Typescript, etc.

Fraser oats were used to study populations of cereal aphids in 1972,1973 and 1974. The most commonly found species were Macrosiphum avenae (F.) (the English grain aphid), Metopolophium dirhodum (Wlk.) (Rose-grain aphid) and Rhopalosiphum padi (L.) (Oat bird-cherry aphid). Aphid density was highest in 1972, lower in 1973 and lowest in 1974. Generally M. avenae had the highest population with M. dirhodum slightly lower. Rhopalosiphum padi was found infrequently with low numbers. Fecundity trials, used to examine whether the difference between numbers of species was because of a difference in fecundity, did not substantiate field results but instead indicated that R.padi should have produced the highest population. Differences were not found in the population dynamics when the oats were planted in solid blocks instead of rows. A one month delay in the planting date did not change the total aphid population but did result ira higher proportion of M. avenae than found in any other plot. Coccinellid numbers in two out of the three years were considered negligible. In 1972 rain was thought to destroy many coccinellid before they reached large enough numbers to greatly affect the aphid population. No direct samples were taken of hymenopterous parasites but any found were collected and identified. Water experiments were conducted to study the effect of water on the fecundity of R. padi. It. was concluded - that R. padi definitely preferred wet conditions. Temperature and rainfall readings were used to show the effect of weather on aphid numbers. Weather was shown to be a major regulatory factor in the population dynamics of cereal aphids. Considerations were made for aphid mortality caused by sparrows. / Land and Food Systems, Faculty of / Graduate

Bibliography: p. 410-429. / 429 p., [20] leaves of plates : ill. (some col.), map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1995?

Bibliography: p. 410-429.

Victoria blight of oats is caused by the fungus Cochhobolus victoriae. This fungus is pathogenic due to its ability to produce the host-selective toxin victorin. Previously, a 100-kD protein that binds victorin in vivo only in susceptible genotypes was identified as the P protein of the glycine decarboxylase complex (GDC). Victorin is a potent in vivo inhibitor of GDC. Leaf slices pretreated with victorin displayed an effective Victorin inhibited the concentration for 50% inhibition (EC������) of 81 ��M for GDA. glycine-bicarbonate exchange reaction in vitro with an EC������ of 23 ��M. We also identified a 15-kD mitochondrial protein in susceptible and resistant genotypes that hound victorin. Amino acid sequence analysis indicated this protein is the H protein component of the GDC. Thus, victorin specifically binds to two components of the GDC. Victorin had no detectable effect on GDC in isolated mitochondria, apparently due to the inability of isolated mitochondria to import victorin. The interaction of victorin with the GDC may be central to victorin's mode of action. Supporting this observation is the finding that CO��� gives partial protection against victorin. Elevated CO��� is known to ameliorate the effect of GDC inhibition. Victorin treated plants incubated in the light develop more severe symptoms than dark-incubated plants. Victorin appears to induce a plant-wide signal transduction cascade, resulting in diverse effects. Victorin induces specific proteolytic cleavage of the Rubisco large subunit (LSU). Leaf slices incubated with victorin for 4 hours in the dark accumulate a form of LSU which is cleaved after the N-terminal lysine 14. LSU cleavage in leaf slices is prevented by the protease inhibitors E-64 and calpeptin. LaCl��� prevents this cleavage of LSU and LaCl��� also confers complete protection against victorin at the whole plant level. Victorin also causes lipid peroxidation as measured by MDA accumulation. DNA laddering is seen in leaves after 3 hr treatment with toxin. The ethylene inhibitors AOA and STS give significant protection against victorin at the whole plant level, and also prevent LSU cleavage. / Graduation date: 1998

Graduation date: 2003