Allelopathic Potential of Various Plant Species on Downy Brome: Implications for Weed Control in Wheat Production

Allelopathy, the ability of plants to inhibit germination of other plants, is an untapped resource for weed control in crops that could revolutionize organic crop production. The main objective of the study was to evaluate allelopathic potential of various plant species on downy brome (Bromus tectorum L.), a major pest of wheat (Triticum aestivum L.). To screen for potential allelopathy, plants were grown to flowering stage in a greenhouse, separated into shoots and roots, dried, and ground. Five percent aqueous extracts (w/v) were prepared by extracting 5 g of dried, ground plant samples with 100 mL of deionized water. Downy brome seeds were germinated on extractamended sand. Extracts from most plant species tested inhibited downy brome and wheat seed germination. Extracts from broadleaf plants were more inhibitory than extracts from cereal plants. In most plant species, shoot extracts were more inhibitory to growth of the root and shoot of downy brome than root extracts. Meadowfoam seed meal (Limnanthes alba Hartw.), yard-long bean [Vigna sesquipedalis (L.) Fruw.], blue spruce (Picea pungens pungens Engelm), and pine (Pinus spp.) extracts, which completely inhibited the germination of downy brome seed, have the potential for use in the control of downy brome in wheat-based cropping systems. Meadowfoam seed meal extract inhibited wheat germination by 77% and root and shoot growth by 97 and 96%, respectively. Radishes reduced wheat germination by 75 to 100%, root growth by 54 to 80% and shoot growth by 45 to 81%. Plants evaluated in this study have the potential to be used for biologically based weed control methods in organic cropping systems. A the ability of plants to inhibit germination of other plants, is so far, an untapped resource for weed control in crops. Yet, it shows considerable promise in both conventional and organic agriculture. The U.S. Pacific Northwest (PNW) agriculture has traditionally focused on conventional farming systems using synthesized pesticides. In conventional agriculture, weeds can and do develop resistance to pesticides being used to control them, making pesticides less and less effective (Putwain, 1982; Alizadeh et al., 1998; Tranel and Wright, 2002; De Prado and Franco, 2004). Concerns of ecological, environmental, and health problems possibly associated with synthesized pesticides has increased the interest in organic agriculture (Dayan et al., 1999; Walz, 1999). Under organic farming, no synthesized herbicides or fertilizers are tolerated (Wallace, 2001). Weeds are, however, controlled by tillage, a practice that is labor intensive. Furthermore, tillage to control weeds depletes organic matter and exposes the soil to wind and water erosion (Rasmussen and Parton, 1994). The development of biosynthesized herbicides to control weeds can permit the development of no-till (directseed) organic wheat production. Many plant species have allelopathic effects on other plant species (Rice, 1974, 1984; Putman and Tang, 1986; Rice, 1995; Cutler and Cutler, 1999; Marcı́as et al., 2004; Vasilakoglou et al., 2005; Dhima et al., 2006). Information on the chemical nature and mode of action of allelochemicals is expanding (Rice, 1984; Cutler and Cutler, 1999; Dayan et al., 2000; Dayan, 2002; Inderjit and Duke, 2003; Marcı́as et al., 2004; Singh et al., 2005). Allelopathy may be used in several ways in weed control. Just as crop plants are bred for disease resistance, crop plants can be bred to be allelopathic to weeds common to specific regions (Rice, 1984, 1995; Jensen et al., 2001;Wu et al., 2000, 2003; Olofsdotter et al., 2002; He et al., 2004). The most practical and immediate way to use allelopathy in weed control is to use allelopathic cover crops in rotations, or apply residues of allelopathic weeds or crops as mulches (Rice, 1984; CaamalMaldonaldo et al., 2001; Dhima et al., 2006). An equally promising way to use allelopathy in weed control is using extracts of allelopathic plants as herbicides (Dayan, 2002; Singh et al., 2005). Because biosynthesized herbicides are easily biodegradable, they are believed to be much safer than synthesized herbicides (Rice, 1984, 1995; Dayan et al., 1999; Duke et al., 2000). The use of biosynthesized herbicides in the control of weeds common to the PNW should be evaluated. The main objective of this research was to screen various plants for allelopathic effects on downy brome, a major weed in wheat cropping systems of the PNW. This information is a prerequisite for the development of biological weed control methods that can allow for no-till organic crop production in the PNW. Materials and Methods The screening of different plant species for allelopathic potential on downy brome and on wheat injury was conducted at the Columbia Basin Agricultural Research Center (CBARC) near Pendleton (45.78 N lat, 118.68 W long, with elevation of 438 m), OR. To screen for allelopathic potential, a rapid bioassay technique (Gliessman, 2000) was used. Extract Preparations Forty-two plant species were screened for allelopathic potential on downy brome and wheat. Plants, except meadowfoam seed meal, Austrian pine (Pinus spp.), and blue spruce, were grown in pots in a greenhouse. At the beginning of flowering, the plants were harvested, separated into leaves and roots, and air-dried for |96 h. Needles of blue spruce and pine Oregon State Univ., Columbia Basin Agric. Research Center, P.O. Box 370, Pendleton, OR 97801. Received 19 Apr. 2006. *Corresponding author ([email protected]). Published in Agron. J. 99:127–132 (2007). Notes & Unique Phenomena doi:10.2134/agronj2006.0122 a American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: CBARC, Columbia Basin Agricultural Research Center; PNW, U.S. Pacific Northwest. R e p ro d u c e d fr o m A g ro n o m y J o u rn a l. P u b lis h e d b y A m e ri c a n S o c ie ty o f A g ro n o m y . A ll c o p y ri g h ts re s e rv e d .