Intrapopulation variation in Abutilon theophrasti seed mass and its relationship to seed germinability

The relationship between seed mass variation and germinability in ten Abutilon theophrasti Medic. plants from a single agricultural population was examined under controlled environmental conditions. Seeds were collected in the autumn of 1995 and dry-stored in paper bags at 4°C until the start of trials in the spring of 1998. For each plant, between 549 and 1000 randomly selected seeds were separated into seven mass fractions based on individual seed mass, with classes ranging from <6.0 to >11.0 mg. Subjecting the seeds to a cold stratification (4°C) period for 7 d followed by a 21-d alternating day/night (25/14°C) temperature and 14-h photoperiod regime, resulted in 75% overall germination, 24% dormancy and 1% non-viable seeds. The majority of the seeds germinated within 7 d of being exposed to the alternating temperature/light regimes. There was a significant (P < 0.001) difference in mean seed mass between the ten plants, with mean mass ranging from 8.8 to 9.6 mg. For nine of the ten plants, the greatest proportion of seeds occurred in the 9.0–9.9 mg mass fraction, while the lowest proportion of seeds was generally found within the 6.0–6.9 mg mass fraction. Most seeds (96%) having a mass below 6.0 mg were non-viable and, of the viable seeds, none germinated. There was a significant (P < 0.0001) relationship between seed mass and total germination, but not rate of germination. Germination peaked for seed mass fractions comprising the greatest proportion of total seeds (8.0–9.9 mg) and was lowest for seeds with high or low mass. There was a weak trend of lower germinability for heavier seeds (>10.0 mg) compared with lighter seeds. Maternal source had a significant effect (P < 0.05) on total germination and germination rate. Findings from this study suggest that intrapopulation variation in Abutilon theophrasti seed mass and its influence on germinability of seeds may play a significant role in maintaining a variable germination pattern and persistent seed bank in this troublesome annual agricultural weed.