Ex. No. 13                           Dissection specimens  

Guava red rust or Algal spot or Parasitic algal infection 

Causal organism: Cephaleuros spp.  (Cephaleuros virescens, Cephaleuros mycoidea; Cephaleuros parasiticus)

Taxonomic position:

Phylum: Chlorophyta , Order : Trentepohliales,   Division: Trentepohiliaceae,   Genus: Cephaleuros Species: virescens Affected crops: Guava, Mango, Papaya, Citrus, Avocado, Tea, Coffee, Pepper and Sapota.

Symptoms:          Sexual spore : Microzoospore, Asexual spore : Zoospore

1. Orange yellow rust pustules are appear on adaxial surface of the leaves (mostly)                             

 2. Yellow coloured pustules are due to hematochrome                                                                                 

   3. The alga takes up water and minerals from the host by osmosis

Life cycle

1.       Zoospores are biflagellate, and about 30 are produced from each sporangium.

2.       The infection may be initiated by zoospores washed in to the stomata by rain

3.       Zoosporangia are disseminated by the wind (Anemochory)

4.       The end of the rainy season, the disease becomes severe

Management

1.       Avoid heavy application of nitrogen and potassium to reduce the disease incidence.

2.       All badly diseased or dead wood should be removed

3.       Spray Bordeaux mixture or Copper Oxy Chloride at 0.1 per cent

Ground nut Tikka leaf sport 

Causal organism: Cercospora  arachidicola (Mycosphaerella arachidis) (Early leaf spot/ Brown leaf spot )                                     Cercospora  personata (Mycosphaerella berkeleyi) (Late leaf spot/ Black leaf spot)

Symptoms

Characteristics	Early leaf spot	Late leaf spot
Seasonal development	Early season	Late season
Shape of spots	Circular to irregular	Circular
Leaf surface where first, most spores produced	Upper	Lower
Yellow halo	Present	Absent
Colour of spots	Brown (reddish brown)	Black (dark brown)
Conidiophore	Yellowish brown	Olivaceous brown
Conidia	Hyaline, Obclavate	Cylindrical

Epidemiology

1.       25 to 30⁰C with high RH favour for disease development

2.       Heavy application of nitrogen and phosphorus fertilizers increases severity of this disease

Management

Spray Carbendazim 0.5 or Hexaconazole 0.2 percent per cent are effective. Diseased materials are removed from the field.  

Banana black freckle leaf spot

Causal organism: Phyllostictina musarum                                                                                                         Telemorphic stage: Macrophoma musae (Guignardia musae)

Taxonomic position:

Domain: Eukarya, Kingdom: Fungi, Division : : Ascomycota, Class: Dothideomycetes, Order: Botryosphaeriales, Family: Botryosphaeriaceae Genus: Macrophoma

Symptoms:   

                The upper surfaces of older leaves are affected. Dark brown to black spots are appear (Oblong, muddy brown to black dots)

 Pycnidium; It is a flask shaped asexual fruiting body and Psudoparaenchymatous cells are lined with pycnidiophore with an anterior opening called ostiole. Through their ostiole only the pycnidiospores (conidia) are released out or ejected out from the Pycnidium. Conidia are Aseptate, cylindrical. In sexual stage perithecia and ascospores are formed.

Epidemiology: Conidia dispersed through Hydrochory and usually travel through short distance.

Management:                                                                                                                                                                                      1. Removal of infected leaves from the banana.      

               2. Spray Mancozeb at 0.2 per cent