PLANT PROTECTION 1 â Pests, Diseases and Weeds

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PLANT PROTECTION 1 – Pests, Diseases and Weeds BIOLOGY, IDENTIFICATION AND CLASSIFICATION Fungal diseases NO. DISEASES IN AUSTRALIA SOME DISTINCTIVE FEATURES Hyphae produce enzymes which change the plant tissues into substances the fungus can use for nourishment Several thousand species of fungi can cause diseases of plants in Australia. Some fungal diseases are considered to have altered the course of history, eg the devastating effect of coffee rust in Ceylon in the 19 th century is given as the main reason for the British being now mainly tea drinkers. Fungimap www.rbg.vic.gov.au/fungimap_/fungi_down_under The Australasian Plant Pathology Society (APPSnet) Pathogen of the Month www.australasianplantpathologysociety.org.au/ The American Phytopathology Society (APSnet) www.apsnet.org/ Australasian Mycological Society www.australasianmycology.com/ Fungi were originally considered to be very simple members of the plant kingdom but are now in a separate kingdom of their own: MYCELIUM Fungi have a very simple plant body called a mycelium which is made up of thread-like filaments called hyphae which usually can only be seen under a microscope (x 100). Hyphae obtain food from the host which makes them similar to plant roots, sometimes forming structures which help the fungus survive and spread. CHLOROPHYLL They contain no chlorophyll and so cannot manufacture their own food. REPRODUCTION They reproduce by spores which are important in the spread and ‘overwintering’ of disease. Mycelium and spores Mycelium (x 100) of powdery mildew (x 100) LIFE CYCLE THE MAIN METHOD OF REPRODUCTION IS BY SPORES. Spores may be single-celled or multi-celled. Although single spores can be seen only with the aid of a microscope, larger masses of spores can be seen with the naked eye, eg the fine blue or green powder on a mouldy orange or lemon is in fact, billions of tiny spores. Generally 2 types of spores are produced, ie asexual repeating spores produced during the growing season and sexual ‘overwintering’ spores. Spores are produced near the outside of the plant or on the soil surface so they can be easily spread by wind, etc. Spores may or may not be produced in fruiting bodies which may be as large as mushrooms. However, the fruiting bodies of fungi that attack plants are usually much smaller and may appear as pinhead-size black dots on an area of damaged leaf eg Septoria. Fungi obviously produce millions of spores. While most spores never reach a site suitable for their germination, those that do only germinate and successfully cause infection if some moisture is present. At germination fungal spores produce a small tube which begins to elongate and branch forming hyphae . Spores not in fruiting bodies (x 100) Spores in fruiting bodies 314 Fungal diseases - Biology, identification and classification
PLANT PROTECTION 1 – Pests, Diseases and Weeds SYMPTOMS, DAMAGE Many fungal diseases cause several symptoms to develop, eg Shothole of stone fruit may cause shotholes on leaves, cankers, gumming and dieback of stems; gumming and scabs may develop on fruit DIRECT SYMPTOMS/DAMAGE. LEAVES Anthracnose*, eg anthracnose of rose Defoliation, eg black spot of rose Galls, eg azalea leaf gall Leaf curls, eg peach leaf curl Leaf rolls, eg powdery mildew of rose, apple Leaf spots, eg leaf spot of celery Pigmentation, eg leaf spot of azalea Spores present, eg Red, orange or black, eg rust White (on upper & lower surface), eg powdery mildew White (on under surface only), eg downy mildew Scabs, eg apple scab, shothole of stone fruit Witches' broom*, eg shothole of apricot Wilt, eg Verticillium wilt of chrysanthemum FLOWERS Blights*, eg blossom blight of azalea Grey spores, eg blossom blight (Botrytis sp.), brown rot of stone fruits, some powdery mildews look grey Pink spots, eg early stages of blossom blight (Botrytis sp.) on white flowered varieties FRUIT Freckle*, eg freckle of stone fruit Gumming, eg shothole of almond Rots, eg storage rots of fruit and vegetables Russet*, eg powdery mildew of apple Scabs, eg apple scab, citrus scab Spots, eg black spot of grape Spores present, eg blue mould of citrus, brown rot of peach STEMS, Cankers*, eg shothole of stone fruit TRUNK Dieback, eg Phytophthora root rot of eucalypts Galls, eg gall rust of wattle Gumming, eg shothole Rot, eg wood rot, basal stem rots SEEDS Ergots, eg rye ergot, paspalum ergot Smuts, eg loose smut SEEDLINGS Damping-off*, eg seedlings, cuttings BULBS, Rots, eg Fusarium rots CORMS Scabs, warts, eg powdery scab of potato CROWNS Rot, eg Rhizoctonia stem rot, Sclerotium stem rot ROOTS Galls, eg clubroot of crucifers Rot, eg Phytophthora root rot INDIRECT DAMAGE Nematode-fungal disease complexes are described on page 253. Aflatoxins. Aspergillus flavus produces aflatoxin when growing on certain crops eg peanuts. As it is poisonous to animals and humans in minute concentrations, there is a legal maximum permitted concentration of aflatoxin in peanuts in Australia. Mushroom poisonings. – Yellow stainer (Agaricus xanthodermus) mushroom causes most mushroom poisonings in southern Australia (looks similar to field mushrooms). – Death cap (Amanita phalloides) has a mycorrhizal relationship with exotic oak trees and came from its native Europe on one of the first oak seedlings to arrive in Australia. Extending root systems of older trees in Australia means that fruiting bodies could be found up to 200 metres away from any given oak tree. Mycologists are now concerned that it could naturalize onto eucalypts and spread into native forest reserves and suburban backyards around Australia. Allergic responses, breathing difficulties and hay fever may be caused by the spores of some fungi. Diseases of animals and humans, eg ringworm, tinia; also thrush (Candida albicans) and Sauna-taker’s disease (Aurobasidium pallulans). Cryptococcisus (Cryptococcus neoformans var. gatti) occurs in the tropics and sub-tropics in association with some eucalypt species, eg Corymbia camaldulensis, causing a range of diseases in susceptible individuals. Sporotrichosis (Sporothrix schenckii) occurs worldwide in tropical and temperate regions and is commonly found in soil and decaying vegetation and is well known to infect humans and animals. * Terms marked with an asterisk have a special meaning and are described in the glossary. Fungal diseases - Biology, identification and classification 315
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Root structure of dock (Rumex spp.)
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PLANT PROTECTION 1 â Pests, Diseases and Weeds

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