Grain Yield and Oil content Post flowering temperature effects POST FLOWERING TEMPERATURE AS MAIN FACTOR REGULATIONG CANOLA YIELD AND OIL CONTENT Pilar Vilariño*, Déborah Rondanini , Daniel Miralles & Luis A.N. Aguirrezábal Faculty of Agronomy, University of Buenos Aires. ARGENTINA. *mdpvilar@agro.uba.ar Context: Canola or rapeseed (Brassica napus L.) is an excellent oilseed crop for use as edible oil or biodiesel, but the lack of accurate studies on genotypic adaptation to the great inter-annual climatic variability limit its cropping in Argentina. Contrasting genotypes combined with different sowing dates, expose the critical period for yield determination (post flowering) to changing environmental conditions, especially post-flowering temperatures. Objective: to assess main factors influencing crop yield so as to elaborate adequate crop management strategies MATERIALS AND METHODS SD1 SD2 A two year experiment (2008 and 2009) was carried out in potential conditions ( irrigated, fertilized and pests controlled) in Buenos Aires (34º35’S, 58º29’O) in two sowing dates each year. Sowing dates were: 30/4/08 (SD1 08); 1/7/08 (SD2 08), 15/4/09 (SD1 09) and 9/6/09 (SD2 09). Genotypes: BioAureo 2486 (Bi) and Hyola (Hy), spring short cycle cultivars (SS); Gladiator (Gl) and Jura (Ju), spring intermediate (SI) Barrel (Ba) and Gospel (Go), winter long cycle genotypes (WI). Genotypes were sown in 6-rowed plots, 3m long, 0.20 m apart, in a RCBD with 3 replications, achieved density (at harvest) was between 50-75 pl.m-2 for SD1 08; 80-120, SD2 08 and lower in 2009 (25-45 pl.m-2 for SD1 and 30-65 for SD2) due to pre-harvest environment (rainy and windy days). Crop phenology was recorded and at maturity plants in 0.5 m2 were harvested for yield determination. Grain oil content (Soxhlet), protein (Kjeldhal) and fatty acid profile (GLC) was determined. RESULTS Among sowing dates (SD), SD2 resulted in a cycle length ca. 20% shorter than SD1, for both years. SD2 08 shortenings were equally distributed between pre and post flowering, while SD2 09 shortenings were mostly related to pre-flowering duration. Late sowings also exposed post flowering period to higher temperatures. WI genotypes were unable to fulfill their vernalization requirements in SD2 08, so they did not flower and they could not be harvested. Grain quality Grain Yield and Oil content Yields were higher in 2008. All spring cultivars yielded more (p≤0.01) than winter genotypes (Ba and Go). SD1 yielded more than SD2. 18 19 20 21 22 23 24 25 26 27 28 30 35 40 45 50 Bi Hy Gl Ju Ba r 2 =0.48 y= 72.9 -1.497x Go protein content (%) oil content (%) SD 1 08 SD 2 09 Max.mean yield: 3545 Oil and protein concentration in grains were negatively correlated Oil content showed a more than proportional drop when 1% protein increased (slope=ca.-1.5%) Variation in yield was mostly associated to variations in grain number (r2= 0.86; p<0.001) than to grain weight (r2=0.25; p<0.001). The relationship between grain number and weight was highly variable, showing the crop ability to compensate for failures in any yield component. Min.mean yield: 422 Fig 1: Grain yield (kg.ha-1 )±SE. for Bi and Hy (SS), Gl and Ju (SI) and Ba and Go (WI) genotypes in early (SD1) or late (SD2) sowing dates 2008 (08) and 2009(09). For 2009 , mean drop of 7000 grains per m-2 for each 1ºC increased (r2= 0.43) Fig 3: Relationship between oil and protein content in grains (mean % ±S.E.) for all genotypes. Max Bi SD1 08 Min. Go SD2 09 Even though the great effect of temperatures on oil content in grains, fatty acid composition remained quite stable for all temperature range (14-22ºC) Mean oil concentrations were low: 39.7% for 2008 and 36.1% for 2009. Significant differences (p≤0.01) were found between years, SD (1>2) and genotypes (all superior to GO) Interestingly, grain oil content was positively associated to grain yield in a broad range of yield values (500-3800 kg ha-1) Fig 2: Relationship between oil content and grain yield in early (SD1) or late (SD2) sowing dates 2008 (08) and 2009 (09). Fig 4: Oleic acid (18:1) and omega 3 +6 (18:2+18:3) fatty acid in oil for a broad range of post flowering mean temperatures. Post flowering temperature effects The higher the mean post flowering temperature, the smaller the grain yield. Higher temperatures were experienced by long cycle genotypes (WI) and late sowings (SD 2). In 2008 as WI did not flower in SD2, the higher temperatures corresponded to WI SD 1. Higher temperatures affected both grain number (main yield component), specially in 2009 and individual grain weight. WI SD108 WI SD209 P<0.05 P<0.001 In both years, grain oil content (%) decreased as post-flowering temperature increased, with a drop of ca. 1.2% per ºC, resulting in less oil yield (kg oil .ha-1). Differences in intercepts were related to grain filling conditions (rainy and windy days in 2009). Slope: ca. 1.2%/ºC increased Fig 5: Grain yield (mean kg.ha-1 ±SE) as a function of mean temperature between first flowering (Ff) and Physiological maturity (PM) Fig 6: Grain oil content (%±SE) as a function of mean temperature between first flowering (Ff) and Physiological maturity (PM) CONCLUSIONS Post-flowering temperatures were strongly related to canola yield and oil content, due to its effect on both grain number, grain weight, and also on oil/protein content. Fatty acid profile was hardly affected by post-flowering temperatures in a broad range (14-22ºC). It is possible to get good yield and quality in our latitude (34ºS) with early sowings of spring cultivars that allow avoiding exposition to high post -flowering temperatures.