Genetics of resistance to Stenocarpella maydis ear rot of maize
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Date
2001-05
Authors
Rossouw, Johannes Daniƫl
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The objective of this study was to determine if germplasm available in South Africa
and elsewhere, have sufficient variation in resistance to be used for the improvement of
resistance to Stenocarpella maydis, and to assess the viability of using recurrent
selection as a breeding method under conditions of artificial infection with the
pathogen. The study attempted to provide a better understanding of effective methods
to screen for resistance without sacrificing other favorable agronomic traits. The
inheritance and combining ability of resistance, as well as genetic and phenotypic
correlation of resistance parameters with other characteristics, were investigated.
The study comprised of three experiments. The first experiment was a complete diallel
cross containing 10 commercial and experimental inbred lines, ranging from resistant
to susceptible. Five South African developed inbreds, four USA developed and one
Brazilian inbred were used. The diallel was evaluated during the 1999/2000 season at
three environments across the South African maize growing area. Plants were
artificially inoculated twice, two weeks prior to anthesis. Different S. maydis related
and agronomic characteristics were measured. The second experiment was a trial
containing both South African developed hybrids and hybrids derived from crosses
between South African developed germplasm and those of exotic and temperate origin.
The trial was evaluated at one environment in the South African maize growing area.
Again, plants were artificially inoculated twice, two weeks prior to anthesis.
Flowering data were taken along with S. maydis incidence and grain moisture at
harvest. The third experiment involved the evaluation of a recurrent selection
program, using three previously identified resistant inbreds as donor parents for the
development of new genotypes with superior resistance to S. maydis. Selection was
done on an ear-to-row basis over three years, using the segregating progenies derived
from crosses between the three inbreds.
Highly significant differences were obtained between genotypes for all characteristics
measured, indicating variation for resistance in germplasm used in local breeding
programs. Across all three environments, the general combining ability (GCA) and
specific combining ability (SeA) effects were significant. Inbreds D0620Y, MON1
and F2834T had the greatest negative GCA effects for S. maydis related characteristics
that contributed towards resistance, with MONI being heterotically unique, combining
to all the other inbreds. PI combinations with inbred B37 had the greatest negative
SeA effects of all genotype combinations evaluated. GCA:SCA ratio's indicated that
resistance is controlled by additive gene effects, with low dominance and interaction
effects. Genetic correlations existed between the S. maydis related characteristics,
with very high heritability and high correlated response between them. Due to it's
simplicity, percentage rotted ears was the best method to measure resistance. Upright
ears were found to result from S. maydis infection, rather than to predispose ears to
the disease.
Significant differences were found between maturity classification and S. maydis
incidence for South African developed germplasm crossed to temperate and tropical
germplasm. Later flowering hybrids showed less S. maydis infection compared to
earlier hybrids. Using resistant parents in breeding populations, superior genotypes
could be selected by applying artificial inoculation and recurrent selection on an ear-torow
basis.
Description
Keywords
Disease measurement, Ear rot, Inheritance, Maturity, StenocarpelIa maydis, Zea mays, Corn -- Genetics -- South Africa, Corn -- Disease and pest resistance -- Genetic aspects, Dissertation (M.Sc.Agric. (Plant Breeding))--University of the Free State, 2001