This document summarizes several plant diseases that affect yams, taro, and dasheen. It describes the symptoms, pathogens, and modes of spread for anthracnose, dry rot, collar rot, Phytophthora leaf blight, Pythium rot, and mosaic diseases. For each disease, it provides details on the visual symptoms, identifies the causal pathogen, and explains how the pathogen is spread both initially and subsequently. Management strategies are also outlined, such as soil drenching with fungicides, crop rotation, and removing plant debris.

1. YAM
1. ANTHRACNOSE - Colletotrichum gloeosporioides
Symptoms appeared at first as small dark brown or black lesion on the leaves,
petioles and stems.
The lesion is often surrounded by a chlorotic halo enlarged and coalesces,
resulting in extensive necrosis of the leaves and die-back of the stem
Pathogen: Pathogen produces conidia single celled, hyaline slightly curved with
oil globule. Asexual fruiting body is acervuli
Mode of spread:
Primary : Through dormant mycelium and ascospores from infected debris
Secondary :Through wind borne conidia

3. DRY ROT - Botryodiplodia theobromae
The symptoms though vary with varying coloration depending on the invading
Pathogen, the infected tissues become hard and dry. The infected tubers first
turned grey and then black, such tubers become pulverulent, breaking into
small dry particles. In case of Fusarium inducing pinkish with yellowish border
on the infected tissues
Pathogen: Inside the pycnidia, conidiogenous cells produce hyaline thin walled
pycnidiospores which become brown, thick walled, two celled with
longitudinal striations.
Mode of spread:
Primary and Secondary spread is through Air borne conidia

5. •Management
•Soil drenching with carbendazim 0.1% or COC 0.25 per cent
•Crop rotation for 4 years or more is practised.
•Land should be well drained
•Crop debris and diseased plants should be burnt

6. COLLAR ROT:
Collar rot caused by Sclerotium rolfsii and Rhizoctonia solani
is commonly found in two to three months old plants.
The collar region is get rot which leads to death of the plants.
In severe cases leaf become brownish and dry leads to death
of the plant.

8. •Management
•Soil drenching with carbendazim 0.1% or COC 0.25 per cent
•Crop rotation for 4 years or more is practised.
•Land should be well drained
•Crop debris and diseased plants should be burnt

9. COLOCASSIA (TARO)
1. PHYTOPHTHORA LEAF BLIGHT - Phytophthora colocasiae
The early stages of the disease are characterized by small circular water-
soaked lesions, generally dark brown or purple.
A clear amber fluid exudes from the center of the lesion.
After initial establishment lesion development is rapid until the leaf is
entirely colonized and collapses.
Pathogen: Phytophthora produces coenocytic mycelium with sporangiphore
bearing papillate sporangia which bears the zoospores.
Mode of spread:
Primary: Oospore, dormant mycelium in plant debris
Secondary: Zoospores produced in sporangia

11. PYTHIUM ROT - Pythium aphanidermatum
The normally firm flesh of the corm is transformed into a soft, mushy, often
malodorous mass.
In wetland culture, the root system is destroyed except for a small fringe near
the apex of the corm.
The plants become stunted, with leaf stalks shortened and leaf blades curled and
crinkled, yellowish and spotted.
Pathogen :
Coenocytic mycelium ,produces sporangiospore bearing irregular shaped
sporangia which bears the vesicle.
Inside the vesicle the zoospores are produced.
Mode of spread:
Primary: Soil borne Oospores
Secondary: Water borne zoospores

13. MOSAIC- Dasheen Mosaic virus
Plants generally become asymptomatic three to four months
after initial symptom expression.
The foliar symptoms include a dispersed and veinal mosaic
pattern on the leaves.
Leaf distortion is generally mild to moderate.
It is a stylet-borne virus carried by aphids Myzus persicae.