This paper reports on the first advanced backcross-QTL (quantitative trait locus) project which utilizes spring barley as a model. A BC(2)F(2) population was derived from the initial cross Apex ( Hordeum vulgare ssp. vulgare, hereafter abbreviated with Hv) x ISR101-23 ( H. v. ssp. spontaneum, hereafter abbreviated with Hsp). Altogether 136 BC(2)F(2) individuals were genotyped with 45 SSR (simple sequence repeat) markers. Subsequently, field data for 136 BC(2)F(2) families were collected for 13 quantitative traits measured in a maximum of six environments. QTLs were detected by means of a two-factorial ANOVA with a significance level of P < 0.01 for a marker main effect and a marker x environment (M x E) interaction, respectively. Among 585 marker x trait combinations tested, 86 putative QTLs were identified. At 64 putative QTLs, the marker main effect and at 27 putative QTLs, the M x E interaction were significant. In five cases, both effects were significant. Among the putative QTLs, 29 (34%) favorable effects were identified from the exotic parent. At these marker loci the homozygous Hsp genotype was associated with an improvement of the trait compared to the homozygous Hv genotype. In one case, the Hsp allele was associated with a yield increase of 7.7% averaged across the six environments tested. A yield QTL in the same chromosomal region was already reported in earlier barley QTL studies.

This paper reports on the first comparative advanced backcross quantitative trait locus (AB-QTL) study in barley. The BC(2)F(2) population Hx101 was generated from crossing var. Harry [H; Hordeum vulgare ssp. vulgare ( Hv)] with ISR101-23 [101; H. v. ssp. spontaneum ( Hsp)]. The results of the AB-QTL analysis for 13 quantitative traits are presented and, subsequently, compared with the AB-QTL study of the barley cross Apex x ISR101-23 (Ax101; Pillen et al., Theor Appl Genet 107:340-352). Both AB populations share the exotic Hsp donor accession ISR101-23. In Hx101, 108 putative QTLs (17%) were identified among the 650 markerxtrait combinations tested. Altogether 52 (48 %) favorable effects were identified from the exotic parent. At these marker loci, the homozygous Hsp genotype was associated with an improvement in the trait compared to the homozygous Hv genotype. The percentage of QTLs detected in Hx101 was comparable to that in Ax101 (17% vs. 15%), however more favorable exotic QTL alleles were located in Hx101 than in Ax101 (48% vs. 34%). In Hx101, the Hsp QTL allele at EBmac0679([4H]) was associated with a yield increase of 5.9% averaged across the six environments tested. A comparison of putative QTLs between Hx101 and Ax101 was based on 26 shared SSR markers. In total, 26% of the putative QTLs could be detected simultaneously in both AB populations. This finding indicates that only a portion of the QTL effects of the donor allele can be transferred from one elite recipient to the next.

Promising genome regions for improving cold tolerance of sorghum were identified on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Chlorophyll fluorescence had no major effect on growth rates at low temperatures. Developing fast growing sorghum seedlings is an important breeding goal for temperate climates since low springtime temperatures are resulting in a prolonged juvenile development. The adaptation of sorghum to tropical and subtropical highlands gives hint for certain genetic variation. The goals of the present study were to detect marker-trait associations for leaf and dry matter growth rate and for chlorophyll fluorescence and content (SPAD) in relation to temperature. A diversity set comprising 194 genotypes was tested in eight controlled environments with temperatures ranging from 9.4 to 20.8 °C. Significant marker-trait associations (p < 0.05) were identified for each individual temperature regime and on the parameters of regression analyses describing the responses of growth or chlorophyll related traits to temperatures. The diversity set was fingerprinted with 171 diversity array technology (DArT) and 31 simple-sequence repeat (SSR) markers. SSRs were used to analyze the population structure while association studies were performed on DArT markers. Promising marker-trait associations for growth rates in relation to temperature were detected on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Many promising loci were also significantly associated to the results obtained in individual low-temperature environments. Marker-trait associations for chlorophyll content and fluorescence did occasionally co-locate to those for growth during juvenile development but there was no evidence supporting our hypothesis that seedling growth at low temperatures is largely influenced by SPAD or fluorescence.

Among the major limitations for cultivating biomass sorghum in temperate regions is low temperature in spring that results in low and non-uniform emergence. The adaptation of sorghum to tropical and subtropical highlands gives hint of genetic variation in cold tolerance during emergence. The objective of the present study was to detect marker-trait associations for parameters describing the emergence process under different temperature regimes. A diversity set comprising 194 genotypes was tested in nine controlled environments with temperatures ranging from 9.4 to 19.9 °C. The genotypes were fingerprinted with 171 DArT markers. A piecewise linear regression model carried out on cumulative emergence was used to estimate genotype mean performance across environments and to carry out stability analysis on the parameters of the regression model. Base temperature (T (b)) and thermal time required for emergence (E (TS)) were determined based on median time to emergence data. Identified QTL positions were compared to marker-trait associations for final emergence percentages under low (FEP(cold)) and normal (FEP(normal)) temperatures. QTL for mean final emergence percentage (FEP), FEP(cold) and FEP(normal,) T (b) and E (TS) were detected on SBI-01. Other QTL-rich regions were located on SBI-03, SBI-04, SBI-06, SBI-08, and SBI-09. Marker-trait associations for T (b) and E (TS) co-localized to QTL for the across environment stability of FEP and the median time to emergence or emergence rate, respectively. We conclude that genome regions on six chromosomes highly influencing cold tolerance during emergence are promising for regional association studies and for the development of stable markers for marker-assisted selection.

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