CCN Cereal cyst nematode, (Heterodera avenae), a major pest of cereals in southeastern Australia CCN – Heterodera avenae • Stylet- bearing, tylenchid nematode • Dead female is a lemon-shaped cyst, full of eggs. The brown,tanned cyst is full of eggs. • Alive female is a white cyst • Eggs have diapause, hatching only after exposure to ~10 degrees C in autumn, but also need moisture to hatch and to move through soil • Conditions ideal for cereals also ideal for CCN! • Only ~80% of eggs hatch in a season – carry over effect • Males present • Juveniles attracted to root tips of hosts (grasses and cereals- alternative hosts) • Move to stele and initiate syncitea (cell walls dissolve to form multinucleate giant cells which act as transfer cells) continued • Juveniles lose ability to move, become sedentary, sausage-like • When males become adult, worm-like again and recover movement • Move around seeking females (role of pheromones) • Fertilized females become white cysts • One generation/year • Root knots on plants produced in response to overproduction of auxins • CCN occurs world-wide and probably evolved in West Asia • Introduced into Australia which has only one race Fumigation(bright red strips) and fertilizer trial in the Murray Mallee, photographed in IR, about 1970 (Rovira) Uninoculated (left) and inoculated intolerant showing the root branching and depth restriction which follows invasion Root system grown in the absence of pathogenic and saprophytic fungal invasion illustrating developing “white female” cysts containing nema eggs Nemas released from the mature brown cyst (upper left) . Adult nematodes Root system of paddock grown wheat plant illustrating root rotting in the presence of other nematodes (probably Pratelenchus neglectus) and a range of fungi (Rathjen) CCN control (Heterodera avenae) • Rotations • Chemicals • Resistant varieties • Education Life cycle of CCN The chart used to rate likely severity of CCN symptoms, used in recommendations for rotations and varieties (Rovira) Bioassay in summer and autumn months Field symptoms on Adelaide plains showing effect of the „Hay cut‟ (either fallow or resistant cereal variety in previous crop) compared to the heavily infested paddock. Paddock symptoms in spring - CCN probably exacerbating N deficiency Grain yields of samples relative to rating of severity of symptoms in spring . Survey by A Rovira on 21 paddocks on the Adelaide plains Survey by J Lewis. SA Dept of Agriculture of the prevalence of CCN in SA, 1989 Chemical control • Nemadi • Insecticides An early experimental control of CCN by chemicals,late 1970‟s, on the Adelaide plains, (Rovira). Treatment plot on right Another example of chemical control at Streaky Bay pre1980 (Rovira), with treated plot on left of photograph. Another example of chemical control, with untreated in centre of frame Genetics • Resistance, the nematode has almost no reproduction on the particular genotype. The host may however be severely damaged eg Avon variety of oats • Tolerance, describes the host response with a tolerant variety showing little effect of the invasion even though the pest might be reproducing on the roots Tolerant variety on right, intolerant on left (Rathjen) Come of growing a resistant variety rather than a susceptible one in terms of nematode population and grain yields (Dube and Fisher) Breeding plots at Palmer showing segregation for tolerance. Individual plots are 4 rows 4.2m in length, with a pathway,wheel tracks, between each bed of plots (Rathjen). Variation in tolerance in oat lines. Paler varieties probably exhibiting Fe deficiency as a result of rooting depth restrictions Screening for resistance in controlled environment cabinet to enable out of season breeding Effect of different varieties grown in 1975 (Festiguay, resistant , and Sabre, susceptible) on grain yields and nematode population in 1978). (Rovera) Control strategy advocated to farmers as part of project 70 (Dube). The ‟70‟ derived from the estimated annual losses to the pest of $70m Listing of the Tolerance and resistance of various cereal varieties in the early 1980‟s A summary of some of the features of the barley variety Galleon, released 1981, the first major release of a resistant variety, with a resistance derived from the north coast of Egypt where barley is grown continuously in the wadis Farmer‟s crop at Booleroo, where a CCN resistant variety had been grown in the left side of the paddock and a susceptible in the centre when the farmer ran out of seed in the previous cropping cycle. The earlier maturing section had about twice the yield Don Whiting at his variety trials. Don began his own variety trials in 1969 and the results from these was responsible for the rapid uptake of Festiguay in the Wallaroo zone The Festiguay story • Festiguay was bred in northern NSW as a rust resistant variety • It was brought to SA when two bags were brought back by visiting SA farmers • Don entered it in his trials where it outyielded local wheats (later it was realised that this was a result of the severe CCN infestation on his farm as was the case on almost all the farms in the district) • Its initial spread was enhanced by its resistance to stem rust in the 1973 and 1974 epidemics and then by its yield results in Don‟s trials • It formed about 60% of the deliveries in the Wallaroo Zone in 1980 even though it was clearly lower yielding in the absence of CCN Major Resistant Varieties • WHEAT – (Festiguay, post 1973), Molineux (1988), Frame (1992), Yitpi(1998). • BARLEY – Galleon (1981), Barque (1997), Keel(1999), SloopSA (2002), all SA varieties since then have been resistant. • OATS – Wallaroo and Marloo Outcomes • CCN damage is now vastly reduced from the estimated $70m, mostly as a result of growing resistant varieties. • The better root systems are associated with the widespread adoption of nitrogenous fertilizers during the 1990‟s. • Farmers are now concerned with „canopy management‟, ie too lush a canopy, rather the thin yellowish crops of the CCN era. • Direct drilling has been adopted following the CCN control with the Victorian Mallee being the last to adopt the technique following widespread cultivation of the resistant wheats Frame and Yitpi. • Land values in the area dominated by CCN have increased disporportionally.