Infection Structures of Host-Specialized Isolates of Uromyces viciae-fabae and of Other Species of Uromyces Infecting Leguminous Crops

A study was made of the morphology of urediniospores and primary infection structures of 12 isolates of six legume-infecting species of Uromyces. Infection structures were sufficient to distinguish among species. Isolates of Uromyces viciae-fabae proved to be specialized with respect to host, because each isolate infected only cultivars of the species from which it was collected. Host-specialized isolates of U. viciae-fabae also were morphologically distinct, differing in both spore dimensions and infection structure morphology. In particular, the shape and dimensions of the substomatal vesicle were distinctive. These results support the view that U. viciae-fabae sensu lato is a species complex.

Sources of Resistance to Crenate Broomrape Among Species of Vicia

Crenate broomrape is a parasitic weed that represents a major constraint for pulse and forage legume production in the Mediterranean and West Asia regions. Control strategies have centered around agronomic practices and the use of herbicides, although success has been marginal. Resistance breeding is hampered by scarcity of proper sources of resistance and of a reliable and practical screening procedure. A germ plasm collection of 208 accessions of vetch belonging to 42 Vicia spp. was screened for resistance to crenate broomrape under field conditions. High levels of resistance were found in several species. Resistance of selected accessions was confirmed by a low induction of broomrape seed germination in pot and in vitro experiments. This was followed by a scarce establishment of broomrape radicles in contact with host roots and a limited development of established tubercles. In addition, a hypersensitive-like necrosis occasionally was observed, but at low frequency.

Isolate and organ-specific QTLs for ascochyta blight resistance in faba bean ( Vicia faba L)

The main objective of the present study was to locate the genomic regions responsible for ascochyta blight resistance in faba bean. Six QTLs were identified with the help of a linkage map constructed from a F(2) population from the cross between the inbred lines 29H (resistant) and VF136 (susceptible). Two pathogenically distinct Ascochyta isolates were used to study the genetic control against them and disease evaluations were performed separately on leaves and stems to investigate whether different genetic systems control resistance in each plant organ, as previously suggested. The six QTLs detected were named Af3 to Af8. Af3 and Af4 were effective against both Ascochyta isolates, Af5 was only effective against isolate CO99-01 while Af6, Af7 and Af8 were only effective against isolate LO98-01. Af3, Af4, Af5 and Af7 were revealed in both leaves and stems. By contrast, Af6 was only effective in leaves and Af8 only in stems. The validity and application of these results in a MAS program is discussed.

Identification of RAPD markers linked to the Uvf-1 gene conferring hypersensitive resistance against rust (Uromyces viciae-fabae) in Vicia faba L

Bulk segregant analysis was used to identify random amplified polymorphic DNA (RAPD) markers linked to a gene determining hypersensitive resistance in Vicia faba line 2N52 against race 1 of the rust fungus Uromyces viciae-fabae. The monogenic nature of the resistance was determined by analyzing the F(2) population from a cross between resistant line 2N52 and susceptible line VF-176, and further confirmed in the F(2:3)-derived families. Linkage of the RAPD markers was confirmed by screening 55 F(2) plants segregating for resistance. Three RAPD markers (OPD13(736), OPL18(1032) and OPI20(900)) were mapped in coupling phase to the resistance gene for race 1 ( Uvf-1). No recombinants between OPI20(900) and Uvf-1 were detected. Two additional markers (OPP02(1172) and OPR07(930)) were linked to the gene in repulsion phase at a distance of 9.9 and 11.5 cM, respectively. The application of marker-assisted selection to develop new faba bean varieties with rust resistance genes is discussed.

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. In addition, necrosis of the host cells associated with infection hyphae was detectable in some lines from the beginning of colony development. This microscopically visible necrosis became stronger from 4 days after inoculation, resulting in a reduced growth of the colony. Differences in resistance levels were more marked in adult plants than in seedlings.