1 research outputs found
Pathogenic diversity within field populations of Orobanche cumana and different reactions on sunflower genotypes
8 pages; 5 tables; 3 figuresDifferent races of the parasitic Orobanche cumana
(sunflower broomrape) have been reported in Spain,
race F being the most virulent. Full resistance in
sunflower to races A–E is achieved with each of the
single major genes Or1 to Or5 respectively. However,
parasitised hybrids allegedly resistant to race F were
observed in early 2002. The purpose of this study was to
verify broomrape incidences (BI) on resistant sunflower
genotypes, to assess the mixture of races within field
populations and to test for partial resistance to race F in
the sunflower hybrids showing a low degree of attack
(DA) by the weed. Tests were conducted under field
conditions in two locations of southern Spain. While no
significant differences were found for yield and BI
between locations, the DA on the cultivars depended on
the location. With high infection levels and significantly
lower yield in susceptible controls, marked differences in
BI and DA were found within resistant cultivars, but all
of them showed similar crop yield. When artificially
inoculated with several populations of race F, line P96
and mainly line L86, were consistently slightly infected,
suggesting they were inbred lines responsible for horizontal
resistance in infested fields. L86 was extremely
susceptible to race E populations, which is unusual as
sunflower resistance to one race provided resistance to
all the previously described races of O. cumana. No
different virulences were detected within two groups of
subpopulations (races E and F) inoculated onto resistant
sunflower genotypes. However, race F subpopulations
showed significant differences in aggressiveness, which
seems to be related to horizontal (multigenic) resistance of the crop to the parasitic weed.ERDF funds through the IFAPA-RAEA programme and Research Project RTA01131 (Spanish Ministry for Science and Education)Peer reviewe