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December, 2008
Source: Plant Breeding News,
Edition 196
Contributed by Aloísio
Sartorato, former Embrapa Rice and Bean scientist (Embrapa
Arroz e Feijão, C. P. 179, CEP 75375-000 Santo Antonio de Goias,
Brazil)
Bean rust is a very important diseases in several bean
production areas of Brazil. This disease is caused by the fungus
Uromyces appendiculatus. Control measurements of the disease
includes aerial spray of fungicides and the use of resistant
genotypes. Nowadays, consumers have demonstrated high preference
to the consumption of organic foods, i.e., food production
without the use of fungicides or any other dangerous chemical.
So, the most important way to control the disease is through
resistant cultivars. However, as it does occur with other bean
diseases, the fungal pathological variability makes the
development of new resistant cultivars more difficult. As a
result new sources of disease resistance have to be identified.
Seven experiments, each one including one U. appendiculatus
isolate, were undertaken under greenhouse conditions to identify
a genotype with the broadest resistance spectrum. Five seeds of
each genotype were sown in a 2,0 kg aluminum pot (3 parts of
soil + 1 part of sand). Plants were inoculated 14-16 days after
seeding and disease was recorded 14 days after inoculation using
a 1 to 6 scale (Stavely, JR, Freytag, GF, Steadman, JR &
Schwartz, HF. The bean rust workshop. Annual Report of the Bean
Improvement Cooperative, v. 26, p. 4-6, 1983). Plants exhibiting
grades 1 to 3 were considered resistant and 4 to 6 susceptible.
Genotypes ARC 100-4, BRS REQUINTE, CNFC 07824, CNFC 08017, CNFC
08063, CNFC 08075, JURITI, LARANJA and SUPREMO were resistant to
all seven isolates (different pathotypes) tested. Some of this
genotypes showed complete resistance (including hypersensitive
reaction) to most isolates. Others cultivars besides presenting
these symptoms to some isolates also showed incomplete
resistance (grade 3) to others isolates. These genotypes
together with those that were resistant to six isolates (ARC
100T-5, CNFC 08013, CNFC 09461, CNFM 07958, OPNS 0331 –
MAJESTOSO, PÉROLA and PONTAL) must have their resistance
reaction confirmed. Besides, they have to be tested to a greater
pathogenic variability of the fungus before being introduced in
a bean breeding program to develop more resistant cultivars to
this disease. |
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