FIELD-STUDY OF THE INTERACTION BETWEEN OROBANCHE-CRENATA FORSK AND SOME NEW LINES OF VICIA-FABA L IN EGYPT

In Egypt, some newly derived lines of faba bean (Vicia faba L.) as wel l as Giza 402, all of which had shown a certain resistance against the parasitic weed Orobanche crenata Forsk., were tested in the field. Fo r reasons of comparison, the susceptible cultivars Giza 3 and Reina Bl anca were included in this test. Faba bean plants and Orobanche attach ments were regularly harvested and examined. The susceptible cultivars completely collapsed before the end of the growing season, whereas ot hers, particularly line 402/294, remained alive until pod formation wa s completed. It appeared that fewer Orobanche spikes emerged on the ne w lines and Giza 402. Evidence is given that this was not due to avoid ance mechanisms, such as smaller root mass, a deeper root system or la ck of germination stimulants. Numbers of Orobanche attachments per uni t of lateral root length were found to be low. Hence, it could be conc luded that these lines are partially resistant; this resistance must b e due to some defence mechanism in their roots. The few Orobanche plan ts attached grew very fast so that final Orobanche dry weight was simi lar in resistant and susceptible host plants. Further experiments, inc luding broomrape-free controls, are required to study whether some tol erance mechanism might be involved.