No description available.

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

No description available.

Studies on the seasonal changes in the moisture content of western hemlock Tsuga heterophylla (Raf.) Sargent, demonstrated two moisture minima, one in the spring and one in the fall, and two maxima, one in the spring and the second in the winter. Significant differences were noted for both bark and wood moistures between good and poor sites, between seasons of the year and for the interaction between site and seasons of the year. The relative turgidity of bark from the good site was below the 80 per cent level for 95 days through an entire year. On the poor site it remained under this critical value for 123 days of the 8 months observation period. Dwarf mistletoe did not appear to affect the water economy of the portion of branches that had not been invaded by the endophytic system. However the parasite produced moisture stress in the bark at the central area of infections. An investigation of the fungi that were associated with cankered areas of dwarf mistletoe infections revealed the occurrence of twelve different species of fungi. Nine of these were Ascomycetes and three were Fungi Imperfecti. There were two undescribed species, and one species, Mytilidion decipiens Karst. had not been reported previously for North America. Preliminary tests of the parasitism of seven species indicated that one, a member of the Fungi Imperfecti, was mildly parasitic. / Science, Faculty of / Botany, Department of / Zoology, Department of / Graduate

Poria weirii Murr. isolates cultured from various hosts may be divided into two groups on the basis of their ability to parasitize Thuja plicata Donn and to grow on media containing water-soluble T. plicata heartwood extractives. The role of these extractives in determining whether a Poria weirii isolate can parasitize Thuja plicata was examined. Measurement of linear growth along wood micro-sections confirmed that substances inhibitory to one isolate group are hot-water soluble T. plicata heartwood extractives. The tolerance of isolates from T. plicata (Thuja) and Pseudotsuga menziesii (Mirb.) Franco (non-Thuja) to a hot-water extract of Thuja plicata heartwood and its hexane soluble (principally thujaplicins) and insoluble (thujaplicin-free) fractions was studied in detail. Dry weight of mycelium produced in liquid glucose-asparagine medium was measured. Thuja isolates were more tolerant than non-Thuja of the hot-water extract and its fractions; thujaplicins caused the greatest response differences. Thuja isolates showed greater stimulation than non-Thuja at subinhibitory thujaplicin concentrations. Higher thujaplicin concentrations were required to produce fungistatic and -toxic conditions in Thuja isolates than in non-Thuja. There were highly significant differences between isolate groups in response to 7.5 ppm thujaplicin. Tolerance was not related to date of isolation or geographical location. With sufficient inoculum potential, a non-Thuja isolate may overcome T. plicata heartwood toxicity. The resulting infection is usually localized. Unlike Thuja isolates, non-Thuja were unable to increase thujaplicin tolerance during three serial generations on liquid medium containing thujaplicins. Long exposure of non-Thuja isolates to T. plicata heartwood under field conditions did not increase their thujaplicin tolerance. Thuja isolates may be able to adapt the enzyme systems blocked by thujaplicin or to detoxify thujaplicins. These results have significance for control of Poria weirii. Planting Thuja plicata in and around infection centers caused by non-Thuja, isolates could limit their size by reducing the number of root contacts between susceptible species. / Science, Faculty of / Botany, Department of / Graduate

Tree-ring chronologies from ten mixed conifer stands in the Colorado Front Ranges and New Mexico Sangre de Cristo Mountains were used to reconstruct timing, duration, and radial growth impacts of past outbreaks of western spruce budworm, Choristoneura occidentalis Freeman. Graphical and statistical comparisons of tree-ring chronologies from host and non-host tree species, in conjunction with Forest Service records of outbreaks during the twentieth century, revealed that outbreaks were identifiable only in the host chronologies as sharply reduced growth periods. These comparisons also showed that host and non-host tree-ring chronologies were generally similar between outbreaks and that both were responding in a similar manner to climatic variation. A study of defoliation and insect population data that was available for the New Mexico stands demonstrated that host radial growth from 1978 to 1983 was highly correlated with budworm activity. The non-host chronologies from each stand were used to correct the host chronologies for climatic and other non-budworm environmental variations by a differencing procedure. The corrected chronologies were then used to estimate the dates and radial growth effects of past budworm outbreaks. Tree-ring characteristics of twentieth century documented outbreaks were used as criteria for inferring the occurrence of outbreaks in previous centuries. At least nine periods of increased budworm activity were identified in the region from 1700 to 1983. The mean duration of reduced growth periods caused by known and inferred budworm outbreaks was 12.6 years, and the mean interval between initial years of successive outbreaks was 34.9 years. The mean maximum radial growth loss was 50 percent of expected growth, and the mean periodic growth loss was 21.6 percent. There was an unusually long period of reduced budworm activity in the first few decades of the twentieth century, and since that time outbreaks have been markedly more synchronous between stands. Increased synchroneity of outbreaks in the latter half of the twentieth century suggests that areal extent of outbreaks has increased. This phenomenon may be due to changes in the age structure and species composition of forests following harvesting and fire suppression in the late nineteenth and early twentieth centuries.

Five virus isolates RS 2, RS 25, RS 26, RS 28 and RS 29, were transmitted by juice-inoculation technique from sour and sweet cherry trees to cucumber. Four isolates were obtained from trees growing in the Kootenay cherry district of British Columbia. Another one was isolated from a tree growing in the coastal area of this province. Viruses known to occur in the source trees are Necrotic Ring Spot Virus, Sour Cherry Yellows Virus, Twisted Leaf Virus and Little Cherry Virus. The relationship and the complexity of the virus isolates was studied with herbaceous hosts, using a mechanical transmission technique. Pincherry (Prunus pennsylvanica L.) was inoculated by the same technique as a means for provisional identification of the virus isolates. The cucumber syndrome of isolate RS 25 was very mild, that of isolate RS 2 mild, that of isolate RS 29 was of medium severity and those of isolates RS 26 and RS 28 were very severe. Inoculates RS 2 and RS 29 varied greatly in symptom expression on cucumber, whereas the symptom expression of the other isolates was less variable. Isolate RS 29 was characterized by symptomless systemic infection of Nemesia sp.. var. Triumph. Isolates RS 26 and RS 28 both infected Petunia hybr., var. Blue Bee, without expressing symptoms, whereas the other isolates did not infect this species. Other host species too carried the isolates without expressing symptoms, whereas symptoms were produced on cucurbit hosts. Isolates RS 2, RS 26, RS 28 and RS 29 appeared to consist of more than one virus. Strains of a virus P occur in all isolates and isolate RS 25 itself is also a strain of this virus. All five strains of virus P express similar very mild symptoms on cucumber, whereas a characteristic severe savoying type of symptom is produced on squash (var. Table Queen). Species susceptible to virus P are cucumber, pincherry, squash, sweet pea, tobacco (under conditions of long day) and other species. Lathyrus odoratus L. and Lens culinaris Medic. are species useful in separating virus P from the other viruses occurring in isolates RS 2, RS 26, RS 28 and RS 29. It is possible that virus P is related to cucumber-mosaic virus as suggested by symptoms on squash and tobacco. In previous work by other investigators a strain of cucumber-mosaic virus was also isolated from Prunus hosts. On pincherry (P. pennsylvanica L.) isolate RS 28 caused acute symptoms of necrosis and shothole. The plants recovered but symptoms of mottling were systemic. Necrotic Ring Spot Virus caused similar symptoms on Prunus hosts and this virus and Sour Cherry Yellows Virus was present in the original source tree. The other isolates in pincherry all caused similar symptoms of mottling on the young leaves. A few necrotic lesions were produced also. On reisolation from pincherry virus P was obtained in case of isolates RS 2, RS 26 and RS 29. No virus was reisolated in the case of isolate RS 25. The complete parent isolate was reisolated in case of isolate RS 28. The results with pincherry suggest that virus P is responsible for the mild symptoms whereas virus P in conjunction with an additional virus as in isolate RS 28 incites the severe shock symptoms. The identification of the viruses present in the isolates can be carried out by scion inoculation of a set of suitable Prunus indicator hosts. / Land and Food Systems, Faculty of / Graduate

Volatile constituents of bark from the two species of pine hosts of the mountain pine beetle, (Dendroctonus ponderosae Hopkins) were investigated as postulated factors in host tree discovery and selective attack by the insect. The anemo-olfactory, klinokinetic and klinotactic responses of pedestrian adult flown females to odors of different aged pines of the species Pinus ponderosa Laws, (ponderosa pine) and Pinus monticola Dougl. (western white pine) were used as criteria to test for evidence as to possible involvement of host tree volatiles in host selection. Volatile substances from pine bark were collected through sublimation under vacuum from frozen state. The volatile extracts were analyzed by Gas-Liquid Chromatography. Total volatile extracts and their ether soluble fraction from mature pine trees were "attractive" to beetles, whereas those from saplings were "repellent." No qualitative differences were found in the ether-soluble fraction of mature trees and saplings respectively, but proportions of individual constituents in the extracts differed. Ethanol at various concentrations caused arrestance of the anemo-olfactory response of pedestrian beetles. As a constituent of trees under stress ethanol may thus play an important role in the programme of responses which lead ultimately to attack. Problems encountered during the storage of tree samples and their extracts have been discussed. / Forestry, Faculty of / Graduate

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfillment of the requirements for the degree Master of Science Johannesburg, 2018 / Seed recalcitrance in avocado (Persea americana) has meant that avocado genetic material cannot be conserved in orthodox seed banks. Thus, biotechnological approaches have been considered for the long-term conservation of this species’ genetic material, through the cryopreservation of tissue culture-generated axillary buds. A study was conducted to develop a system for the proliferation of in vitro avocado cv. ‘Edranol’ axillary buds for the purpose of cryopreservation. Experiments were conducted to optimise avocado mother plant establishment and pretreatment. It was determined that potting soil mixes comprising of either 1:1:1 pine bark, perlite, river sand or 1:1:1 peat, perlite, river sand were suitable to culture healthy avocado mother plant seedlings. With these soil mixes approximately 2 shoots per plant developed after 11 weeks of transplanting and between 2.9 ± 0.31 and 3.37 ± 0.32 secondary shoots were produced after 5 months. Additionally, the mother plants produced well extended shoots (7.30 ± 1.29 cm; 8.77 ± 1.39 cm) with a sufficient number of axillary buds (7.75 ± 0.39; 6.33 ± 0.53), which were subsequently used as nodal explants. After surface decontamination, the establishment of an aseptic culture in vitro was successfully achieved. Six semi-solid tissue culture media were tested for the proliferation of in vitro axillary buds. Four media comprised of half (½) and full strength Murashige and Skoog (MS) medium (Murashige and Skoog, 1962), with either 0.5 or 1mg/l 6-Benzylaminopurine (BAP). Two media were based on the P. indica medium as proposed by Nel et al. (1983), and comprised of half strength MS macronutrients, full strength MS micronutrients, 2mg/l BAP and 1mg/l GA3. All media were supplemented with 3g/l Gelrite and 30g/l sucrose at pH 5.6-5.8. Physiological measurements were taken six weeks after establishment, the first, the second and the third subculture. Tissue browning, death and contamination were observed in explants cultured on the media containing 0.5mg/l BAP, suggesting that this concentration of BAP was not suitable for cv. ‘Edranol’. Additionally, hyperhydricity appeared to be associated with the media containing ½ MS, which could be attributed to mineral deficiencies. Overall, there was no significant difference in the number of shoots and axillary buds developed across all the media tested, suggesting that endogenous auxin levels were higher than the concentration of cytokinin used in the media tested. In support of this, strong apical dominance and callus formation was observed. An increase in tissue browning, death and hyperhydricity on all the media tested, coupled with a decrease in shoot length, suggested a decline in the vigour of explants in vitro. 1MS + 1mg/l BAP was selected as the most appropriate medium for the initiation of cv. ‘Edranol’ cultures, producing between 3.2 ± 0.2 and 4.9 ± 0.5 axillary buds per explant. However, hyperhydricity, browning and death were observed in explants cultured on this medium. Overall, the in vitro axillary bud explants did not behave predictably or uniformly. Thus, the system was not optimised, indicating that further study is needed for the mass multiplication of axillary buds to be used for the cryo-conservation of avocado genetic material. It is recommended that future experiments will be needed to further test tissue culture media, with a focus on the optimisation of the nutrient and plant growth regulator concentrations. Additionally, the recalcitrance of explants to the in vitro environment may have been influenced by the physiological state of the mother plants, indicating that research should be focused on the effect which the mother plants may have on the endogenous responses of the in vitro explants. / MT 2018

No description available.