On the design of early generation variety trials with correlated data On the design of early generation variety trials with correlated data

The cotiipet(ti.ve abilities of a wide range of genotypes of wheat {Trilicwnaestivum L.) and durum wheat {Triticum durum Desf.) against Lolium rigidunt Gatud. (annual ryegrassj were examined lo determine the potential for breeders to select strongly competiti-ve varieties. Considerable potential within the wheat genonie to hreed varieties with greater competitive ability was demonstrated. In 1993. 250 genotypes from aroimd the world were screened and in 1994 st subset of 45 (mainly Australian) genotypes were further examined. A uniform deasity of L. rigidum reduced grain peld of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated with i. rigidum dry matter. Wheats varied in competitive ability with source, and durum wheats were less competiifive than T. aestivum. The old' standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight Fi hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass of L. rigidum by an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high deosity was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were taU with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discussed.

Resistance to pod shattering (shatter resistance) is a target trait for global rapeseed (canola, Brassica napus L.), improvement programs to minimise grain loss in the mature standing crop, and during windrowing and mechanical harvest. We describe the genetic basis of natural variation for shatter resistance in B. napus and show that several quantitative trait loci (QTL) control this trait. To identify loci underlying shatter resistance, we used a novel genotyping-by-sequencing approach DArT-Seq. QTL analysis detected a total of 12 significant QTL on chromosomes A03, A07, A09, C03, C04, C06, and C08; which jointly account for approximately 57% of the genotypic variation in shatter resistance. Through Genome-Wide Association Studies, we show that a large number of loci, including those that are involved in shattering in Arabidopsis, account for variation in shatter resistance in diverse B. napus germplasm. Our results indicate that genetic diversity for shatter resistance genes in B. napus is limited; many of the genes that might control this trait were not included during the natural creation of this species, or were not retained during the domestication and selection process. We speculate that valuable diversity for this trait was lost during the natural creation of B. napus. To improve shatter resistance, breeders will need to target the introduction of useful alleles especially from genotypes of other related species of Brassica, such as those that we have identified.

Blackleg, caused by Leptosphaeria maculans, is one of the most important diseases of oilseed and vegetable crucifiers worldwide. The present study describes (1) the construction of a genetic linkage map, comprising 255 markers, based upon simple sequence repeats (SSR), sequence-related amplified polymorphism, sequence tagged sites, and EST-SSRs and (2) the localization of qualitative (race-specific) and quantitative (race non-specific) trait loci controlling blackleg resistance in a doubled-haploid population derived from the Australian canola (Brassica napus L.) cultivars Skipton and Ag-Spectrum using the whole-genome average interval mapping approach. Marker regression analyses revealed that at least 14 genomic regions with LOD ≥ 2.0 were associated with qualitative and quantitative blackleg resistance, explaining 4.6-88.9 % of genotypic variation. A major qualitative locus, designated RlmSkipton (Rlm4), was mapped on chromosome A7, within 0.8 cM of the SSR marker Xbrms075. Alignment of the molecular markers underlying this QTL region with the genome sequence data of B. rapa L. suggests that RlmSkipton is located approximately 80 kb from the Xbrms075 locus. Molecular marker-RlmSkipton linkage was further validated in an F(2) population from Skipton/Ag-Spectrum. Our results show that SSR markers linked to consistent genomic regions are suitable for enrichment of favourable alleles for blackleg resistance in canola breeding programs.

We identified quantitative trait loci (QTL) underlying variation for flowering time in a doubled haploid (DH) population of vernalisation-responsive canola (Brassica napus L.) cultivars Skipton and Ag-Spectrum and aligned them with physical map positions of predicted flowering genes from the Brassica rapa genome. Significant genetic variation in flowering time and response to vernalisation were observed among the DH lines from Skipton/Ag-Spectrum. A molecular linkage map was generated comprising 674 simple sequence repeat, sequence-related amplified polymorphism, sequence characterised amplified region, Diversity Array Technology, and candidate gene based markers loci. QTL analysis indicated that flowering time is a complex trait and is controlled by at least 20 loci, localised on ten different chromosomes. These loci each accounted for between 2.4 and 28.6% of the total genotypic variation for first flowering and response to vernalisation. However, identification of consistent QTL was found to be dependant upon growing environments. We compared the locations of QTL with the physical positions of predicted flowering time genes located on the sequenced genome of B. rapa. Some QTL associated with flowering time on A02, A03, A07, and C06 may represent homologues of known flowering time genes in Arabidopsis; VERNALISATION INSENSITIVE 3, APETALA1, CAULIFLOWER, FLOWERING LOCUS C, FLOWERING LOCUS T, CURLY LEAF, SHORT VEGETATIVE PHASE, GA3 OXIDASE, and LEAFY. Identification of the chromosomal location and effect of the genes influencing flowering time may hasten the development of canola varieties having an optimal time for flowering in target environments such as for low rainfall areas, via marker-assisted selection.

Optimum flowering time is the key to maximize canola production in order to meet global demand of vegetable oil, biodiesel and canola-meal. We reveal extensive variation in flowering time across diverse genotypes of canola under f ield, glasshouse and controlled environmental conditions. We conduct a genome-wide association study and identify 69 single nucleotide polymorphism (SNP) markers associated with flowering time, which are repeatedly detected across experiments. Several associated SNPs occur in clusters across the canola genome; seven of them were detected within 20 Kb regions of a priori candidate genes; FLOWERING LOCUS T, FRUIT-FUL, FLOWERING LOCUS C, CONSTANS, FRIGIDA, PHYTOCHROME B and an additional five SNPs were localized within 14 Kb of a previously identified quantitative trait loci for flowering time. Expression analyses showed that among FLC paralogs, BnFLC.A2 accounts for~23% of natural variation in diverse accessions. Genome-wide association analysis for FLC expression levels mapped not only BnFLC. C2 but also other loci that contribute to variation in FLC expression. In addition to revealing the complex genetic architecture of flowering time variation, we demonstrate that the identified SNPs can be modelled to predict flowering time in diverse canola germplasm accurately and hence are suitable for genomic selection of adaptative traits in canola improvement programmes.

SummaiyThe competitive abilities of eight winter crops were compared against Lolium rigidum Gaud, (annual ryegrass), an important weed of southem Australia, as a potential strategy to suppress weeds and reduce dependence on herbicides. Two cultivais of each species were chosen to represent the range of competitive ability within each crop and grown in field experiments in 1992 and 1993. The order of decreasing competitive ability (with the ranges of percentage yield reduction from L. rigidum at 300 plants m"-^ in parenthesis) was as follows: oats {Avena saliva L.), 2-14%; cereal rye {Secale cereale L.), 14-20%; and triticale (X Triticosecale), 5-24%; followed by oilseed rape, (Brassica napus L.). 9-30%; spring wheat {Triticum aestivum L.), 22-40%; spring barley {Hordeum vulgarel..), 10-55%; and, lastly, field pea {Pisum sativum L.), 100%, and lupin (Lupinus angustifolius L.), 100%. Differences in competitive ability of cultivars within each species were identified, but competition was strongly influenced by seasonal conditions.'Competition for nutrients (N, P and K) and hght was demonstrated. L. rigidum dry matter and seed production were negatively correlated with grain yield of the weedy crops. More competitive crops offer the potential to suppress grass weeds while maintaining acceptable grain yields. Ways of improv-© 1995 European Weed Research Society ing the competitive abilities of grain legume crops are discussed. LoUum rigidum Gaud, (annual ryegrass) on yield of wheat.

Aluminium (Al) tolerance in barley is conditioned by the Alp locus on the long arm of chromosome 4H, which is associated with Al-activated release of citrate from roots. We developed a high-resolution map of the Alp locus using 132 doubled haploid (DH) lines from a cross between Dayton (Al-tolerant) and Zhepi 2 (Al-sensitive) and 2,070 F(2 )individuals from a cross between Dayton and Gairdner (Al-sensitive). The Al-activated efflux of citrate from the root apices of Al-tolerant Dayton was 10-fold greater than from the Al-sensitive parents Zhepi 2 and Gairdner. A suite of markers (ABG715, Bmag353, GBM1071, GWM165, HvMATE and HvGABP) exhibited complete linkage with the Alp locus in the DH population accounting 72% of the variation for Al tolerance evaluated as relative root elongation. These markers were used to map this genomic region in the Dayton/Gairdner population in more detail. Flanking markers HvGABP and ABG715 delineated the Alp locus to a 0.2 cM interval. Since the HvMATE marker was not polymorphic in the Dayton/Gairdner population we instead investigated the expression of the HvMATE gene. Relative expression of the HvMATE gene was 30-fold greater in Dayton than Gardiner. Furthermore, HvMATE expression in the F(2:3) families tested, including all the informative recombinant lines identified between HvGABP and ABG715 was significantly correlated with Al tolerance and Al-activated citrate efflux. These results identify HvMATE, a gene encoding a multidrug and toxic compound extrusion protein, as a candidate controlling Al tolerance in barley.