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The cereal cyst nematode,Heterodera avenue Wollenweber, is a serious pest of cereals in many countries. A high level of resistance to the unique Australian pathotype of the nematode has been demonstrated in a triticale line (T701-4-6), which was originally obtained from CIMMYT. The level of resistance is similar to that in rye cultivar, South Australian, but higher than that in the wheat line (AUS 10894), hitherto reported to have useful resistance to the Australian pathotype. The gene for resistance was located on rye chromosome 6 (6R) after backcrossing the T701-4-6 line to wheat and correlating the resistance with the presence of individual rye chromosomes identified by morphological, cytological, and isozyme markers. Preliminary evidence suggests that the gene is located on the long arm of6R. To transfer the resistance to wheat, double monosomics of6R and6D in aph1bph1b homozygous background were selected from F2 progeny from a cross of disomic6R substitution for6D to theph1b mutant. Selfed seeds from these F2 plants will be screened for wheat-rye chromosome recombinants.

Resistance of 800 wheat, 83 oat, and 36 barley cultivars to the cereal cyst nematode, Heterodera avenae, was tested in South Australia. A wide range of reactions of selected cultivars, assessed by numbers of females produced on the roots, was obtained for each of the cereals with populations of the nematode from two sites. Good resistance was recorded in only two wheat cultivars; Spring wheat (AUS No. 10894) showed moderate resistance in all tests and Loros (AUS No. 90248), although recorded as susceptible in one test, showed moderate resistance in other tests with a different population of the nematode. The importance of method of assessment, initial density of inoculum and relative growth of the cultivars are discussed.

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Population changes of the cereal cyst nematode (Heterodera avenae Woll.) under various rotational regimes in the field were examined. A density of 5 eggs/g soils caused a loss of about 10% in yield of wheat cv. Bayonet under the experimental conditions. Maximum multiplication rate at low initial densities was about l0x, but this rapidly decreased as initial density increased. Equilibrium levels ranged from 15 eggs/g soil up to 40 eggs/g under different conditions. The resistant wheat, Aus 10894, maintained an equilibrium level of about 1 egg/g soil-a level low enough to avoid damage in a following crop. Annual percentage hatch varied from 70-90% with an average of 85%. Presence or absence of plant species had little effect on per cent hatch. About 7.5% of the nematodes successfully penetrated and became established in the root systems of seedlings, invading both seminal and nodal roots, but only about 0.5% became established in the principal axes of the seminal roots. The implications of these data for various rotational practices are discussed.

SummaryMoulting of fourth-stage larvae of ParatylenchuB nanus was stimulated by apricot root secretion but the activity was lost on boiling. Dormant apricot seedlings did not produce an active secretion. The effect was on the anterior part of the nematode and 1 day in secretion was sufficient to initiate the moult. Five to 10 days after stimulation the larvae became motionless and the moult was complete about 3 days later. Moulting took place most rapidly at about 20°0 and was not affected by pH between 4 and 7. Moulting but not stimulation was inhibited at temperatures of 25 and 30°0. Shedding of the cuticle differed from exsheathment of trichostrongyle larvae in that no refractile ring formed in the anterior part of the cuticle.

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