GENE ACTION AND INHERITANCE OF RESISTANCE TO RHIZOCTONIA SOLANI AND PYTHIUM ULTIMUM IN COTTON SEEDLINGS
GENE ACTION AND INHERITANCE OF RESISTANCE TO RHIZOCTONIA SOLANI AND PYTHIUM ULTIMUM IN COTTON SEEDLINGS
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Date
1986-05
Authors
MAXWELL, AMLAI TODI POSWAL
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Abstract
Gene Action and Inheritance of Resistance to Rhizoctonia
solani and Pythium ultimum in Cotton Seedlings
(May, 1986)
Maxwell Amlai Todi Poswal, B.Sc. (Agric.)
Ahmadu Bello University, Zaria, Nigeria
M.Sc. (Crop Protection) Ahmadu Bello University,
Zaria, Nigeria.
Chairman of Advisory Committee: Dr. K.M. El-Zik
Six cotton cultivars, three multi-adversity resistant
(MAR) and three non-MAR, and their 15 Fi and 15 F2 progenies
obtained from a diallel set of crosses (no reciprocals)
were used to determine the genetic system controlling
traits associated with resistance to R. solani
and P. ultimum. Experiments were conducted for two years
in a field naturally infested with both pathogens, and in
temperature controlled water bath tanks, using soil artificially
inoculated with each of R. solani and P. ultimum
separately at two inoculum densities. Genetic information
based on the diallel analyses of Hayman, Jinks and
Griffing for the data collected in the field were inconclusive.
However, measures of gene action and interaction,
and the inheritance of resistance to the two pathogens
were obtained from the temperature tank experiments.
Independent action of non-allelic genes (no epistasis)
was the only genetic assumption of the diallel analysis
that was not valid for all traits for both pathogens.
Dominance effects (H1 and H2) were the most predominant in
the F1 and F2 diallel analyses for most traits associated
with resistance to both R. solani and p. ultimum. The
additive effects (D) were smaller in magnitude than the
dominance effects. Average degree of dominance ranged
from partial to overdominance with different responses to
both pathogens. The analysis of F2 data detected a significant
epistatic effects for all traits and for both
pathogens.
Heritabilities in the narrow sense were low, ranging
from 0.0% to 20.7% for R. solani. For P. ultimum, heritabilities
ranged from 0.0% to 10.2%. General combining
ability effects were important for the expression of resistance
to R. solani and specific combining ability effects
for P. ultimum.
The results indicated that resistance in cotton seedlings
to both R. solani and P. ultimum was polygenically
inherited and conditioned by a complex of minor genes.
Extension of the genetic analysis to the F2 provided more
reliable information on the genetic system.
The most important trait associated with final stand
establishment of cotton seedlings in the presence of R.
solani was post-emergence damping-off, explaining 92% of
the variability in final stand. Pre-emergence damping-off
due to P. ultimum, explained 62% of the variability in
final stand.
Description
A Dissertation
BY
MAXWELL AMLAI TODI POSWAL
Submitted to the Graduate College of
Texas A&M University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
MAY, 1986
Keywords
GENE ACTION,, INHERITANCE,, RESISTANCE,, RHIZOCTONIA,, SOLANI,, PYTHIUM ULTIMUM,, COTTON SEEDLINGS