Development of F2 and Backcross populations
The broccoli DH lines HX-16 with KGLT and HX-11 with TPLT were selected
as paternal and maternal lines, respectively, and were crossed to
develop the F1 hybrid. The BC1 was
obtained by pollinating the F1 hybrid with HX-16, and
the individuals with TPLT were selected to cross with HX-16 again to
produce the BC2 population. In the BC2population, the individuals with TPLT were selected and selfed to
construct the BC2F2 segregation
population. An F2 segregation population was obtained by
selfing the hybrid F1 derived from a mutant GS with
green buds and the wild line PS with purple buds at low temperature.
Plug-seedlings were obtained and seedlings were transplanted in a tunnel
greenhouse at Yangdu experimental farm of Zhejiang academy of
agricultural sciences in the autumn of 2017 (HX-11, HX-16 and their
F1, the mutant GS and wild DH line PS), 2018 (HX-11,
HX-16 and their F1, BC1, the mutant GS
and the wild DH line PS), 2019 (HX-11, HX-16 and their
F1, BC1 and BC2, the
hybrid F1 of the mutant GS and the wild lines PS and
germplasm materials in Brassica oleracea (Table 1), 2020 (HX-11,
HX-16 and their F1 and
BC2F2, the mutant GS and the wild lines
PS and their F2 segregation population,) and 2021
(HX-11, HX-16 and their F1, the mutant GS and the wild
lines PS, purple broccoli (PB)). Meanwhile, the wild line PS plants were
cultured in an artificial chamber with 20℃/25℃ night/day temperature and
a 14-hour photoperiod for the experiment of the temperature effect on
the bud color in 2021 in order to check the effect of temperature on
anthocyanin. Phenotyping of the buds in the segregation populations,
respective parents, and the germplasm materials was conducted after
experiencing cold air (0-50 C) for 10 days as the
temperature of this range could make the buds of the maternal line HX-11
turn purple completely.
Table 1 Germplasm materials in Brassica oleracea