Abstract:
Ralstonia solanacearum race 3 biovar 2 (phylotype II)
is the causal agent of bacterial wilt of tomato, the most
destructive bacterial disease of this crop in Ethiopia for
which no effective control measures are available. In
this study, the effects of amending topsoil with three different levels (1, 5 and 10%) of cocopeat, farmyard manure (FYM) compost and green compost, and two levels of bacterial inoculations were tested on infection of
tomato by R. solanacearum compared to non-inoculated
treatments. Non-amended topsoil with and without R.
solanacearum were included as control treatments. Survival of and infection by R. solanacearum and yield-associated agronomic responses were used for evaluation
along with physico-chemical and biological characteristics of amended soils. Amendments resulted in changes
in physico-chemical properties (such as electrical conductivity, organic matter content, total carbon, dissolved
organic carbon, NH4
+, NO3
-
) and microbial activity of
the amended soil and the effects were found to be higher at the higher rate of application. Effects on disease
suppression and survival of the pathogen in the soil differed depending on amendment type and application
rate. Higher disease severity was recorded in soil
amended with 10% green compost compared to the
control treatment. Complete suppression of R.
solanacearum was observed in pots amended with 5 and
10% farm yard manure (FYM), 1% green compost and
10% cocopeat. Absence of disease at the highest rate of
FYM was supported by a lower number of culturable R.
solanacearum bacteria recovered from rhizosphere soil
two months post-inoculation in soil amended with 10%
FYM. Soil amended with 10% FYM gave higher root
and above-ground dry weight. Moreover, FYM added
to topsoil at 5 and 10% gave significantly higher aboveground fresh weight. This study indicated that amending topsoil with different types and rates of amendment
can suppress bacterial wilt severity and pathogen survival in the soil. Amendments also enhanced tomato
Corresponding author: G.B. Yadessa
Fax: +251.471110934
E-mail: gberecha@yahoo.com
yield, the higher rates of amendments being the most effective except green compost at 10% which gave a 27%
lower yield compared with the higher rate of FYM.
Among the amendments tested, FYM at 5 or 10% would
be an interesting option to manage R. solanacearum in
the major tomato-growing regions of Ethiopia. However,
the mechanisms of disease suppression at higher rates of
FYM need to be investigated
