R2103 4.3 Describe the biology of diseases

Question 1

Method of spreading: Grey mould

Botrytis cinerea

Answer 1

1. Airborne spores
2. On green plants will infect wounds
3. Flowers and fruit it can infect without wounds - particularly under humid conditions
4. Black sclerotia can form in dead plant tissue which can carry fungus through peroids when host plants are scarce

Question 2

Method of spreading: Strawberry powdery mildew

Podosphaera aphanis

Answer 2

1. Spores carried by wind
2. Above 15 degrees C can infect leaf tissue without there being a layer of water
3. Humid and damp conditions do favour the disease
4. Serious problem at end of summer when night humidity increases

Question 3

Method of spreading: Damping off

Phytophthora and Pythium

Answer 3

1. Occur naturally in soils
2. Under damp conditions they produce asexual spores that cause infection, they are spread by water.

Question 4

Method of spreading: Honey fungus

Armillaria mellea

Answer 4

1. Rhizomorphs spread out underground from infected trees or stumps
2. By contact between roots of infected and healthy plants

Question 5

Method of spreading: Rose black spot

Diplocarpon rosae

Answer 5

1. Spores on upper leaves spread in water to initiate new infections
2. Fungus spends winter in resting structures on fallen leaves and dormant infection in young stems and buds.

Question 6

Method of spreading: Potato blight

Answer 6

1. Spores spread by wind
2. Actual infective spores are released from sporangia into water and need to swim in water film before settling on the plant surface and penetrating into leaf tissue; this is why the disease is so serious in wet summers.

Question 7

Method of spreading: Club root

Plasmodiophora brassicae

Answer 7

1. Resting spores survive in ground for up to 20 years
2. Can be spread by moving infected plants, or on tools or wheels of garden machinery such as rotavators
3. In peat soil-growing areas winds may carry the disease over a considerable distance

Question 8

Method of spreading: Hollyhock rust

Puccina malvacearum

Answer 8

1. Spread by airborne spores (basidiospores)
2. Larger spores (teliospores) carried by rain droplets

Question 9

Method of spreading: Apple and pear canker

Fungi: Nectria galligena

Answer 9

1. White, water-dispersed spores from edge of lesions in summer
2. Airborne spores from small red structures in winter and spring

Question 10

Method of spreading: Fireblight
Bacteria: Erwinia amylovora

Answer 10

1. Wind blown rain
2. Insects, including bees and aphids
3. Stomata and lenticels common sites for infection

Question 11

Method of spreading: Bacterial canker on prunus

Answer 11

1. Bacteria present in cankers carried by wind blown rain droplets, infecting leaf scars and pruning wounds in autumn and young developing leaves in summer.

Question 12

Method of spreading: potato leaf curl virus (and vector peach potato aphid)

Answer 12

1. Aphid spread
2. Virus remains active in aphid for entire season
3. High winds may blow aphid over long distances

Question 13

Method of spreading: Tobacco mosaic virus

Answer 13

1. Spreads easily from fingers of gardeners
2. Insects which have recently visited a tabacco patch or discard cigarette
3. Discarded tobacco products of any kind in the soil