Proso millet (Panicum miliaceumL.) is both a crop and a weed in many parts of the world. The weedy biotypes exhibit a wide range of seed colours, but the strains with the most persistent seeds are distinguished by darker seeds. This paper compares the seed biology of a range of biotypes from Canada and demonstrates that darker seeds have heavier seed coats, imbibe and germinate more slowly, and suffer less imbibition damage (measured as electrolyte leakage). It is concluded that all these attributes contribute to the increased persistence in the soil of the dark-seeded weedy biotypes. Imbibition damage is widely implicated in poor emergence and low vigour of crop seeds, but has not previously been considered in the context of weed seed persistence.

Seedlings of proso millet usually were killed by discing and rototilling in field experiments but populations were not reduced by mowing or by compressing under tractor wheels. In greenhouse experiments, recently emerged seedlings had the greatest mortality after raking and desiccation treatments but were less affected by shoot and/or root damage. In contrast, seedlings treated several weeks after emergence suffered greater mortality from shoot damage and less from desiccation. Two weedy proso millet biotypes, black and Crown, were used in the field experiments, and up to six biotypes were used in the greenhouse. Few significant differences among biotypes were found. Young (emerging) seedlings were extremely resilient to all treatments.

Proso millet has become a major weed in North America during the past 20 yr. Experiments were conducted to assess the role of the soil seedbank in proso millet's success as a weed. Proso millet has at least eight distinct biotypes, all weeds, which exhibit a wide range of seedbank behavior. At one extreme, weed biotypes resembling crop varieties form transient seedbanks where all viable seed germinate or die before newly ripened seed enter the seedbank. In contrast, the black- and dark-red-seeded biotypes form persistent seedbanks that last several years in the soil. These latter seedbanks differ from those previously described in that there is always a fraction of the seedbank that is not capable of immediate germination. The black-seeded biotype of proso millet can establish a persistent seedbank quickly and that makes the weed very difficult to eradicate.

this article has been changed to the CC BY 4.0 license. The PDF and HTML versions of the article have been modified accordingly.Abstract: Proso millet, Panicum miliaceum L. (Poaceae), has been a crop in Asia and Europe for 10 000 years and for over 300 years in Canada, where it is grown for grain, rescue crops, birdseed, forage, and recently for swath grazing. Crop-like biotypes have escaped from cultivation throughout Canada, but these infestations were generally temporary. Probably the first persistent, weedy biotype in Canada (Quebec) has large, dormant, dark red seeds. Its eradication has been attempted for many years. In the 1970s, a worse problem, a black-seeded biotype with many weedy attributes, including shattering as seeds ripen and strongly dormant seeds distasteful to many birds, spread across southern Ontario and became labelled as noxious. Concurrently, it was described as the worst weed in the US Corn Belt. In the 1980s, Canadian studies revealed infestations of other weedy biotypes, differing in seed colour and other attributes. Panicum miliaceum is an extremely variable species world-wide. Since the late 1990s, weedy proso millet has declined dramatically after the adoption of newer herbicides, particularly glyphosate. This development may lead to increases in cultivated proso millet, especially where climate change favours short-season crops grown under drier conditions. Key words: weed biology, proso millet, Panicum miliaceum L., weed/crop, intraspecific variation, global distribution and history.Résumé : On cultive le millet, Panicum miliaceum L. (poacées), depuis 10 000 ans en Asie et en Europe et depuis plus de trois siècles au Canada pour ses graines, comme provende de secours, pour nourrir les oiseaux, pour son fourrage et, plus récemment, pour la paissance en andain. Des biotypes domestiqués sont redevenus sauvages un peu partout au Canada, mais les infestations restent le plus souvent temporaires. Le premier biotype envahissant persistant du Canada a probablement été observé au Québec. Il se caractérise par de grosses semences rouges dormantes. On s'est efforcé de l'éradiquer pendant de nombreuses années. Dans les années 1970, un biotype à graines noires, possédant de nombreuses caractéristiques d'une mauvaise herbe (notamment l'égrenage prématuré quand les semences parviennent à maturité et des graines à dormance prolongée que peu d'oiseaux aiment), a soulevé un problème plus épineux en se répandant dans le sud de l'Ontario. Ce biotype a été qualifié de nuisible avant de devenir la pire adventice dans la ceinture du maïs des États-Unis. Dans les années 1980, des études canadiennes ont révélé l'existence de peuplements d'autres biotypes envahissants, aux semences de couleur différente et présentant d'autres caractères. Panicum miliaceum est une espèce extrêmement variable dans le monde. Depuis la fin des années 1990, les variétés envahissantes ont diminué de façon draconienne avec l'apparition de nouveaux herbicides, particulièrement le glyphosate. Ce développement pourrait déboucher su...

KANE, M., and CAVERS, P. B. 1992. Patterns of seed weight distribution and germination with time in a weedy biotype of proso millet (Panicum miliaceum). Can. J . Bot. 70: 562-567. Three plants from each of 10 populations of the black biotype of proso millet (Panicum miliaceum) were grown in a common garden in London, Ontario. Seeds were collected from individual plants as they ripened. Each seed was identified as to location on the plant and weighed separately. Mean seed weight decreased over the growing season, both on individual inflorescences and on entire plants. Despite this trend, seeds at the upper end of the weight range were produced throughout the season. The decline in the mean resulted from an increasing proportion of smaller seeds. There was also increased variability in seed weight later in the growing season. In subsequent germination tests there was no discernable relationship between total percent viability and date of seed ripening. Total percent viability was above 70% for each sampling date.Key words: seed weight, positional effects, proso millet, germination, seasonal variation. KANE, M., et CAVERS, P. B. 1992. Patterns of seed weight distribution and germination with time in a weedy biotype of proso millet (Panicum miliaceum). Can. J . Bot. 70 : 562-567. Les auteurs ont cultivC trois plants de chacune des dix populations du biotype noir du millet proso (Panicum miliaceurn)dans un mEmejardin, B London en Ontario. Les graines ont Ct C rCcoltCes de plantes individuelles au moment de la maturitC. Chaque graine a Ct C identifiCe quant B sa localisation sur le plant, et pesCe sCparCment. Le poids moyen des graines diminue au cours de la saison de croissance, aussi bien au niveau des inflorescences individuelles que des plantes entikres. En dCpit de cette tendance, des graines se situant B la limite supCrieure de la distribution des poids, apparaisent tout au cours de la saison. La chiite de la moyenne provient d'une proportion accrue de graines plus petites. On retrouve Cgalement une variabilit6 plus grande dans le poids des graines, plus tard au cours de la saison de croissance. Les essais subsCquents conduits sur la germination ne montrent pas de relation claire entre le pourcentage total de viabilitC et la date de maturation de la graine.Le pourcentage total de viabilitt est supCrieur B 70% pour chacune des dates d'Cchantillonage.