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1961 - 196921970 - 19771

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    A study of the leafspot disease of lettuce caused by Stemphylium botryosum Wallr. : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand, Massey Agricultural College
    (Massey University, 1961) Slade, Donald Arthur
    Lettuce (Lactuca stavia L) is the most important salad crop and a principal vegetable of New Zealand where in many districts it can be grown out of doors all the year round. Winter lettuce growers commonly plant from 1/2 - 5 acres of lettuce, and a good crop will cut 400 cases an acre. In late winter and early spring when other vegetables are scarce, returns to the grower from lettuce may be as high as 20/- to 60/- a case. Returns per acre from winter lettuce are therefore relatively high compared with other winter crops. The success of this crop is of major importance to the grower who commonly depends on it to cover the high winter and spring labour expenses which usually coincide with a period of low production. From season to season and even from week to week in the same season, the quality and quantity of lettuce available is a direct reflection of the prevailing weather conditions. Weather may act directly on the lettuce plant affecting its rate of maturation, appearance and plant size. Weather may also have a profound indirect effect by providing conditions conducive to disease development. It is well recognised that a disease may reach epiphytotic proportions only if weather conditions are favourable to the causual organism. [From Introduction]
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    Identity, taxonomy and seed-borne aspects of the gray leaf spot organism on blue lupin : a thesis submitted in partial fulfilment of the requirements for the degree Master of Agricultural Science at Massey University
    (Massey University, 1968) Tate, Kenneth Gregory
    While conducting studies in the Manawatu on the brown spot disease of blue lupins 1/ caused by Pleiochaeta setosa (Kirchn.) Hughes, Milne (1964) frequently encountered a Stemphylium disease characterised by necrotic lesions on leaves, stems and pods. A disease caused by a species of this genus had not previously been reported on blue lupins in New Zealand, but in the United States of America Wells, Forbes, Webb and Edwardson (1956) described two previously unrecognised diseases on this host, namely "little leaf spot" caused by Stemphylium botryosum Wallroth and "gray leaf spot" caused by S. solani Weber. Milne considered his isolates to be S• botryosum but was confused by the symptoms being typical of those recorded for S.solani (gray leaf spot). He did not pursue the matter further and at the completion of his studies on P• setosa there remained the unresolved question of the identity of the Stemphylium species present on blue lupin in the Manawatu. [From Introduction]
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    Plant pathogenic species of Stemphylium wallr. in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1977) Singh, Gurmit
    A taxonomic study was conducted of 48 isolates of plant pathogenic Stemphylium Wallroth species, all of which produced a Pleospora Rabenhorst perfect state in culture. Specific identification was attempted using gross colony characters and morphological features of the imperfect and perfect states. Only conidial and ascospore features proved to be of taxonomic value. The diagnostic conidial features were shape, dimensions, length/width ratio, number of longitudinal and lateral septa, number of lateral septal constrictions, ornamentations and pigmentation. Ascospore features of taxonomic significance were dimensions, and shape of both juvenile and mature spores. On the basis of these criteria it was concluded that three Stemphylium species were present, namely Stemphylium botryosum Wallroth, Stemphylium globuliferum (Vestergen) Simmons, and Stemphylium vesicarium (Wallroth) Simmons, each with a corresponding Pleospora state. This cross-pairing had value since identification of form-species allowed reliable prediction of the Pleospora species, and vice-versa. The cultural conditions providing the best expression of conidial features (and thus facilitating separation of Stemphylium species) were 5% V-8 agar, pH 7.5, 20C and an 8h photoperiod. Synchronous production of conidia was induced with an injury technique and ascostromata were matured most rapidly at either 12C or a diurnal temperature regime of 8h at 16C/16h at 8C. A taxonomic survey of 166 Stemphylium isolates from 12 host species revealed the three previously mentioned species and a further undescribed species. The latter was isolated from annual phlox and was characterized by exceptionally large ascospores. S. vesicarium was by far the most common species, occurring on asparagus, chrysanthemum, blue lupin, Russell lupin, tree lupin, onion, pepper and tomato. The legumes were hosts of more than one species; lucerne for instance was a host for S. botryosum, S. globuliferum and S. vesicarium, while Russell lupin and tree lupin were only infected by S. botryosum. and S. vesicarium. By contrast, lettuce and carnation were only infected by S. botryosum. Cross-pathogenicity tests indicated that host specialization was relatively uncommon. S. botryosum from lettuce and the Stemphylium sp. from annual phlox were the only isolates exhibiting host specificity. The results of ultrastructural studies of conidiogenesis, the phenomenon of vegetative reversion of conidiophores and juvenile conidia, and the mechanism of ascospore release in Pleospora are discussed. A previously undescribed, saprophytic, chain-forming species of Stemphylium is also described.