History and current trends in the use of allelopathy for weed management

Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization and root exudation. Allelochemical structures and modes of action are diverse, and may offer potential for development of future herbicides. In the past, allelopathy was described by the Romans as a process resulting in the "sickening" of the soil; in particular, chickpea (Cicer arietinum) was described as problematic when successively cropped with other species. Other early plant scientists, such as De Candolle in the 1800s, first described the ability of plant roots to produce toxic exudates. More recently, research has focused on development of weed management strategies using allelopathic crop residues, mechanism of allelochemical action, and gene regulation of allelochemical production. This paper briefly describes a variety of weed and crop species that establishes some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are more highly weed suppressive in managed settings. A new challenge that exists for plant scientists is to generate additional information on allelochemical mechanisms of release, selectivity and persistence, mode of action, and genetic regulation. Armed with this specific information, we can further protect plant biodiversity and enhance weed management strategies in a variety of ecosystems.