2.1. Field Experiments and Plant Materials
Field trials were carried out in 2017 and 2018, at three different locations. Two of the locations were the on-farm breeding locations coordinated by Kultursaat e.V.: De Beersche Hoeve (Oostelbeers, Netherlands), and Horticulture station Heinze (Bingenheim, Hessia, Germany). The third location was the research station for organic farming Kleinhohenheim (University of Hohenheim, Stuttgart, Baden-Wuerttemberg, Germany).
The on-farm breeding location De Beersche Hoeve is located at a latitude of 51°28′47 N, longitude of 5°15′35 E, and 17 m above sea level. In 2017, during the growth period (July–October), the mean temperature was 16 °C and the mean precipitation reached 47 mm. In 2018, the mean temperature and precipitation during the growth period (June to September) were 16.5 °C and 27.7 mm, respectively. The soil texture is fine sand with a low clay content.
The Horticulture station Heinze (50°22′28 N, 8°53′45 E) is located at an altitude of 129 m above sea level. In 2017, during the growth period (June to September), the mean temperature was 16.2 °C and the mean rainfall was 53.5 mm. In 2018, the mean temperature and the precipitation during June to September were 20.7 °C and 24.1 mm, respectively. The soil texture is clayey loam.
The research station Kleinhohenheim is located at a latitude of 48°44′14 N, longitude 9°12′01 E, and 430 m above the sea level. In 2017, during the months July to October, the mean precipitation was 77.42 mm and the mean temperature 17.6 °C. In 2018, the mean rainfall reached to 38.2 mm and the mean temperature was 19.0 °C between June and September. The soil texture is considered as loess to loamy clay.
Total monthly precipitation as well as monthly mean temperature of all three research stations during the experimental period in 2017 and 2018 are shown in Figure 1
All field trials were conducted under organic farming conditions in accordance with the European Commission’s main regulations for organic farming. Briefly, no synthetic fertilizer was applied to the soil. Pests and disease control were done using biological controls. Frequent mechanical or manual weeding was conducted to suppress the weeds. The genotypes were allocated to the six field trials according to a non-resolvable row column design or a randomized complete block design (Table A1
). In 2017, on each on-farm breeding location 30, and in Kleinhohenheim, 40 open pollinating genotypes were cultivated in three field replicates. In 2018, 16 open pollinating genotypes were assessed on each on-farm breeding location, while 36 genotypes were tested in Kleinhohenheim. Over both years 15 genotypes were assessed on all locations forming the orthogonal core of the experiment. Note that data from all genotypes were analyzed, but the presented results were limited to the 15 genotypes which occurred in all location-by-year combinations. The 15 investigated genotypes were 13 red-colored beets: Akela, Betina, Bona, Bordo AS, BoRu1, Carillon RZ, Cervena Kulata, Detroit 3, Jawor, Monty RZ F1, Nobol, Nochowski, Ronjana, one white genotype, Sniezna Kula, and one yellow-colored beet, Burpees Golden. BoRu1 is a breeding line of the breeding organization, Kultursaat e.V., which was used in order to assess its market potential as a new open-pollinated genotype. Table 1
depicts the information regarding shape and color of the beets as well as the seed origin of the 15 selected genotypes. The seeds needed for all six trials were ordered in spring 2017 and stored in a dark and dry place until the sowing day.
At De Beersche Hoeve, the field experiments were conducted as row-column design in 2017 and as randomized complete block design in 2018. In the first trial year, the field was fertilized with compost equivalent to 60 kg N ha−1 and in the second year, compost equivalent to 90 kg N ha−1 was incorporated into the soil. The preceding crops were clover grass and Romanesco broccoli in 2017 and 2018, respectively. The field was ploughed two months before each experiment to a depth of 20 cm. Harrowing was done twice before sowing to a depth of approximately 3 cm. The plot size was set as 9 m2 with three cultivation rows per plot and an inter-row spacing of 50 cm. In the first field trial, sowing was conducted using a precision seed drill on 14 July 2017, and the harvest was done manually on 26 October 2017. In 2018, the beetroots were seeded on 12 June 2018 and harvested on 27 September 2018. In both trials, weed control was done manually and mechanically by hoeing.
At the Horticulture station Heinze, the field experiment was carried out as randomized complete block design in both 2017 and 2018 with three replicates. In 2017, the preceding crop was broccoli, while in 2018, the preceding crop was carrot. In both experimental years, no fertilizer was applied to the field. The field was prepared by ploughing in autumn to a depth of 25 cm and harrowed three months before sowing to a depth of 8 cm. The plot size was 8.75 m2 with three rows per plot and an inter-row spacing of 42 cm. In 2017, the sowing took place on 08 June 2017 using a hand-sowing machine and the harvest was carried out manually on 30 September 2017. In 2018, the trial started on 09 June 2018 and the beetroots were harvested on 10 September 2018. Weeding was performed by hand and by a wheel hoe.
At the research station Kleinhohenheim, the experimental design was set up as row-column with three replicates in 2017 and as non-resolvable block design, with a block size of ten and a number of treatment of 36, in 2018, with three replicates for 32 genotypes and six replicates for four genotypes. The unequal replications were due to the point that the four genotypes with six replicates belonged to breeding lines, and their performance in the field was unknown. Therefore, in order to have sufficient samples, more replicates were considered for them. In 2017, the preceding crop was clover grass which was considered as green manure, and additionally, the field was fertilized with Vinasse, equivalent to 8.3 kg N ha−1, one month after seeding. In 2018, no additional fertilizer was used due to the N fixation by the pre-crop clover grass. In January 2017, the field was ploughed to a depth of 20 cm and the seed bed was prepared using a rotary harrow to a depth of 6 cm. In the second year of the experiment, ploughing was carried out in January 2018 and harrowing was done about 40 days before sowing. The plot size was 14 m2 with four rows per plot and an inter-row spacing of 35 cm. In the first experiment, sowing was done on 06 July 2017 and beetroots were harvested manually on 16 October 2017. The sowing and harvest date in the second field trial was on 06 June 2018 and 10 September 2018, respectively. In both years, sowing was conducted using a pneumatic single-seed drill. Inter-row weed control was performed manually and intra-row weeding was carried out mechanically by hoeing.