Morphogenetic responses of embryo culture of wheat related to environment culture conditions of the explant donor plant

Availability of immature embryos as explants to establish wheat (Triticum aestivum L.) by tissue culture can be limited by climatic factors and the lack of high quality embryos frequently hampers experimentation. This study evaluates the effects of rainfall, various temperature-based variables and sunshine duration on tissue culture response (TCR) traits including callus formation (CF), regenerating calli (RC), and number of plants per embryo (PPE) for 96 wheat genotypes of worldwide origin. The objectives of this study were to evaluate the significance of a particular climatic factor on TCR traits and to determine the period of wheat growth during which these factors were the most effective. The genotypes were grown in an experimental field during three seasons differing in meteorological conditions. The relationships between TCR traits and climatic factors within three time periods of wheat growth: 2, 6 and 10 weeks prior to embryo sampling were analysed by biplot analysis. The tissue culture traits were influenced at very different degrees by climatic factors: from 16.8% (RC) to 69.8% (CF). Donor plant environment with high temperatures and low rainfalls reduced (p lt 0.05) the tissue culture performance of wheat genotypes. Callus formation was most sensitive to the temperature based factors. The environmental conditions between flowering and the medium milk stage were the most important for CF, while RC and PPE were not particularly related to any period

Regions of the genome that affect agronomic performance in two-row barley

Quantitative trait locus (QTL) main effects and QTL by environment (QTL × E) interactions for seven agronomic traits (grain yield, days to heading, days to maturity, plant height, lodging severity, kernel weight, and test weight) were investigated in a two-row barley (Hordeum vulgare L.) cross, Harrington/TR306. A 127-point base map was constructed from markers (mostly RFLP) scored in 146 random double-haploid (DH) lines from the Harrington/TR306 cross. Field experiments involving the two parents and 145 random DH lines were grown in 1992 and/or 1993 at 17 locations in North America. Analysis of QTL was based on simple and composite interval mapping. Primary QTL were declared at positions where both methods gave evidence for QTL. The number of primary QTL ranged from three to six per trait, collectively explaining 34 to 52% of the genetic variance. None of these primary QTL showed major effects, but many showed effects that were consistent across environments. The addition of secondary QTL gave models that explained 39 to 80% of the genetic variance. The QTL were dispersed throughout the barley genome and some were detected in regions where QTL have been found in previous studies. Eight chromosome regions contained pleiotropic loci and/or linked clusters of loci that affected multiple traits. One region on chromosome 7 affected all traits except days to heading. This study was an intensive effort to evaluate QTL in a narrow-base population grown in a large set of environments. The results reveal the types and distributions of QTL effects manipulated by plant breeders and provide opportunities for future testing of marker-assisted selection

Biotype differences for resistance to Russian Wheat Aphid in barley

Russian wheat aphid [RWA; Diuraphis noxia (Mordvilko)] is a worldwide insect pest of barley (Hordeum vulgare L.), causing crop losses each year. Previously identified resistant barley lines do not show variable reactions to the eight United States RWA biotypes identified by wheat reactions. However, additional RWA isolates have been identified outside the United States. The objective of this research was to determine whether additional RWA biotypes that impact resistance in barley exist and whether resistance to these biotypes is present in the resistant barley germplasm and cultivars that have been developed by the USDA-ARS. A total of 166 barley lines were rated for chlorosis and leaf rolling in response to infestation with RWA United States’ biotype 1 and to individual isolates from Hungary, Chile, Mexico, and Iran. Each barley line was genotyped for 5912 single nucleotide polymorphism (SNP) markers, and the combined data were used for association mapping of loci associated with resistance to each RWA isolate. A total of 40 loci were associated with resistance to the five RWA isolates. Biotype differences were evident, with only 23 lines showing resistance to all five biotypes. Loci with large effects on mean chlorosis and rolling differences were found for resistance to biotypes from the United States, Hungary, and Chile, while the loci for resistance to biotypes from Mexico and Iran had small effects on these traits, which may pose problems for developing resistant germplasm. The 23 lines resistant to all biotypes included 10 unadapted germplasm accessions and 13 improved germplasm lines and provide useful germplasm for developing new barley cultivars with resistance to multiple RWA biotypes

Agronomic, cytogenetic, and isoenzymatic characterizations of oat somaclones

Immature embryo-derived somaclones regenerated from genotypes UPF 12, UPF 89S080 and UFRGS 7 were analyzed for eight agronomic traits and two enzymatic systems in order to evaluate the potential of tissue cultures to induce genetic variability in oats (Avena sativa L.). Some somaclones were also analyzed cytogenetically. Agronomic traits were evaluated in the field for all somaclones in 1993 and 1994. Bi-directional variation (P < 0.05) was detected for all characteristics, and the average frequency of variation observed in 1993 in somaclones from genotypes UPF 12 and UPF 89S080 was 35.2%. Variation observed for agronomic characteristics was heritable through two generations. Isoenzymatic analysis showed variation for both enzymatic systems in four somaclones. In general, the frequency of abnormalities at the cytogenetic level was low. The few that were observed had no effect on the meiotic index. Tissue culture can generate variability in oats in breeding programs.<br>Para avaliar o potencial da cultura de tecidos na indução de variabilidade genética em aveia (Avena sativa L.), somaclones regenerados de embriões imaturos dos genótipos UPF 12, UPF 89S080 e UFRGS 7 foram analisados em relação a oito características agronômicas e dois sistemas enzimáticos. A avaliação foi realizada em dois anos consecutivos, 1993 e 1994, em relação aos caracteres agronômicos. Foram observadas variações bidirecionais significativas (P < 0.05) para todos os caracteres, sendo que a freqüência média de variações detectadas em 1993, em populações somaclonais provenientes dos genótipos UPF 12 e UPF 89S080, foi de 35,2%. A maioria das alterações observadas em 1993 se mantiveram em 1994. A análise isoenzimática mostrou variações para os dois sistemas enzimáticos em quatro somaclones. A freqüência de anormalidades citogenéticas, de uma forma geral, foi baixa, porém mesmo nos somaclones onde a mesma foi alta, estas anormalidades não se refletiram na estabilidade meiótica. O processo de cultura de tecidos como gerador de variabilidade apresenta potencial como estratégia de apoio aos programas de melhoramento genético de aveia