ANTHRACNOSE An update ...
Anthracnose has increased in frequency and severity over the past ten years, both here in the UK and also in the USA. This article is intended to provide up to date
information on the fungus that causes Anthracnose diseases and on the two disease types that are increasingly seen in amenity situations.
By Dr Kate Entwistle F
irstly, we should look at the fungus and discuss the reason for its recent change of name. Anthracnose in amenity turf is caused by a fungus that is now called Colletotrichum cereale. In cereals and grasses there are four distinct Colletotrichum species that can cause disease and they are differentiated by their main host plant and by certain specific fungal characteristics (Crouch et al, 2006).
One of the four species, Colletotrichum graminicola, is thought to inhabit a wide range of cereals, grains and turf grasses and this species name has historically been the one used for turfgrass Anthracnose. However, it has generally now been considered that this species should only be correctly applied to Colletotrichum on corn. Since recent research work has identified clear differences between C. graminicola and the fungus found to cause Anthracnose on turfgrasses, the name C. cereale has been proposed as the new and more correct name for the causal fungus in disease in turf. It is likely that both of these two fungal names, i.e. C. cereale and C. graminicola, will continue to be used to describe this pathogen in turf, but it is important to realise that there is no new fungus - just a new name. C. cereale is a fungus that produces small, asexual spores (conidia) from specific structures that develop on infected plant tissues. The structures are called acervuli (singular: acervulus) and they have dark, hair-like projections that protect the central spore-producing tissues and cause the affected areas to
appear dark in colour. The spores are released on to the turf and are moved across the sward by irrigation/rainfall, wind or direct means. However, free water or humidity is essential for the successful germination of the spores and entry of the fungus in to the plant. Once inside the plant tissues the fungus is protected from the environmental conditions but, prior to that, it is susceptible to desiccation which would kill the fungus before it could initiate infection. Assuming the availability of humid/damp conditions, the spore germinates to produces a germ (germination) tube which grows over the plant surface until it finds a suitable location for entry in to the plant. At this time, the end of the germ tube develops into a so-called appressorium, which is dark in colour and which has a characteristic ‘boxing glove’ shape. This appressorium is a specialised structure that allows the fungus to adhere to the plant surface. Eventually, the fungus forces its way into the plant cell from directly beneath the appressorium. Once inside the plant cell, the fungus takes in the nutrients that are available to it and grows through the plant tissues. Initially, the fungus causes little visual effect on the plant and the infection may go unnoticed for some time. However, when the turf is put under stress, the infected plants can develop symptoms of infection very quickly and it can appear as though the disease has come in overnight. Development of the disease in the crown tissues will lead to a blackened,
It is important to realise that there is no new fungus - just a new name
42
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120