Barley is the most sensitive among the cereals to aluminium (Al) stress and breeding for more tolerant cultivars is a priority. To enhance selection efficiency for Al tolerance in barley, PCR-based AFLP and microsatellite markers linked to a locus conferring tolerance to aluminium were identified. The study used F(2) progeny derived from a single cross between Yambla (moderately tolerant of Al) and WB229 (tolerant of Al) and developed hydroponic pulse-recovery screening methods to assess tolerance of phenotypes based on root growth. The segregation ratios of tolerant and sensitive genotypes and F(3) progeny testing suggest that a single major gene controlled Al tolerance ( Alt). In order to determine the chromosomal location of the Alt gene, we used the AFLP technique coupled with bulk segregant analysis. We evaluated tolerant and sensitive bulks using 30 combinations of EcoRI/ MseI primers, and 12 of these permitted differentiation of the sensitive and tolerant bulks. More than 1,000 amplified fragments were obtained, and 98 polymorphic bands were scored. AFLP analysis of wheat-barley chromosome addition lines indicated that the Alt gene was located on barley chromosome 4H. Four chromosome 4H-specific microsatellite markers (Bmac310, Bmag353, HVM68 and HVMCABG) were tightly linked to Alt. The large allelic variation detected with microsatellite marker Bmag353 allowed us to implement this marker for routine marker-assisted selection for Al tolerance, and 396 plants could be screened on a single gel.

Factors contributing to variation in heading date in spring barley were examined in several studies commencing with a survey of developmental variation in a large collection of genotypes and concluding with the molecular genetic analysis of 7 doubled haploid populations. Genotypes varied considerably in their specific responses to photoperiod and vernalisation, and in the duration of a pre-inductive (or juvenile) phase defined in this paper as a 'basic vegetative period'. The latter includes differential genotype responses to ambient temperature and their interaction with photoperiod. Combinations of these largely independent environmental variables account for variation in heading date associated with differences in growing season conditions, particularly geographic region, sowing dates, and cultivar adaptation. Under extended and natural (short) photoperiods, in both summer and winter field plantings, conventional genetic analysis was characterised by simple Mendelian segregation combined with considerable transgressive segregation within distinct early and late flowering subpopulations. Equivalent transgressive segregation characterised molecular genetic analysis that identified 16 quantitative trait loci (QTLs) with contributions ranging from >50% of the variation recorded to <10%. These were dominated by 2 QTLs located on chromosome 2, one of which on 2HS was associated with response to extended photoperiod and the other, located near the centromere, with variation in the duration of the basic vegetative period. As only one population segregated for response to vernalisation, all analyses were restricted to parents and progeny homozygous for no response. Three other QTLs on 1HL, 3HL, and 5HL were primarily associated with vernalised parents and progeny characterised by prostrate seedling growth habits, which questions any assumption of a pleiotrophic association between genes for vernalisation and growth habit.The potential for exploiting markers for selection is considered to be limited by the considerable transgressive segregation observed in lines homozygous for parental alleles, and the limited understanding of the causes of variation in the phenotypic expression of the QTLs identified. Such markers would be useful in the selection of backcrossed progeny and in developing materials for investigating fundamental mechanisms contributing to developmental variation.

Abstract. Quantitative trait loci (QTLs) associated with resistance to net blotch and their chromosomal locations were determined from analyses of doubled haploid progeny of Alexis/Sloop, Arapiles/Franklin, Sloop/Halcyon, and recombinant inbred lines of Sloop-sib/Alexis. Five QTLs on chromosomes 2H, 3H, and 4H were found to be associated with seedling resistance to the net form of net blotch. In Arapiles/Franklin and Alexis/Sloop populations, 4 significant QTLs explaining 9-17% of the variation in net blotch resistance were detected on 2H and 3H. A major locus, QRpts4L accounting for 64% of the variation in infection type, was detected on 4H in the Sloop/Halcyon population. In Sloop/Halcyon, 2 microsatellite markers, EBmac0906 and GMS089, and AFLP marker P13/M50-108, co-segregated and detected maximum variability for net blotch resistance as revealed by bootstrap analysis. EBmac0906 and Bmac0181 were validated in F 2 progeny of an Ant29/Halcyon population and reliably predicted phenotypes of 93% of lines resistant and susceptible to net blotch. These markers may be used within breeding programs to select alleles favourable for net blotch resistance derived from Halcyon.A R 0 3 0 2 6 M a p p i n g n e t b l o t c h r e s i s t a n c e H . R a m a n e t a l .

A method for the analysis of early generation variety trials is described. The method is an extension of the analysis proposed by Gleeson and Cull is for replicated trials and uses the residual maximum likelihood estimation method of Patterson and Thompson. Best linear unbiased predictors of test line effects are derived. A small simulation experiment is conducted to assessthe reliability of the method. A wheat trial with a weed density covariate and missing values is analysed to illustrate the method.

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