The effect of straw on the establishment and growth of winter cereals

Tell me again what it is that you do

My job at Pullman, Washington, starting in 1965, was to control the root diseases of wheat and barley, focusing first on fusarium root and crown rot, then including take-all and pythium and rhizoctonia root rots. In the absence of viable alternatives, the agronomic approaches used were implemented through design of cereal-based cropping systems. Starting in the late 1970s, the mission focused further on cereal-intensive direct-seed (no-till) cropping systems. A team effort demonstrated the role of indigenous antibiotic-producing fluorescent pseudomonads in the widespread decline of take-all in response to monoculture wheat (or barley-wheat sequences). Today, the suppression of take-all by these beneficial rhizobacteria is the centerpiece of an integrated system that augments take-all decline while limiting pythium and rhizoctonia root rots and fusarium root and crown rot in direct-seed systems. In such systems, "crop rotation" takes the form of different sequences of winter and spring wheat, barley and triticale varieties, and market classes, all susceptible to all four root diseases.

The in vitro effect of allelopathy and various fungi on marsh reed grass (Calamagrostis canadensis)

Allelopathy and endophytic fungi were evaluated as factors affecting the biological control of marsh reed grass, Calamagrostis canadensis (Michx.) Beauv., a weed of boreal reforestation areas. Leachate from marsh reed grass straw inhibited root growth into liquid and agar media and increased foliar necrosis. Most seedlings harboring endophytic species of Fusarium and Chaetomium were healthy in agar controls, but all such seedlings were diseased when grown in agar with straw leachate. The straw leachate and various fungi had distinct impacts on the virulence of Colletotrichum sp., a potential biocontrol agent for marsh reed grass. In comparisons of control and allelopathic media, Colletotrichum sp. stimulated the overall vigor of reed grass while reducing vigor in the allelopathic medium. Individual isolates of fungi in the genera Epicoccum, Drechslera, and Fusarium were uniformly antagonistic to Colletotrichum, whereas antagonism in individual isolates of Chaetomium, Alternaria, and Stemphylium depended on the presence or absence of allelopathy. Another Fusarium isolate increased the virulence of Colletotrichum sp. in both media, as did two applications of Colletotrichum sp. Allelopathic compounds, Fusarium sp., and Colletotrichum sp. are potential components of a strategy for biological control of marsh reed grass. Key words: weed, biological control, bioherbicide, mycoherbicide.

The microbial upgrading of straw for agricultural use

Straw, particularly when left on the soil surface, can retard cereal establishment and reduce crop yield and therefore, in Britain, it is often burned. Treatment with a microbial consortium attempts to eliminate the negative value of straw while using it as a fertilizer, soil conditioner and biocontrol agent. Cellulolytic fungi, preferably Trichoderma species which are parasitic on some plant pathogenic fungi, convert the cellulosic components of straw to sugars. These sugars become available for growth of an anaerobic N 2 -fixing bacterium, Clostridium butyricum . Part of the N fixed in microbial biomass is recycled to the fungus to stimulate further cellulolysis and ultimately a product rich in N and with no phytotoxicity results. A third organism, Enterobacter cloacae , that produces copious extracellular polysaccharide is co-inoculated as an active member of a microbial community. The O 2 consumption by E. cloacae and its associated gum aids respiratory protection of the anaerobe to form a consortium that is relatively insensitive to O 2 . The gum has additional value as a soil conditioner.