The pure live seed (PLS) index is commonly used to express the quality of forage grass
seeds, representing a practical and convenient way to compare the value of seed lots of these species.
Aiming to link physical and physiological quality to practical marketing and seeding matters, ten
commercial seed lots of Brachiaria brizantha cv. Marandu, harvested by sweeping, were evaluated as
to physical purity at zero month, and as to germination/viability by five methods, whose results were
associated with those of purity at zero month, to calculate the PLS index at zero, six, twelve and eighteen
months of storage under uncontrolled warehouse conditions in the Campinas region, State of São
Paulo, Brazil. Results showed that plain storage for six months increased the commercial value of the
lots due to natural reduction in dormancy and consequent increase in germination and PLS index. On
the other hand, from six months on, the observed deterioration decreased the PLS index, mainly from
twelve to eighteen months. Viability by tetrazolium and germination after preheating at 40°C for seven
days followed by acid scarification for fifteen minutes were the most efficient tests to monitor the
germination potential and trend of deterioration, and to provide the seed lots with PLS values above the
present minimun standards required by federal and State of São Paulo regulations