Resistances to bean common mosaic virus, halo, common and Ascochyta
blight, angular leaf spot, anthracnose and rust pathogens of beans in
South Africa were combined by reverse dichotomous crossing. Full
resistance to Uromyces appendiculatus from Carioca 80 was conditioned by
a single dominant gene. Partially dominant resistance to Phaeoisariopsis
griseola was conditioned by a single gene in Carioca 80 and two genes in
PAl 127. Differences in aggressiveness of isolates of Phoma exigua var.
exigua were found. Different levels of Ascochyta blight resistance were
found in the glasshouse, but field testing showed little difference after
flowering.
Inoculations of differential cultivars indicated the presence of at least
eight races of U. appendiculatus and the a-Brazil race of Colletotrichum
lindemuthianum . Inoculations of the old set of halo blight differential
cultivars identified races 1 and 2.
Forty-five lines with partial resistance to rust were obtained by
recurrent selection. Very highly significant differences were noted
between ratings of percentage leaf area affected by rust and yield of 23
cultivars planted in field trials. Significant genotype x environment
interaction was noted for rust ratings. Ratings at different dates
within a trial were correlated with one another, showing few ratings are
required per trial, and a correlation of -0.678 between yield and rust
rating was found.
Inheritance of partial resistance and improved yield of eight cultivars
crossed in a full diallel was mostly due to additive effects but non-additive
effects were also very highly significant. Reciprocal effects
were not significant for yield and rust ratings. Genotype x environment
interactions were significant for rust ratings and yield. High estimates
of narrow-sense heritability for rust resistance were obtained.
No relationship between resistance and time to flowering, pustule size, leaf
hairs and stomata was found. Latent periods in unifoliate leaves did not
correlate with resistance but a closer match was found in the fourth trifoliate leaves. Inoculations with three additional single-pustule
isolates of the 23 parent cultivars indicated the cultivars had similar
levels of resistance.
Ring necrosis was found in nine cultivars or crosses with them. The ring
reaction was conditioned by a single dominant gene and possibly by the
epistatic interaction of two dominant genes in Carioca 80. Differences in
symptom severity in plants derived from Epicure indicated the possibility
of additional gene interaction. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9405 |
| Date | January 1994 |
| Creators | Edington, Brian Ross. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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