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Two trials were conducted at the Mexican National Institute of Agricultural Research (INIA) experimental station, Yaqui Valley, Sonora, Mexico, to determine the genetic yield potential of bread wheat (Triticum aestivum L.) cultivars released in northwest Mexico over the period from 1950 to 1982, with emphasis on progress since 1970. Nonlimiting levels of fertility and moisture, a preventative pest and disease program, and netting to prevent lodging were used. Grain yield, yield components, and rates of phytomass production and grain filling were determined. Yield data on selected genotypes grown in 4 yrs of the International Spring Wheat Yield Nursery (ISWYN) at the same station were also examined. The grain yield potential of cultivars, successively released since 1950, has risen at an estimated (from a regression slope) average of 59 kg/ha/yr of release, or about 1.1%/yr. Although yield potential may have plateaued in the early 1970s, cultivars released since 1979, i.e., modern genotypes (e.g., ‘Ciano 79’, ‘Genaro 81’, ‘Glennson 81’, and ‘Seri 82’) have improved yield potential at an estimated rate similar to that prior to 1970. Improvements in grain yield were associated with increases in grain number per unit area (r = 0.74, P < 0.01), which has risen by about 34% in modern genotypes compared to pre‐1970 cultivars, and grain number per spike (r = 0.51, P<0.05). The 1000‐grain weight, was reduced slightly in the modern high grain number cultivars (r = −0.76, P<0.01). Harvest indices for modern genotypes were lower than those of the landmark cultivar ‘Yecora 70’, but the modern genotypes had, on average, 16% greater phytomass than pre‐1970 cultivars. However, only 43% of the variation in grain yield was attributable to phytomass. The improvements in yield potential are mainly the result of empirical selection for grain yield. Indications were that rates of grain filling and phytomass production in modern genotypes were similar to those in Yecora 70. The higher grain yield and phytomass in modern genotypes compared to Yecora 70 was probably due to the formation and survival of a larger grain sink (more grains/m2) and greater C assimilation during a longer preanthesis phase.

Northern, Diabrotica barberi Smith & Lawrence, and western, D. virgifera virgifera LeConte, corn rootworms (Coleoptera: Chrysomelidae) are major economic pests of corn, Zea mays L., in North America. Corn hybrids expressing Bacillus thuringiensis Berliner (Bt) toxins are commonly used by growers to manage these pests. Several cases of field-evolved resistance to insecticidal proteins expressed by Bt corn hybrids have been documented in many corn-producing areas of North America, but only for D. v. virgifera. In 2016, beetles of both species were collected from five eastern North Dakota corn fields and reared in a growth chamber. In 2017, larvae reared from those populations were subjected to single-plant bioassays to screen for potential resistance to Cry3Bb1, Cry34/35Ab1, and pyramided Cry3Bb1 + Cry34/35Ab1 Bt toxins. Our results provide the first documented report of field-evolved resistance in D. barberi to corn hybrids expressing Cry3Bb1 (Arthur problem population) and Cry34/35Ab1 (Arthur and Page problem populations, and the Ransom and Sargent populations) proteins in North America. Resistance to Cry3Bb1 was also observed in the Ransom population of D. v. virgifera. Increased larval survival on the pyramided Cry3Bb1 + Cry34/35Ab1 hybrid was observed in both species. No cross-resistance was evident between Cry3Bb1 and Cry34/35Ab1 in any of the D. barberi populations tested. Our experiments identified field-evolved resistance to Bt toxins in some North Dakota populations of D. barberi and D. v. virgifera. Thus, more effective control tools and improved resistance management strategies are needed to prolong the durability of this technology for managing these important pests.

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Willyerd, K. T., Li, C., Madden, L. V., Bradley, C. A., Bergstrom, G. C., Sweets, L. E., McMullen, M., Ransom, J. K., Grybauskas, A., Osborne, L., Wegulo, S. N., Hershman, D. E., Wise, K., Bockus, W. W., Groth, D., Dill-Macky, R., Milus, E., Esker, P. D., Waxman, K. D., Adee, E. A., Ebelhar, S. E., Young, B. G., and Paul, P. A. 2012 [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( C ) 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 C 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.