Characterization and inheritance of partial resistance to downy mildew, Peronospora parasitica, in breeding material of broccoli, Brassica oleracea convar. botrytis var. italica
Bd. Jensen et al., Characterization and inheritance of partial resistance to downy mildew, Peronospora parasitica, in breeding material of broccoli, Brassica oleracea convar. botrytis var. italica, PLANT BREED, 118(6), 1999, pp. 549-554
Twenty doubled haploid broccoli lines from breeding material were evaluated
for resistance to Peronospora parasitica at the seedling stage. All lines
supported sporulation of the pathogen, but to varying extents and intensiti
es. Partial resistance of the more resistant lines, 'br8' and 'br9', reduce
d conidia production on cotyledons by 50-70% compared with the most suscept
ible lines. Inoculation of the two most resistant lines with 13 isolates of
different geographical origins revealed that 'br9' showed a rather uniform
level of resistance to all isolates while 'br8' showed some isolate specif
icity. Partial resistance was evaluated in six of the broccoli lines in a h
alf diallel set of crosses. Disease assessment of seedlings showed that add
itive genetic effects explained 45.8% and 31.8% of the total variation of s
porulation score and conidia production, respectively. This suggests that r
ecurrent selection for partial resistance to P. parasitica in early generat
ion inbreds or in populations of broccoli will be efficient to obtain cotyl
edon resistance.