Effect Of Selection For Resistance Research Articles

Effects of selection for resistance to Sesamia nonagrioides on maize yield, performance and stability under infestation with Sesamia nonagrioides and Ostrinia nubilalis in Spain

A maize synthetic population was improved for resistance to the Mediterranean corn borer (MCB, Sesamia nonagrioides) while maintaining yield. The objectives of this research were to investigate whether yield and yield stability of the maize synthetic population named EPS12 were affected by selection for MCB resistance; also to determine which genotypic and environmental covariates could explain the genotype (G), environment (E) and genotype × environment (GE) effects for yield under corn borer infestation. Plants from three cycles of selection and their testcrosses to three inbred testers (A639, B93 and EP42) were evaluated at two locations in 2 years, under MCB and European corn borer infestations. After selection EPS12 was a more stable genotype. Hybrids derived from crosses between B93 and inbreds obtained from the initial cycles of selection could be recommended for cultivation in northern Spain. The yield of crosses between cycles of selection and testers increased when there were fewer days with temperatures >25°C and higher mean maximum temperatures. Differences in yield among these genotypes were mostly explained by resistance to corn borer attack. In general, among EPS12‐derived materials, genetic characteristics that contribute to increased grain yield were also responsible for increased abiotic stress tolerance.

Effect of Selection for Resistance and Susceptibility to Viral Diseases on Concentrations of Dopamine and Immunological Parameters in Six-Week-Old Chickens

White Leghorn chickens were inbred respectively from their parent lines, which were diversely selected for resistance (line 63) or susceptibility (lines 72 and 15I5) to Marek’s disease and lymphoid leukosis. The differences in disease resistance may have been due to differential regulation of immune and neuroendocrine homeostasis. At 5 wk of age, chickens from the same line were randomly assigned to cages at 4 birds per cage. Blood samples were collected from the chickens at 6 wk of age (n = 10/line). Subsets of T lymphocytes (CD4+ and CD8+) and B cells were measured using flow cytometry. Concentrations of plasma IgG and dopamine were quantified with ELISA and HPLC assay, respectively. Line 63 chickens had a higher percentage of CD8+ cells but not CD4+ cells than the chickens of the lines 72 and 15I5 (P < 0.01). In contrast, both lines 72 and 15I5 had a greater percentage of B cells (P < 0.01). The concentrations of plasma IgG and dopamine were also regulated differently among the lines; both were in an order of 72 > 15I5 > 63 (P < 0.05 and P < 0.01, respectively). These results suggested that genetic selection for disease resistance also directly or indirectly modified the corresponding genetic components that govern the immune and neuroendocrine systems. The genetic lines of chickens may be used as animal models for investigation of the cellular mechanisms of genetic-environmental interactions on disease resistance.

Evaluation of F2 and F3 plants introgressed with QTLs for clubroot resistance in cabbage developed by using SCAR markers

Clubroot disease caused by Plasmodiophora brassicae is one of the major diseases of Brassica crops, often devastating to the cultivation of cruciferous crops in temperate regions. In a previous study (Moriguchi et al. 1999) identified three major quantitative trait loci (QTLs) for clubroot resistance, each in a separate linkage group, in a population derived from a cross between a clubroot-susceptible inbred cabbage line, Y2A and a resistant inbred kale line, K269. In this study, the original random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers were converted into sequence-characterized amplified region (SCAR) markers to facilitate large-scale marker-assisted screening of clubroot resistance in cabbage breeding. Of 15 RAPD markers closely linked to the three QTLs, nine SCARs were developed as dominant markers after cloning and sequencing. In addition, two RAPD markers were converted into co-dominant cleaved amplified polymorphic sequence (CAPS) markers, and one RFLP marker out of three tested was converted to a dominant SCAR marker. The effect of selection for resistance by the improved markers was evaluated in progeny plants in the F 2 and F 3 . A total of 138 F 2 plants were genotyped with nine SCARs and 121 well-distributed makers consisting of 98 RAPD, 19 RFLP, two isozymes, and two morphological markers in order to estimate the level of resistance and the proportion of undesirable alleles from the kale in non-target areas in each of the F 2 populations. An F 2 plant, YK118, had kale alleles at QTL1, QTL3 and QTL9. Three F 2 plants, namely, YK107, YK25 and YK51 had kale alleles at only QTL1, QTL3 and QTL9, respectively. These F 2 plants were selected for their low proportion of alleles derived from kale in non-target regions. YK118, like the resistant kale parent, expressed very high resistance to three field isolates of Plasmodiophora brassicae, whereas the mean disease index in the F 2 and F 3 plants carrying only single QTLs was intermediate. The QTLs showed no differential response to the isolates. These plants with improved resistance will be useful as parental inbred lines for F 1 hybrids.

Molecular changes in the maize composite EPS12 during selection for resistance to pink stem borer

The pink stem borer (Sesamia nonagrioides Lefèvbre) is the most important pest of maize (Zea mays L.) throughout the Mediterranean area. The maize composite EPS12 has been chosen as the base population for a breeding program based on its resistance to pink stem borer, with the main selection criterion being resistance to stem tunneling. Yield was taken as a secondary selection criterion to avoid any unwanted negatively correlated response on this character. The aims of investigation were: (1) to monitor the effects of selection for resistance to pink stem borer on allele frequency at 70 simple sequence repeat (SSR) markers and their impact on the genetic structure of EPS12 and (2) to identify loci at which allelic frequencies changed significantly due to directional selection. Genetic diversity was reduced during the selection process (as expected since random genetic drift as well as selection could reduce genetic variability), but not significantly so. Although the loss of genetic variation was generally consistent with that expected in a model in which random genetic drift acts alone on neutral alleles, the changes observed in the frequency of five alleles were significantly greater than expected. Further, the linear trend of the departure from the random genetic drift model was significant for some allelic versions of two SSR markers, umc1329 and phi076; directional selection was therefore acting on these loci. The significant effect of directional selection on those markers suggests the presence of quantitative trait loci (QTLs) for tunnel length and/or for yield under artificial infestation with Sesamia nonagrioides on the long arm of chromosome 4.

Evaluación de habichuela (Phaseolus vulgaris L.) en generaciones tempranas para resistencia a Xanthomonas campestris pv. phaseoli (Smith) dye

Se evaluaron las generaciones F3 y F4 en ensayos de campo, y la F5 a nivel de invernadero, de dos poblaciones provenientes de los cruces DOR 364 x XAN 176 y DOR 364 x WBB-20-1. Los objetivos fueron evaluar la utilidad de seleccionar en generaciones tempranas líneas resistentes a Xanthomonas campestris pv. phaseoli (Xcp) y determinar la heredabilidad (h2) de la resistencia del follaje a Xcp. El estudio se realizó en 1991 en la Subestación de Isabela, de la Universidad de Puerto Rico. Los progenitores XAN 176 y WBB-20-1 mostraron más resistencia a Xcp que DOR 364. En las tres generaciones evaluadas y en ambas poblaciones se observaron diferencias significativas en resistencia entre las líneas. El valor de heredabilidad de la resistencia del follaje en la población DOR 364 x XAN 176 fue de intermedia a alta (&gt; 0.60). En la población DOR 364 x WBB-20-1, la h2 fue baja (0.30) en la generación F3 y de intermedia a alta (&gt; 0.60) en las generaciones F4 y F5. Las evaluaciones en la generación F3 requieren por lo menos tres repeticiones para obtener un nivel adecuado de precisión para detectar diferencias entre líneas. La selección en la generación F4 fue más efectiva debido a que en dicha generación existe un mayor grado de heredabilidad. La evaluación de la enfermedad mediante una escala de 1 a 9 fue mejor que mediante el porcentaje de área foliar afectada, ya que con el primer criterio se obtuvo menos variación entre generaciones. Además, las varianzas también fueron homogéneas entre grupos de líneas.

The effect of selection for resistance to clover infertility on the reproductive performances of Merino ewes grazed on oestrogenic pastures

Rams were bred from ewes which had either maintained their fertility after grazing highly oestrogenic pastures for three to seven years. or, over the same period grazed �control� on or lowly oestrogenic pastures In 1977 and 1978 these rams were joined with a random selection of ewes, which had been grazed on lowly oestrogenic pastures, to produce contemporary Resistant and Control ewes.The Resistant and Control ewes were split at weaning into groups which subsequently were grazed on oestrogenic or non-oestrogenic pastures during each pasture growing season (May to October) of the experiment During the dry spring-summer period the ewes were regrouped and entire rams were joined with them for 42 days from early in January to determine whether resistance to the development of clover infertility had been inherited.The reproductive performances of the ewes were measured from two until eight years of age over the period from 1979 to 1986. In addition, the masculinization of the vulvas was monitored, mucus product ion was measured in the second last year, and the histology of the cervixes was observed when the experiment was terminated.The fertility of the Resistant ewes was affected by the oestrogenic pasture in the later years of the experiment, but the level of depression was significantly lower than that measured in the Control ewes grazed on oestrogenic pasture The realized 'heritability' of the ewes' fertile lifetime on oestrogenic pasture was estimated to be 0.73 with a standard error of 0.30.This resistance was associated with histological changes, which confirmed that the Resistant ewes were protected against oestrogen-induced damage. These results support the hypothesis that res istance to the development of clover infertility was present in these ewesA more intensive selection programme involving both ewes and rams may impart a higher level of resistance to ewes This would reduce the adverse effects of oestrogenic pastures on ewe flock productivity.

The perturbation ofDrosophila melanogaster esterase-6 allozyme frequencies by selection for malathion resistance

The effects of selection for resistance to the organophosphate insecticide malathion on esterase-6 polymorphism was studied in laboratory populations ofD. melanogaster. A genetically well-mixed population was constructed from 40 locally-caught, iso-female lines, divided into control and malathion-selected lines and the frequency of the majorEst-6 alleles was followed for more than 100 generations. The main findings were: (1) The allele frequency in control replicates remained stable for over one hundred generations; (2) the allele frequency in the populations exposed to malathion changed dramatically and in the opposite direction between replicates during the early generations of the selection experiment; (3) all selected populations eventually returned to the controlEst-6 allele frequencies. This return was more rapid in populations exposed to lower selection intensity compared to those exposed to higher selection intensity; (4) the convergence ofEst-6 allele frequencies to control values was also observed in three populations obtained by mixing flies of appropriate genotypes from the control population to give different initial frequencies. These results have been interpreted to mean that esterase-6 does not have a direct role in malathion resistance, and that theEst-6 polymorphism in our experimental population was maintained by balancing selection.

Effects of selection for resistance to organophosphorus insecticides on two esterase loci in Drosophila melanogaster

Two laboratory populations of Drosophila melanogaster were exposed to the insecticides ethyl-parathion and fenthion respectively. Three parameters were studied in each generation: resistance to the insecticide (LC 50), AChE activity, and allele frequencies at the Est-6 locus. In both treated populations a significant increase in the resistance was observed within a few generations. This rise in the resistance levels was accompanied by parallel changes in the two esterases AChE and Est-6. With AChE the enzyme activity became considerably higher indicating either structural modification of the enzyme molecule or mutations in the regulatory system of the AChE gene locus. At the Est-6 locus the S allele was eliminated during the selection process which might be due to greater sensitivity of the Est-6S allozyme.