subterraneum L.)

Graduation date: 1983A seed maturation study was conducted to determine the earliest\ud date seed of subterranean clover (Trifolium subterraneum L.) may be\ud safely harvested without reduction in yield or seed quality. In 1981\ud and 1982, seed and bur weight, seed and bur moisture content, germination and seedling vigor were studied to determine when seeds were\ud mature in 'Mt. Barker1 and 'Nangeela' subclover. Indirect maturity\ud indices were evaluated for use in determining when maximum dry weight\ud is attained. Sampling was begun after flowers had formed on the\ud uppermost reproductive nodes and was continued for 70 days in 1981\ud and 62 days in 1982.\ud Maximum seed dry weight occurred in Mt. Barker at 54% moisture\ud and 44 days after flowering in 1981 and at 52% seed moisture and 38\ud days after flowering in 1982. Nangeela attained maximum seed dry\ud weight 46 and 40 days after flowering at seed moisture contents of\ud 53% and 51% in 1981 and 1982, respectively.\ud Seed and bur moisture were closely correlated (r = 0.98 and r =\ud 0.99 for Mt. Barker and r = 0.98 and r = 0.99 for Nangeela) in 1981 and 1982. Seed and bur dry weight were also highly correlated (r =\ud 0.94 and 0.98 for Mt. Barker and r = 0.96 and r = 0.95 for Nangeela)\ud in 1981 and 1982.\ud Scarified seeds attained the 90% level of germination shortly\ud after seed development. Seed weight and germination were not closely\ud correlated. Unscarified seeds attained the 95% level of\ud impermeability 26 to 30 days after flowering.\ud Maximum seedling vigor was reached 6 and 10 days after maximum\ud dry weight for Mt. Barker, and 2 and 10 days after maximum dry weight\ud for Nangeela in 1981 and 1982, respectively. Seeds at this stage\ud were capable of germinating quickly and produced large, strong\ud seedlings.\ud Bur moisture content can be used as a simple index of seed\ud maturity in subclover. Under Willamette Valley conditions, maximum\ud seed dry weight and vigor of Mt. Barker and Nangeela are reached at\ud bur moisture contents of 49 to 58%