No abstract

For crops grown in Mediterranean environments, translocation of pre-anthesis assimilates to the fruit is of great importance, because hot and dry conditions during fruit ripening diminish net assimilation rate and nitrogen (N) uptake. This field study was conducted to assess the pattern of dry matter and N accumulation and the role of assimilate translocation in pod development of oilseed rape plants in a Mediterranean environment. Four cultivars of winter oilseed rape (Brassica napus L.), i.e. three hybrids (Royal, Exact, Excalibur) and an inbred line (Fortis), were grown for two growing seasons (2005–06 and 2006–07) in northern Greece. On average, 581, 1247, 1609, and 2749 growing degree-days (GDD) were required for six leaves, stem elongation, 50% anthesis in main stem, and physiological maturity in the first year, and 539, 1085, 1601, and 2728 GDD in the second year. The R2 of the modified Richards function indicated that aboveground biomass and N accumulation were described with high approximation efficacy. The across-cultivars genotype mean maximum predicted total aboveground dry matter and N content were 1368.8 and 21.4 g m–2 in 2006 and 1655.1 and 25.4 g m–2 in 2007. In 2007, dry matter and N translocation from vegetative tissues to pods were 464.4 and 21.0 g m–2, and significantly higher than the corresponding values recorded in 2006 (264.4 and 17.0 g m–2). These differences were due to greater amounts of dry matter and N accumulating at anthesis and the greater sink capacity of plants (pod number) in 2007. The fact that pod development occurred in a period when N accumulation by oilseed rape plants had stopped led to high values of contribution of pre-anthesis N accumulation to pod N content in both years (92.8% in 2006 and 96.6% in 2007). Results indicated that hot and dry weather post anthesis reduced dramatically the net assimilation rates; thus, translocation of pre-anthesis assimilates was crucial for pod development. The results demonstrate that variation in weather conditions between growing seasons is one of the main causes of seasonal variation in oilseed rape productivity under Mediterranean conditions.

Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments.

SUMMARYWinter rapeseed was introduced into Greece a decade ago to provide oil for biodiesel. To identify agronomic traits affecting yield and quality, three hybrids and an inbred line were tested over two seasons (2005–2006 and 2006–2007) and four locations, in central and northern Greece, varying in pedo-climatic conditions. The large variations in seed yield, quality and agronomic traits were largely ascribed to location; in contrast, cultivar accounted for ⩽0·010 of the variation for many traits. Below 40°N, rapeseed is a risky crop; short season, high temperatures and low rainfall during reproductive growth diminished seed yield and oil content, increased oleic and erucic acid and minimized linolenic acid. A hybrid, Exact, with tall stature and large seeds was adaptive to such conditions. The most productive location had dense stands with tall plants bearing numerous pods on the main raceme. At the site with the coldest winter, plant density (PD) was lowest (ca. 30 plants/m2) but rapeseed compensated by producing large seeds, with high oil content and harvest index (HI). A biplot revealed that the hybrid Excalibur, outperforming the other cultivars for oil content in six out of eight trials, produced the highest and most stable oil yield. Combined data showed that seed yield and oil yield were positively correlated with PD, seed size and HI and negatively to the number of pods on branches and per plant. Large seeds had high seed oil content. Oleic acid was negatively correlated to linolenic acid concentration. High temperatures and low rainfall favoured oleic acid, which was positively associated with seed number per pod.

Petri dish bioassays, based on root response of corn grown in soil and perlite, were used to study the activity, adsorption, and leaching of pyrithiobac in a clay, loam, and a clay loam soils containing 2.3, 1.4, and 1.3% organic matter, respectively. Both bioassays indicated that activity of pyrithiobac (reduction of corn root length) increased with increasing herbicide concentration, but in a nonlinear manner, particularly at higher concentrations. Activity of pyrithiobac was similar in clay loam and loam soils, but was lower in clay soil. Adsorption distribution coefficients (K d) for the clay, loam, and clay loam soils were 0.56, 0.10, and 0.24, respectively. Pyrithiobac leached through all three soils, and biologically available herbicide was detected below 30 cm in all soils; however, the amount leached through the clay soil was lower than that leached through the other two soils. Field persistence of pyrithiobac applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST) at 68, 102, or 136 g ha−1 was similar in loam and clay loam soils, but was more persistent in clay soil. Pyrithiobac applied POST in clay and loam soils was more persistent than that applied PPI or PRE; however, in clay soil field persistence of POST pyrithiobac was similar with that applied PPI or PRE. Biologically available residues were not detected in 0- to 10-cm soil depth 120 d after any herbicide treatment applied either PPI or PRE in all soils, but this was not the case for pyrithiobac applied POST in the loam soil. Adsorption of pyrithiobac was very low in all three soils, and this was the reason for its increased mobility even below 30-cm depth in all soils. The field persistence of pyrithiobac was generally less than one growing season. However, some pyrithiobac may have moved deeper in the soil and could be harmful to rotational crops after plowing or through capillary movement upward.