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Studies at a regional scale suggest that although maize (Zea maysL.) yield increased substantially, sensitivity to water deficit also increased concurrently with crop improvement. This study assessed changes in yield and yield stability after two decades of breeding by evaluating two cohorts of hybrids released by the AQUAmax program and comparing them to a non‐AQUAmax control. Studies were conducted in 2019 and 2020 seasons at four sites under well‐watered, moderate and severe stress conditions. Plant densities varied from 2.5 to 12.5 pl m−2. AQUAmax hybrids yielded more than non‐AQUAmax hybrids under water deficit conditions with the magnitude of the difference dependent on plant density. The sensitivity in yield across environments with a wide range of total crop evapotranspiration (350–800 mm) was lower for AQUAmax than non‐AQUAmax, so both yield and yield under stress conditions (yield stability), were enhanced for AQUAmax hybrids. The median differences between observed yields and the 80% quantile yield–evapotranspiration front were 379 for AQUAmax and 427 g m−2for non‐AQUAmax hybrids. We conclude that deliberate selection of hybrids for yield performance under water deficit underpinned the sustained improvement in yield stability after two decades of drought breeding. Future research should focus on understanding the root causes for the suboptimal utilization of drought tolerant maize for the diversity of environments at a regional scale. Yield improvement for drought is critical to enable a circular bioeconomy.Maize susceptibility to drought at regional scale is increasing with crop improvement.Genotype × management technology (G×M‐tech) is not the root cause of the higher instability.Socioeconomic factors and policy may underpin suboptimal use of G×M‐tech at regional scale.

Since 1980, 150 North Carolina State University (NCSU) maize (Zea maysL.) inbreds have been developed and released on the basis of superior performance for topcross yield and other traits of agronomic importance. During this time, there has been great emphasis placed on breeding with exotic germplasm, with 86 NCSU inbreds having at least 50% exotic parentage and 40 of those having all‐tropical parentage. Maize germplasm released by NCSU represents a potentially useful resource for increasing maize diversity and performance in the United States. The objectives of this study were to characterize the genetic relationships among inbreds released from this unique breeding program and to compare them genetically with inbreds from other public and private breeding programs. The NCSU maize inbreds can be classified into five germplasm pools: Lancaster, Temperate‐adapted all tropical (TAAT), Lancaster × Tropical, Stiff Stalk, and Southern non‐Stiff Stalk; detailed analysis of pedigree records and molecular marker genotypes reveals additional substructure within each of these pools. There is general agreement among the four cluster analyses performed, three using single nucleotide polymorphism (SNP) data and one using pedigree‐derived coefficients of coancestry. We introduce a novel application of Procrustes analysis to identify disagreements between pedigree and marker similarities. The NCSU maize breeding germplasm includes diverse genetic backgrounds, as evidenced by the number of unique alleles compared with publically available inbreds from both public and off‐protection, private‐sector sources.

We compared yield, genetic gain, and morphology for two sets of maize (Zea maysL.) hybrids using yield test plots grown in China at different planting densities. One set comprised 29 Chinese maize hybrids that were individually widely grown in China during 1964 through 2001. A second set comprised U.S. hybrids that were used either during the 1960s or during the 2000s. The U.S. hybrids had higher yields for both 1960s and 2000s comparisons. United States hybrids showed highest genetic gain (81 kg ha−1) at the highest planting density (67,550 plants ha−1) whereas the highest rate of gain for Chinese hybrids was 62 kg ha−1at the medium planting density (52,500 plants ha−1). Unlike the Chinese hybrids, U.S. hybrids showed significant interaction with planting density. Chronologically, all hybrids showed morphological changes for many characteristics, often at different rates, and occasionally in different directions. Pedigree and molecular marker data showed U.S. and Chinese hybrids to be very different germplasm with decades‐old U.S. germplasm contributing even to recently developed and widely used Chinese hybrids. Chinese maize agricultural production can rapidly and significantly benefit from adopting breeding and agronomic strategies that allow for improved yield under higher planting densities.

The objectives of this study were to (i) measure genetic gain using a set of maize (Zea maysL.) single‐cross hybrids that were widely used in Chinese maize production from 1964 to 2001, (ii) determine if there were changes in morphological characteristics, and (iii) examine the germplasm backgrounds of these hybrids. Yield trials were conducted for 3 yr, using a split‐plot design. Each hybrid was planted at three different densities in four locations, two locations each representing summer and spring corn areas. Mean rates of genetic gain were 52 kg ha−1yr−1when measured at the spring locations, 69 kg ha−1yr−1when measured at the summer locations, and 60 kg ha−1yr−1when measured across all locations. There was no significant effect of planting density on genetic gain. Genetic gain has been largely contributed by increased yield per plant and this strategy was reflected in changes in ear and plant morphology. Analyses of pedigree backgrounds showed continuing dependence on U.S. germplasm backgrounds, notably C103, Oh43, Mo17, and Iowa Stiff Stalk Synthetic (BSSS).

Maize inbred lines with expired Plant Variety Protection Act (PVPA) certificates are publicly available and potentially represent a new germplasm resource for many public and private breeding programs. However, accurate pedigree and genetic background information for ex‐PVPA maize inbreds is necessary if they are to be effectively utilized in breeding efforts. We have used single nucleotide polymorphism (SNP) markers to evaluate the relationships and population structure among 92 ex‐PVPA inbred lines in relation to 17 well‐known public inbreds. Based on unweighted pair group method with arithmetic mean clustering, principal components analysis, and model‐based clustering, we identified six primary genetic clusters represented by the prominent inbred lines B73, Mo17, PH207, A632, Oh43, and B37. We also determined the genetic background of ex‐PVPA inbreds with conflicting, ambiguous, or undisclosed pedigrees. We assessed genetic diversity across subsets of ex‐PVPA lines and concluded that the ex‐PVPA lines are no more diverse than the public set evaluated here. Additionally, all alleles present in the ex‐PVPA inbreds, for the 614 SNPs included in this study, are also found in public temperate maize germplasm.

Gray leaf spot (GLS) (caused Cercospora zeae‐maydisTheon & Daniels) is a fungal disease of the maize (Zea maysL.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type‐of‐gene action for GLS resistance in segregating families of three single‐cross populations of maize using restriction fragment length polymorphisms (RFLPs). We also attempted to determine the consistency of QTL over environments and populations. Population 1 (POP1) consisted of 139 F2:3families evaluated in three environments. Population 2 (POP2) consisted 193 F2:3families and Population 3 (POP3) had 144 F2:3families; POP2 and POP3 were considered as replicate populations evaluated in separate environments. Families were rated for GLS on a plot basis by a scale of 1 (susceptible) to 9 (resistant), and ratings were taken at 5‐ to 18‐d intervals in each environment. The QTL were identified on the basis of marker associations with GLS means over all ratings taken in an environment, as well as a GLS mean over environments for POP1 and over POP2 and POP3 for the replicate populations. Based on single‐factor ANOVA, detectable individual markers accounted for 4 to 26% of the phenotypic variation. The QTL associated with GLS were inconsistent over environments, but the cause of these differences could not be determined. One region on chromosome 2 was associated with GLS resistance in POP1, POP2, and POP3. Additive gene action was displayed for nearly all markers associated with resistance.

Soybean [Glycine max(L.) Merr.] cultivars with increased levels of palmitic or stearic acid in the seed oil could reduce the need for chemical modifications during processing for some vegetable oil products. Mutants with altered levels of the fatty acids were developed by artificial mutagenesis with ethyl methane sulfonate (EMS). Four of the mutants had 128 to 182 g kg−1palmitic acid compared with 90 to 100 g kg−1in their parents, and four mutants had 132 to 301 g kg−1stearic acid compared with 33 to 51 g kg−1in their parents. The objective of this study was to determine the inheritance of palmitic or stearic acid in the seed oil of the eight mutants. Reciprocal crosses were made between each mutant and the cultivar Coles, among three of the palmitic mutants, and between the high‐stearic acid line A6 and the four stearic mutants. Fatty acid analysis of the parents and F1, F2, and F3generations indicated that the allele controlling low palmitic and low stearic acid in Coles exhibited partial dominance to the alleles in PA1, PA2, PA3, ST1, ST2, ST3, and ST4 and no dominance to the allele in PA4. The crosses between A6 and the stearic mutants indicated that the alleles controlling high stearic acid in ST1, ST3, and ST4 occurred at the same locus as the fasaallele in A6 and that the allele in ST2 may occur at a different locus. Significant maternal and cytoplasmic effects on palmitic and stearic acid content were not confirmed in any of the mutants.

The linolenic acid content in soybean [Glycine max(L.) Merr.] seed oil generally is determined by gas chromatography (GC). A more rapid method of comparing the linolenic acid content of soybean seed samples would be useful for screening a large number of lines in a soybean breeding program. The objective of this study was to determine if the 2‐thiobarbituric acid (TBA) reaction could be used as a rapid method for determining the relative differences in linolenic acid content of soybean seed samples. Sixty‐eight random F2plants from each of two populations were used to compare TBA scores with linolenic acid content as measured by GC. The correlations between TBA score and linolenic acid percentages were 0.71 for Cross 1 and 0.60 for Cross 2. The results indicated that the TBA test cannot be used as a substitute for GC analysis in evaluating soybean samples. However, the TBA test may be a useful method to rapidly eliminate genotypes with excessively high linolenic acid before GC analysis.