Maize streak virus (MSV) disease may cause significant grain yield reductions in maize in Africa. Réunion island maize germplasm is a proven source of strong resistance. Its genetic control was investigated using 123 RFLP markers in an F(2) population of D211 (resistant) × B73 (susceptible). This population of 165 F(2:3) families was carefully evaluated in Harare (Zimbabwe) and in Réunion. Artificial infestation was done with viruliferous leafhoppers. Each plant was rated weekly six times after infestation on a 1-9 scale previously adjusted by image analysis. QTL analyses were conducted for each scoring date, and for the areas under the disease, incidence and severity progress curves. The composite interval mapping method used allowed the estimation of the additive and dominance effects and QTL × environment interactions. Heritabilities ranged from 73% to 98%, increasing with time after infestation. Resistance to streak virus in D211 was provided by one region on chromosome 1, with a major effect, and four other regions on chromosomes 2, 3 (two regions) and 10, with moderate or minor effects. Overall, they explained 48-62% of the phenotypic variation for the different variables. On chromosome 3, one of the two regions seemed to be more involved in early resistance, whereas the second was detected at the latest scoring date. Other QTLs were found to be stable over time and across environments. Mild QTL × environment interactions were detected. Global gene action appeared to be partially dominant, in favor of resistance, except at the earliest scoring dates, where it was additive. From this population, 32 families were chosen, representing the whole range of susceptibility to MSV. They were tested in Réunion against three MSV clones, along with a co-inoculation of two of them. Virulence differences between clones were significant. There were genotype × clone interactions, and these were more marked for disease incidence than for severity. Although these interactions were not significant for the mean disease scores, it is suggested that breeders should select for completely resistant genotypes.
El comportamiento del cultivar Waych'a (Solanum tuberosum spp. andigena) fue evaluado en microparcelas inoculadas con ocho densidades (O, 0.125, 0.25, 0.5, 1, 2, 4 y 8 indv./g suelo) de Nacobbus aberrans. Las evaluaciones se efectuaron a los 90, 118 y 146 días de la siembra, considerando las variables agrofisiológicas: altura de planta, longitud radical, peso fresco del follaje y peso de la raíz, y las variables nematológicas (número de nódulos, fluctuación poblacional, número de hembras y machos por nódulo). A la cosecha (160 días) se determinó el peso total y por tamaño de los tubérculos. Las densidades iniciales del nematodo afectaron principalmente a las variables agrofisiológicas.El rendimiento total fue negativamente afectado en peso y número, conforme se incrementaron las densidades de N. aberrans. En las variables nematológicas, se observaron diferencias en la nodulación y proporción de sexos. Los nódulos disecados presentaron por lo menos una hembra en cada uno de los estadios. Aceptado para publicación: julio 1997.
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