PATH 372 Diseases of Horticultural Crops
PATH 372 Diseases of Horticultural Crops
PATH 372 Diseases of Horticultural Crops
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Typical browning <strong>of</strong> vascular tissues <strong>of</strong> roots and stems can be seen<br />
From cross sections <strong>of</strong> infected plants whitish bacterial exudate comes out.<br />
Pathogen: the bacterium is Gram negative motile rod having rounded ends with 1-4<br />
polar flagella. Race 1 <strong>of</strong> R. solanacearum affects solanaceous plants such as tomato,<br />
egg plant and many other non-solanaceous plants also.<br />
Mode <strong>of</strong> survival and spread<br />
The bacterium isboth soil and seed borne in nature and overwinters in infected<br />
plant parts, in wild host plants and weeds.<br />
Spread through irrigation water or infested soil and agricultural implements.<br />
Favourable conditions<br />
Relatively high soil moisture and soil temperature favour the disease development.<br />
Management<br />
Grow resistant varieties like Pant Samrat, Arka Nidhi, Arkas Kashav, Arka<br />
Neelakantha, Surya and BB 1, 44 & 49.<br />
Crop rotation with non solanaceous hosts<br />
Green manuring with Brassica species (Bi<strong>of</strong>umigation)<br />
Soil solarization with a transparent polyethylene sheet (125 µm thick) for 8-10<br />
weeks during March-June<br />
Biological control with Pseudomonas fluorescens, P. glumae, P. cepacia, Bacillus<br />
sp. & Erwinia sp.<br />
3) Phomopsis fruit rot or blight – Phomopsis vexans (P.S: Diaporthe vexans)<br />
The disease is severe in tropical and sub-tropical areas <strong>of</strong> the world. In India, it was<br />
reported in 1935 in Gujarat. The pathogen attacks foliage and fruits, but the latter<br />
phase is more destructive.<br />
Symptoms<br />
The plants are attacked at all stages <strong>of</strong> growth, producing damping-<strong>of</strong>f symptoms<br />
in nurseries and collar rot on young plants<br />
On leaves, circular to irregular, clearly defined grayish brown spots having light<br />
centers appear. The diseased leaves become yellowish in colour nd may drop <strong>of</strong>f.<br />
Several black pycnidia can be seen on older spots.<br />
The lesions on stem are dark brown, round to oval and have grayish centers where<br />
pycnidia develop. At the base <strong>of</strong> the stem, the fungus causes characteristic<br />
constrictions leading to canker development and toppling <strong>of</strong> plants.<br />
On fruits, small pale sunken spots appear which on enlargement cover entire fruit<br />
surface. These spots become watery leading to s<strong>of</strong>t rot phase <strong>of</strong> the disease. A large<br />
number <strong>of</strong> dot like pycnidia also develop on such spots.<br />
The infection <strong>of</strong> fruit through calyx leads to development <strong>of</strong> dry rot and fruits<br />
appear black and mummified.<br />
Pathogen: The mycelium <strong>of</strong> the pathogen is septate and hyaline becoming dark with<br />
age. Pycnidia are submerged and later becoming erumpent with a prominent ostiole.<br />
Conidia are produced on simple to branched conidiophores and are <strong>of</strong> 2 types: Alpha<br />
conidia, which are sub cylindrical and beta conidia, which are filiform and curved.<br />
Role <strong>of</strong> beta-conidia in the epidemiology <strong>of</strong> the disease is not very clear. The perfect<br />
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