Quantitative aspects of Orobanche crenata infestation in faba beans as affected by abiotic factors and parasite soil seedbank

The interactions between the root parasitic weed Orobanche crenata Forsk. a nd its host plant faba bean (Vicia faba L.) were quantified under controlle d and field conditions at ICARDA's Tel Hadya research station. In the field experiments conducted in 1993-94 and 1994-95 faba beans were sown on two d ates, in plots with 0, 50. 200 and 600 O. crenata seeds kg(-1) soil, under both limited and sufficient moisture supply. The effects of temperature on the duration of the early developmental stages of O. crenata were investiga ted in a growth chamber. The extent of O. crenata infestation was closely r elated to the number of parasite seeds in the soil. The seed-density treatm ent with 600 seeds kg(-1) soil resulted in complete crop failure. Furthermo re. O. crenata infestation was higher under sufficient than under limiting water supply conditions. irrespective of sowing date. Only in the moderatel y infested plots, did shifting of the planting time of faba bean result in a significant decrease in parasite dry weight and an increase in crop seed yield. The timing of germination, attachment and further developmental stag es of O. Crenata was not related to faba bean growth stage and was affected primarily by soil temperature. The duration of O. crenata developmental st ages was estimated using the thermal time concept. The relationship between total number of parasite attachments at the harvest of the faba bean crop and O. crenata seed density was dependent on maximum faba bean root-length density measured by the start of pod-filling in each treatment combination of sowing date and moisture supply. The results are discussed with referenc e to implications for the development of a dynamic simulation model for the prediction of faba bean yield losses caused by O. crenata.