L.Legzdina, I.Mezaka, I.Beinarovica, A.Kokare, G.Usele, N.Rostoks (2013) Variability of spring barley traits essential for organic farming in association mapping population. In: C.Li, G. Zhang, X. Liu (eds.) Advances in Barley Sciences: Proceedings of 11th International Barley Genetics Symposium, Springer, 227-234 Variability of spring barley traits essential for organic farming in association mapping population 1 Linda Legzdina, 1 Ieva Mezaka, 1 Indra Beinarovica, 1 Aina Kokare, 1 Guna Usele, 1 Dace Piliksere, 2 Nils Rostoks 1 State Priekuli Plant Breeding Institute, Zinatnes street 1a, Priekuli LV-4126, Latvia, lindaleg@navigator.lv 2 Faculty of Biology, University of Latvia, 4 Kronvalda Blvd., Riga, LV-1586, Latvia Abstract Association mapping population consisting of 154 Latvian and foreign spring barley genotypes contrasting for traits that are important for organic agriculture was established with the aim to develop molecular markers useful in breeding for organic farming. The mapping population was genotyped at 3072 single nucleotide polymorphism loci using Illumina GoldenGate platform to provide marker data for association mapping. Field trials in two organically and two conventionally managed locations are being carried out during three seasons. The following traits essential for organic farming were phenotyped: plant morphological traits ensuring competitive ability against weeds, grain yield in organic farming, yield stability/adaptability to organic conditions, nutrient use efficiency (measured as ability to form acceptable grain yield and accumulate protein in grain under conditions of organic farming) and prevalence of diseases. This paper gives an overview on preliminary phenotyping results. ANOVA showed that genotype and location significantly influenced most of analysed traits (p<0.01). The average yield reduction in organic trials, when compared to conventional was 1.2 t ha -1 and it ranged from 4.2 t ha -1 reduction to 1.2 t ha -1 increase. In respect to morphological traits related to competitive ability against weeds (canopy height in beginning of plant elongation, plant ground cover in tillering, length and width of flag leaves, tillering capacity, plant height before harvest) there was a tendency that average trait values were higher in conventional farming locations, but the coefficients of variation were higher in organic locations in most of the cases. The differences in protein content between conventional and organic trials correlated significantly (r=0.732) and its variation was significantly effected by genotype. The average reduction of protein content in organic fields, if compared to conventional was 2% and it ranged 0-6.5%. Keywords Phenotyping, competitive ability against weeds, nutrient use efficiency Introduction Development of organic agriculture in general has been much slower in comparison to conventional agriculture; one of the reasons is considerably greater environmental variability wherewith the need for adaptation of varieties to varied environmental conditions is important issue in organic agriculture (Wolfe et al., 2008). Backes and Østergård (2008) concluded that there might be a high potential for marker assisted selection (MAS) if markers that contain information about GxE interaction in plant breeding for organic farming would be used. For certain traits QTL effect may differ between environments: there is significant effect in one environment and no effect in another. In this case the gene responds only to the specific environmental factors. A possible solution can be inclusion of GxE interaction in QTL analysis (Backes and Østergård, 2008). Standards of organic agriculture do not exclude use of molecular markers as such; one of reservations of organic sector is the use of harmful chemicals and enzymes produced from genetically modified organisms in marker development. MAS could be used efficiently in breeding for organic farming besides to phenotypic selection for particular traits if markers for relevant traits are available. There is a need to discuss this issue between molecular scientists and representatives of organic sector (Lammerts et al., 2010).