Author
 |
Kennedy, Ann |
|
STUBBS, TAMI - WASHINGTON STATE UNIV |
|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/1/2006 Publication Date: 1/1/2007 Citation: Kennedy, A.C., Stubbs, T.L. Management effects on the incidence of jointed goatgrass inhibitory rhizobacteria. Biological Control 40:213-221. 2007. Interpretive Summary: Effective weed management is one of the critical factors limiting optimum crop yield. Alternative weed management strategies are needed as the use of synthetic chemical herbicides for weed control becomes more restricted. Biological weed control arises from the fact that biotic factors significantly influence the distribution, abundance, and competitive abilities of plant species. Biological control offers an alternative means of suppressing weed growth and establishment. We evaluated bacterial communities that were isolated from winter wheat, downy brome, and jointed goatgrass roots to understand the role of soil microbes in jointed goatgrass growth. The bacteria were screened in laboratory bioassays, and in growth chamber and field studies for their effect on jointed goatgrass and winter wheat root growth. In laboratory studies, 50% of the 2450 naturally-occurring soil bacteria were inhibitory to jointed goatgrass seedling growth. Less than 1 percent of the isolates inhibited jointed goatgrass but not winter wheat root or shoot growth in soil. Conventional tillage systems maintained higher populations of inhibitory bacteria than no-tillage systems. The number of bacteria inhibitory to jointed goatgrass was greater in the spring sampling and at the highest level of nitrogen fertilization. Crop rotation had little effect on the incidence of jointed goatgrass inhibitory bacteria. Different jointed goatgrass accessions from various sites in the western U.S. were diverse in their response to the inhibitory bacteria. Microbes can have a profound affect on plant growth, and thus have a place in modern weed management strategies. Ecologically based approaches, such as those using microbial communities in the soils, which take into consideration the weed, the pathogen, and the environment are important in weed management strategies. Technical Abstract: Jointed goatgrass (Aegilops cylindrica Host., JGG), a winter annual grass weed, is a major threat to small grain production in the United States. It infests an estimated 2 million hectares in the U.S. and causes annual losses of $145 million in crop yield and quality. Selective herbicides for its control are available only for certain herbicide-resistant crop varieties and alternative management practices are tillage, burning, or rotation to less profitable crops. We evaluated bacteria that were isolated from winter wheat (Triticum aestivum L., WW), downy brome (Bromus tectorum L., DB), and JGG roots to determine their potential as biological control agents for JGG. The bacteria were screened in laboratory bioassays, and in growth chamber and field studies for their effect on JGG and WW root growth. In laboratory studies, 50% of the 2450 naturally-occurring soil bacteria were inhibitory to JGG seedling growth. Only 3% inhibited JGG and not the crop in the in vitro bioassay. In soil-grown plants, only 0.3% of the isolates inhibited JGG root or shoot growth and not WW. Conventional tillage systems maintained higher populations of inhibitory bacteria than no-tillage systems. The number of bacteria inhibitory to JGG was greater in the spring sampling and at the highest level of nitrogen fertilization. Crop rotation had little effect on the incidence of jointed goatgrass inhibitory bacteria. Different JGG accessions from various sites in the western U.S. were diverse in their response to the inhibitory bacteria. Weed-suppressive bacteria have the potential to be used as biological control agents for JGG. |
