Winter wheat (TriticumTriticumaestivum aestivumL.) assessment of weed competitive L.) assessment of weed competitive ability using weed competitor and naturally weed ability using weed competitor and naturally weed--infested methodinfested method Aleš Kolmanic1; Andrej Zemljič1; Matej Knapič2; Andrej Vončina 2; Uroš Žibrat 2; Vladimir Meglič1 1 Agricultural Institute of Slovenia, Crop science department, Ljubljana, Slovenia 2 Agricultural Institute of Slovenia, Plant protection department, Ljubljana, Slovenia The weed competitor method was more reliable for evaluating the weed competitive ability of wheat and showed smaller variation compared to naturally weeded trials. The number of weed competitor plants correlated strongly and negatively with wheat height and wheat biomass, while the dry biomass of weed competitor correlated strongly and positively with the number of competitor plants and negatively with the wheat biomass and wheat height. On the contrary, only weak to moderate correlations were observed between soil cover and number of wheat leaves or LAI and weed number/biomass regardless of the wheat growth stage. First analysis of multispectral data by comparing weed biomass and Optimized Soil Adjusted Vegetation index (OSAVI) showed significant differences; however, r2 values show only weak relationships. Results indicate that the weed competitive ability of wheat cultivars differs. Rather than being attributed to a single trait, competitive ability encompasses a combination of different traits. Based on the dry biomass of weed competitor, tested varieties can be grouped into varieties with good weed competitive ability (Primorka, Marinka, Bernstein, and Vulkan); varieties with moderate weed competitive ability (Izalco CS, Savinja, Illico, Alixan, Gorolka, Reska); and varieties with low weed competitive ability (CCB Ingenio, Tata Mata).C ConclusiononclusionssMaterial and Material and methodsmethodsResults Results Widespread intensive and repeated herbicide use causes environmental pollution problems and the emergence of resistant weed biotypes, increasing concerns about the sustainability of such approaches. The adoption of weed-competitive genotypes is regarded as an effective tool in integrated weed management. Furthermore, as organic cultivation omits the use of synthetic herbicides, the adoption of weed-competitive genotypes is high on the priority list to increase the productivity of organic cultivation. Selection of wheat cultivars for competitive ability against weeds requires identification of relevant traits and development of reliable procedures to measure/estimate them. This ongoing study is focused on the assessment of weed competitive ability using the standard and advanced phenotyping techniques and the development of reliable and high-throughput screening method for identification of genotypes with higher weed competitivness. Three separate trials, i.e. weed-free trial (weeds eliminated with the use of herbicides), weed competitor trial (barley used as the weed and weeds eliminated with the herbicide), and naturally weed-infested trial (no weed management applied) were established with 12 wheat cultivars in growing seasons 2019/2020 and 2020/2021 to study traits contributing to weed competitive ability. The design of each of the trials was a randomized block with 4 replications. The size of the individual plots was 7.5 m2. Traits were scored using classical phenotyping (field measurements) and multispectral sensing tools at different growing stages of wheat. Traits scored were wheat/weed soil cover, biomass, height, and a number of plants; number, square surface, and dry weight of leaves, wheat growth type, grain yield, grain moisture, and thousand kernel weights. Field scorings and spectral signatures of cultivars were recorded at booting, heading, anthesis, and ripening growth stages. Biomass was sampled using the 30 x 30 cm square. At maturity, plots were harvested and grain yield was determined.