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The mistletoe species Tapinanthus leendertziae, T. natalitius and Viscum combreticola and their avian dispersal agents were studied in the field during February 1977 - May 1978. The study was carried out in seven different plant communities. Year-round surveys were made of the reproductive phenology of the mistletoes. Aspects of pollination and germination of mistletoes were investigated. The birds visiting mistletoe plants were studied with respect to the rate at which they removed fruit and the way they dealt with mistletoe seeds. The diet of the Yellowfronted Tinker Barbet Pogoniulus chrysoconus, the main dispersor of the seeds of the mistletoes, was studied. Comparisons are made between mistletoes and their dispersal agents in savanna and forest biomes in South Africa, and the dispersal of mistletoes by birds in other continents of the world is· reviewed.

Wound periderm is formed by Juniperus occidentalis and Calocedrus decurrens in resistance to infection by the dwarf mistletoe Arceuthobium campylopodum. The pattern of wound periderm formation suggests that chemical as well as mechanical factors are involved. The concentration of hydrolases in the radicular apex of the parasite suggests that they may facilitate the penetration process by which dwarf mistletoes infect their hosts. Emzymatic assistance may also provide a partial explanation for the specificity with which dwarf mistletoes are adapted to given hosts. These resistance responses by the the non-host species were compared with the normal infection process Pinus ponderosa.

Thesis (M. Tech. (Homoeopathy))--Technikon Witwatersrand, 2004. / Specialist supervisor: D. Mycock ; supervisor: E. Solomon. Also available via World Wide Web.

3 pp. / Originally published: 2003 / Dwarf mistletoes are parasitic flowering plants that grow within host plants for about two years before producing characteristic yellow to orange or green to brown leafless aerial shoots on the outside of infected host tissue. They occur only on conifers in the pine family in Arizona and are usually host specific. This article gives information about the disease cycle, the symptoms and prevention and control methods for dwarf mistletoes.

In this thesis I investigated the importance of plant-animal mutualisms to the reproductive success of three West African mistletoe species in two genera, Globimetula braunii, Agelanthus brunneus and A. djurensis, in Ngel Nyaki Forest Reserve, Nigeria. The flowers of all three mistletoes were visited by 3 - 4 species of sunbird. Agelanthus flowers were also visited by honeybees (Apis mellifera) and a small social wasp species (Vespinae). A. mellifera appeared to be robbing nectar from the flowers of A. brunneus. To investigate the relative role of pollinators, I compared flower opening and fruit set amongst bagged, caged, natural, hand-selfed and hand-crossed treatments. The flowers of G. braunii were able to selfopen on average 66% of the time when pollinators were excluded, whereas pollinators were essential to the flower opening mechanism of both Agelanthus spp. Insects were as effective at opening the flowers of Agelanthus spp. as sunbirds. However, flower opening ability did not translate directly into pollination effectiveness, as insect access alone did not result in significantly higher fruit set than that observed under the bagged condition. There was no significant evidence for autonomous selfing within any of the three mistletoes and thus reproduction was almost entirely reliant on 3 – 4 species of sunbird. Hand-pollinations of all three species indicated a high level of self-compatibility, and in one species, G. braunii, pollen limitation was evident (PLI = 0.504). To investigate dispersal mutualisms amongst the three mistletoe species, fruit ripening and removal were monitored. The fruits of all three mistletoe species appeared to be removed rapidly from plants as they ripened, with few ripe or overripe fruits present on the branches at any time. Dispersal efficiency, or the total proportion of fruit crop removed across the fruiting season, was also very high (>90%) for the Agelanthus spp. but lower in G. braunii, for which almost a third of the total fruit crop was recorded undispersed in fruit nets beneath plants. Mistletoes are an important component of West African montane forests. Disruption to mistletoe reproductive mutualisms may affect not only mistletoes and their mutualists directly, but also an entire network of species, all linked within a web of interactions. To protect these ecosystems from further degradation, increased community involvement and greater enforcement of laws set out to manage montane forest habitat across the region is essential. Without this support, the future of these ecosystems and the web of interacting species within remains tenuous.

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

The viscin coating of seeds from Arceuthobium tsugense was analyzed histochemically. The results indicated that the viscin is composed of two components. The first is a muculagenous pectic compound which surrounds the entire seed and accounts for a number of observed phenomenon such as stickiness, water holding capacity and the ability to undergo repeated drying and rehydration. The second component is made up of a large number of cellulose strands which are attached to the endocarp and run throughout the pectic coating. Scanning electron micrographs show that they are thought to be important in maintaining the integrity of the pectic coating. The significance of these findings is discussed with respect to establishment of the parasite.

3 pp. / Originally published: 2003 / True mistletoes are parasitic flowering plants with characteristic clumps of growth that are easily visible on the host plant. They reduce the growth of infected hosts, but it usually takes many years for true mistletoe infections to kill a mature tree or shrub. This article gives information about the disease cycle, the symptoms and prevention and control methods for true mistletoes.

This research examines the influence of western dwarf mistletoe (Arceuthobium campylopodum) infection on the radial growth response of mature ponderosa pines (Pinus ponderosa) and its effects on dendroclimatic reconstructions. I hypothesize that trees with mistletoe have lower annual growth rates than uninfected trees, but exhibit higher mean sensitivities and stronger relationships between growth and climate variation. I tested these hypotheses using correlation and regression analyses to compare 100-year crossdated and standardized tree-ring chronologies from 26 infected and 29 uninfected trees. I compared both chronologies to climate variation as measured by changes in total precipitation, minimum, mean, and maximum temperature, and the Palmer Drought Severity Index (PDSI). Results show that trees infected with dwarf mistletoe have higher radial growth rates, exhibit greater sensitivity, and respond more strongly to climate variation. Both infected and uninfected chronologies are significantly correlated with the respective climate variables, but exhibit different patterns. The strongest correlations are between infected trees and PDSI for all months tested; significant correlations between uninfected trees and PDSI are limited to May through December lagged from the previous year. These results suggest mistletoe-infected trees are more sensitive to climatic factors than uninfected trees and may be useful for dendroclimatic analyses.