The 2NS Translocation from Aegilops ventricosa Confers Resistance to the Triticum Pathotype of Magnaporthe oryzae.

Wheat blast is a serious disease caused by the fungus Magnaporthe oryzae (Triticum pathotype) (MoT). The objective of this study was to determine the effect of the 2NS translocation from Aegilops ventricosa (Zhuk.) Chennav on wheat head and leaf blast resistance. Disease phenotyping experiments were conducted in growth chamber, greenhouse, and field environments. Among 418 cultivars of wheat (Triticum aestivum L.), those with 2NS had 50.4 to 72.3% less head blast than those without 2NS when inoculated with an older MoT isolate under growth chamber conditions. When inoculated with recently collected isolates, cultivars with 2NS had 64.0 to 80.5% less head blast. Under greenhouse conditions when lines were inoculated with an older MoT isolate, those with 2NS had a significant head blast reduction. With newer isolates, not all lines with 2NS showed a significant reduction in head blast, suggesting that the genetic background and/or environment may influence the expression of any resistance conferred by 2NS. However, when near-isogenic lines (NILs) with and without 2NS were planted in the field, there was strong evidence that 2NS conferred resistance to head blast. Results from foliar inoculations suggest that the resistance to head infection that is imparted by the 2NS translocation does not confer resistance to foliar disease. In conclusion, the 2NS translocation was associated with significant reductions in head blast in both spring and winter wheat.

Efficacy and Stability of Integrating Fungicide and Cultivar Resistance to Manage Fusarium Head Blight and Deoxynivalenol in Wheat.

Integration of host resistance and prothioconazole + tebuconazole fungicide application at anthesis to manage Fusarium head blight (FHB) and deoxynivalenol (DON) in wheat was evaluated using data from over 40 trials in 12 U.S. states. Means of FHB index (index) and DON from up to six resistance class-fungicide management combinations per trial (susceptible treated [S_TR] and untreated [S_UT]; moderately susceptible treated [MS_TR] and untreated [MS_UT]; moderately resistant treated [MR_TR] and untreated [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( ) due to the management combinations relative to S_UT. All combinations led to a significant reduction in index and DON (P < 0.001). MR_TR was the most effective combination, with a of 76% for index and 71% for DON, followed by MS_TR (71 and 58%, respectively), MR_UT (54 and 51%, respectively), S_TR (53 and 39%, respectively), and MS_UT (43 and 30%, respectively). Calculations based on the principle of treatment independence showed that the combination of fungicide application and resistance was additive in terms of percent control for index and DON. Management combinations were ranked based on percent control relative to S_UT within each trial, and nonparametric analyses were performed to determine management combination stability across environments (trials) using the Kendall coefficient of concordance (W). There was a significant concordance of management combinations for both index and DON (P < 0.001), indicating a nonrandom ranking across environments and relatively low variability in the within-environment ranking of management combinations. MR_TR had the highest mean rank (best control relative to S_UT) and was one of the most stable management combinations across environments, with low rank stability variance (0.99 for index and 0.67 for DON). MS_UT had the lowest mean rank (poorest control) but was also one of the most stable management combinations. Based on Piepho's nonparametric rank-based variance homogeneity U test, there was an interaction of management combination and environment for index (P = 0.011) but not for DON (P = 0.147), indicating that the rank ordering for index depended somewhat on environment. In conclusion, although the magnitude of percent control will likely vary among environments, integrating a single tebuconazole + prothioconazole application at anthesis with cultivar resistance will be a more effective and stable management practice for both index and DON than either approach used alone.

Competition, facilitation, and niche differentiation in two foliar pathogens.

We studied competition between the obligate biotroph Puccinia triticina (designated here as Puccinia) and the facultative saprophyte Pyrenophora tritici-repentis (designated here as Pyrenophora) in older and younger leaves in a set of three host genotypes selected to be resistant to Puccinia only, Pyrenophora only, or neither. Age-related resistance is important for both of these pathogens. The facultative saprophyte Pyrenophora was generally a stronger competitor than the biotrophic Puccinia, even experiencing facilitation from the presence of Puccinia when Pyrenophora had the advantage of earlier inoculation. Both pathogen species produced the most spores when they were introduced before the competing species and more spores when introduced simultaneously compared to after the competitor. The pre-interactive niche of Puccinia was larger than the post-interactive niche and sporulation by Puccinia was substantially reduced in environments in which Pyrenophora had high sporulation rates. The pre-interactive niche of Pyrenophora was similar to the post-interactive niche and Pyrenophora had proportionally lower reductions in sporulation due to interspecific competition in the pre-interactive niche.

Reactions of Perennial Grain Accessions to Four Major Cereal Pathogens of the Great Plains.

Methods of disease management used in annual grain crops, especially cultural practices designed to disrupt the disease cycle of a particular pathogen, will not necessarily be applicable to perennial grain crops. Resistance to multiple pathogens, therefore, will clearly be important in disease management. The objective of this research was to evaluate disease resistance in 10 perennial grain accessions (one to two accessions of each: perennial wheat (Thinopyrum sp. × Triticum aestivum), intermediate wheatgrass (Thinopyrum intermedium), perennial rye (Secale montanum), hexaploid triticale (Triticum turgidum × S. montanum), octoploid triticale (Triticum aestivum × S. montanum), tetraploid perennial rye (Secale cereale × S. montanum), and tall wheat-grass (Thinopyrum ponticum)) to tan spot (caused by Pyrenophora tritici-repentis), take-all (caused by Gaeumannomyces graminis var. tritici), wheat streak mosaic, and barley yellow dwarf, four important diseases of the Great Plains. Several of the grasses were resistant to tan spot, barley yellow dwarf, and wheat streak mosaic. Indeed, the wild grasses and perennial donors T. intermedium (including BFPMC1), T. ponticum, and S. montanum, in addition to Permontra, a tetraploid perennial rye, were highly resistant to all three diseases. Additionally, the remaining grasses tested were also more resistant to tan spot than the susceptible wheat control. However, none of the 10 grass accessions appeared highly resistant to take-all, and substantial losses in biomass were observed, although such effects may be moderated under field conditions due to the potential for take-all decline in perennial plantings.

Evidence for a Pythium sp. as a Chronic Yield Reducer in a Continuous Grain Sorghum Field.

Pythium spp. have been reported to reduce stands and cause stalk rot of grain sorghum. Evidence is presented that it also can cause a serious seed and root rot in the field under a continuous grain sorghum production system. Experiments were conducted for 4 years in a field that had been cropped continuously to grain sorghum for at least 10 years. Effects of seed treatments with captan and metalaxyl on plant stands, early to mid-season plant vigor, and grain yields were evaluated. In five field experiments, seed treatment with metalaxyl (73 g a.i./100 kg) increased grain yields by an average of 24.0% compared with nontreated seed. In three out of four field experiments, seed treatment with metalaxyl increased grain yields by an average of 13.1% above seed treated with captan (73 g a.i./100 kg). The yield increases could not always be explained in terms of differences among treatments in plant stands or in visual estimates of the amount of top growth 26 to 72 days after sowing. Apparently, the Pythium sp. causes a chronic root and seed rot that has a significant negative effect on grain production without necessarily affecting stands or early to mid-season growth. P. ultimum var. ultimum was the fungus most commonly isolated from roots and seeds collected from the field. Tests for Koch's postulates conducted in a greenhouse verified it as the causal organism. In the greenhouse, treatment with metalaxyl protected seeds and roots from attack by P. ultimum var. ultimum for at least 28 days after planting.

Triazole Seed Treatments Suppress Spore Production by Puccinia recondita, Septoria tritici, and Stagonospora nodorum from Wheat Leaves.

Treatments of winter wheat seed with the systemic triazole fungicides triadimenol (31 g a.i./100 kg = Baytan 30F at 1.5 fl oz/cwt) and difenoconazole (24 g a.i./100 kg = Dividend 3FS at 1.0 fl. oz/cwt) were tested for effect on asexual sporulation by Puccinia recondita, Septoria tritici, and Stagonospora nodorum. Spore production was measured on seedlings grown in a growth chamber (24°C day/15°C night, 12-h photoperiod) and inoculated with the pathogens 3, 5, or 7 weeks after sowing. Spore production was converted to a percentage of the non-treated control and regressed against weeks after planting when plants were inoculated. Linear models fit data for both fungicides against all three pathogens. According to the models, difenoconazole suppressed sporulation levels of P. recondita and Septoria tritici to 10% of the levels on plants from non-treated seed for about 3 weeks after sowing. Spore production for all three fungi was suppressed to 25% of the non-treated level for at least 4.2 weeks and to 50% for at least 6.5 weeks. Similarly, triadimenol suppressed all three pathogens to 50% of the non-treated level for at least 3.2 weeks. The two fungicides showed similar effects against S. tritici; however, difenoconazole showed significantly greater suppression of sporulation by P. recondita and Stagonospora nodorum compared with triadimenol. Responses occurred even though large concentrations of spores were used to inoculate plants and environmental conditions were optimized for spore production. Reduced sporulation should help protect fall-planted wheat seedlings and may significantly delay epidemics in the following spring.

The impact of reduced tillage on soilborne plant pathogens.

Farmers increasingly leave crop residues on the soil surface rather than incorporating them into the soil. This practice helps reduce soil erosion, conserve energy, increase soil moisture, and increase crop yields. However, many soilborne plant pathogens survive in the previous year's crop residue, making diseases more problematic under reduced-tillage conditions. Reduced tillage can favor pathogens by such mechanisms as protecting the pathogen's refuge in the residue from microbial degradation, lowering soil temperature, increasing soil moisture, and leaving soil undisturbed. In order for reduced tillage to become more popular, additional controls are needed for pathogens. The four major control tactics (disease-control chemicals, biological control, host resistance, and cultural controls) can be used to limit damage from diseases. It is highly recommended, however, that crop rotation be coupled with reduced tillage. This practice controls many diseases and yet allows as much of the crop residue as possible to be retained on the soil surface.