The dynamics of faba bean (Vicia faba L.) parasitism by Orobanche foetida

The dynamics of Orobanche foetida parasitizing faba bean are examined using Petri dish experiments. Rates of broomrape seed germination and seedling attachment to the host roots were quantified on three resistant genotypes (the Egyptian line Giza 429, the Spanish cultivar Baraca, and the Tunisian cultivar Najeh [XBJ90.03-16-1-1-1]) and the susceptible cv. Bachaar. The percentage of O. foetida seed germination (11 to 38%) was lower near the roots of resistant host plants than it was near the roots of 'Bachaar' (67%). O. foetida parasitism was followed using three parametric logistic functions. In this way some major parameters of the infection process were quantified: the maximal number (N-max) and the maximal rate (R-max) of broomrape attachments to the host roots, the median time required for attachment (T-50), the maximal percentage of established tubercles reaching the final growth stage at 70 days after inoculation (DAI) (%(max)), and the maximal rate of established tubercle growth (R-max'). Broomrape attachment was lower and slower in resistant plants, as indicated by low N-max and R-max values combined with high T-50 values. Furthermore the precocity of the resistant genotypes was correlated with low attachment. The parameters %(max) and R-max' did not discriminate the susceptible cultivar Bachaar from Giza 429 or Baraca. On the other hand, the %(max) and the R-max', were lower in the 'Najeh' plants. The findings indicated that both low attachment and limited growth of established tubercles contributed to resistance in the Najeh cultivar.