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Highlights • Partial diallel analysis is promising for production of second-generation ethanol. • Treatment × environment interaction was observed for all the evaluated traits. • Genetic variability was detected between the lines A and R of biomass sorghum. • The pyramiding of favorable alleles, aim at the development of superior hybrids. Abstract Mutant genotypes of biomass sorghum for low lignin - bmr (brown midrib) and sensitive to photoperiod are interesting for the production of second-generation ethanol. This research aimed to estimate the combining ability between lines A and R of biomass sorghum, both carrying the bmr-6 allele, for bioenergy potential. Three male-sterile lines (A) and ten fertility restorative lines (R) were used, generating 30 hybrids bmr and sensitive to photoperiod. The 30 hybrids, their parents, and six controls were evaluated in a triple lattice design (7 × 7), in two experimental areas of Embrapa Maize and Sorghum, in Sete Lagoas and Nova Porteirinha (Minas Gerais). These lines were crossed in a partial diallel design, based on the Griffing IV model (1956) adapted for partial diallel by Miranda Filho and Geraldi (1984). The evaluated traits were: days to flowering (DTF, days after sowing), plant height (PH, m), fresh biomass yield (FBY, ton.ha−1), dry matter (DM, %), and dry matter yield (DMY, t. ha−1). In addition, the FAI-BLUP selection Index was used to assist the selection of hybrids that simultaneously meet favorable traits. Results revealed that treatments x environment interaction had a significant effect (p < 0.01) for all traits. Moreover, genetic variability was detected between lines A and R, which can be explored by the pyramiding of their favorable alleles, aiming at developing superior hybrids for the production of second-generation bioethanol. [ABSTRACT FROM AUTHOR]

Key message: A multiparental random mating population used in sorghum breeding is amenable for the detection of QTLs related to tropical soil adaptation, fine mapping of underlying genes and genomic selection approaches. Tropical soils where low phosphorus (P) and aluminum (Al) toxicity limit sorghum [Sorghum bicolor (L.) Moench] production are widespread in the developing world. We report on BRP13R, a multiparental random mating population (MP-RMP), which is commonly used in sorghum recurrent selection targeting tropical soil adaptation. Recombination dissipated much of BRP13R's likely original population structure and average linkage disequilibrium (LD) persisted up to 2.5 Mb, establishing BRP13R as a middle ground between biparental populations and sorghum association panels. Genome-wide association mapping (GWAS) identified conserved QTL from previous studies, such as for root morphology and grain yield under low-P, and indicated the importance of dominance in the genetic architecture of grain yield. By overlapping consensus QTL regions, we mapped two candidate P efficiency genes to a ~ 5 Mb region on chromosomes 6 (ALMT) and 9 (PHO2). Remarkably, we find that only 200 progeny genotyped with ~ 45,000 markers in BRP13R can lead to GWAS-based positional cloning of naturally rare, subpopulation-specific alleles, such as for SbMATE-conditioned Al tolerance. Genomic selection was found to be useful in such MP-RMP, particularly if markers in LD with major genes are fitted as fixed effects into GBLUP models accommodating dominance. Shifts in allele frequencies in progeny contrasting for grain yield indicated that intermediate to minor-effect genes on P efficiency, such as SbPSTOL1 genes, can be employed in pre-breeding via allele mining in the base population. Therefore, MP-RMPs such as BRP13R emerge as multipurpose resources for efficient gene discovery and deployment for breeding sorghum cultivars adapted to tropical soils. [ABSTRACT FROM AUTHOR]

Sorghum [Sorghum bicolor (L.) Moench] biomass hybrids with high productivity and enhanced levels of lignin are seen as a promising alternative of feedstock for direct burning in ovens designed for cogeneration of electricity. The objective of this study was to estimate the genetic combing capacity of biomass sorghum lines and conduct multivariable selection of photosensitive biomass sorghum hybrids for use in cogeneration. Thirty‐six photosensitive hybrids, the control BRS716, and 12 parental lines were evaluated in a seven‐by‐seven triple lattice design at two locations, and 12 characters were evaluated. There was superiority of additive effects on the genetic control of all the characteristics studied in both environments, less for female lines in the diallelic analysis of F1 hybrids. The inclusion of parents in the estimates of combining capacities indicated predominance of dominance effects involved in the genetic control of the traits analyzed. The results demonstrate the action of epistasis of the dwarf genes present in the female lines for the biomass parameter and the false interpretation when these lines are included in the diallelic analysis. With the use of the index based on factor analysis and genotype–ideotype distance (FAI‐BLUP index), four factors were established, which separated the characteristics of production and quality, as well as the two environments, resulting from the high hybrid × environment interaction. With the index, five hybrids with higher potential for burning (H5‐5, H2‐1, H1‐1, H1‐5, and H5‐1) were selected. However, no hybrids obtained gains for the characteristics of production and quality, simultaneously, which indicates the need for genetic improvement of the parents used in the program. [ABSTRACT FROM AUTHOR]

Sweet sorghum [Sorghum bicolor (L.) Moench] is a type of cultivated sorghum characterized by the accumulation of high levels of sugar in the stems and high biomass accumulation, making this crop an important feedstock for bioenergy production. Sweet sorghum breeding programs that focus on bioenergy have two main goals: to improve quantity and quality of sugars in the juicy stem and to increase fresh biomass productivity. Genetic diversity studies are very important for the success of a breeding program, especially in the early stages, where understanding the genetic relationship between accessions is essential to identify superior parents for the development of improved breeding lines. The objectives of this study were: to perform phenotypic and molecular characterization of 100 sweet sorghum accessions from the germplasm bank of the Embrapa Maize and Sorghum breeding program; to examine the relationship between the phenotypic and the molecular diversity matrices; and to infer about the population structure in the sweet sorghum accessions. Morphological and agro-industrial traits related to sugar and biomass production were used for phenotypic characterization, and single nucleotide polymorphisms (SNPs) were used for molecular diversity analysis. Both phenotypic and molecular characterizations revealed the existence of considerable genetic diversity among the 100 sweet sorghum accessions. The correlation between the phenotypic and the molecular diversity matrices was low (0.35), which is in agreement with the inconsistencies observed between the clusters formed by the phenotypic and the molecular diversity analyses. Furthermore, the clusters obtained by the molecular diversity analysis were more consistent with the genealogy and the historic background of the sweet sorghum accessions than the clusters obtained through the phenotypic diversity analysis. The low correlation observed between the molecular and the phenotypic diversity matrices highlights the complementarity between the molecular and the phenotypic characterization to assist a breeding program. [ABSTRACT FROM AUTHOR]

• FA models allow G × E studies even for highly unbalanced historical datasets. • G × E studies are valuable tools to optimize resources in sorghum breeding programs. • FA loadings can be successfully used to investigate the main factors affecting G × E. Biomass sorghum has emerged as an alternative crop for biofuel and bioelectricity production. Fresh biomass yield (FBY) is a quantitative trait highly correlated with the calorific power of energy sorghum cultivars, but also highly affected by the environment. The main goal of this study was to investigate the genotype-by-environment interaction (G × E) and the stability of sorghum hybrids evaluated for FBY across different locations and years, using factor analytic (FA) mixed models and environmental covariates. Pairwise genetic correlations between environments ranged from -0.21 to 0.99, indicating the existence of null to high G × E. The FA analysis unveiled that solely three factors explained more than 79% of the genetic variance, and that more than 60% of the environments were clustered in the first factor. Moderate correlations were found between some environmental covariates and the loadings of FA models for environments, suggesting the possible factors to explain the high G × E between environments clustered in a given factor. For example: precipitation, minimum temperature and speed wind were correlated to the environmental loadings of factor 1; minimum temperature, solar radiation and altitude to factor 2; and crop growth cycle to factor 3. The latent regression analysis was used to identify hybrids more responsive to a set of environments, as well as hybrids specifically adapted to a given environment. Finally, FA models can be successfully used to identify the main environmental factors affecting G × E, such as minimum temperature, precipitation, solar radiation, crop growth cycle and altitude. [ABSTRACT FROM AUTHOR]

• A-lines from the sorghum breeding program of Embrapa have the potential for use as parents in the development of superior sweet sorghum hybrids. • The development of a tester with genotype " drydry " and " Ma1Ma1 " is important to develop superior hybrids involving the A, B and R scheme. There is a growing demand for the development of alternative fuels from renewable sources, thus sweet sorghum an autogamous species has potential for bioethanol production. Traditionally recommended cultivars were varieties, however, with the development of cytoplasmic male sterile sweet sorghum lines, sweet sorghum hybrids have become economically viable. The sweet sorghum breeding program of the Brazilian Agricultural Research Corporation (Embrapa Milho e Sorgo) has been developing sweet sorghum hybrids for bioethanol production according to the scheme of A, B and R-lines are used, where A-lines are used as females in the production of hybrid seeds. A and B-lines are isogenic, which differ only its cytoplasm source, sterile and normal, respectively, and fertility restorers R-lines. Thus the objective of this work was to evaluate the genetic potential of new male-sterile sweet sorghum A-lines using testcross hybrids developed with two sweet sorghum R-line as testers for agroindustry characteristics for bioethanol production. Forty testcross hybrids were developed using 20 experimental A-lines and two testers sweet sorghum R-lines. Experiments were conducted at experimental stations in Sete Lagoas-MG and Nova Porteirinha-MG, to evaluate 20 A-lines, two 2 R-lines, the resulting 40 testcross hybrids, and two controls. The 64 treatments were evaluated for days to flowering, fresh biomass yield and total soluble solids (Brix). The data obtained were analyzed using the ASReml package, for the estimation of variance components and the prediction of genetic and non-genetic values via REML/BLUP. Two models were adopted, called Multi-Tester and Single-Tester. The genotypic values of the A-lines when crossed with tester T2, were positive for nine A-lines (12, 17, 6, 20, 18, 16, 19, 11 and 3) with emphasis on A-lines 12, 17 and 6, which were the highest values, respectively, the same tester for the trait FLOW, ten A-lines were positive values (3, 16, 17, 4, 12, 15, 5, 6, 8, 20) with emphasis on 3, 16 and 17. The genotypic values for TSS (Brix) trait of the A-lines when crossed with tester T1 were positive for A-lines (19, 18, 20, 16, 1, 5, and 6) with emphasis on lines 19, 18, 20, and 16, with the highest values, respectively. Only two A-lines showed positive genotypic values for three traits, A-line 16 and 20. These results indicate the need for continuing simultaneous improvement of A-lines for FLOW, FBY, and TSS. A-lines from the sorghum breeding program of Embrapa Milho e Sorgo have the potential for use as parents in the development of superior sweet sorghum hybrids for bioethanol production. The A-lines 6 and 20 have positive genotypic values for three traits, this A-lines has a potential for producing hybrids dedicated to bioethanol production. The T1-L tester was more efficient in discriminating the genetic values between the A lines for TSS, while the T2-L tester for FBY and FLOW. The development of a tester with genotype " drydry " and " Ma 1 Ma 1 " is important in order to develop superior hybrids to produce bioethanol involving the A, B and R scheme. [ABSTRACT FROM AUTHOR]

Background: Phosphorus (P) fixation on aluminum (Al) and iron (Fe) oxides in soil clays restricts P availability for crops cultivated on highly weathered tropical soils, which are common in developing countries. Hence, P deficiency becomes a major obstacle for global food security. We used multi-trait quantitative trait loci (QTL) mapping to study the genetic architecture of P efficiency and to explore the importance of root traits on sorghum grain yield on a tropical low-P soil. Results: P acquisition efficiency was the most important component of P efficiency, and both traits were highly correlated with grain yield under low P availability. Root surface area was positively associated with grain yield. The guinea parent, SC283, contributed 58% of all favorable alleles detected by single-trait mapping. Multi-trait mapping detected 14 grain yield and/or root morphology QTLs. Tightly linked or pleiotropic QTL underlying the surface area of fine roots (1–2 mm in diameter) and grain yield were detected at positions 1–7 megabase pairs (Mb) and 71 Mb on chromosome 3, respectively, and a root diameter/grain yield QTL was detected at 7 Mb on chromosome 7. All these QTLs were near sorghum homologs of the rice serine/threonine kinase, OsPSTOL1. The SbPSTOL1 genes on chromosome 3, Sb03g006765 at 7 Mb and Sb03g031690 at 60 Mb were more highly expressed in SC283, which donated the favorable alleles at all QTLs found nearby SbPSTOL1 genes. The Al tolerance gene, SbMATE, may also influence a grain yield QTL on chromosome 3. Another PSTOL1-like gene, Sb07g02840, appears to enhance grain yield via small increases in root diameter. Co-localization analyses suggested a role for other genes, such as a sorghum homolog of the Arabidopsis ubiquitin-conjugating E2 enzyme, phosphate 2 (PHO2), on grain yield advantage conferred by the elite parent, BR007 allele. Conclusions: Genetic determinants conferring higher root surface area and slight increases in fine root diameter may favor P uptake, thereby enhancing grain yield under low-P availability in the soil. Molecular markers for SbPSTOL1 genes and for QTL increasing grain yield by non-root morphology-based mechanisms hold promise in breeding strategies aimed at developing sorghum cultivars adapted to low-P soils. [ABSTRACT FROM AUTHOR]