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Inheritance of resistance to Septoria leaf blotch in selected spring bread wheat genotypes (Triticum aestivum L.)Briceno Felix, Guillermo Ariel 03 August 1992 (has links)
Septoria leaf blotch of wheat is a major biotic factor limiting the grain yield.
To determine the nature of inheritance involving selected genotypes, three resistant
semidwarf spring wheat lines exhibiting durable global resistance and one susceptible
cultivar were crossed in all possible combinations, excluding reciprocals. Parents, Fl,
F2, and F3 generations were inoculated with one pathogenic strain of Septoria tritici
and evaluated under field conditions. Data were collected on an individual plant
basis. F2 and F3 frequency distributions were computed to determine the nature of
inheritance. Combining ability analysis of the 4x4 diallel cross and narrow-sense
heritability were employed to estimate the nature of gene action. Phenotypic
correlations were obtained to examined the possible association between disease
severity traits and their relationship with heading date and plant height.
The continuous distribution of the F2 and F3 populations among crosses made
it impossible to classify plants into discrete classes in crosses between resistant x
susceptible genotypes. Mean values of the disease traits Septoria progress coefficient,
Relative coefficient of infection, and Septoria severity of flag leaf among the
segregating populations were similar to the midparent values. Transgressive
segregation was also observed in the F2 and F3 suggesting that parents had different
resistance genes. Additive gene effects were found to be the major component of
variation although nonadditive gene action played an important role in the expression
of all three disease traits. The resistant parents Bobwhite"S" and Kavkaz /K4500
L.A.4 were found to have the largest negative general combining ability effects for
the disease traits suggesting that these parents would be the best source for resistance
to Septoria leaf blotch. High general combining ability and high narrow sense
heritability estimates in the F3 population, indicated that substantial progress for
resistance to Septoria tritici would be effective selecting in this generation. Of the
three disease measures it would appear that selection for the lowest percentage of
Septoria infection on the flag leaf would provide the most progress in developing
resistant cultivars. Moderate and low negative phenotypic correlations were found
among generations for the disease traits with heading date and plant height. From the
results of this study the selection of early maturing short stature progeny would be
possible within the genetic materials employed in this study. / Graduation date: 1993
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Effects of host resistance on Mycosphaerella graminicola populationsCowger, Christina 19 March 2002 (has links)
Mycosphaerella graminicola (anamorph Septoria tritici) causes Septoria tritici blotch, a
globally important disease of winter wheat. Resistance and pathogenicity generally vary
quantitatively. The pathogen reproduces both sexually and asexually, and the pathogen
population is highly genetically variable. Several unresolved questions about the
epidemiology of this pathosystem are addressed by this research. Among them are
whether cultivar-isolate specificity exists, how partial host resistance affects pathogen
aggressiveness and sexual reproduction, and how host genotype mixtures influence
epidemic progression and pathogenicity.
At its release in 1992, the cultivar Gene was highly resistant to M. graminicola, but that
resistance had substantially dissolved by 1995. Six of seven isolates collected in 1997
from field plots of Gene were virulent to Gene seedlings in the greenhouse, while 14 of
15 isolates collected from two other cultivars were avirulent to Gene. Gene apparently
selected for strains of M. graminicola with specific virulence to it.
In a two-year experiment, isolates were collected early and late in the growing season
from field plots of three moderately resistant and three susceptible cultivars, and tested on
seedlings of the same cultivars in the greenhouse. Isolates were also collected from plots
of two susceptible cultivars sprayed with a fungicide to suppress epidemic development.
Isolate populations were more aggressive when derived from moderately resistant than
from susceptible cultivars, and more aggressive from fungicide-sprayed plots than from
unsprayed plots of the same cultivars.
Over 5,000 fruiting bodies were collected in three years from replicated field plots of
eight cultivars with different levels of resistance. The fruiting bodies were identified as
M. graminicola ascocarps or pycnidia, or other. In all three years, the frequency of
ascocarps was positively correlated with cultivar susceptibility, as measured by area
under the disease progress curve, and was also positively associated with epidemic
intensity.
For three years, four 1:1 mixtures of a moderately resistant and a susceptible wheat
cultivar were planted in replicated field plots. Isolates from the plots were inoculated as
bulked populations on greenhouse-grown seedlings of the same four cultivars. Mixture
effects on disease progression varied among the years, and were moderately correlated
with mixture effects on pathogenicity. / Graduation date: 2002
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Genetics and Quantitative Trait Loci Mapping of Septoria Tritici Blotch Resistance, Agronomic, and Quality Traits in WheatHarilal, Vibin Eranezhath January 2013 (has links)
Most breeding programs aim at developing superior germplasm and better cultivars that combine high yield, disease and pest resistance, and end-use quality to satisfy the requirements of the growers as well as industry. A population, consisting of 138 F2-8 recombinant inbred lines (RILs) derived from a cross between ‘Steele-ND’ and ND 735, was evaluated to study the inheritance pattern of the septoria tritici blotch (STB)-resistant genes, agronomic and quality traits. The framework map made of 392 markers, including 28 simple sequence repeat (SSR) markers and 364 DArT markers, spanned a total distance of 1789.3 cM and consisted of 17 linkage groups. The map position of quantitative trait loci (QTL) found in this study coincided with the map position of durable STB resistance genes, Stb1. Thirteen QTL were detected for agronomic and quality traits. More saturation of the current map is needed to explore more QTL for this population.
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