PATH 372 Diseases of Horticultural Crops

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