Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
disease. Soil may adhere to the tubers at the eyes. Cutting the diseased tuber will reveal a
browning and eventual necrosis of the vascular ring and immediately surrounding tissues. Creamy
fluid exudates usually appear spontaneously on the vascular ring of the cut surface a few minutes
after cutting. The vascular tissues of the stem show a brown discoloration.
Tomato, chilli and brinjal
The wilting symptom of these solanaceous crops can be induced by bacterial and fungal
pathogen, root-knot nematode and deficit or excess of soil moisture. The most characteristics
symptoms of tomato, chilli and brinjal are very rapid wilting, especially where the plants are young
and succulent. The flowering stage is the most critically stage where a plant shows sudden wilting.
The first visible symptom is the flaccid appearance of the youngest leaves and in the field. Other
primary indications of infection are stunting, downward curling of leaflets and petioles. Usually
infected plants collapse quickly, but where this fails to happen there is a development of
blackening of vascular system at the junction between stem and leaf. Further down the stem, the
whole vascular system may be completely blackened and when cut oozes creamy bacterial slime.
Under favourable environmental conditions for the pathogen (soil temperatures of approximately
25 °C; saturated humidity), epinasty and wilting of one side or of the whole plant follows within a
few days leading to total plant collapse. Under less favourable conditions (soil temperature below
21 °C), less wilting occurs, but large numbers of adventitious roots may develop on the stem. It is
possible to observe water soaked streaks from the base of the stem, which is evidence of necrosis
in the vascular system. When the stem is cut crosswise, discoloured brown vascular tissues exude
white or yellowish bacterial ooze.
2. Bacterial Ooze test
Ralstonia solanacearum is a limited xylem-invading pathogen and plants wilted by this
pathogen have > 10 8 cfu/ g of tissue. A common sign of bacterial wilt of tomato observed at the
surface of freshly-cut sections from severely infected stems is a sticky, milky-white exudates,
which indicates the presence of dense masses of bacterial cells in infected vascular bundles, and
particularly in the xylem, which is responsible for transportation of raw sap (water and nutrients)
from roots to aerial parts of the plant. Ooze also may accumulate on the cut surface on the
infected surface. Allen et al. (2001) reported that even if ooze does not form spontaneously a
streaming test may be positive. Other wilt inducing pathogens do not produce comparable ooze.
The ooze is usually an almost pure culture of Ralstonia solanacearum, which can be cultured on
standard, low ionic strength bacteriological media. This water streaming test (Ooze test) is of
presumptive diagnostic value in the field.
3. Morphological, biochemical and physiological characters
Ralstonia is a non fluorescent pseudomonas. R. solanacearum is in rRNA homology group
II where as the fluorescent pseudomonas in rRNA homology group I in 1992, Yabuuchi et al.,
(1992) transferred even species in rRNA homology group II including P. solanacearum into the
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