Ecology, epidemiology and pathogenic variability of pseudomonas syringae pv. phaseolicola in the southern highlands of Tanzania.
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Date
1998
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Sokoine University of Agriculture
Abstract
Investigations were carried out to determine
races of Pseudomonas syringae pv.
phaseolicola existing in the Southern Highlands of Tanzania and the relationship
between motility and virulence of the pathogen. The epiphytic survival of a brown
diffusible pigment producing strain (9337- uncertain race type) and a non brown
diffusible pigment producing strain (9359-racc 6) of P.s.phaseolicola was also studied
in bean genotypes Kablanketi and Uyole-90.
On the basis of cultural, biochemical and pathogenicity tests, 260 isolates were
identified as P.s.phaseolicola. Using the
Biolog Microplate identification system,
other isolates of fluorescent pseudomonads encountered were confirmed to be
Pseudomonas fluorescens A and Pseudomonas syringae pv. syringae A.
Race determination, using eight halo blight differential bean cultivars, showed that
races 1,2, 3, 4. 5, 6. 7b and 8 exist in the Southern Highlands of Tanzania. In addition,
7.6% of the strains characterized were of uncertain race type, suggesting occurrence of
wider pathogenic variability than could be categorized using the current set of halo
blight differential cultivars. Races 3 and 6 were the most prevalent. Race 3 occurred at
a high frequency in Mbeya and was predominant in Nkasi and Sumbawanga districts.
About 32% of the isolates collected produced the brown diffusible pigment in vitro.
Some brown pigment producing strains were found to be race 3. Race 3 strains, which
cause a very strong hypersensitive reaction associated with systemic necrosis on
several bean genotypes including Tendergreen and A53, exist in the region.
Strains isolated from N.wighlii and Desmodium sp. and characterized as race 7b were
less virulent on bean cultivars A52 and A53 than race 7b strains originating from
P. vulgar is.I hirly-six germplasm accessions were tested for resistance to eight strains of
P.s.pliasi'olicola. New sources of resistance to races 1. 3, 4, 5, 7b, and strains 9337
(brown diffusible pigment producing strain) and 14494 (closely related to race 9) were
identified. Differences in motility between and within races of P.s.phaseolicola were
also demonstrated.
Results from epiphytic population studies showed that there were differences between
bean genotypes Kablanketi and Uyole-90 in supporting the epiphytic populations of
die brown diffusible pigment producing strain 9337 and race 6 (strain 9359) of
I’.s.p/iiixeolieolii. The resulting halo blight disease severity scores were generally low
but comparably higher on Kablanketi inoculated with race 6.
In vitro and in vivo studies under greenhouse conditions were conducted to determine
the inhibitors effect of garlic bulb extract on growth of races 3, 6 and a brown
diffusible pigment producing strain 9337 (uncertain race type) of P.s.phaseolicola.
Antibacterial activity was shown as clear zones of inhibition. Halo blight disease
incidence and severity on bean genotypes Uyole-90. Canadian Wonder and Kablanketi
were significantly reduced.
Pseudomonas syringae pv. phaseolicola strains 9337 (a diffusible brown pigment
producer of an uncertain race type) and 9359 (race 6) survived in immature flat green
pod tissues at 18 to 25°C in the laboratory for nine months.
Description
PhD-Thesis
Keywords
Pseudomonas syringae, Ecology, Pathogen, Symptomatology, Southern highlands-Tanzania