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CONSERVATION TILLAGE HANDBOOK SERIES
New Disease Resistant Varieties on the Horizon
Development and selection of soft white winter wheat varieties that are disease resistant and are adapted to the higher surface residue conditions of conservation tillage is a part of the STEEP research program. One of the STEEP researchers involved in this effort is Robert Allan, USDA-ARS geneticist at Pullman, WA. Allan's research involves developing winter wheat varieties that are resistant to diseases that prevent early seeding. Another research area is the selection of varieties and development of genetically unfixed lines that are adapted to conservation tillage.
The benefits of early seeding of winter wheat are primarily two-fold: first, a higher yield potential with overwintering of larger, more-vigorous plants, and second, decreased soil erosion due to increased soil cover during the critical fall and winter months, Some progress is being made in developing lines resistant to diseases associated with early seeding. Two of the more important diseases accentuated by early seeding in the Palouse and surrounding region are strawbreaker foot rot (Pseudocercosporella) and Cephalosporium stripe. After 4 years of testing (1981-84) Allan has identified several experimental lines that have good resistance to strawbreaker foot rot. Table 1 summarizes the yields of 7 promising lines and 3 established varieties where no fungicide was applied. Experimental lines yielded 95 to 113 bushels/acre compared to 62 to 72 for Nugaines, Daws and Stephens. Table 2 shows yields of the same lines and varieties where Benlate fungicide was applied for foot rot control. The natural resistance to foot rot is illustrated in Table 3 which shows the percent yield loss which occurred without Benlate protection (from Tables 1 and 2). The resistant experimental lines had less than 5 percent yield loss compared to 15 to 41 percent for Stephens, Daws and Nugaines. Since the incidence of foot rot is reduced with higher surface residue levels, more resistant varieties will provide good disease control potential under conservation tillage systems.
The low yields of Stephens in 1983 and 1984 were due in part to Cephalosporium stripe infections. To help eliminate this disease factor from the foot rot research, Allan planted the 1985 winter wheat trial after peas in a 3-year winter wheat-spring barley-spring pea rotation, instead of the 2-year wheat-pea rotation.
Several experimental lines show good combined resistance to both Cephalosporium stripe and strawbreaker root rot, as well as stripe rust, leaf rust and stem rust. Table 4 shows the resistance ratings of several promising lines and established varieties. Four of the lines have been placed in the 1985 regional trials. One or two of the lines were to be released as new varieties by the fall of 1986.
Table 1. Yields of 7 strawbreaker foot rot resistant Lines and 3 varieties inoculated with foot rot fungus: no fungicide applied (Allan, USDA-ARS, Pullman).
Table 2. Yields of 7 strawbreaker foot rot resistant lines and 3 varieties inoculated with foot rot fungus: Benlate fungicide applied (Allan, USDA-ARS, Pullman).
Table 3. Percent yield loss from strawbreaker foot rot between benlate protected and no fungicide treatment with 7 foot rot resistant lines and 3 varieties (Allan, USDA-ARS, Pullman).
One approach that Allan and other STEEP researchers are using to develop varieties adapted to conservation tillage is to grow genetically unfixed populations under higher residue tillage systems. Wheat populations capable of a small amount of outcrossing can adjust to the new environmental conditions. Research results from 1981 through 1984 identified shifts in plant traits such as percent stand, plant height, tiller number, maturity date and yield. The next step in Allan's research is to characterize these plant populations for the distribution of individual plant traits responsive to higher residue conditions. This information should help researchers to develop models of wheat plant types suited to no-till and reduced tillage systems.
An evaluation of 11 different mixtures of Daws, Lewjain, Stephens and Nugaines is being made by Allan to see if there is any yield advantage of mixtures over single varieties under different tillage systems. In 2-year rotations, winter wheat followed spring barley at Pullman in 1983 and 1984, and spring wheat at Colton in 1983. A John Deere HZ drill, modified to place fertilizer 2 inches below the seed, was used under conventional tillage, mini mum tillage and no-till systems.
Although the blends yielded equal to or slightly greater than the varieties alone in about 90 percent of all the comparisons, yield advantage was not significant. Also, the blends did not appear to have any special fitness to a particular tillage system. The study was to be conducted at Pullman one last time with the 1985 winter wheat trial which was planted in a 3-year spring barley-spring pea winter wheat rotation.
Table 4. Disease resistance ratings1 of 10 promising Lines with combined disease resistance and 5 varieties, 1984 (Allan, USDA-ARS, Pullman).
us: Hans Kok, (208)885-5971
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