We should not underestimate the complexity of the infection process and the ability of these parasitic microorganisms to breach plant defences in order to obtain the nutrition that is vital for their survival
which serve to anchor the fungus to the plant surface prior to penetration. In Colletotrichum cereale (formerly C. graminicola), the pathogen responsible for anthracnose diseases in turfgrass, the germinating spores produce a darkly pigmented (or melanised) appressorium that is of characteristic size and shape. These structures adhere to the plant cell and may release one or more enzymes that help to break down and weaken the structural components of the plant cell wall. In addition to this, there is a build-up of pressure inside the appressorium which is used to mechanically force a penetration peg through a pore in the appressorium and in to the plant cell. Following the breakthrough of the plant cell wall, the fungus produces infection hyphae which ultimately grow in to the surrounding plant cells. The fungus Gaeumannomyces graminis (the Take-all patch pathogen) also produces specialised infection structures but, in this case, they develop from the fungal mycelium rather than from the germinating spore. These infection structures are referred to as hyphopodia and take on a range of shapes depending on the variety of the fungus. G. graminis var. avenae which causes take-all patch disease in cool- season turfgrasses, produces simple hyphopodia whereas G. graminis var. graminis which causes root decline in warm-season turfgrasses, produces
distinctly lobed hyphopodia. The shape of these structures is used as one characteristic in fungal identification but, regardless of their shape, these hyphopodia all aid fungal penetration in the same way.
Nematodes also tend to enter the plant
cell through direct penetration and they primarily use mechanical force to achieve this. Once the nematode comes in to contact with the plant, it firmly attaches itself onto the outer surface, using a sucker action by pressing its lips onto the plant surface. Once it is firmly attached, the nematode uses the muscles in its head to repeatedly thrust the stylet towards the cell wall. After a few attempts, the stylet eventually penetrates the cell and the nematode can either feed on the cell content whilst maintaining its body outside the plant cell or it will move in to and through the plant tissues, destroying their integrity as it does so. Nematodes may also release enzymes to help weaken the cell wall prior to penetration and to facilitate feeding once the cell barrier has been breached.
Plants have various physical and chemical defences that they can use to limit infection and to restrict development of disease. Different parts of the plant will support different physical barriers and even cultivars of the same grass type will show a range of susceptibility to infection by various pathogens due to their physical and chemical make-up. Plant cells can also perceive when they have been damaged
Sheath nematode feeding through stylet on root tip
or invaded and the cells are able to initiate defence mechanisms to contain the activity of any invading parasite. Susceptible varieties are less well equipped at doing this and will allow a greater amount of infection to develop before they inhibit further movement of the pathogen. Fungal and nematode pathogens will do all that they can to enter host tissues in order to feed and to complete their life cycle. By ensuring strong plant development, we can limit the opportunity for easy entry of these organisms and help the plant to respond quickly to infection and repair itself. We should not underestimate the complexity of the infection process and the ability of these parasitic microorganisms to breach plant defences in order to obtain the nutrition that is vital for their survival.
Dr. Kate Entwistle The Turf Disease Centre Email:
kate@theturfdiseasecentre.co.uk
What are you like?
Jonathan Abbott, Managing Director of contractors M J Abbott, is having trouble with his Titleist Pro V1s and getting a little miffed with Government Red Tape!
What would you change about yourself? I’d like to lose some weight!
Who are you? Jonathan Abbott, Managing Director, MJ Abbott Limited
Status? Married with two boys aged 12 and 10
Who’s your hero and why? Bruce Springsteen - he always makes fantastic music!
What is your dream holiday? Walking to Machu Picchu in Peru
What annoys you the most? Government Red Tape
Who wouldn’t you like to be? Gordon Brown
Favourite record, and why? Born in the USA by Bruce Springsteen. It takes me back to my school days
Who would you choose to spend a romantic evening with? My wife
If you won the lottery, what is the first thing you would do? Buy a holiday home in the South of France
If you were to describe yourself as a musical instrument, what would you be? A cello
What’s the best advice you have ever been given? Always look at the bigger picture
What’s your favourite smell? Freshly baked bread
What three words would you use to describe yourself? Astute, thorough and caring
What talent would you like to have? I’d like to be able to hit a golf ball straight!
What makes you angry? Never being able to hit a golf ball straight!
What law/legislation would you like to see introduced? A total ban on smoking
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