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The absence of symptoms does not mean absence of A. tritici (Thorne, 1949). Slight elevations occur on the upper leaf surface with indentations on the lower side. Other symptoms include wrinkling, twisting, curling of the margins towards the midrib, distortion, buckling, swelling and bulging. A tight spiral coil evolves, and dwarfing, loss of colour or a mottled, yellowed appearance and stem bending may also occur (Byars, 1920; Leukel, 1924). In severe infection, the entire above-ground plant is distorted to some degree and a disease problem is usually obvious.
Wheat heads are reduced with glumes protruding at an abnormal angle exposing the galls to view. This does not occur in rye heads.
Young galls are short-thick, smooth, light to dark green, turning brown to black with age, 3.5-4.5 mm long and 2-3 mm wide. Rye galls are small, buff-coloured and longer than wide, 2-4.5 mm long by 1-2.5 mm wide (Byars, 1920; Leukel, 1924).
Ear-cockles are the only source for perpetuation of the disease and their removal from contaminated seed lots can completely eradicate the disease (Luc et al., 2005). A. tritici has been eliminated, or reduced to a minimal number of infestations, in Europe and the USA by seed cleaning, crop rotation and fallow (Brown, 1987).
Cultural Control and Sanitary Methods
Salt brine method (Byars, 1920; Leukel, 1957): seed (1 peck per treatment) is poured into a salt solution (8 lbs salt in 5 gallons water) and stirred vigorously. Sound galls sink, and debris and galls float to the surface. The galls and debris are skimmed from the surface and steamed, boiled or chemically treated to kill the nematodes. The salt solution is drained into another container and the cleaned seed is rinsed several times in fresh water to remove salt and then spread in thin layers on a clean surface to dry. The cleaned seed is ready to sow when dry. It is important that the seed is washed two or three times in plain water after brine treatment to remove salt particles which may impair germination.
Crop rotation or fallow:
A. tritici cannot survive in soil for more than 1 year if the soil is left fallow or planted to a non-host crop. The pest will be eliminated in more than a year.
Hot-water treatments may be used to eradicate A. tritici from seed lots (Suryanarayana and Mukhopadhaya, 1971). Marcinowski (1909) demonstrated that nematode galls in a seed lot could be destroyed by keeping the mixture in water at 54-56°C for 10-12 minutes. Pre-soaking the seeds before the hot-water treatment has also been advocated (Byars, 1919; Chu, 1945).
Another hot-water treatment involves pre-soaking the seed at 21-27°C for 2-4 hours, then placing them in water for 30 minutes at 50°C. The seeds are rinsed in tap water, then spread in thin layers on a clean surface till dry (Byars, 1920; Leukel, 1924).
Jones et al. (1938) developed an indented cylinder machine which separated oval wheat seeds from globular nematode galls; the device was claimed to be 98% effective in removing the seed galls. Chu (1945) also designed a machine to separate nematode galls from healthy grain.
Nematicidal plants are not as effective as the clean seed or fallow method and offer little hope as an effective method of controlling A. tritici.
There are few reports concerning biological control of A. tritici.
A large number of plants have been evaluated for resistance to A. tritici over a period of more than 60 years. A few resistant plants have been found, such as the wheat cultivar Kanred (Leukel, 1924); however, resistance does not appear to be a viable solution to the problem of seed gall nematodes.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
A. tritici has been practically eliminated from grainfields in Europe by using clean seed and crop rotation. Up to 100% losses have been reported in wheat, with wheat grain ears totally infected (Paruthi et al., 1987). Reddy (1983) also reported high losses (90%) in wheat seedlings; and 8.5% of sowed wheat seeds galled, resulting in 69% loss. In China, A. tritici causes an annual market reduction in wheat (Chu, 1945). The conversion of wheat grains to galls caused losses of 6.54 million rupees in India (Sakhuja et al., 1990). Paruthi and Bhatti (1988) reported 23-48% losses and a market price reduction when 5% of wheat seed were galled and flour which contained 2% seed galls was also unacceptable. Losses of 50 and 65% were reported in wheat and rye, respectively (Leukel, 1957), and 52% losses occurred through infestation of the inoculated wheat field market (Paruthi and Bhatti, 1981). These losses were recorded in the absence of control measures, before the introduction of phytosanitary programmes.