Three virulent populations (CU194, SE193, and SE194) of the parasitic plant
Orobanche cumana were inoculated onto four lines (KA-41, J-8281, HA-89, an
d RHA-273) of sunflower (Helianthus annuus L.). Pots were transferred to gr
owth chambers set at 15, 19, 23, and 27 degreesC. Emergence of broomrape pl
ants and infection incidence were determinants of disease reaction. All bro
omrape populations were pathogenic to the sunflower lines KA-II, HA-89, and
RHA-273, although differences in virulence were found. At 15 to 23 degrees
C, the populations of broomrape infected these three sunflower lines, but a
delay in emergence of broomrape was found at 15 degreesC; whereas, at 27 d
egreesC, the level of infection was restricted. Only population CU194 infec
ted the resistant line J-8281, with infection occurring mainly at 23 and 27
degreesC, but few broomrape plants emerged. Our results suggest that the e
ffect of temperature on the host-parasite relationship is complex.