I believe that these nematodes have always been present but our recently acquired knowledge has encouraged us to be more vigilant and to look more closely for them in turf that we may have otherwise reported as ‘stressed’
fungal disease, the cause was identified as the Root-knot nematode Meloidogyne minor (new species), something that was confirmed through extensive research by Dr Colin Fleming at AFBI Northern Ireland (AFBI NI), contracted by Headland Amenity.
This plant parasitic nematode disease has been well documented over recent years and since that initial confirmation of a plant parasitic nematode causing disease in amenity turfgrasses, we have been actively looking at turfgrass roots and rootzones to determine which plant parasitic nematodes are present and which are associated with symptoms of turfgrass disease. All rootzones are likely to possess some plant parasitic nematodes and, during any one year, but the species diversity and individual species populations will fluctuate in response to rootzone and environmental conditions. Therefore, as with fungal pathogens, the presence of these nematodes does not necessarily mean that they are causing (or likely to cause) any problem. Compared to weaker turf, a stronger turf area can tolerate higher nematode populations without significant symptoms developing on the turf.
However, since plant parasitic nematodes feed on, or within, the root (and occasionally in the leaf) tissues, they adversely affect the function of the roots such that water and nutrient uptake is compromised. In addition, these nematodes can introduce certain compounds in to the plant whilst they are feeding, or the plant can respond to their feeding by producing certain metabolic products which may directly and adversely change the physiology of the plant.
Plant parasitic nematodes feed by
repeatedly forcing their spear-like stylet in to the plant cells until they puncture the cell wall and gain access to the cell content. Some nematodes, like the Root- knot nematode Meloidogyne, induce changes in the root development which result in the formation of so-call giant cells which act as a sink for
photosynthetic materials and serve as a constant food source for the parasite. There are two main groups of plant parasitic nematodes, the endo- and the ecto-parasites which have their body inside or outside of the plant tissues whilst feeding. To further complicate things, some nematodes are classed as semiendo- and these have the front part of their body inside the plant tissues whilst keeping their rear end in the rootzone. Plant parasitic nematodes can be sedentary whilst feeding (staying in
the same location) or migratory, moving through the rootzone or the plant tissues where, in the latter case, they will destroy the structural integrity of the plant tissues by their physical movement. Although there will be slight difference between nematode species, their life cycles are fairly straightforward. The juveniles emerge from the egg after they have passed through the first moult. After a total of four moults, during which time the nematodes increase in size, the adult male and female nematodes will emerge, the female will lay a number of eggs and the life cycle will begin again. In some species, e.g. the Root-knot nematode, only the emerging juveniles are the infective stage and can enter the plant to cause initial infection. In others, e.g. the Lesion nematode, all stages from emerging juvenile to adult can enter the plant root and initiate infection. A recent article in the Institute of Biology
magazine (Fleming, et al, 2008), comprehensively details the problem of plant parasitic nematodes in amenity situations. A copy of this article in PDF format is available, via email, on request. We are now aware that the endo- parasitic Root-knot nematodes, initially seen to be a problem on creeping bentgrass, can also cause damage to the roots of ryegrass and annual meadowgrass sward alike. There are two main species of Meloidogyne that are frequently recorded, but both appear to go through several life cycles each year under the ideal conditions provided by modern amenity constructions. The Root-gall nematode, Subanguina radicicola has been found extensively causing problems on golf course putting greens, bowling greens, soccer pitches and racecourses but always on Poa species in the turf. It is a relatively easy nematode to identify due to the development of characteristic swellings on the roots that contain the entire life cycle of the nematode. Perhaps one of the most frequently
recorded nematodes is the Spiral nematode, Helicotylenchus, and this can build to massive populations both in the
rootzone and within the root tissues themselves. This is an endo- ecto- parasite that can cause severe deformity to root development, adversely affecting plant growth and development. Although all grasses can be affected by the feeding activity of this nematode, I am frequently recording high populations in Poa annua dominated, close-mown turf in which the
Symptoms caused by the Root-knot nematode Meloidogyne
sward has developed small (10-20mm diameter) chlorotic patches that progressively develop into decaying, bleached turf. Often, these small patches will appear to coalesce and, in most cases, no fungal mycelium has been seen to develop across the affected areas. Occasionally, fungal mycelium may be seen around the perimeter of the affected plants but, in all cases that have so far been analysed, this mycelium has been found not to be that of any known fungal pathogen. The fungus appears to be related to a secondary infection that develops on the weakened and dying leaf tissues of these nematode-infected plans. These symptoms tend to appear as if the problem was dollar spot but on these Poa swards, the dollar spot fungus has not been conclusively identified. The ecto-parasitic Stunt nematode
Tylenchorhynchus is also commonly identified in amenity rootzones that are showing symptoms of discolouration and decline. The affected area of individual patches can range from 100mm to 1500mm or more and the plants appear to show a tan/chlorosis and, again, no evidence of any fungal mycelium. During May and June, I recorded an
99
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 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140