Abstract
The 40 million hectare southern Australian winter cropping region suffers from widespread infestation by Lolium rigidum (commonly known as annual or rigid ryegrass), a Mediterranean species initially introduced as a pasture plant. Along with its high competitiveness within crops, rapid adaptability and widespread resistance to herbicides, the dormancy of its seeds means that L. rigidum is the primary weed in southern Australian agriculture. With the individuals within a L. rigidum population exhibiting varying levels of seed dormancy, germination can be staggered across the crop-growing season, making complete weed removal virtually impossible, and ensuring that the weed seed bank is constantly replenished. By understanding the processes involved in induction and release of dormancy in L. rigidum seeds, it may be possible to develop strategies to more effectively manage this pest without further stretching herbicide resources. This review examines L. rigidum seed dormancy and germination from a weed-management perspective and explains how the seed bank can be depleted by control strategies encompassing all stages in the lifecycle of a seed, from development to germination.
Highlights
The Australian wool industry was the country’s leading agricultural exporter in the mid- to late 19th century, had its last boom in 1950
This means that practical application of dark stratification as a means of stimulating germination and depleting the weed seed bank is likely to be challenging, it is useful for research into mechanisms of dormancy maintenance and release and may be relevant in situations where seeds previously buried in moist soil are brought to the surface by tillage
L. rigidum seeds is so often staggered due to a continuum of the dormancy levels and specific germination requirements within a population means that some plants will always escape management practices such as cultivation and herbicide application, and survive to replenish the seed bank once more
Summary
The Australian wool industry was the country’s leading agricultural exporter in the mid- to late 19th century, had its last boom in 1950. Sheep were fed on the native grass understorey of Eucalyptus woodland, but the extensive grazing led to dramatic changes in the native vegetation, and pasture grasses and legumes were introduced to improve the pasture. This was especially true in Western Australia, where the native plants were far less palatable than those in the east and so pastures became almost exclusively composed of Mediterranean annuals [1]. Once the land was dedicated to cropping instead of used for pasture, these species were transformed instantly from valuable sources of sheep nutrition to problematic weeds.
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