3 The sugar beet biology, geographical distribution and gene flow

The genus Beta is classified into four genetically differing sections, namely Beta, Corollinae, Nanae and Procumbentes (Lange et al., 1999; Frese, 1998*). The species B. vulgaris ssp. vulgaris comprises the cultivated forms sugar beet (var. altissima), fodder beet (var. crassa), Swiss chard (var. vulgaris) and red beet (var. conditiva). The sugar beet has cultivar, wild and weed forms. Wild beet species are quite common among the Beta section, comprising the subspecies Vulgaris, Maritima, Adanensis and the closely related species B. patula and B. macrocarpa. They occur along the coasts of northern and western Europe and in the Mediterranean area including north-west Africa and the Canary Islands, the Balkans, the Caucasus and from Asia Minor to Bangladesh (Table 1) (Frese, 1998*).

Sugar beets are most often self-incompatible and usually wind-pollinated, although insect pollination is also possible (Bartsch et al., 1999*). Sugar beet hybridises easily with cultivated and wild forms of Beta vulgaris. It has normally vigorous and fertile progeny without incompatibilities with members within the Beta section (OECD, 2006*). Natural interspecific hybridisation between the species of section Beta is also possible, but is very unlikely with species of the other three Beta sections. If hybridisation between B. vulgaris and other sections occurs either naturally or through artificial techniques, the resulting progeny is not viable and does not reach the generative phase (Van Geyt et al., 1990*). Thus, a gene transfer from cultivated beets to wild beets is likely only for the Beta section.

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Figure 2: Intra- and interspecific gene flow of cultivated, weedy, wild sugar beet and related wild species within and between agricultural fields and the environment (Bartsch et al., 2003*, modified).

Sugar beets are biennial plants forming a beet in their first season. If the beets are not harvested, flowering shoots appear in the second year after vernalisation. However, the formation of flowering shoots and completion of the whole life cycle in the first year is possible (bolters) (probability < 0.05%) due to the genetic constitution of the plants and/or certain weather conditions such as drought or frost (Keller et al., 1999*; Geisler, 1980*). In practice, bolters are usually removed or destroyed before flowering. Seeds from bolters that have not been removed before seed maturity fall off and pass into the soil seed bank. From these seeds, weed beets can emerge within and between rows in the crop stand in the following years (May, 2009*). The seeds can have a life span of over 10 years, but are depleted with time or may germinate under favourable conditions. Small beets or beet sections left in the field after harvesting can regenerate (groundkeepers) (Elliott and Weston, 1993*) depending on the part of the plant, size, depth of placement, survival ratio, and management of the following crop (Buddemeyer and Petersen, 2002*). Bolters and volunteers in some years with special conditions can become overwhelming, hindering their management or eradication by farmers. Hence, gene flow via seed, pollen or clonal plant parts within and between agroecosystem and the environment is possible in various ways and directions (Figure 2*).

Table 1: Biological properties relevant to the ERA and PMEM across different spatial scale levels.

Biological properties of Beta vulgaris L.

Chain of potential agro-environmental effects





laboratory or greenhouse experiments

field trials or observations

landscape-scale experiments or observations


widespread geographical distribution of Beta vulgaris L., wild beets and bastards in some EU regions

 potential of HR sugar beet to hybridise with neighbouring cultivated, feral and weed beets


1, 8

1, 2, 3


widespread geographical distribution of related wild species of the genus Beta L.

 potential of HR sugar beet to hybridise with wild relatives



3, 4, 13


formation of bolters

 in case of flowering: hybridisation of HR sugar beet with neighbouring cultivated, feral and weed beets, and with related species  seed production

2, 5, 6,10, 11

2, 5, 6, 7, 8, 10, 11, 14, 15, 16, 31, 32

2, 7, 8, 9, 10, 11, 12, 20, 27


regeneration of vegetative plant residues for the next season (groundkeepers)

 in case of flowering: hybridisation of HR sugar beet with neighbouring cultivated, weed and wild beets, and with related species  seed production

2, 5, 6, 18

2, 5, 6, 7, 8, 14, 17, 18, 25, 26, 31, 32

7, 8, 9, 12, 20, 27,


stable weed beet populations

 increase of HR seed bank,  hybridisation with neighbouring cultivated and/or wild relatives  in case of a selective advantage and/or genetic drift: HR sugar beet and related species may persist and become invasive


12, 14, 16, 19, 25, 26; 31, 32

19, 20, 30



 unpredictable combinatory effects with cultivated and/or wild relatives






 adverse effects on neighbouring habitats such as ecosystem food chains; impacts on biodiversity





horizontal gene transfer

 transgenes may be transferred to other species such as bacteria

21, 22, 29




1References legend (E: Expert opinions; M: Models; R: Review; O: Original data): 1 (Drießen et al., 2001* / O, R); 2 (OECD, 2006* / R); 3 (Frese, 1998* / R); 4 (Frese et al., 2001* / O, R); 5 (Van Geyt et al., 1990 / R); 6 (Bartsch and Schmidt, 1997 / O); 7 (Bartsch et al., 1999* / O); 8 (Bartsch et al., 2003* / O, R); 9 (Sukopp et al., 2005* / O, R); 10 (Keller et al., 1999* / R); 11 (Geisler, 1980 / R); 12 (Beckie, 2006 / E); 13 (De Bock, 1986 / R); 14 (May, 2009 / E); 15 (Lehnert, 2007 / E); 16 (Viard et al., 2002* / O); 17 (Elliott and Weston, 1993 / E); 18 (Buddemeyer and Petersen, 2002 / O); 19 (Soukup et al., 2002); 20 (Desplanque et al., 2002* / O, E); 21 (Heinemann and Traavik, 2004* / O); 22 (Nielsen and Townsend, 2004* / O); 23 (Pessel et al., 2001); 24 (Watkinson et al., 2000* / M, E); 25 (Märländer et al., 2010* / R); 26 (Viard et al., 2002*); 27 (Boudry et al., 1993); 28 (Züghart and Breckling, 2003* / R); 29 (Rensing et al., 2002 / O); 30 (Cerdeira and Duke, 2006* / R); 31 (Arnaud et al., 2003* / O); 32 (Arnaud et al., 2009 / O)

2Evidence among the references based on the data quality aspects a) how closely the measured or observed features, effects and indicators resemble the actual features, effects and indicators about which information is desired; b) quality, mode and accuracy of the methodological design and the degree to which empirical or expert observations have been used to produce the data; c) statistical design, number of replications, spatio-temporal representativeness (Graef, 2009*)

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