Lecture 10b: Plant-Pathogen Fungi and OOmycetes

Question 1

Major types of plant diseases

Answer 1

Vascular wilts
Leaf spots
Smuts and Rusts
Root rots
Crankers
Galls
Mildews

Question 2

Soil-borne pathogens

Answer 2

Vascular wilts and root rot diseases

Question 3

Vascular wilt diseases

Answer 3

Blockage of xylem vessels, impending water transport

Question 4

Fungal causal agents and symptoms of vascular wilt disease

Answer 4

• Fusarium oxysporum
• Verticillium albo-atrum
• Verticillium dahlia
  Symptoms:
• Progressive yellowing of the leaves
• Early

Question 5

Panama wild

Answer 5

Host: Banana and plantain
Pathogen: Fusarium oxysporum
first reported in Australia

Question 6

Symptoms of Fusarium wilt of banana

Answer 6

• Chlorosis and death of oldest leaves
• Yellowing and wilting of leaves
• Young leaves develop symptoms and skirt the stem
• Plant collapse
• No symptoms on fruit

Question 7

Fusarium wilt of banana disease cycle

Answer 7

• Infection of young fleshy/wounded roots
• colonisation: Proliferates up into the xylem vessels and produces spores that act as second inoculum
• Survival: Chlamydospores are produced when the plant dies. They germinate under favourable conditions and the cycle is repeated
• Pathogen introduced to plantation when planting infected material

Question 8

Epidemiology of Fusarium wilt of bananas

Answer 8

• Polycyclic disease (more than one infection cycle per crop cycle)

Question 9

Pathogen dissemination of fusarium banana wilting

Answer 9

• Infected rhizomes
• Surface water
• Poor sanitation practices
• Banana weevil

Question 10

Management of Fusarium wilt of banana

Answer 10

• Pathogen exclusion
  *Rapid containment of affected sites (destruction of symptomatic and surrounding plants)
• Disease-free tissue planting material
• Resistant cultivars

Question 11

Smut diseases

Answer 11

• Affect members of the family Poaceae: maize, wheat, sugarcane and sorghum
• Fungal spore accumulate in sooty-like masses, formed within ‘blisters’

Question 12

Sugarcane Smuts host and pathogen

Answer 12

Host: sugarcane
Pathogen: Sporisorium scitamineum

Question 13

Favoured environment of Sporisorium scitamineum

Answer 13

Long, dry and warm winters followed by good spring rains

Question 14

Symptoms of Sugarcane smut diseases

Answer 14

• Black whip-like structures develop from tops of infected shoots
• Shortening and crinkling of spindle leaves, and elongated internodes
• Infected plants are stunted
• Thin stalks with grass-like appearance

Question 15

Disease cycle of Sugarcane smuts

Answer 15

• Transmission: airborne teliospores, vegetative propagation of infected canes, infected plant debris or soil
• Infection: Teliospores deposited at the leaf and the sheath junction; travel to the bud
  Moisture required for teliospore germination
  Basidiospores fuse to form dikaryon, which germinate to produce hyphae
  Infection of meristem tissue

Question 16

Epidemiology of sugarcane smuts

Answer 16

• spore adapted to aerial dispersal
• Spore survival in soil about 2-3 months
• Requires living host plant to produce spores

Question 17

Management of sugarcane smuts

Answer 17

• Resistant sugarcane varieties
• Disease-free seedcane (Hot water treatment/ fungicide application)
• Rogue infected stools, plough out severely smutted flieds

Question 18

Host and pathogen of cob and tassel smuts

Answer 18

Host: Maize
Pathogen: Sphacelotheca reiliana

Question 19

Symptoms of cob and tassel smuts

Answer 19

• ear infections: round and swollen, lack silks, black powdery spore mass
• Tassel infections: Few spikelets to entire tassel, leafy structures
• Other symptoms: aborted ears, stunting, excessive tillering

Question 20

epidemiology of cob and tassel smuts

Answer 20

• Soil-borne
• Teliospores = wind dispersal
• Condition optimal for maize germination: 21 DC, moderate to low soil moisture

Question 21

Management of cob and tassel smut management

Answer 21

• Resistant hybrids
• Sanitation systems: crop rotation, burning infected plants
• Planting later, in high soil temp and frequent rainfall
• Fungicide seed treatment
• Quaratine