Soybean improvement via plant breeding has been critical for the success of the crop. The objective of this study was to quantify genetic change in yield and other traits that occurred during the past 80 yr of North American soybean breeding in Maturity Groups (MGs) II, III, and IV. Historic sets of 60 MG II, 59 MG III, and 49 MG IV soybean cultivars, released from 1923 to 2008, were evaluated in field trials conducted in 17 U.S. states and one Canadian province during 2010 to 2011. Averaged over 27 MG II and MG IV and 26 MG III site-years of data, the estimated rates of yield improvement during the 80 yr were 23 kg ha -1 yr -1 for MGs II and III, and 20 kg ha -1 yr -1 for MG IV cultivars. However, a two-segment linear regression model provided a better fit to the data and indicated that the average current rate of genetic yield gain across MGs is 29 kg ha -1 yr -1 . Modern cultivars yielded more than old cultivars in all environments, but particularly in high-yielding environments. New cultivars in the historic sets used in this study are shorter in height, mature later, lodge less, and have seeds with less protein and greater oil concentration. Given that on-farm soybean yields in the United States are also increasing at a rate of 29 kg ha -1 yr -1 , it can be inferred that continual release of greater-yielding cultivars has been a substantive driver of the U.S. onfarm realized yield increases.
Genetic resistance to brown stem rot (BSR) of soybean [Glycine max (L.) Merr.
Brown stem rot (BSR) of soybean [Glycine max (L.) Merr.] caused by Cadophora gregata (Allington & Chamb.) T.C. Harr. & McNew can be controlled effectively with genetic host resistance. Three BSR resistance genes Rbs1, Rbs2, and Rbs3, have been identified and mapped to a large region on chromosome 16. Marker-assisted selection (MAS) will be more efficient and gene cloning will be facilitated with a narrowed genomic interval containing an Rbs gene. The objective of this study was to fine map the positions of Rbs genes from five sources. Mapping populations were developed by crossing the resistant sources 'Bell', PI 84946-2, PI 437833, PI 437970, L84-5873, and PI 86150 with either the susceptible cultivar Colfax or Century 84. Plants identified as having a recombination event near Rbs genes were selected and individually harvested to create recombinant lines. Progeny from recombinant lines were tested in a C. gregata root-dip assay and evaluated for foliar and stem BSR symptom development. Overall, 4878 plants were screened for recombination, and progeny from 52 recombinant plants were evaluated with simple-sequence repeat (SSR) genetic markers and assessed for symptom development. Brown stem rot resistance was mapped to intervals ranging from 0.34 to 0.04
Soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) of soybean [Glycine max (L.) Merr.] causes extensive yield loss, and host resistance has been an effective strategy to minimize this loss. However, shifts in SCN population virulence compatibility have resulted from the extensive use of PI 88788 as a source of resistance in the northern United States. The Northern Regional Soybean Cyst Nematode Tests offer a vast amount of yield testing, combined with resistance screening of entries and the characterization of the SCN infection of test fields. The objectives of this study were to use regional test results (i) to quantify the impact of resistance as the initial field SCN egg counts increase, (ii) to explore effects of maturity group (MG) on resistance, and (iii) to gain insights into how the ability of SCN to infect germplasm with resistance from PI 88788 affects yield. Yield tests across 11 yr were combined into a single dataset with over 1247 test–environment combinations. Analysis of these data showed that the yield advantage of SCN resistant entries increased as initial egg counts increased, and a larger advantage was found in early MGs (00–II) than in later MGs (III–IV). A yield advantage was documented at environments with an initial egg count as low as 100 eggs 100 cm−3 soil. At the levels of SCN infection on PI 88788 found in infested locations, breeding lines with resistance from PI 88788 yielded more than susceptible entries. Analysis of this dataset offers a unique view of the impact SCN resistance provides to soybean.
Core Ideas Genetic differences in dollar spot susceptibility among bentgrasses are consistent across the Central U.S.A. at putting green and fairway mowing heights and with or without fungicides. ‘Kingpin’ or ‘Memorial’ creeping bentgrass had the least dollar spot injury and ‘Crystal BlueLinks’, ‘Declaration’, ‘L‐93’, and ‘SR1150’ were consistently in the same statistical grouping as these cultivars. Golf course superintendents should use National Turfgrass Evaluation Program or similar data from as near their location as possible to assess seasonal cultivar performance, but relative dollar spot susceptibility should be applicable across broader regions if nearby data are not available.
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