With the hope of being able to demonstrate the relative effect of predator species on the young sockeye (Oncorhynchus nerka) in different lakes, the Skeena river investigation instituted a program of standard gill-netting in 1945. Study of the catches and information obtained from netting experiments indicated that the catch per net-night was the best estimation of the concentration of each preying species in different areas. Coupling this catch per net-night with the average volume of sockeye found in the stomachs of predators caught, a measure of predation called the "predation index" was calculated. On the basis of this index, the populations of nine lakes of the Skeena drainage were classified as either high, low or intermediate in effect on young sockeye. / Science, Faculty of / Zoology, Department of / Graduate

Samples of sapwood and bark of western redcedar were collected at 3 day to 6 week intervals after injury and extracted with water, chloroform and acetone. Extracts were tested for the presence of some common heart-wood compounds and in vitro fungi toxic properties. Extracted samples collected 6 weeks after injury were inoculated with a decay fungus, and the resulting weight losses determined. No heartwood compounds were detected in any extracts, and no extracts were fungi toxic in vitro. Weight losses following decay of extracted chips indicated that decay resistance was initiated in the bark and sapwood. Thus, these tissues possess a mechanism of disease resistance induced by injury. It is concluded that this resistance results from the deposition of a toxic substance that is unextractable with water, chloroform, or acetone. The alteration of sapwood, if not the bark, is analogous in certain respects to the formation of reaction zones in the sapwood of various trees, since these zones are induced by injury and are characterized by abnormal toxin formation. However, the toxins formed in other trees are normal heartwood constituents, and in this respect apparently not parallel to the toxic substance induced in western redcedar. / Forestry, Faculty of / Graduate

Studies of Saprolegnia infections of fish in British Columbia were made to determine disease causing agents and infection conditions. Saprolegnia diclina Humphrey was the most frequently observed parasite. This fungus reproduced sexually both on fish tissue and hemp seed cultures. No definite isolations of S. parasitica Coker were made although some non-sexually reproducing isolates of a Saprolegnia sp. were found. The validity of the species, S. parasitica, has been examined and questioned on the basis of present identification characteristics. Infection studies using S. diclina as the parasite and fingerling coho (Oncorhynchus kisutch) as the host indicated a distinct correlation between temperature and infection. At normal cool temperatures, e.g., 8° C, no infection occurred; at 9°C or above, some infection resulted. Above 9° C, the rate of infection increased as temperature increased. Temperature was also associated with the time at which infection occurred after inoculation. At 18°C, infection began earlier than at 13 C, Heat-shock treatment tended to reduce the temperature-time effect causing initial infection at 13°and at 18° C to occur almost simultaneously. Cold-shock treatment resulted in some infection. Such treatment, however, did not produce the same immediate infection as heat-shock. Histological studies demonstrated the infection to be concentrated in the host epidermis with fungal hyphae at sites of heaviest infection extending through the dermis and into underlying muscle tissues. / Science, Faculty of / Botany, Department of / Graduate

Blotchy ripening (BR) of tomatoes is an irregular ripening of tomato fruits. This world-wide disorder has been a problem of the spring crop, particularly during the later part of May, in greenhouse tomatoes in British Columbia. For the investigation of the factors which affect the occurrence of BR in B.C., the following were considered: Correlation between the hours of bright sunshine and the incidence of BR, the influence of weekly alternation of light and temperature conditions on the incidence of BR, and the association of the incidence of BR and virus diseases. Examination of weather records led to a hypothesis which was tested in growth chambers. The light regimes employed consisted of a high and a low light condition. Concurrently two temperature regimes were used, one with a high maximum-temperature and the other with a low maximum temperature. Both regimes employed the same minimum temperature. The results of the studies were as follows: The cyclic occurrence of sunny weeks and cloudy weeks was associated with the incidence of BR in the B.C. greenhouse tomatoes. The weekly alternation of the light conditions produced 37% BR fruits when the plants were subjected to a constant day- night temperature cycle, but only 11% BR fruits, which was not significantly different from 6% BR in the control, was produced when the temperature conditions were alternated simultaneously and directly with light regimes. The role of tobacco mosaic virus (TMV) on the Incidence of BR in the B.C. greenhouse tomatoes did not appear to be important. The effect of potato virus (PVX) on the incidence of BR was not clear. / Land and Food Systems, Faculty of / Graduate

Forest insects and diseases active in immature interior spruce stands in the central interior of British Columbia and their possible implications in forest management practices have been surveyed. Collection records, spanning the period 1949 to 1982, from the Forest Insect and Disease Survey of the Canadian Forestry Service were reviewed for the Prince George Timber Supply Area and the pest incidence in immature interior spruce stands summarized. Twenty-two plantations, established between 1963 and 1973, were surveyed to determine the relative incidence of the major insect and pathogen pests of immature spruce in Supply Block 'G' of the Prince George Timber Supply Area. A bud midge, likely Rhabdophaga swainei Felt (Diptera: Cecidomyiidae), and a terminal weevil, Pissodes strobi Peck (Coleoptera: Curculionidae), were found to consistently infest and damage a significant number of immature interior spruce trees. A spruce stand stocking profile was developed as a basis for discussion of management practices in plantations and immature stands. The stocking profile can be used in the determination of not only pest management policy decisions but in stand management decisions affecting stand density and, ultimately, merchantable yield at harvest. The findings confirmed that forest management must be actively practiced throughout the life of a forest stand. To be successful, however, stand management guidelines and merchantable yield projections are required. These guidelines and projections must include the influences of insects and diseases upon the forest crop in their development model. This information is particularly important in the development of complete Timber Supply Area plans and for the flagging of pest hazard periods during the development of spruce forests. / Forestry, Faculty of / Graduate

Because of recent advances in genotic insect control theory, it has become important to investigate the fitness effects of, and isolation procedures for, homozygous autosomal translocations. I isolated 57 autosomal translocations in Drosophila melanoqaster. Of these 21 were homozygous viable. From data obtained during the isolation of these trunslocations and from fitness tests and competition cage experiments, rhe following points can be made; (1) Between one in ten and one in one hundred homozygous viable laboratory produced translocations are likely to be of value in field tests of genetic insect control procedures. (2) Translocations which produce high levels of unbalanced gametes when heterozygous do not tend to be lass fit in the homozygous state than others. Therefore screening procedures dependent only on reduced progeny production from translocation heterozygote parents should be satisfactory for the isolation of useable stocks. (3) Translocations whose breakpoints are vary near the center of chromosomes tend to produce small progeny reduction in the heterozygous state, making these translocations useless as negative heterotic carriers of useful genes. (4) Those translocations which are the result of multiple break events tend to be less fit than simple double-break translocations and therefore should be discarded. / Science, Faculty of / Zoology, Department of / Graduate

Olpidium was correlated with the frequency of precipitation greater than one half inch but was not correlated with root temperature, CO₂ or 0₂ concentration, saturated hydraulic conductivity, the height of the carrot beds, marketable yield or cull rate. Olpidium isolates with and without TNV did not produce lesions on carrot roots under greenhouse conditions. TNV was detected in both brown and white roots but only from problem fields. Carrot rootlets rub-inoculated with TNV failed to produce necrotic symptoms. Olpidium and TNV were found in onion, lettuce, celery and some weed species common to PRD problem fields. However, no root tip browning was observed in any of these hosts. Fast growing Pythium species were recovered equally frequently in brown and symptomless rootlets and from problem and non-problem soils. Most weeds, celery, onion and lettuce also had a high incidence of fast growing Pythium. The highly pathogenic, slow growing Pythium sulcatum was recovered only from problem soil. The recovery rate from symptomless roots was very low compared to brown roots. P. sulcatum was not isolated from celery or any of the weed species common in problem soil. Lettuce and onion were found to support low levels of infection. Evidence suggests that P. sulcatum is a primary incitant. PRD losses can be kept to a minimum and marketable yields increased by using tolerant varieties, such as HiPak; raised beds, if there is a readily available supply of irrigation water; precision seeding at 1 1/4 inches; and a crop rotation of onions preceding carrots. Matric potential was controlled in small containers separated from osmotic solutions of polyethylene glycol (PEG) 6000 by Pellicon ultrafiltration membranes (nominal molecular weight cutoff:500, Millipore Corp.). Matric potentials could be maintained for periods of 3-5 weeks before microbial breakdown of membranes occurred. Flow rate for the membranes was 1.0 cm³ cm⁻² day⁻¹ for a water potential difference across the membrane of 0.2 bar. Water potential measured with tensiometers or thermocouple psychrometers in a cylindrical container (4.3 cm diam. x 10 cm) with a membrane acrosss the bottom, remained relatively constant under conditions of soil surface evaporation but decreased rapidly when young plants were grown in the system. Soil cells (5.5 x 2.0 x 10 cm with one 43 mm diameter membrane in each side), containing two young carrots, and emersed in a -0.2 and -2.0 bar PEG solution had an average matric potential of -0.4 and -2.5 bars respectively over a three week period. The carrots transpired 7.8 and 3.9 ml/day at osmotic potentials of -0.2 and -2.0 bars respectively which suggests that sufficient water was passing through the membrane to meet the needs of a growing carrot. / Land and Food Systems, Faculty of / Graduate

A carlavirus was isolated from naturally-infected dandelions in the Okanagan Valley, B.C. In total, 31 plant species belonging to 12 families were tested as possible hosts for the dandelion virus. In only four families (Amaranthaceae, Chenopodiaceae, Compositae, Solanaceae) were susceptible species found. The virus was contained as local lesions in Gomphrena globosa and Datura stramonium and became systemic in Chenopodium amaranticolor, C. quinoa and Taraxacum officinale. The carlavirus, for which the name Dandelion Virus S (DVS) is proposed, has slightly curved particles with normal length 637 nm and width 12-13 nm. A purification scheme was developed that yielded 20-30 mg of virus per kg of C. quinoa leaf and stem tissue. Partially purified virus preparations had a single nucleoprotein component in rate zonal sucrose and cesium chloride density gradient centrifugation. The UV absorption spectrum has a maximum at 259 nm and a minimum at 245 nm. The ratio, of A[sub max]/A[sub min] is approximately 1.1; of A₂₆₀/A₂₈₀,1.4. In sap from infected C. quinoa, DVS had a thermal inactivation point of 75-80°; an infectivity dilution end point of 2 x 10⁻⁵ to 2 x 10⁻⁶ ; a longevity in vitro of 4-5 days at 23°, 28-56 days at 4° and at least 16.5 months in a lyophilized state at 23°. An antiserum against DVS was prepared by four intramuscular injections of 1 mg each and the maximum homologous titre was 40,960. Two carlaviruses with similar symptoms in C. quinoa, Peru virus S (PeVS) and Helenium virus S (HVS) were purified for antisera production and comparative serological testing. Antisera to other carlaviruses were also used to determine if serological relationships existed with DVS and other members of the group. Serologically, DVS is related to potato virus S (PVS) and PeVS, and distantly related to chrysanthemum virus B (CVB), Helenium virus S (HVS) and narcissus latent virus (NLV). / Land and Food Systems, Faculty of / Graduate

Pseudomonas syringae van Hall was recovered from 31 of 32 samples of red raspberry tissue showing typical symptoms of bacterial blight. Of the 99 isolates recovered, 85 were physiologically-typical, P. syringae isolates, three did not produce the fluorescent pigment, six did not utilize lactate and five did not produce toxin as determined by the Geotrichum candidum bioassay. When a suspension of 10⁷ CFU/ml was sprayed on the leaves of 6-week-old raspberry plants, 42 of 48 isolates caused necrosis within 4 days. No other bacterium recovered from the diseased raspberry tissue was pathogenic to raspberry in greenhouse tests. P. syringae isolates remained viable and retained their toxin-producing ability when stored for one year on nutrient glycerol agar at 5°C. Identical isolates stored on nutrient agar at 5°C or in sterile distilled water at room temperature either did not survive or lost their toxin-producing ability. There seemed to be a relationship between toxin-producing ability and an isolate's virulence as about 50% of toxin-producing isolates were rated pathogenic and 35% weakly pathogenic while none of the non-toxin-producing isolates were rated pathogenic and 60% were rated weakly pathogenic. A scheme was devised for rapid identification of P. syringae from raspberry tissue. An isolate was determined to be P. syringae if it produced a distinctive raised mucoid colony on nutrient sucrose agar, produced a fluorescent pigment, was oxidase negative and reacted in drop agglutination tests with an antiserum prepared against syringae. These tests could be done within three days. This scheme was used to study the overwintering site of P. syringae on raspberry. P. syringae was found to naturally populate 25-75% of raspberry buds during the winter months. Populations of 10⁴ CFU/six bud sample were most common in the buds that contained P. syringae. During the spring and summer months, P. syringae survived as an epiphyte on raspberry leaves both in the field and in the greenhouse trials. P. syringae was also shown to cause brownish-red spots surrounded by yellow halos on the leaves of raspberry during the summer months. About 90% of the P. syringae isolates from raspberry were ice nucleation active. Raspberry plants that had been sprayed with a suspension of 10⁷ CFU/ml and then held at -2°C for 4 hours developed symptoms similar to those of bacterial blight within 12 hours of the freeze treatment. In preliminary tests, raspberry cultivars showed varying degrees of resistance to P. syringae infection. Raspberry cultivar Chilcotin showed greatest resistance and cultivar Mailing Leo showed greatest susceptibility to Pseudomonas syringae infection. Three different species of bacteria were found in the normal microflora of the raspberry that were antagonistic to P. syringae in vitro. / Land and Food Systems, Faculty of / Graduate

Laboratory experiments and some field and greenhouse studies were carried out to determine the mode of action of radiant energy in the development of a post-harvest sunscald disorder of tomato (Lycopersicon esculentum Mill c.v.Vendor) fruits. The effects of the disorder on post-harvest fruit quality and physiology were evaluated by the physical determination of textural characteristics, the analysis of some chemical constituents and the measurement of fruit gas exchange. The ability of various storage temperatures, photoperiods and oxygen concentrations to alleviate injury was also examined. The effectiveness of radiant energy in causing sunscald injury was found to depend on the amount of radiant energy in the infra-red waveband. The action of infra-red radiation was thermal rather than photochemical. The use of high air temperatures to heat fruits produced symptoms similar to sunscald except that the colour of the fruit surface became greyish rather than white. Injury can develop at all stages of ripeness but symptoms vary with stage of ripeness. Injury also develops in light in the absence of oxygen or in darkness. Photooxidation does not appear to be a prerequisite for injury development. Injurious radiation treatments caused a loss of green colour and injured fruits failed to synthesize the red pigment; lycopene, in storage. Injury did not result in any appreciable loss in lycopene content once the pigment had formed. The mode of action of intense electromagnetic radiation on fruit colour therefore appears to be by destruction of the mechanism of carotenoid synthesis rather than by increased carotenoid degradation. Injury prevented protopectin solubilization during subsequent storage. It also led to a large reduction in ascorbic acid content and an increase in pH. The changes in ascorbic acid content and pH occurred progressively during the development of injury. Changes in the textural attributes of tomato fruits were assessed by measurements of six force-deformation characteristics: Deformation, Pericarp strength, Mesocarp resistance, Compliance, Firmness and Toughness. Toughness did not significantly change during ripeness. Although the effect of injury on Mesocarp resistance was not significant, the interaction of injury with storage was significant for the characteristic. Four characteristics: Pericarp strength, Mesocarp resistance, Compliance and Firmness were highly correlated with protopectin content. Of the textural indices, Compliance was the best predictor (R² = 90.4%; SŶ = 1.97) of protopectin content at different levels of injury, irrespective of ripeness or storage. It is therefore recommended that Compliance, rather than Firmness be used for detecting changes in the "softness" of tomato fruits. "Induction" and "incipient" types of injury accelerated the onset of the respiratory climacteric. "Advanced" type of injury reduced rates of respiration during fruit ripening. The failure of injured fruits to ripen normally was not due to lack of ethylene production since rates of ethylene production were high in injured fruits. The relationship between the respiratory climacteric and ethylene production was shifted by injury. Storage treatments involving different temperatures, photoperiods and oxygen concentrations did not alleviate injury. It is suggested that efforts aimed at controlling injury should emphasize prevention of exposure to radiation rather than attempt to cure injury in exposed fruit. / Land and Food Systems, Faculty of / Graduate