226 – II.3. BRASSICA CROPS (BRASSICA SPP.)
Lefol, Fleury and Darmency (1996) detected 6 hybrids in 50 000 seeds analysed. In hand
crosses using S. arvensis females from different UK and French populations, Moyes et al.
(2002) detected one completely sterile hybrid. No such hybrid had previously been
reported without embryo rescue or ovule culture (Inomata, 1988; Kerlan et al., 1992;
Bing et al., 1996, 1991; Chèvre et al., 1996; Lefol, Fleury and Darmency, 1996). All
hybrids produced were weak, largely or completely sterile, and unlikely to survive in
nature (Moyes et al., 2002). None of the hybrids were able to backcross to S. arvensis.
Daniels et al. (2005) identified a single plant in the United Kingdom that they
believed to be a S. arvensis × B. napus hybrid. It was growing in a patch of S. arvensis
plants adjacent to a field that had grown a crop of glufosinate resistant B. napus the
previous year. The hybrid classification was based on a null reaction to the application of
glufosinate to a single leaf followed by a positive DNA test for the glufosinate resistance
gene. However, only morphological characteristics were used to classify the plant as a
S. arvensis × B. napus hybrid. The lack of any information on chromosome number
and/or markers, and in the light of previous studies, the question remains as to whether
the plant was indeed a S. arvensis × B. napus hybrid rather than another interspecific
cross such as B. rapa × B. napus. In the words of the report’s reviewer “such a finding
needs to be interpreted with caution.”
Despite the one hybrid produced by Moyes et al. (2002) on an emasculated
S. arvensis plant, there is general agreement among researchers that the possibility of
gene flow between B. napus and S. arvensis is extremely low (Moyes et al., 2002) to
non-existent (Downey, 1999a; 1999b).
B. napus – Raphanus sativus
R. sativus is a vegetable crop in many parts of the world, but when grown for seed it
can escape from cultivation and colonise disturbed sites such as roadsides, fields and
coastal sand dunes (Snow, Uthus and Culley, 2001). Daniels et al. (2005) reported
flowering of R. sativus plants could coincide with either winter or spring B. napus. In
R. sativus plants growing in or near a field of glufosinate resistant B. napus in the United
Kingdom, Daniels et al. (2005) found no R. sativus × B. napus hybrids. Further, progeny
from the sampled R. sativus plants were all susceptible to glufosinate. Hybrids between
B. napus and R. sativus have been obtained in several studies with the aid of ovule culture
or embryo rescue (Lelivelt et al., 1993; Paulmann and Röbbelen, 1988; Sundberg and
Glimelius, 1991; Metz, Nap and Stiekema, 1995; Takeshita, Kato and Tokumasu, 1980)
and also by hand pollination (Gupta, 1997). All artificially produced hybrids were male
sterile. However, in natural crosses Ammitzbøll and Jørgensen (2006) obtained an
average of 0.6 seeds per pod when male sterile B. napus plants were used as the female
and a radish cultivar as the pollen parent. Huang et al. (2002) in hand crosses also
produced many hybrids on Ogura male sterile plants. All seeds produced proved to be
F 1 triploid hybrids with low pollen fertility (0-15%). It is highly probable that the
presence of radish cytoplasm in the male sterile B. napus parent greatly facilitated
R. sativa pollen penetration of the stigma. Further studies need to be carried out with this
cross since R. sativa crosses easily with R. raphanistrum (Snow, Uthus and Culley,
2001).
B. napus – Erucastrum gallicum
E. gallium is a self-compatible, annual or winter annual with very small seeds. It is a
minor weed of cultivated fields and waste places in many oilseed rape growing countries.
Batra, Shivanna and Prakash (1989) obtained three hybrids from the cross E. gallicum ×
