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A Microbiological Control of Melampsora Medusae Thum

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A Microbiological Control of Melampsora Medusae Thum A MICROBIOLOGICAL CONTROL OF MELAMPSORA MEDUSAE THUM. RUST ON PSEUDOTSUGA MENZIESII(Mirb.)Franco SEEDLINGS by RICHARD P. McBRIDE B.Sc, University of British Columbia, 1964 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Bio]ogy and Botany We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1965 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that per• mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives,, It is understood that copying or publi• cation of this thesis for financial gain shall not be allowed without my written permission. Department of < p f 7 (y The University of British Columbia Vancouver 8, Canada Date /'' ABSTRACT Saprophytic fungi and bacteria were recovered from healthy foliage of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). The populations of microorganisms on foliage were variable and changed through the growing season. Three species of the bacteria isolated from Douglas fir foliage were used in attempts to control the development of the rust, Melampsora medusae Thum.. on Douglas fir seedlings in the greenhouse. Effective control was obtained when Bac? 1 lus cereus Frankland and Frankland and B_. mvcoides Flugge were applied to the seedlings in pure cultures of nutr• ient broth. The most effective control was obtained from the application of a mixture of these two species and a third unidentified species of Baci1lus in nutrient broth. Less effective control resulted from the ap• plication of bacteria suspended in water and cell free filtrates of the bacterial cultures. The numbers of bacteria on the foliage of Douglas fir were estim• ated using a modification of the soil dilution and bacterial plate count technique. The bacterial populations on foliage of Douglas fir in the greenhouse and in the field were increased by the application of bacteria in nutrient broth and sterile nutrient broth. • • • I I I CONTENTS Page INTRODUCTION I LITERATURE REVIEW 2 Leaf microfloras 2 Biological control of disease using foliage saprophytes 3 METHODS 1. Recovery of leaf microfloras 6 2. The pathogen: collection, storage and germination of teliospores 6 3. The host 7 h. The disease 7 5. Preparation of treatments 9 6. Estimation of bacterial populations 11 RESULTS Observations on foliage microfloras of Douglas fir 13 Inoculation experiments 13 Field study 23 DISCUSSION 27 SUMMARY 31 LITERATURE CITED 32 APPENDIX 35 TABLES The effect of water, nutrient broth, cell free filtrate and bacterial treatments on the develop• ment of Mel ampsora medusae on the foliage of Douglas fir seedlings The effect of nutrient broth, cell free filtrate, and bacterial treatments on the development of Melampsora medusae and the number of bacteria on the foliage of Douglas fir seedlings The effect of pure cultures in nutrient broth of Bacil lus cereus. B_. mycoides. Baci 1 lus sp., and of a mixture of these bacteria on the development of Melampsora medusae on the foliage of Douglas f i r seedl ings , FIGURES Page Figure 1. Pycnial droplets of Melampsora medusae on a Douglas fir seedl ing 8 Figure 2. Aecia of Melampsora medusae on a Douglas fir seedl• ing 10 Figure 3. The method of inoculations. From left to right: aspen leaves bearing germinating teliospores placed on a wire screen above the pot of seedlings; moist cotton placed over the aspen leaves; poly• ethylene bag placed over the pot 10 Figure 4. A comparison of the percent seedlings diseased in the first inoculation experiment with Melampsora medusae 16 Figure 5. A comparison of the percent seedlings diseased in the second inoculation experiment with Melampsora medusae 19 Figure 6. A comparison of the effects of pure cultures of three species of bacteria and a mixture of the cultures on the development of Melampsora medusae 2k Figure 7. The effect of bacterial and water treatments on the number of bacteria recovered from Douglas fir foliage in the field 26 vi ACKNOWLEDGEMENTS Grateful acknowledgement is given to the National Research Council, Ottawa, for providing a Bursary in 1964-65 in support of this study. The writer expresses his appreciation to Dr. J.E. Bier, Professor of Forest Pathology, Department of Botany, University of British Columbia, for his guidance and encouragement throughout this study, and to Dr. J. Basaraba of Acadia University, Nova Scota, for the identification of two bacterial isolates. Miss P. Ackland and Miss G.D. Pentland are kindly thanked for their helpful suggestions and advice in writing this thesis. 1. INTRODUCTION Frequently immature plant tissues are highly susceptible to para• sitic microorganisms that are unable to infect more mature tissues of the same plant (9). Presumably this susceptibility could be eliminated only by chemical control methods because natural resistance was thought to depend on the development of anatomical and physiological defenses. Bier (2,3,4,5) and others (6,7,15,16,21,22,23,24) have shown that aerial por• tions of plants are complex biological communities comprised of numerous saprophytic bacteria and fungi as well as the host plant tissues. Further• more, Bier (2,3,4,5) has demonstrated that the interactional phenomena related to these saprophytic microorganisms may provide a natural form of defense against infection and/or disease development. It has been report• ed by Ruinen (24) and Last (15) that immature leaves had considerably low• er populations of saprophytes than mature leaves. Thus, if the relatively low microorganism populations of immature tissues could be supplemented by the application of saprophytes, perhaps natural resistance could be improv• ed. The present study was undertaken to investigate this concept in regard to the development of the rust, Melampsora medusae Thum., on the immature foliage of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). The aecial stage of M. medusae occurs in May and June on immature needles of Douglas fir. The uredial and telial stages develop on leaves of trembling aspen (Populus tremuloides Michx.) from June until autumn de• foliation. Molnar and Sivak (18) have investigated the life history of the rust pathogen. Ziller (29,30) has presented detailed studies on the host range and nomenclature of the rust fungus. 2 LITERATURE REVIEW Leaf microfloras The existence of non-paras itic microfloras on aerial plant struct• ures has been known since the studies of Pasteur (21,22). These studies were concerned with the distribution of yeasts on fruits and suggested that physiological changes of the ripening fruit influenced the number of yeast microorganisms occurring on its surface. Burri (6) and Duggeli (7) isolated bacteria from the leaves of a wide range of plant species and es• tablished the fact that bacterial microfloras were ubiquitous on plant h q leaves. Their bacterial counts varied from 10 to 10-7 bacteria per gram fresh weight of leaf. Last (15), after studying the seasonal incidence of the yeast, Sporobolomyces. on wheat and barley leaves, concluded that the two main factors influencing the numbers of yeast cells were the age of the leaf and atmospheric humidity. The results of his investigation showed that the yeast population remained low through the first half of the leaf's life and then increased rapidly. Ruinen (24) studied the populations of microorganisms on leaves in Indonesia and Surinam. She found distinct differences in the species com• position of the microfloras on (a) leaves of different plant species; (b) leaves of different ages; (c) leaves at different heights; and (d) leaves with different exposures to rain and to sunlight. Furthermore, the results of her studies indicated a definite succession in the populations during growth and senescence of the leaf. The succession began with bacteria, some of which were present on even the youngest leaves. After this juven- 3. ile stage the most rapid increase in the population began. This increase coincided with the most active period of photosynthesis and transpiration of the host and resulted in a mixture of filamentous fungi, yeasts, and bacteria. The bacteria at this time were the major component. The decline of leaf activity correlated with a change to a predominantly fungal micro• flora. The succession in the microflora apparently reflects a change in the quantity and quality of nutrients on the leaf surface. Last (15) found that the populations of Sporobolomyces were significantly higher on fertilized plants than on unfertilized plants. Tukey et al_. (25) reported that large quantities of nutrients were leached out of the leaf into water films on the leaf surface, with more nutrients being leached from fertil• ized plants than from unfertilized plants. The quantities lost in this manner increased when the leaf's activity began to decline at the start of leaf senescence. Thus, the amount of nutrients on the leaf and size of the microflora appear to be closely connected with the physiological condition of the host plant. Biological control of disease using foliage saprophytes The possibility that foliage saprophytes influence the development of parasitic microorganisms on plants has received only scant attention from plant pathologists. In 1910, when discussing epiphyllous bacteria, Potter (23) raised the question, "Are these bacteria at all concerned in the problem of immunity?" Fifty-five years later, in a review of the research on non-parasitic leaf microfloras, Last and Deighton (16) ask, "Do saprophytes play an important part in controlling the incidence of disease?" As the similarity of the two questions suggests, the knowledge k of this aspect of plant pathology has not developed rapidly! The fact that certain leaf saprophytes produce antifungal substances in vitro has been demonstrated by many workers (8,13,14, and others).
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