Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
Diagnosis and Management of Bacterial wilt of Solanaceous Crops
caused by Ralstonia solanacearum
Dinesh Singh
Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi -110 012
Bacterial wilt caused by Ralstonia solanacearum (Smith, 1896) Yabuuchi et al., 1995 is
highly challenging and one of the most destructive diseases of solanaceous crops including
tomato, potato, chilli and brinjal worldwide. The disease is predominant in warm humid tropical and
temperate regions of the world (Hayward, 2005). In India, it occurs across the country mainly
states of coastal areas, foot hills and lower altitude of hills (Singh et al., 2010). It has a wide host
range of about 200 different groups of plants with 50 families, which accounts severe damage to
the crops. This wilt disease is a very serious in solanaceous crops. and. The damage caused by
this disease to the crop was > 60% depends on environmental conditions and variety of crops.
Bringing about severe crop losses worldwide, the disease is now receiving global profile (Allen et
al., 2005). It is disturbing agriculture and even trade negotiations in the developing as well as
developed world. It is listed as one of the top ten microorganisms affecting agriculture in U.S.
Agro-terrorism Protection Act of USDA (2002) and subjected to strict quarantine regulations
throughout Europe and America.
Recently, a new classification scheme has been described for strains of R. solanacearum,
based on comparison of DNA sequences is commonly used for classification studies of strains of
microorganism. It is basically assumed that the higher the homology is between two strains, the
more closely related the strains are in terms of evolution. These types of studies are known as
phylogenetic studies. A sequevar or sequevance variant is defined as a group of strains with a
highly conserved sequence within the area sequenced sequevars. A phylotype is defined as a
group of strains that are closely related based on phylogenetic analysis of sequence data.
Phylotypes were identified within the species that broadly reflects the ancestral relationships and
geographical origins of the strains In R. solanacearum four phylotype viz., Phylotype I, Phylotype
II, Phylotype III and Phylotype IV has been reported by Fegan and Prior, (2005). Each phylotype is
composed of a number of sequevars (Figure 1). Distribution of five races of R. solanacearum,
host, biovars and RFLP divisions are presented in Table 1. In India, race 1 biovar 3 and 4 of R.
solanacearum causes bacterial wilt of solanaceous crops (Table 1). Race 3 (biovar 2) strains are
widely distributed in Asia (including Pakistan, India, Bangladesh, China and Philippines) and
Middle East countries (Lebonan and Iran). Majority of the strains isolated from Asia belong to
phylotype 1. However, Race 3 (biovar 2) strains belonging to phylotype II predominate in South
America. In India All major strains reported from India fall under phylotype I and North America
Phylotype II (Fegan and Prior, 2005). Main crops affected are tomato and tobacco.
- 43 -