caused by endoparasitic nematodes
The loose arrangement of outer root cells
I
Olpidium colonising a root hair cell
Typical galls of root-knot nematode on ryegrass
am always on the look-out for research or general articles and text books that can help with my work or my understanding of turfgrass diseases and, to this end, I recently bought a book entitled Plant Roots. Not really as sad as it may sound because it has already proved to be quite a useful purchase and it got me thinking again about the importance of roots in relation to the overall health of the sward. All too often when we see turfgrass diseases or damage, it is the symptoms on the sward that get our attention and we automatically assume that the sward is the part of the plant that is infected. Increasingly, however, I receive samples from areas of discoloured turf that have developed as a direct result of the decline or distortion in root development or function and it is the cause of the root problem that needs to be addressed rather than the turf discolouration itself. I have long considered that too little attention is paid to roots quality when assessing the health of the sward and, so, the following article aims to offer some information, based purely on my experience of the past seventeen years, on the ways in which root structure and function can be adversely affected, resulting in symptoms on the sward that may or may not be fungal disease.
In most of the work that I do, a decline in root development is often found to have developed as a result of fungal infection but, interestingly, not all fungal infections will necessarily lead to disease. Some fungi will, and Gaeumannomyces graminis var avenae is arguably the
best-known cause of a fungal root disease (take-all patch) in amenity grasses. The fungus initially grows along the outer surface of the turfgrass root but eventually penetrates and colonises the root cells. The infection compromises the plant’s ability to take up water and nutrients and, as a result, causes an initial discolouration of the leaf that can eventually result in the death of the plant. The turfgrass plant will always show a foliar discolouration if its normal water and nutrient requirement is interrupted. In the case of take-all patch, the fungal colonisation of the roots leads to just such a situation developing through the summer months, although the initial root infection will have taken place during the late spring. The length of the delay in the expression of the so-called ‘symptoms of stress’ on the sward will depend on the quality of the sward, the quality and quantity of roots and the rootzone condition itself. Other fungi, like Colletotrichum cereale (formerly called C. graminicola) also infect and colonise the root/crown tissues and like G. graminis var avenae, restrict water and nutrient movement through the plant. As a result, plants infected, in this case by anthracnose diseases, will also show a foliar colour change associated with the nutritional and water stress imposed by the reduced functioning of the roots and crown. Looking at the general root discolouration alone will not necessarily lead you to the correct cause of the problem. The infection of the roots by these fungi can only really be confirmed if the roots are viewed under a microscope but, in the case of
ROOTS? When did you last check your
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