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Genetic resistance to Potato Leafroll Virus (PLRV) is polygenic, which hinders the obtainment of resistant cultivars. However, works carried out at the International Potato Center have identified an andigena accession, LOP-868, with high resistance level and low accumulation of PLRV due to the gene of major effect Rladg. We verify the transfer of the Rladg allele to clones of the cross between LOP-868 and UFLA clones, by using the SCAR RGASC850 molecular marker; to evaluate the reaction of these clones to PLRV by inoculating the virus using aphids; and to analyze their agronomic performance of clones. Among the clones inoculated with viruliferous aphids, 49.3% were negative to the serological test, indicating possible resistance. Clones containing the Rladg allele were identified by the RGASC850 molecular marker, which demonstrates the possibility of transferring the Rladg allele of resistance to PLRV from LOP-868 to Solanum tuberosum. Some clones that presented the Rladg allele are also promising for agronomic performance.

The Ry adg allele is widely used by breeders to confer extreme resistance to all strains of PVY. However, the necrotic strain has increased recombination resulting in recent considerable losses in productivity. Thus far, not all necrotic recombinant strains of PVY have been tested for their reaction to the Ry gene. The objective of this study was to identify potato clones carrying the resistant allele and to assess their reaction to the following recombinant strains: NTN (PVY NTN), Wilga (PVY N-Wi), and "curly top" (PVY E). Advanced clones from the potato breeding program at Universidade Federal de Lavras were evaluated through a specific molecular marker for the Ry adg allele. The clones carrying the resistance allele were grafted on tobacco plants infected with necrotic recombinant strains of PVY. The clones carrying the allele for resistance to PVY were not infected with any of the recombinants during the grafting test. These results confirm that resistance to necrotic recombinant strains has not yet been overcome and that the Ry adg allele also confers resistance to the three recombinant strains tested.

Potato (Solanum tuberosum L.) breeding for PVY resistance is of utmost importance, in view of the greatdamage this disease can cause. The establishment of triplex (RyRyRyry) or quadruplex (RyRyRyRy) clones as parents facilitatebreeding work because their progenies have a high proportion of clones with the resistant allele. The purpose of this study wasto select clones with three to four copies of the Ryadg allele from a population derived from duplex (RyRyryry) crosses and toevaluate the agricultural traits. Testcrosses with a nulliplex genotype (ryryryry) were performed to identify the genotypes forthe Ryadg allele, using the SCAR RYSC3 marker. Triplex and quadruplex clones were identified by the marker, but a largernumber of progenies of the test-cross must be tested for the confirmation of their genotypes. The agricultural performance ofthe clones with the Ryadg allele was better than of the control cultivars.

The cooking time of common bean grains is one of the determinant factors for the consumer acceptance of acultivar. Since in the segregating populations tegument and cotyledons are in different generations, one needs to know whichone of these structures influences the cooking quality to define breeding objectives. We evaluated the parentals, the F1, F2, andF3 generations and the reciprocals of the crosses CI-107 x Carioca-80, CI-107 x Amarelinho and CI-107 x G2333. A maternaleffect was stated in the trait expression since bean cooking quality was mainly determined by the tegument constitution. Theinferences derived from genetic and phenotypic parameters were not expressively affected by storing, whereas the cookingtime increased with higher grain ages.

ABSTRACT: Early blight is one of the most important fungal diseases of potato. The objective of this study was to evaluate the in vitro reaction of potato genotypes to the severity of early blight and compare the species Alternaria solani and Alternaria grandis , etiologic agents of disease, through the evaluation of physiological characteristics. Twenty-two genotypes of the Potato Breeding Program at UFLA, two cultivars, Aracy and Bintje, patterns of resistance and susceptibility, respectively were evaluated. For inoculation, three isolates of A. grandis and two isolates of A. solani were used. Plantlets obtained in vitro were inoculated with a 5mm diameter mycelial disk of isolates Alternaria spp. of. These were incubated in severity and classified according to the rating scale. Isolates of Alternaria spp. were evaluated for mycelial growth index (MGI) and for formation of mycelial compatibility groups (MCG). The methodology for evaluating the in vitro reaction of genotypes to severity of early blight was efficient for both isolates. The isolates of A. solani and A. grandis were similar in their aggressiveness. The isolates of A. grandis MGI's had higher, and therefore mycelium grew faster when compared to those isolated from A. solani . The occurrence of mycelial compatibility among isolates of A. solani and A. grandis indicated the possible occurrence of parasexual cycle.