Histological characterization of resistance to Uromyces viciae-fabae in faba bean

ABSTRACT Components of resistance to the faba bean rust (Uromyces viciae-fabae) were studied at the histological level in seedlings and adult plants of nine faba bean (Vicia faba) lines differing in their level of resistance. Resistance of these lines was previously shown to be characterized macroscopically by an increased latent period, a decreased colony size, and a relatively decreased infection frequency. In some lines, the resistance also was associated with macroscopically visible necrosis. Histological investigations revealed few differences in spore germination and appressorium formation. Significant levels of aborted stomatal penetration by the rust fungus were found on all resistant lines. However, differences among lines were more evident once the stomata were penetrated by the infection structures. Resistance was mainly due to a restriction of haustorium formation with varying levels of early abortion of the colonies, a reduction in the number of haustoria per colony, and smaller colony size. ...