Disease symptoms often have diagnostic value. They are used also to determine the nature of the alterations in the physiology of the diseased plant, and to estimate the severity or extent of the damage caused. The search for diagnostic features is usually performed in white light. Descriptions of symptoms and conclusions as to the nature and extent of damage reflected by symptoms are usually based on the appearance of symptoms in that light. [...]

Very high infestation levels of Thrips tabaci Lindeman were observed on onions at Ste-Clotilde (Quebec) with seasonal means of 149 and 161 thrips/plant for 1988 and 1989 respectively. No significant differences in thrips densities were detected among six yellow onion cultivars (Capable, Flame, Norstar, Progress, Rocket, Taurus) through weekly comparisons in 1988 and biweekly comparisons in 1989. / A new variable, the cumulative number of thrips-days/plant, was used to model the impact of T. tabaci on onion yields. This variable allowed for better-fitted models, especially in 1989 where greater variability of the onion yields was observed. A modified Gompertz equation gave the best fit for 1988. No yield reduction due to T. tabaci was observed up to the 1000 cumulative thrips-days/plant point, beyond which the thrips impact first increased with the feeding pressure and then gradually decreased to a minimal level corresponding to a yield loss of 43%. In 1989, thrips impact was immediate and best described by an exponential model with a maximal yield loss of 34,5%. / Economic thresholds of 964 and 251 cumulative thrips-days/plant were calculated for 1988 and 1989 respectively. Converted to thrips/leaf these correspond to 2,2 and 0,9 thrips/leaf. This conversion could facilitate their use in a field situation. / Spatial distribution of T. tabaci was analyzed in ten commercial onion fields. Within field, density was homogeneous in the majority of cases. In some fields, higher thrips densities were temporary (two consecutive weeks at most) in one or two field margins. / The Iwao method was used to calculate the acceptance boundaries of sequential sampling plans for the economic thresholds of 0,9 and 2,2 thrips/leaf and onion growth stages of 6, 7, 8, 9 and 10 green leaves. (Abstract shortened by UMI.)

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This research investigated early transcriptional responses of the model legume, Medicago truncatula, to herbivory by caterpillars of the beet armyworm, Spodoptera exigua. Differentially expressed genes were identified by the differential display technique, cDNA-amplified fragment length polymorphism (cDNA-AFLP). To distinguish between caterpillar-specific responses and general wound responses, a subset of plants was mechanically damaged. Furthermore, to identify responses to salivary elicitors, plants were subject to herbivory by caterpillars with normal salivary secretions and those that had their spinneret, the appendage through which labial saliva is secreted, cauterized shut. Eighteen differentially expressed gene fragments, representing 16 genes, were identified. The expression pattern of 5 of these genes was analyzed by Northern analysis, confirming a caterpillar-specific reduction in transcripts encoding rubisco activase and glyceraldehyde-3-phosphate dehydrogenase. This research shows that plants are able to differentiate between caterpillar herbivory and mechanical damage and that transcriptional response are initiated within one hour after caterpillar infestation.

Death of flower parts near bloom due to inflorescence necrosis (IN) is associated with high ammonium (NH₄⁺) concentration in flower clusters, shade, cool wet weather preceding bloom, and excessive vigor. Faults in NH₄⁺ assimilation are suspected to cause a rise in NH₄⁺ concentration to toxic levels in flower cluster but not other tissues. In this study, shading whole vines of Pinot noir increased flower NH₄⁺ concentration if applied at budbreak (early) or 1 wk before bloom (late), but only late application of shade to individual shoots raised it. Late, complete shoot defoliation raised flower cluster NH₄⁺ in all three years of the experiment. Early or late removal of lower leaves on a shoot also increased flower cluster NH₄⁺. Lamina, petiole, and other shoot tissue NH₄⁺ levels responded differently to treatments than flower clusters. IN severity was not affected by treatments; however, on shoots whose primary clusters had been removed at bloom secondary clusters did show significant differences, with IN being more severe in the early defoliation and late, lower defoliation treatments. Ethephon, sprayed on whole vines, slowed shoot growth to zero and increased IN severity greatly, however, flower cluster NH₄⁺ concentration was increased only 20% over the controls. Methionine sulfoximine applied as a cluster dip, increased flower cluster NH₄⁺ by 100%, yet resulted in little necrosis. Rootstock and clone affected Pinot noir flower cluster NH₄⁺ and IN severity. Rootstocks 420A caused lower and 101-14 and 3309 higher NH₄⁺ concentrations than the average. IN severity and flower cluster NH₄⁺ varied between vineyard sites, possibly due to environment and management differences. Pinot noir clones UCD23 and 32 had lower and UCD4 higher than average flower cluster NH₄⁺. IN in clones UCD4 and DJN115 was the least and UCD23 the most severe. A single 73kDa protein from grape shoot tissues reacted with anti-rice Fd-GOGAT IgG. An extraction method and assay for Fd-GOGAT activity from grape tissues was developed and gel filtration was used to show that the native enzyme is a dimer or trimer of the 73kDa protein. Activity was found in lamina, petiole, flower, rachis, and tendril, but not pedicel tissue. / Graduation date: 1997

Graduation date: 1966

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 95-107). / Microfiche. / x, 107 leaves, bound ill. (some col.) 29 cm