Topic 6 - Plant Disease

plants can suffer from many ________ caused by _______ ___ deficiencies or _________. They can also be damaged by ______ pests.

diseases, mineral ion, pathogens, insect

define a pathogen

a microbe that causes disease, e.g. bacteria, viruses, or fungi

symptoms of plant disease (7)

• stunted growth

• spots on leaves

• areas of decay / rot

• abnormal growth, e.g. lumps

• malformed stems / leaves

• discolouration

• presence of pests

If there is a nitrate ion deficiency, the plant will experience ________ ______, because nitrate is needed to make ________. If there is a _________ deficiency, the leaves will become yellow due to __________, because they are needed for plants to make ____________.

stunted growth, proteins, magnesium, chlorosis, chlorophyll

TMV (_______ ______ _____) is a widespread plant pathogen affecting many species including _______ and ________. Its main symptom is a distinctive ______ pattern of ______________ on the ______. The virus invades and kills _____, reducing ______________, reducing growth and _____ too. There is no _________, and the virus can remain infectious in the soil for ___ years. You can limit the spread by removing and __________ infected plants, and _______ hands and _____.

Tobacco Mosaic Virus, tobacco, tomatoes, mosaic, discolouration, leaves, cells, photosynthesis, yield, treatment, 50, destroying, washing, tools

The main symptom of Rose _____ Spot ______ when ____ leaves develop ______ / black spots. Leaves often turn ______ and drop off early. The lack of leaves causes reduced ______________ and therefore, reduced growth and _________. There are four main treatments: spraying with _________, removing and destroying infected ______, planting roses with space for ___ ____ between them, and ________ infected plants to stop _____ production.

Black, Fungus, rose, purple, yellow, photosynthesis, flowering, fungicide, leaves, air flow, cutting, spore

Aphids (________) are small _______ that pierce _____ _____ tubes and feed on the ___. Aphids can _________ quickly. The main symptom is _______ of the plant, and aphid feeding _______ the plant and can ______ disease. The main treatments are killing aphids with ___________ or biological control, e.g. using _________.

greenfly, insects, phloem sieve, sap, reproduce, wilting, weakens, spread, insecticide, ladybirds

Main ways plant diseases can spread (5)

• by air - fungal spores can be blown in the wind

• by water droplets - rain can splash pathogens to other plants

• direct contact - plants may touch as they grow / a small piece of infected plant left on the soil may infect the next plant

• insect vectors - aphids feeding on infected plants may feed on another plant that is healthy and infect it through its mouthparts

• equipment - gardeners / farmers may use the same tools on infected and healthy plants

main ways farmers / gardeners can prevent plant disease (6)

• ensuring plants have enough mineral ions, e.g. using fertiliser, compost, or manure

• treating / destroying infected plants to prevent spread

• using fungicide and insecticide

• biological control, e.g. ladybirds

• washing gardening tools and machinery

• breeding resistant plants

mechanical defenses against insect pests and herbivores (3)

• thorns and hairs deter animals

• leaves which suddenly droop / fold when touched dislodge small insects and frighten others

• mimicry - passionflower leaves have yellow spots to mimic butterfly eggs, so butterflies won’t lay their eggs on them. Pebble plants are camouflaged as pebbles, and are rarely noticed by herbivores

physical plant defences (3)

• cellulose cell walls

• tough waxy cuticles on leaves

• layers of dead cells around stems, e.g. tree bark. When they fall off, the pathogen is lost with them.

chemical plant defenses (2)

• antibacterial chemicals, e.g. mint and witch hazel

• poisons to herbivores, e.g. tobacco plants, fox gloves, and deadly nightshade