'33 '13? if?” 4 A33 3333333 ’3fo 343 .433 3'3"“ -,~ 3/ f A; 334.37 3U. .433. . .3 "( 4.4.44 :3'5‘. 33:31]“ “WWJW‘Ifl 19441 ti' ;:: '31" 33433. 4.4 344333" 333”} ., 3'33 "' 333.33 33434 3*1‘334'3' I;- ":3; '1. l4 4- 3 4 4 3‘ ”5 :l 33‘ .0 3'3 3 42143;,334'33'30' 143.]; 3' ' '9’ 44* ,_ .4. ,_ 3,433 3 :4 13 m... ._ 44144444444444444444444444401‘444 19 300672 7022 This is to certify that the dissertation entitled SOURCES, COMPONENTS, AND INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS IN _P____RUNUS SPECIES presented by Thomas Martin Sjuiin has been accepted towards fulfillment of the requirements for Ph.D. degree in HorticuIture 7.42%.... Major rrofessor Date /9/77/X/ MS U is an Affirmative Action/Equal Opportunity Institution 0-12771 MSU RETURNING MATERIALS: PIace in book drop to remove this checkout from LIBRARIES 4-“. your record. FINES will be charged if book is returned after the date stamped beiow. ”MW C 8 6 4 314 -. SOURCES, COMPONENTS, AND INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS IN PRUNUS SPECIES By Thomas Martin Sjulin A DISSERTATION Submitted to Michigan State University in partia1 fu1fi11ment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1981 l. . I , // /..4— / 4 V‘ ‘1' L7 ABSTRACT SOURCES, COMPONENTS, AND INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS IN PRUNUS SPECIES By Thomas Martin Sjulin Resistance to Coccomyces hiemalis, the cause of fungal leaf spot of cherry, was evaluated in field and greenhouse studies with several Prunus species. In a field planting of a total of 25 culti- vars of E. aviumz E. cerasus, E. gondouinii, and E. fruticosa, culti- vars differed in rate and severity of both infection and defoliation, but none was completely resistant. E. _a_vi_um_ cultivars were more resistant to defoliation than_E. cerasus and E, gondouinii cultivars. Field resistance to defoliation was negatively correlated with lesion development and sporulation in the greenhouse. In greenhouse studies, cultivars of E, axing, g. cerasus, and £,ggndouinii differed in components of resistance, including numbers of lesions, time, and rate of lesion appearance, and lesion size and sporulation. Lesions on E, avigm appeared later, were smaller, and produced fewer spores than lesions on E. cerasus and .3. gondouinii. Numbers of spores per lesion varied with lesion size, time of lesion appearance, leaf age, and numbers of lesions per unit area of inoculated leaf. Cultivar x isolate interactions Thomas Martin Sjulin were not significant for cultivars of these three species and six fungal isolates. These isolates differed in all components except time and rate of lesion appearance. Inheritance of components of resistance was evaluated in families of juvenile seedlings from an incomplete diallel of four .E- cerasus and one_fi. gondouinii cultivars. No discrete classes of resistance were observed and broad-sense heritabilities of all com- ponents except lesion size were less than 0.5 on an individual plant basis. Thus, resistance did not appear to be simply inherited. General combining ability differed among cultivars at two of three dates of inoculation, but family x date of inoculation interactions were detected for all components except numbers of spores per lesion. Seedlings and clones representing 15 33233; species and inter- specific hybrids were inoculated with an isolate from E. cerasus. Members of the Padus subgenus, the Pseudocerasus and Mahaleb sections of Prunus, and interspecific hybrids between these sections and the Eucerasus section of Prunus exhibited complete resistance. To Kay and Scott Michael ii ACKNOWLEDGMENTS My special thanks to my major professor, Dr. R. L. Andersen, who helped me become a horticulturist and plant breeder as well as a close friend of his family. I also deeply appreciate the special part Dr. A. L. Jones played by allowing me full access to his labora- tory and greenhouse facilities; without his generosity, this research would not have been possible. I would also like to thank the other guidance committee mem- bers: Dr. A. H. Ellingboe for valuable advice early in this research; Drs. M. J. Bukovac, J. F. Fobes, and R. P. Scheffer for their critique and suggestions; and Dr. J. A. Flore for helping on such short notice. Many others must also be thanked: my fellow graduate students in Horticulture and Botany Plant Pathology, especially Scott Eisen- smith and Mike Dessert; Mr. Gail Ehret and Mr. Fred Richey for valu- able assistance; and Mrs. Nancy Heath for her excellent preparation of the manuscript. Finally, warmest thanks of all to my wife Kay, who spent many long hours at my side in the field, laboratory, and greenhouse during this research. Her assistance, advice, and support had no equal. iii TABLE OF CONTENTS LIST OF TABLES . LIST OF FIGURES INTRODUCTION AND LITERATURE REVIEW Chapter I. II. III. Resistance in Cherry to Coccomyces Hiemalis Variation in Coccomyces Hiemalis . Research Objectives Literature Cited FIELD RESISTANCE OF CHERRY CULTIVARS AND SELECTIONS TO COCCOMYCES HIEMALIS . Abstract . Introduction . Materials and Methods Results . . Discussion . Literature Cited COMPONENTS OF PARTIAL RESISTANCE TO COCCOMYCES HIEMALIS IN PRUNUS SPECIES . . Abstract. Introduction Materials and Methods Results Discussion . Literature Cited INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS in JUVENILE SEEDLINGS OF CHERRY . . . Abstract . . . . . Introduction . Materials and Methods Results . . iv Page vi viii u—l $000010.) 35 36 38 38 45 67 7O Chapter Discussion . . . . Literature Cited . . . IV. VARIABILITY OF COCCOMYCES HIEMALIS TO COMPONENTS OF RESISTANCE IN PRUNUS SPECIES. . Abstract. . Introduction . . Materials and Methods Results Discussion . . Literature Cited V. POSSIBLE SOURCES OF COMPLETE RESISTANCE TO COCCOMYCES HIEMALIS IN PRUNUS SPECIES Abstract. Introduction . . Materials and Methods Results and Discussion Literature Cited SUMMARY AND CONCLUSIONS . Summary of Results Suggestions for Future Research Literature Cited . . Page 88 92 108 109 110 111 113 119 121 122 124 133 Table LIST OF TABLES Resistance of cherry cultivars and selections to infec- tion by Coccomyces hiemalis . . . . . . . . . Resistance of Prunus species to infection by Coccomyces hiemalis . . . . . . . . . . . . . . . . Resistance of cherry cultivars and selections to defo- liation by Coccomyces hiemalis . . . . . Resistance of Prunus species to defoliation by Cocco- myces hiemalis . . . . . . . . . . . Components of resistance to Coccomyces hiemalis in cultivars of Prunus cerasus and E, gondouinii Infection efficiency and lesion development in culti- vars of Prunus species inoculated with Coccomyces hiemalis . . . . . . . . . . . Spore production and reproductive efficiency in culti- vars of Prunus species inoculated with Coccomyces hiemalis . . . . . . . . Correlations of components of resistance with the reported field resistance of l9 cherry cultivars Components of resistance to Coccomyces hiemalis in parent cultivars of each experiment . . . . . . Components of resistance to Coccomyces hiemalis in progeny of experiment l . . . Components of resistance to Coccomyces hiemalis in progeny of experiment 2 . . . . . . . Components of resistance to Coccomyces hiemalis in progeny of experiment 3 . . . . . . . . . Mean squares for components of resistance to Coccomyces hiemalis in progeny of experiment l . . . . . vi Page 22 24 25 46 48 50 66 79 81 82 83 84 Table Page 6. Mean squares for components of resistance to Coccomyces hiemalis in progeny of experiment 2 . . . . . . . 85 7. Mean squares for components of resistance to Coccomyces hiemalis in progeny of experiment 3 . . . . . . . 86 8. General combining ability estimates for components of resistance to Coccomyces hiemalis in each experiment . 87 9. Parent and progeny broad-sense heritability estimates for components of resistance to Coccomyces hiemalis . 89 1. Mean squares for components of resistance to six iso- lates of Coccomyces hiemalis in eight cherry culti- vars . . . . . . . . . . . . . . . . . 101 2. Response of six Coccomyces hiemalis isolates to com- ponents of resistance in cultivars of Prunus species . 102 3. Components of resistance to Coccomyces hiemalis in cultivars of three Prunus species . . . . . . . 103 1. Resistance of cherry species to Coccomyces hiemalis . 114 vii LIST OF FIGURES Figure Page 1. Mean percent infection curves for cultivars of four cherry species inoculated with Coccomyces hiemalis on day 189 . . . . . . . . . . . . . . . 20 2. Mean percent defoliation curves for cultivars of four cherry species inoculated with Coccomyces hiemalis on day 189 . . . . . . . . . . . . . . . . 28 1. Relationship of infection efficiency to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis . . . . . . . . . . . . 52 2. Relationship of time of lesion appearance to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis . . . . . . . . . . . . 55 3. Relationship of spores per lesion averaged over three sampling times to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis . . 58 4. Relationship of spores per lesion to days after inocula- tion for three leaf ages in cultivars of three Prunus species inoculated with Coccomyces hiemalis . . . . 61 5. Relationship of reproductive efficiency to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis . . . . . . . . . . . . 64 viii INTRODUCTION AND LITERATURE REVIEW Cherry leaf spot is a serious fungal disease of cultivated cherries in most cherry producing regions of the world (2). The disease was first described in New York in 1878 on native black cherry (Prunus serotina Ehrh.), although the pathogen was incorrectly named Septoria cerasina (28). The disease was reported in Europe on European bird cherry (Prunus padus L.) in 1884 and the pathogen was named Cylindrosporium_padi (17). American workers subsequently reported Cylindrosporium species on several cherry and plum species. Finally, Higgins in 1914 divided the Cylindrosporium species occurring on Prunus species into three separate species of the Ascomycete genus Coccomyces (11). The fungi occurring on sour cherry (E. cerasus L.), sweet cherry (E. avium L.) and pin cherry (E, pennsylvanica L.) were named Coccomyces hiemalis; those found on plum species were named §,prunophorae; and those found on black cherry, choke cherry (_P_. vifliniana L.) and 3. mahaleb L. were named g. lutescens. Higgin's classification continues to be accepted by most American workers. However, European workers in recent years have accepted von Arx's reclassification of the three Coccomyces species into a single species named Blumeriella jaapii (4). Higgin's classi- fication will be used for the remainder of this dissertation. The disease on cultivated cherries (E. avigm, P. cerasus and _E. gondouinii Rehd.) is characterized by small necrotic lesions on leaves, petioles and occasionally on fruit pedicels (34). Primary infection of expanding leaves in the spring is from ascospores dis- charged from apothecia produced over winter in fallen leaves. Ascospores are discharged during rainy periods from the time of first leaf emergence until about 6 to 7 weeks after petal fall (1). Secon- dary infections are from conidia splashed from acervuli produced on the primary infections and subsequent secondary infections. Secon- dary infections can occur throughout the growing season as long as susceptible host tissue is present and conditions are favorable for infection. Conditions favorable for both primary and secondary infection are determined mainly by temperature and leaf wetness (8). Thus, the increase of disease during the growing season is not con- tinuous, but instead, occurs in discrete stages called infection periods (19). Severely infected leaves usually become chlorotic and subse- quently abscise. If defoliation is severe before harvest, fruit may fail to ripen properly (10). More commonly, premature defoliation reduces both the vigor and hardiness of the tree in subsequent seasons. Reduction in vigor in sour cherry is in turn related to reduction in yield and fruit quality (20). Dutton and Wells (7) observed reduced bud survival, fruit set and fruit size the year following severe defoliation from leaf spot. In addition, fruiting spur development, flower bud survival and fruit set were reduced the second year follow- ing defoliation. Howell and Stackhouse (12) also observed reduced bud survival and fruit set for two seasons following premature defolia- tion by Q. hiemalis. Furthermore, they observed delayed acclimation in the fall and more rapid deacclimation in the spring of both vege- tative and flower buds of prematurely defoliated trees. Fungicidal sprays are currently the principal means for pre- venting leaf spot infection and subsequent defoliation. In Michigan, the initial fungicide application is made at petal fall, followed by four additional sprays at 10 to 14-day intervals until harvest. A final application is made soon after harvest (13). Cherry cultivars with increased resistance to Q, hiemalis would be useful in several ways. First, use of a cultivar immune to g, hiemalis could eliminate several costly fungicide sprays. Second, an increased (but not complete) level of resistance could reduce the number of fungicide sprays. Finally, an increased level of resistance could allow use of less effective fungicides if the preferred fungi- cides became unavailable due to resistant pathogen strains or loss of their use for economic or environmental reasons. Strains of g, hiemalis resistant to benzimidazole fungicides have been found in Michigan (15). Resistance in Cherry to Coccomyces Hiemalis Little is known about the relative resistance of either sour cherry or sweet cherry cultivars to Q. hiemalis. Sweet cherry culti- vars are, in general, more resistant than sour cherry cultivars (32), but little within species variation in resistance was thought to exist (1). Recent reports from Eastern Europe indicate that within species variability for resistance does exist (3,6,16,21,22,29,31, 35.36.40). Although few, if any, cultivars in these studies were found to be completely resistant to Q, hiemalis, there does appear to be potential for selecting for increased resistance in both .3. avigm_and E. cerasus. Enikeyev (9) found that certain cultivars of both E. cerasus and E. avium_produced a higher percentage of resistant seedlings in their progenies than did other cultivars. Also, crosses involving the European ground cherry (P. fruticosa Pall.) were generally much more susceptible than crosses not involv- ing this species. .3. cerasus is thought to have arisen as an allotetraploid of P. fruticosa and P, avium_(25). Several species of cherry in the Pseudocerasus, Lobopetalum and Mahaleb sections of the subgenus Cerasus, and in the subgenus Padus (30) appear to have much greater resistance to g, hiemalis than cultivated cherries. The Pseudocerasus and Lobopetalum sections contain the Japanese flowering cherries. Many of these species appear to remain free of cherry leaf spot infection in ornamental plantings. In addition, a number of these species have been reported to form hybrids with E. avium_(5). However, no systematic evaluation of the resistance of these species to C, hiemalis has been made to date. 3, mahaleb has been observed to be more resistant to C. hiemalis than either 3. avium or E. cerasus (37). A number of .E.Ia!ium.x.fi. mahaleb clones selected as potential cherry rootstocks (38) may be possible sources of increased resistance to C, hiemalis in P. avium. Three cherry species in the subgenus Padus (P. padus, .E. serotina and P. virginiana) were completely resistant to infection by isolates of Q. hiemalis from P. avium or_fl. cerasus (11,18). How- ever, all three species are susceptible to strains of Coccomyces that Higgins considered to be a separate species, C. lutescens (11). The use of any of these cherry species as a source of complete resistance to Q. hiemalis would have to be done guarding against intro- duction of susceptibility to Q. lutescens. Furthermore, no reports have been found to date of interspecific hybrids between these species and the cultivated cherries. A fourth member of this sub- genus, E. maackii Rupr., has been successfully crossed with culti- vated cherries (24). It is not yet known if this species is resistant to Q. hiemalis. There appear to be two basic approaches to breeding cherries resistant to Coccomyces leaf spot. One is to select for increased levels of resistance within the cultivated species (B. aVium, .3. cerasus and E. gondouinii). Most studies indicate that cultivars differ quantitatively in terms of the incidence or severity of disease in the field. This type of resistance, called partial resistance, is a type of incomplete resistance that reduces the rate of pathogen mutiplication even though the host is susceptible to infection (26,33). Breeding for partial resistance is sometimes enhanced or simplified by selecting for one or more component of resistance contributing to partial resistance (26). The alternate approach is to identify sources of complete resistance in other cherry species, and incorporate the resistance into cultivated cherries, if complete resistance is not found within cultivated cherries to begin with. This approach has been used successfully in Mglu§_to breed scab resistant apple cultivars (39). Which approach is chosen depends upon several factors, including (1) the level of resistance needed; (2) the horticultural characteristics of the resistance sources; (3) the number and nature of the genes controlling resistance; and (4) the genetic variability of the pathogen to the resistance. At present our understanding of these factors is too poor to wisely choose the best approach. Variation in Coccomyces Hiemalis Higgins (11) first examined pathogenic variation among Coccomyces strains isolated from Prunus species. The results of cross- inoculation studies indicated pathogenic specialization by Coccomyces among several species of Prunus, Isolates from hosts in the subgenus, Padus would not infect hosts in the subgenera, Cerasus and Prunophora, with the exception of E, mahaleb in Cerasus. Isolates from hosts in the subgenera Cerasus and Prunophora would not infect hosts outside of their respective subgenus. Higgins assigned these three groupings of isolates to separate species of Coccomyces, because there were morphological differences between the groups of isolates when grown in culture. Keitt (18) examined in greater detail the ability of Coccomyces isolates to cross-infect other Prunus species. His results generally supported Higgins' conclusions. However, the grouping of isolates was not as distinct as that found by Higgins. Isolates from all seven hosts tested in three subgenera of Prunus (Prunophora, Cerasus and Padus) readily infected P. mahaleb. .3. munsoniana Night & Hedr. (subgenus Prunophora) was readily infected by isolates from E. cerasus (subgenus Cerasus), but not by isolates from .2. domestica L. (subgenus Prunophora). Isolates from_E. virginiana (subgenus Padus) readily infected members of both Padus and Bruno: .phgrg, as well as E. mahaleb. Isolates from E. serotina (subgenus Padus) did not infect other members of Padus. Keitt's work does not support Higgin's decision to assign three species designations within Coccomyces. The use of formae speciales designations for isolates from different hosts would also be confusing, as several hosts are readily infected by more than one group of isolates. It is probably best to designate these groups of isolates as different pathogenic races until the genetic relationships among groups can be determined. Magie (23) studied the variability of Q. hiemalis isolates collected from a single host species, B. cerasus. Isolates differed considerably in growth habit, growth rate and spore production on artificial media. Isolates also differed in the type and number of infections produced on leaves of both sweet cherry and sour cherry. No evidence of pathogenic races was found. However, only one sweet cherry cultivar and one sour cherry cultivar were used, and the condi- tions of the experiments varied considerably. Parlevliet and Zadoks (27) have demonstrated that biologically significant cultivar by isolate interactions may contribute only a small part to the total experimental variance. It is important that experiments of this kind be well controlled to minimize residual error variance. The demonstrated variability in Coccomyces at the species level of the host is of immediate concern if attempts are to be made to introduce complete resistance into cultivated cherries by inter- specific hybridization. Care must be taken that incorporation of resistance to one group of Coccomyces isolates does not introduce susceptibility to another. In addition, utilizing sources of partial resistance apparently existing within cultivated cherries does not preclude consideration of the variability of the pathogen to this type of resistance. Partial resistance in several host-pathogen systems have been found to be race-specific in nature (14). Research Objectives This research presents the first attempts to systematically identify, characterize and utilize resistance in Prunus species to Coccomyces hiemalis. The specific objectives were (1) identify sources of complete or partial resistance in cultivated cherries; (2) identify components of resistance contributing to the resistance identified in the first objective; (3) obtain preliminary estimates of the heritable components of resistance; (4) evaluate the varia- bility of the pathogen population to the resistance identified in the first objective; and (5) identify sources of complete resistance to g, hiemalis in related cherry species. 10. 11. LITERATURE CITED Anderson, H. w. 1956. Diseases of Fruit Crops. McGraw-Hill, New York. 501 pp. Anonymous. 1976. Distribution maps of plant diseases, no. 58, ed. 4. Commonwealth Mycological Institute, Kew, England. 2 pp. Anonymous. 1976. Field resistance of sour cherry and cherry varieties to coccomycosis under the conditions of the Crimea (in Russian). Sadovodstvo 24: 51-61. Abstracted in Rev. Plant Path. 56: 3634 (1977). Arx, J. A. von. 1961. Uber Cylindrosporium padi. Phytopath. Z. 33: 263-290. Cummins,.l.A. 1979. Interspecific hybrids as rootstocks for cherries. Fruit Var. J. 33: 85-89. Daugis, M. 1962. Some data on varietal resistance in cherry to coccomycosis in the conditions of the Latvian S.S.R. (in Russian). Pages 148-149 in: Brief Summaries of Research Work on Plant Protection in the Baltic Zone of the U.S.S.R., Vol. 4. Abstracted in Rev. Plant Path. 45: 940x (1966). Dutton, H. C. and H. M. Wells. 1925. Cherry leaf spot residual effects and control. Michigan Agric. Expt. Sta. Special Bull. 147. 15 pp. Eisensmith, S. P. and A. L. Jones. 1981. A model for detecting infection periods of Coccomyces hiemalis on sour cherry. Phytopathology 71: 728-732. Enikeyev, K. K. 1974. Resistance of cherry hybrid seedlings to the leaf-spot disease (Coccomyces hiemalis). XIX Int. Hort. Congress, Warsaw, Poland, Sept. 1974, V01. IA: 327. Heald, F. D. 1933. Manual of Plant Diseases, 2nd ed. McGraw- Hill, New York. 953 pp. ' Higgin, B. B. 1914. Contribution to the life history and physiology of Cylindrosporium on stone fruits. Amer. J. Bot. 1: 145-173. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 10 Howell, G. S. and S. S. Stackhouse. 1973. The effect of defoliation time on acclimation and dehardening in tart cherry (Prunus cerasus L.). J. Amer. Soc. Hort. Sci. 98: 132-136. Howitt, A. J., J. Hull and A. L. Jones (eds.). 1981. 1981 Sguit Pesticide Handbook. Mich. St. Univ. Extn. Bull. E-154. PP- Johnson, R. and A. J. Taylor. 1976. Spore yield of pathogens in investigations of the race-specificity of host resistance. Ann. Rev. Phytopathol. 14: 97-119. Jones, A. L. and G. R. Ehret. 1980. Resistance of Coccomyces hiemalis to benzimidazole fungicides. Plant Disease : 769. Kan'shina, M. V. and A. I. Astakhov. 1979. The resistance of sour cherries to cherry leaf spot (in Russian). Zashchita Rastenii 6: 29. Abstracted in Hort. Abstr. 49: 711 (1979). Karsten, P. A. 1885. Symbolae ad mycologian Fennicam, XVI. Medel. Soc. Fauna et Flora Fennica 11: 148-161. Keitt, G. W. 1918. Inoculation experiments with species of Coccomyces from stone fruits. J. Agric. Res. 13: 539-569. Keitt, G. W., E. C. Blodgett, E. E. Wilson and R. 0. Magie. 1937. The epidemiology and control of cherry leaf spot. Univ. Wisc. Agric. Expt. Sta. Res. Bull. 132. 117 pp. Kenworthy, A. L. 1974. Sour cherry-tree vigor as related to higher yields and better fruit quality. Mich. St. Univ. Agric. Expt. Res. Rpt. 223. 4 pp. Khokhryakova, T. M., I. I. Minkevich and A. N. Rakhmanova. 1971. The field resistance of cherry to coccomycosis (in Russian). Trudy Prikl. Bot. Genet. Selek. 43: 237-240. Abstracted in Rev. Plant. Path. 51: 1658 (1972). Konstantinova, A. F. and A. G. Vazyulya. 1969. Resistance of cherry varieties to Coccomyces blight (in Russian). Mikol. i Eitopatol. 3: 434-438. Abstracted in Rev. Plant Path. 49: 519 1970 . Magie, R. 0. 1935. Variability of monosporic cultures of Coccomyces hiemalis. Phytopathology 25: 131-159. Michurin, I. V. 1949. Selected Works. Foreign Languages Publ. House, Moscow. 496 pp. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 11 Olden, E. J. and N. Nybom. 1968. On the origin of Prunus cerasus L. Hereditas 59: 327-345. Parlevliet, J. E. 1979. Components of resistance that reduce the rate of epidemic development. Ann. Rev. Phytopathol. 17: 203-222. Parlevliet, J. E. and J. C. Zadoks. 1977. The integrated con- cept of disease resistance: a new view including horizontal and vertical resistance in plants. Euphytica 26: 5-21. Peck, C. H. 1878. Report of the botanist. N. Y. State Mus. Nat. Hist. Rept. 29: 29-82. Radman, L. and M. Ristanovic. 1972. A contribution to studies on Coccomyces hiemalis Higg. in Bosnia and Hercegovinia (in Serbo-Croatian). Jugoslovensko Vocarstvo 6: 803-812. Abstracted in Hort. Abstr. 44: 137 (1974). Rehder, A. 1940. Manual of Cultivated Trees and Shrubs, 2nd ed. MacMillan, New York. 996 pp. Reznikova, L. M. 1976. Resistance of cherry varieties to coccomycosis (in Russian). Zaschita Rastenii l: 56. Abstracted in Rev. Plant Path. 55: 3660 (1976). Roberts, J. W. and L. Pierce. 1919. Control of cherry leaf spot. United States Dept. Agric. Farmers Bull. 1053. 8 pp. Robinson, R. A. 1969. Disease resistance terminology. Rev. Appl. Mycol. 48: 593-606. . Stewart, F. C. and H. J. Eustace. 1901. Notes from the botanical dept. N. Y. (Geneva) Agric. Expt. Sta. Bull. 200: 81-101. Suta, V., G. Moruju, I. Morea, S. Nica, C. Radulescu, and N. Mateescu. 1961. Susceptibility of some apple, pear and cherry varieties to attack by the main diseases in the first nine years after planting at the Voinesti Station, 1951-1959 (in Russian). Lucr. Stiint Inst. Cerc. Horti-Vitic. 4: 865-876. Abstracted in Rev. Appl. Mycol. 43: 1064 (1964). Timoshenko, S. E. 1977. The resistance of different sweet cherry cultivars and hybrids to cherry leaf spot (in Russian). Trudy Stavropol'sk NII s.-Kh. 48: 76-82. Abstracted in Hort. Abstr. 49: 420 (1979). Tukey, H. B. 1929. Seedling fruit stocks. N. Y. (Geneva) Agric. Expt. Sta. Bull. 569. 34 pp. 38. 39. 40. 12 Westwood, M. N., A. N. Roberts and H. 0. Bjornstad. 1976. Comparison of mazzard, mahaleb and hybrid rootstocks for Montmorency cherry (Prunus cerasus L.). J. Amer. Soc. Hort. Sci. 101: 268-269. Williams, E. B. and J. Kuc. 1969. Resistance in Malus to Venturia inaegualis. Ann. Rev. Phytopath. 7: 223-246. Zekovic, P. and D. Vuletic. 1975. A contribution to the knowledge of susceptibility of different sorts of cherries and sour cherries to Coccomyces hiemalis Higg. in Metohiza (in Hungarian with English summary). Zastita Bilja 26: 79-83. CHAPTER I FIELD RESISTANCE OF CHERRY CULTIVARS AND SELECTIONS TO COCCOMYCES HIEMALIS 13 CHAPTER I FIELD RESISTANCE 0F CHERRY CULTIVARS AND SELECTIONS T0 COCCOMYCES HIEMALIS Abstract Resistance to infection and defoliation by Coccomyces hiemalis Higg. was measured in a field planting of 25 cultivars and selections representing four Prunus species (3. avium L., P. cerasus~ L., g. fruticosa Pall. and 3. gondouinii Rehd.). No cultivar was completely resistant to either infection or defoliation. The rates and sever- ity of infection and defoliation, and the estimated dates of 50% infection and defoliation by g, hiemalis differed among cultivars. Correlations between defolia- tion severity and measures ofinfection were poor. Rates of defoliation and dates of 50% defoliation were highly correlated with defoliation severity. Comparisons between species indicated that P. _ay_iu_m cultivars were more resistant than B. cerasus or E. gondouinii culti- vars in terms of infection rate, defoliation rate, date of 50% defoliation and defoliation severity. Defolia- tion severity was less in P, avium cultivars than in P, fruticosa cultivars. P, fruticosa cultivars were 14 15 more resistant than B. cerasus cultivars in terms of infection severity, defoliation rate, date of 50% defolia- tion, and defoliation severity. Introduction Cherry leaf spot, caused by Coccomyces hiemalis, is a serious disease of cultivated cherries throughout the world (2). At present, little information exists on the genetic variation for resistance within sour cherry (Prunus cerasus) or other cultivated cherry spe- cies. An evaluation of the relative resistance of available culti- vars would aid selection of parent material for use in a cherry breeding program. Sweet cherries (E. avium) are considered more resistant to leaf spot than sour cherries (15). The relative resistance of duke cherries (P. gondouinii), which are hybrids between sweet and sour cherries, is uncertain. The European ground cherry (P. fruticosa) was reported to be less resistant than either B. avium or _P_. cerasus (8). Reports from Eastern Europe indicate that genetic variation for resistance also exists within sweet, sour, and duke cherries (3,6,13,19,21). The purpose of this research was to evaluate the relative resistance to infection and defoliation by Q. hiemalis of cultivars and selections within these four species of cherry. In addition, planned statistical comparisons were made between these species on the assumption that the cultivars and selections evaluated were representative of their respective species. 16 Materials and Methods Plant material. Twenty-five cultivars and selections repre- senting four species of cultivated cherries (E. m, P. cerasus, .3. gondouinii and_E. fruticosa) were chip budded in September, 1979, onto seedling rootstocks of P. mahaleb L. All budwood except that of 3. 2M 'Governor Wood', _P. m 'Yellow Glass', 3. cerasus 'SHT-2' and E. gondouinii 'SHT-3' was obtained as virus-free budwood from the U.S.D.A. Interregional Project No. 2 repository in Prosser, WA 99350. Budwood of 'Governor Wood' and 'Yellow Glass' was obtained from Interstate Nurseries, Inc., Hamburg, IA 51640. Budwood of 'SHT-3' and 'SHT-Z' was obtained from the original seedling trees at the South Haven Experiment Station, South Haven, MI. 'SHT-Z' is an open- pollinated seedling of an unknown morello sour cherry. 'SHT-3' is an apparent interspecific hybrid between E. cerasus 'North Star' and an unknown culitvar of E, axiom. Both 'SHT-2' and 'SHT-3' were pre- viously selected at the South Haven Experiment Station for their resistance to Q. hiemalis (R. L. Andersen, unpublished). The remain- ing cultivars were selected to represent a genetically diverse samp- ling of cultivars within each species. The budded trees were dug in November, 1979, and stored at 1-4 C until planting in April, 1980. Trees were planted at 1.5 m by 1.8 m spacing in Locke sandy loam in a randomized complete block with five replications. Trees were irrigated daily throughout the growing season with a biwall drip irrigation system buried 2- to 5-cm deep adjacent to each tree. Seedling tops were removed from each tree 17 within 10 days after planting to force growth from the propagated bud. A single vegetative shoot was forced from each tree and main- tained as a single shoot until terminal bud formation. Each tree received approximately 3090f 12% N-12% P205-12% K20 fertilizer in a single application 2 weeks after budbreak and a supplementary appli- cation of 33 g of urea one month later. Trees were sprayed as needed throughout the growing season to control insects and mites. Pyrazophos (Afugan 30 EC, 0.5%, v/v) was applied twice within 4 weeks after inoculation to control powdery mildew (14). Inoculation with Coccomyces hiemalis. Each tree in the experi- ment was inoculated with C. hiemalis on July 7, 1980. Conidia for inoculation were washed from naturally infected leaves of P. cerasus 'Montmorency' from trees adjacent to the experimental plot. A 2 cm2 area on the lower surface of the second unfolded leaf below the shoot apex was inoculated by spraying a suspension of 105 conidia per ml with a mist bottle. The inoculated leaf was enclosed over night in a polyethylene bag containing a wet paper napkin for approximately 12 hours. Subsequent spread of inoculum and infection occurred through- out the growing season during periods of natural leaf wetness. Evaluation of resistance. Trees were evaluated starting Ju1y 7, 1980, and at 1- to 2-week intervals through October 2, 1980. Percent of total leaves that were infected or defoliated were déter- mined at each evaluation. The total number of leaves for an indi- vidual tree was the number of unfolded leaves present on August 6, 18 1980, when the terminal leaf had unfolded on the first trees to cease terminal growth. Preliminary analysis of angular-transformed data as a split- plot in time (18) indicated that there was a highly significant cultivar by time of evaluation interaction for both percent infection and percent defoliation. In addition, the angular transformation did not adequately linearize the data, as a highly significant non-linear residual term remained after fitting the linear term. Gompertz and logistic equations were fit to the sigmoidal percent infection and percent defoliation curves to determine if at least part of the interaction was due to differences in slope and/or position of the curves. Examination of the residuals and correlation coefficients for individual trees indicated a better fit with the Gompertz transformation (-1n(-1n(y))). Linear regression of Gompertz- transformed values against time of rating was used to estimate rates (k) of infection and defoliation for each tree (4). In addition, the time in days of the year to 50% infection and 50% defoliation were estimated from the regression equations. Estimates of disease severity were made by calculating the areas under the percent infection and percent defoliation curves. Areas for each tree were calculated by the following equation: n Area = 1.:]((R1. f Rifl)/2)(ti+l - ti) 19 where ti = day of the year at evaluation "i," Ri = percent infection or percent defoliation at evaluation "i," and i = 1 to 9. Results Inoculation of a single leaf per tree resulted in the nearly uniform establishment of infection throughout the experimental plot. At the time of inoculation, 57% of the trees showed no visible symptoms of infection on any leaves. All but one of the 125 trees showed visible symptoms of infection on the inoculated leaf 14 days later. The level of infection increased rapidly in the plot. The mean percent of leaves infected was less than 5% on the day of inoculation (Figure l). The mean percent of leaves infected reached 70% at 4 weeks after inoculation (day 219), and increased to greater than 98% at eight weeks after inoculation (day 248). Variation in infection and defoliation existed within and between the four species of cherry (Tables 1-4). No cultivar was free of infection or defoliation, and significant quantitative dif- ferences in infection and defoliation between cultivars were detected. Rates of infection varied over a 2-fold range among the 25 cultivars from a low of 0.062 for E, ayium_'Hedelfingen' to a high of 0.126 for_E. cerasus 'North Star' (Table 1). Estimated date of 50% infection varied by less than 10 days among the 25 cultivars. Infection severity (area under infection curve) ranged from a low of 5754 for g. _av_i_u_m 'Yellow Glass' to a high of 6679 for _P. 211%“. 'Schmidt'. 20 Figure 1. Mean percent infection curves for cultivars of four cherry species inoculated with Coccomyces hiemalis on day 189 (inoc). Curves are the mean of 9,16: 6, and 4 cultivars for Prunus avium, E, cerasus, E, gondouinii and E, fruticosa, respectively. INFECTION PERCENT 21 ‘00 "' I .. u: ----- . ...... B av'um " — E. gerasus ,f - -- 1’. mm o a ,,’ “'1’. gondouinii // I. so - I: I.’ 1.: /.~' I! I: 60 '- 40 '- inoc 20 1- 1- .0i’ .; ,J [I o T 1 1 1 J 180 200 220 240 260 DAY OF THE YEAR 280 223 TABLE l.--Resistance of cherry cultivars and selections to infection by Coccomyces hiemalisV _ . Date of Infection CUIthBV I":§§:&°“ 50% infection severity (day of the (area under year)x inf curve)-y Prunus avium Black Tartarian .086 cdefgz 211.9 bcdefgh 6251 abcdef Emporer Francis .089 bcdefg 212.2 bcdefgh 6191 bcdef Governor Wood .085 cdefg 214.8 defgh 5981 defg Hedelfingen .062 9 210.7 abcde 6451 abc Lambert .071 fg 212.5 bcdefgh 6202 bcdef Napoleon .073 efg 211.5 abcdefg 6269 abcde Schmidt .079 cdefg 208.9 abc 6679 a Windsor .075 defg 213.9 cdefgh 6038 cdefg Yellow Glass .083 cdefg 216.6 h 5754 g .E. cerasus Early Richmond .085 cdefg 210.3 abcd 6424 abc English Morello .078 cdefg 210.2 abcd 6312 abcd Meteor .108 abcd 210.5 abcde 6327 abcd Montmérency .107 abcde 208.6 ab 6560 ab North Star .126 a 215.0 defgh 6011 cdefg SHT-Z .112 abc 215.4 efgh 5924 defg .E. gondouinii Brassington Duke .082 cdefg 216.2 gh 5848 efg Kansas Sweet .091 bcdefg 216.0 fgh 5905 defg Krassa Severa .104 abcdef 206.9 a 6655 ab May Duke .082 cedfg 208.9 abc 6421 abc SHT-3 .085 cdefg 216.2 gh 5818 fg Wczesna Z Prin .100 abcdef 212.0 bcdefgh 6219 bcdef .E. fruticosa Dwarf Rich .109 abcd 213.2 bcdefgh 6095 cdefg IR 323-2 .105 abcdef 215.4 efgh 5926 defg IR 586-3 .121 ab 211.1 abcdef 6315 abcd IR 587-1 .086 cdefg 214.4 defgh 5958 defg vMean of 5 single-tree replications. wSlope of linear regression of Gompertz-transformed percent infection data. xEstimated from the linear regression of Gompertz-transformed percent infection data. 1 tion 1 and Ri - percent of leaves infected at evaluation i (i a 1-9). yArea - 2((Ri + R1+1)/2)(t.+1 - ti)’ where ti = day of the year at evalua- zMean separation by Duncan's multiple range test (p_= 0.05). 23 .mucmwcm> mo mwm>chm socw compcmasou soummcw we mmcmmu mpmc_m go; .»Fm>wuumammc .Po.o ".m.pm acmupw_cmpm new .mo.o u.m pm ucmuwwwcmwm .acmuwwwcmwm no: u as .e ..m.=~ .Amup u wv w cowpmzpm>m um umpummcw mm>mmF we acmogma u Pm ucm P copumspo>o pm com» msu Go saw u _p econ: .Apu + F+FHVA~\AP+_m + Fmvvw u m>g=u coppomwcw Luvs: mmcwu_=o can meowumuwpamc museumymc_m m>Pm> .m... .m... .1 a .M 323 a .M 6:: .m... a a .M 322, Efizoucom .m a .m.: .m.: g .M 39:; www.mglmm .M .m... .mé .. a .M 39:; a .m. .m... .8: us... a .M 333 Nam .M mcomwgmgsou _mcomospgonco: umccmpn mo mucmuwewcm_m 28 :5 me. e 383...: .m SE SE so. 0 15823 .m 88 0.5 m2. 0 338 .m 88 :5 E. m e3: .m afim>cau Gar xAmea A.ocv cone: mmgmv ecu mo xmvv swung >umpmapm>m mmpoma zpvcm>mm cowuumwcw mom cowuummcm mcowuumpmm . m cowuummcH mo mama can mgm>wup=u .mwaEmwr— meNEOUUOQ an cowuumLhw OH mmwumnm mac-Cn— .._.o wucmwmwmmmll.m m4m<._. TABLE 3.--Resistance of cherry cultivars and selections to defoliation by Coccomyces hiemalis.V D f 11 Date of Defoliation . e o ation 50% defoliation severity Cu1t1var ratew (day of the (area under year) def curve)Y Prunus avium Black Tartarian .064 abcdefgz 234.2 abcd 4045 cdef Emporer Francis .052 efgh 246.5 defg 2828 h Governor Wood .057 defgh 236.7 bcde 3724 def Hedelfingen .038 ghi 246.8 defg 2874 gh Lambert .088 ab 238.9 cdefg 3471 fg Napoleon .064 abcdefg 234.4 abcd 3755 def Schmidt .034 hi 247.4 efg 2803 h Windsor .055 defgh 246.6 defg 2879 gh Yellow Glass .049 fghi 249.3 fg 2716 h 3, cerasus Early Richmond .064 abcdefg 228.0 abc 4551 abc English Morello .077 abcde 227.4 abc 4644 abc Meteor .060 cdefgh 228.7 abc 4377 abcd Montmorency .090 a 224.5 ab 4936 ab North Star .044 fghi 237.5 cdef 3736 def SHT-Z .055 defgh 235.2 abcde 3623 ef 2, gondouinii Brassington Duke .063 abcdefg 237.9 cdefg 3686 ef Kansas Sweet .067 abcdef 238.0 cdefg 3542 f Krassa Severa .085 abc 222.8 a 4994 a May Duke .065 abcdefg 230.1 abc 4378 abcd SHT-3 .062 bcdefg 231.3 abc 4219 cde Wczesna Z Prin .082 abcd 227.5 abc 4594 abc E, fruticosa Dwarf Rich .058 cdefgh 240.0 cdefg 3555 f IR 323-2 .066 abcdef 229.4 abc 4342 bcd IR 586-3 .062 bcdefg 234.5 abcd 3996 cdef IR 587-1 .025 1 250.3 g 2934 gh vMean of 5 single-tree replications. wSlope of linear regression of Gompertz-transformed percent defoliation data. xEstimated from linear regression of Gompertz-transformed percent defolia- tion data. yArea under defoliation curve a 2((Di + Di+l)/2)(ti+l - ti)’ where ti = day of year at evaluation i and D i (i - 1-9). zMean separation by Duncan's multiple range test (p,= 0.05). .i = percent of leaves defoliated at evaluation 25 .Fo.o coma mgu Go amt .mocmpcm> mo mwmxpmcm soc; comvcmasoo soummcw mo mwcmmv mpmcpm Low .»Pm>wuumammc m.am pcmuwmwcmwm ucm .mo.o u m.um pcmuvwwcmwm .uzmupepcmwm po: u as .« ..m.c~ .Amup u wv P cowumapm>m an cowummpommu ucmucma u we ucm .p covpmapm>m pm w» mews: .Awu + p+prAN\AF+wa + wovvm u w>c=u copumwpommu pcmugma Laue: mmc_uP=u cog mcovpmuwpamc mmgpumpmcpm m>vw Go cmmz> «a .m.: .m.: Ezw>a .m.m> amouwuzc+ am .2. t. 4.. 5.2:. .m. e, 25828 .m «a «a 4 amou_uzgm .m.m> mammcmu .m. .m.c .m.: .m.c wwcwzoucom am.m> mammcmu am as *4 Ne an>m am.m> mammcmm am mcomwcoaeoo chomogucouco: umccmpa Co mucmuwmwcmwm BR :8 N8. 4 383.5 .m 82. 33 :o. a £5828 a... :8 «58 m8. 6 6328 .m man 3% . 9.8. m as; .m Am>cau you xAcmm» A.o:v move: mmcmv mg» mo amnv 36am; >cmpmzpm>m mmPuma prcm>mm cowpmw_owmu Rom cowpmwrommo meowpumpmm . m co_umwpommo we mama cum mgm>wupzu .mpmemP; mmuxeouooo an cowpmwpoemu op mmwomqm manage mo mocmpmpmmmuu.¢ u4m

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Ne}. 93> .5 :6 wonewee> we wwwapece Eeew emee-e we woneowwwnmwm xfimewv mxee on when mp sweee m xocewowwwe ee>wupeo mewowem w>eeoeeeeewm Amewv cewmep ewe meeeem .emscwucou11.m mnmOzm_0.n_u_w 20....0mn—z_ 31.5 19.5 7.5 (DAYS) LEAF AGE 54 .P. gondouinii cultivars. All cultivars showed a large reduction in infection efficiency in 31.5-day-old leaves. Differences among cultivars in number of days to 50% of lesions present were highly significant. Comparisons between species were significant at each leaf age, and were greatest in 3.15-day-old leaves (Figure 2). The cultivar x leaf age interaction was largely due to differences among species, rather than differences within species. Rate of lesion appearance was significantly slower (p = 0.01) for E, gyium_cultivars (0.44) than for P. cerasus (0.75) and E. gondouinii (0.65) cultivars. Differences between P. cerasus and .3. gondouinii cultivars were not significant. The rate of lesion appearance decreased linearly with increasing leaf age when averaged over all cultivars. Average lesion areas 36 days after inoculation were signifi- cantly smaller (2 = 0.01) for P, gyigm cultivars (0.22 mmz) compared to_£. cerasus (1.24 mm2) and E, gondouinii (0.88 mmz) cultivars. Differences between E. cerasus and P. gondouinii cultivars were also highly significant. Averaged over all cultivars, log lesion area increased linearly with increasing leaf age. Large differences were observed among cultivars in spore production per lesion at all three dates of sampling (Table 3). The significantly lower (9 = 0.01) spore production in lesions of P. avigm cultivars compared to E. cerasus and E, gondouinii cultivars accounted for much of the difference among cultivars. In addition, spore 55 Figure 2. Relationship of time of lesion appearance to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis. DAYS TO 50 % OF LESIONS ..... .. _. Ivlum .0. 0.. E. cerasus ___ g. ondoulnn \\“.’ 7'5 19.5 31.5 57 production in E. cerasus cultivars was significantly greater than that in _P. @ndouinii cultivars. Combined analysis of spores per lesion data over all three dates of sampling indicated that there were highly significant culti- var x leaf age and cultivar x date of sampling interactions. In addi- tion, significant leaf age x date of sampling interactions were present. A large portion of the cultivar x leaf age interaction could again be attributed to significant differences in the linear and non- linear trends 0f.E:.E!i!fl cultivars compared to P. cerasus and E. gondouinii cultivars (Figure 3). In addition, comparisons between .3. cerasus and P. gondouinii indicate that P. gondouinii cultivars show a linear trend of increasing spores per lesion with increasing leaf age, whereas 3. cerasus cultivars show little indication of a linear trend. 0n the basis of the results of experiment 1, numbers of spores per lesion as a function of leaf age for_P. cerasus 'North Star' were compared to the mean of the other_P. cerasus cultivars. Numbers of spores in leaves of North Star were significantly less than those of the other cultivars at each leaf age. In North Star, numbers of spores per lesion increased logarithmically with increas- ing leaf age (4.57 x 102, 1.20 x 103, and 2.09 x 103 for 7.5-, 19.5- and 31.5-day-old leaves, respectively). However, numbers of spores were higher in 7.5-day-old leaves (8.91 x 103) than in 19.5-day-old (4.79 x 103) or 31.5-day-old leaves (7.08 x 103) of the other culti- VdY‘S . Figure 3. 58 Relationship of spores per lesion averaged over three sampling times (9, 18 and 36 days after inoculation) to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis. (LOG) SPORES PER LESION 59 - u IIIII £- I'lum — _P_. cerasus -—- _P_. mdoulnll 7.5 10.5 31.5 LEAF AGE (DAYS) 60 The triple order interaction of cultivar x leaf age x date of sampling for spores per lesions was attributed in large part to between-species comparisons. The general trend was for sporulation to increase logarithmically between dates of sampling. However, numbers of spores per lesion were lowest for youngest age leaves (7.5-day-old) in all three species at 9 days after inoculation while they were lowest for intermediate age leaves (19.5-day-old) at 18 and 36 days after inoculation. Much of this interaction is explained by differences in the slopes of the linear regression of log spores per lesion against log days after inoculation for each species at each leaf age (Figure 4). Overall, the rate (slope of regression line) of increase in spores per lesion as a function of days after inoculation was significantly less (p_= 0.01) for P. avium cultivars than for .P. cerasus and E. gondouinii cultivars. Reproductive efficiency (ratio of spores produced to inoculum applied) differed greatly among the three species at 36 days after inoculation. The average reproductive efficiency of E. gyium culti- vars (5.84) was significantly less (0 = 0.01) than that of P. cerasus and P. gondouinii cultivars. The average reproductive efficiency of .E- cerasus cultivars (285.23) was significantly greater (9 = 0.01) than that of P. gondouinii cultivars (142.25). Log reproductive efficiency averaged over all cultivars decreased linearly (p_= 0.01) with increasing leaf age; however, the slope of this linear trend differed among the three species (Figure 5). .P.‘gvigm;cultivars showed a much greater rate of decrease than B. cerasus and 61 Figure 4. Relationship of spores per lesion to days after inoculation for three leaf ages in cultivars of three Prunus species inoculated with Coccomyces hiemalis. (LOG) 62 A 7.5 day O|d Ie°ves - .ooi..‘..6‘ 5”::...... “ - 6”" B 19.5 day old leaves IOOCDIOIUIIOIOUOD III-ICCCCOQUCOODII. coo-or. ' / 5”, l O 1 use... 2. w .. — g. car—me -_- 2' Miami—i J J l 9 ll 36 DAYS AFTER INOCULATION 63 ,E-,ggflgggigii cultivars. The trend with P. cerasus and P, gondouinii cultivars appeared to be nonlinear. Numbers of spores per lesion were correlated with several other variables in experiment 2. Highly significant negative corre- lations were observed between either log time of 50% lesion appear- ance or log lesions per leaf, and log spores per lesion at 9, 18 and 36 days after inoculation. Highly significant positive correlations were observed between log lesion area, and log spores per lesion at each time of evaluation. Multiple regression equations that included the lesion area, lesions per leaf, time of 50% lesion appearance and leaf age as independent variables accounted for 33%, 70%, and 86% of the total variation hispores per lesion at 9, 18, and 36 days after inoculation, respectively. Simple correlations with the reported defoliation severity of 19 of the 20 cultivars in experiment 2 (field resistance ratings not available for P. avium 'Angela') were highly significant for each component of resistance except infection efficiency (Table 4). Correlations with infection severity were not significant for all components of resistance. Discussion Diseases caused by pathogens such as C, hiemalis with more than one reproductive cycle per season are called Pcompound interest diseasesf (15). The severity of a compound interest disease is the cumulative effect of environmental factors, the level of initial inoculum, genetic factors affecting reproduction of the pathogen 64 Figure 5. Relationship of reproductive efficiency (ratio of spore production to inoculum applied) to leaf age in cultivars of three Prunus species inoculated with Coccomyces hiemalis. (LOG) REPRODUCTIVE EFFICIENCY 65 O. O O Q Q Q Q Q Q Q Q Q Q Q 9 C O Q O O O O O. .. O... O. O. Q. 0.. O... ..... a I 5 I 9 I 5 LEAF AGE (DAYS) 66 TABLE 4.--Correlations of components of resistance with the reported field resistance of 19 cherry cultivars." Field resistance parameterw Component of resistanceV infection defoliation severity severity Infection efficiency .099 n.s.z .313 n.s. Days to 50% of lesions -.091 n.s. -.704** Rate of lesion appearance .261 n.s. .789** Log (lesion area) .359 n.s. .808** Log (spores per lesion)x .231 n.s. .782** Log (reproductive efficiency)y .191 n.s. .815** uCorrelations included each cultivar in experiment 2, except P, avium 'Angela'. vMean of four replications over three leaf ages for each cul- tivar. wMean of five replications for each cultivar. xTotal spores per lesion 36 days after inoculation. y36 days after inoculation. zn.s., ** = correlation coefficient (r) not significant at .p = 0.05 or significant at.p = 0.01, respectively. 67 on its host (components of resistance and pathogenicity), and the ability of the host to endure the presence of the pathogen (tolerance). Prediction of disease severity for a compound interest disease requires an understanding of each of these factors and their inter- relationships. A model has been developed which predicts infection of Montmorency sour cherry from measurements of leaf wetness duration and air temperature (4). The components of resistance measured in this study should allow incorporation of a host resistance factor into the model. The model would then predict not only infection, but also the relative amount of inoculum present at the next infection period. The effect of changes in host resistance components on disease severity could be predicted in different simulated environments. These pre- dictions could then be used to establish the level of resistance (or component of resistance) needed in a breeding program. Prediction of leaf spot severity must also account for changes in resistance due to leaf age (6). The highly significant cultivar x leaf age interactions in the present study indicate that the effect of leaf age is.not uniform over all genotypes. Most of this interaction could be attributed to differences between species (Figures 1 to 5), but some important differences within species remained. For example, sporulation in lesions on young leaves of North Star sour cherry was considerably lower than that in older leaves, but sporulation was generally highest in youngest leaves of other sour cherry cultivars. Thus, prediction of relative leaf spot 68 severity among cultivars or species requires that adjustment be made for changes in relative proportions of leaf age classes during the growing season (5). Also, the level of resistance of a cultivar under conditions of vigorous vegetative growth (where leaf emergence would cease later in the season) may be quite different from that under a less vigorous condition due to differences in the relative proportion of leaf age classes. Identification of components of resistance contributing to observed differences in field resistance provides a systematic approach to breeding for partial resistance. The components can be selected in a breeding program following artificial inoculation under controlled conditions. However, associations between components must be considered. For example, a negative correlation was observed between spore production per lesion and lesion number per inoculated area in these studies. Selection based solely on fewer spores per lesion (or smaller lesion size) could lead to indirect selection for increased infection efficiency. A better selection criterion is reproductive efficiency, which is the combined effect of the com- ponents of infection efficiency and spores per lesion. Reduced reproductive efficiency could be due to reduced infection efficiency or reduced spore production or both. In addition, reproductive efficiency in these studies was measured more rapidly than any other component when a quantitative inoculator (11) was used and spore production was estimated by absorbance measurements of spore washes. Improvement in the level of partial resistance in these cherry species should be possible by selection for components of 69 resistance. Genetic variation was large for each component in experiment 2, except infection efficiency. Reproductive efficiency differed 500-fold among the cultivars at 36 days after inoculation (Table 3). However, the rate of improvement in resistance will be affected by the number and nature of the genes controlling expression of the component selected. Initial studies of the inheritance of components of resistance in juvenile seedlings of P. cerasus and £5 gondouinii indicate that heritabilities calculated on an indi- vidual plant basis are quite low (13), suggesting that the rate of improvement will be slow. This study should be considered only pre- liminary, though, because there were large differences from experi- ment to experiment in expression of resistance among progenies. More work is needed to determine the applicability of this approach to breeding leaf spot resistant cherries. 10. 11. LITERATURE CITED Anonymous. 1976. Field resistance of sour cherry and cherry varieties to coccomycosis under the conditions of the Crimea (in Russian). Sadovodstvo 24: 51-61. Abstracted in Rev. Plant Path. 56: 3634 (1977). Daugis, M. 1962. Some data on varietal resistance in cherry to coccomycosis in the conditions of the Latvian S.S.R. (in Russian). Pages 148-149 in: Brief Summaries of Research Work on Plant Protection in the Baltic Zone of the U.S.S.R., vol. 4 (1961). Abstracted in Rev. Appl. Mycol. 45: 940x (1966). Draper, N. R. and H. Smith. 1966. Applied Regression Analysis. John Wiley & Sons, New York. 407 pp. Eisensmith, S. P. and A. L. Jones. 1981. A model for detecting infection periods of Coccomyces hiemalis on sour cherry. Phytopathology 71: 728-732. Eisensmith, S. P., A. L. Jones and J. A. Flore. 1980. Predict- ing leaf emergence of 'Montmorency' sour cherry form degree-day accumulations. J. Amer. Soc. Hort. Sci. 105: 75-78. Eisensmith, S. P., T. M. Sjulin, A. L. Jones and C. E. Cress. 1981. Effects of leaf age and inoculum concentration on infec- tion of Sour cherry by Coccomyces hiemalis. Phytopathology 71; (in press). Kan'shina, M. V. and A. I. Astakhov. 1979. The resistance of sour cherries to cherry leaf spot (in Russian). Zaschita Rastenii 6: 29. Abstracted in Hort. Abstr. 49: 711 (1979). Little, T. M. and F. J. Hills. 1978. Agricultural Experimenta- tion. John Wiley & Sons, New York. 350 pp. Parlevliet, J. E. 1979. Components of resistance that reduce the rate of epidemic development. Ann. Rev. Phytopathol. 17: 203-222. Robinson, R. A. 1969. Disease resistance terminology. Rev. Appl. Mycol. 48: 593-606. Schein, R. D. 1964. Design, performance and use of a quantita- tive inoculator. Phytopathology 54: 509-513. 70 12. 13. 14. 15. 16. 71 Sjulin, T. M. 1981. Field resistance of cherry cultivars and selections to Coccomyces hiemalis. Chapter I of this disserta- tion. Sjulin, T. M. 1981. Inheritance of resistance to Coccomyces hiemalis in juvenile seedlings of cherry. Chapter II o t is dissertation. Timoshenko, S. E. 1977. The resistance of different sweet cherry cultivars and hybrids to cherry leaf spot (in Russian). Trudy Stavropol'sk NII S.-Kh. 48: 76-82. Abstracted in Hort. Abstr. 49: 420 (1979). Van der Plank, J. E. 1963. Plant Diseases: Epidemics and Control. Academic Press, New York. 349 pp. Zekovic, P. and D. Vuletic. 1975. A contribution to the knowl- edge of susceptibility of different sorts of cherries and sour cherries to Coccomyces hiemalis Higg. in Metohiza (in Hungarian with English summary): Zastita Bilja 26: 79-83. CHAPTER III INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS IN JUVENILE SEEDLINGS OF CHERRY 72 CHAPTER III INHERITANCE OF RESISTANCE TO COCCOMYCES HIEMALIS IN JUVENILE SEEDLINGS OF CHERRY Abstract Components of resistance to Coccomyces hiemalis Higg. of infection efficiency, lesion area, spores per lesion and reproductive efficiency were studied in an incomplete diallel of four Prunus cerasus L. cultivars and one P. (gondouinii Rehd. cultivar. A total of 342 progeny from 14 families plus clonal parent material were inoculated in a series of three experiments that differed in average age of plants. All components of resistance differed among both parents and families. Mean values for each component differed from experiment to experiment in both parents and progenies. Experiment by family inter- actions were present in all components except spores per lesion. No genetic variation between families was detected in the first experiment involving the young- est seedlings. General and specific combining ability effects were present among families in the second experiment. Only general combining ability effects were detected in the third experiment. P, cerasus 73 74 'North Star' had the highest breeding value for reducing spores per lesion and reproductive efficiency. Overall broad-sense heritabilities calculated on a single-plant basis were less than 0.5 for all components except lesion area in progeny. Introduction Cherry leaf spot, caused by Coccomyces hiemalis, is a serious fungal disease of sour cherry (Prunus cerasus) throughout the world (3). Yield, vegetative growth, and wood and bud hardiness of sour cherry are measurably reduced for up to two seasons following severe defoliation by Q. hiemalis (5,8). 'Montmorency' sour cherry, the predominant cultivar in the Michigan sour cherry industry (2), is very susceptible to defoliation by Q. hiemalis (14). Increased resis- tance to Q. hiemalis is an important objective of the sour cherry breeding program at Michigan State University. Previous work (4,9,13,14,17) has demonstrated that variation for resistance to Q. hiemalis occurs within and among several species of cultivated cherries. Complete resistance was not observed in most of these studies. Instead, cultivars of sour cherry, sweet cherry (E. ayium L.) and duke cherry (P, gondouinii) differed quantitatively in the levels of partial resistance to Q. hiemalis, In addition, factors associated with disease development, called components of resistance, differed among cultivars of these species. Components of resistance that measured lesion development and sporulation in infected leaves were the best predictors of resistance in the field (15). 75 Little information exists on the inheritance of resistance to .9. hiemalis in cultivated cherries. Enikeyev (6) reported that cer- tain cultivars of sweet and sour cherry were better parents than others in breeding cherries resistant to C, hiemalis. Crosses involving cultivars of the European ground cherry (P. fruticosa Pall.) gave higher percentages of susceptible seedlings than crosses of E. cerasus or P. am cultivars. This research was undertaken to determine the inheritance of components of resistance to C. hiemalis in progenies of cultivars of _P. cerasus and P.gondouinii. Materials and Methods Plant material. An incomplete diallel of unequal progeny numbers per cross was constructed in 1980 with 4 cultivars of P. cerasus ('English Morello', 'Meteor', 'North Star' and 'HTO 405') and 1 cultivar of P. gondouinii ('Kansas Sweet'). A total of 342 progeny from 14 crosses were used, with each parent represented in 4 to 6 crosses. Seeds from each cross were stratified at 1-4 C for 4-6 months until germination occurred. Germinated seeds were planted in peat pellets (Jiffy-7, Jiffy Products Ltd., Norway) covered with perlite in presterilized flats in a greenhouse at 181:6 C. Seedlings were transplanted at the 1- to 3-1eaf stage in January, 1981, into sand:peat:per1ite (1:1:1, v/v) in lO-cm diameter clay pots, and fertilized with 5 g/L solution of 20% N-20% P205-20% K20 fertilizer (Robert B. Peters, Co., Inc., Allentown, PA 18104) plus 1.3 g per pot of 19% N-6% P205-12% K20 controlled release fertilizer (Osmocote, 76 Sierra Chemical Co., Milpitas, CA 95035). All seedlings were sprayed prior to emergence of the inoculated leaf with four weekly applications of 500 ppm gibberellic acid (Pro-Gibb, Abbott Laboratories, North Chicago, IL 60064). Single-shoot trees of each parent cultivar except 'HTO 405' were grown as previously described (experiment 2 in (15)) hithe same greenhouse as the seedlings. Parent performance of 'HTO 405',a bud mutation of E. cerasus 'Montmorency' from Hilltop Orchards and Nurseries, Inc., Hartford, MI 49057, was estimated with single-shoot trees of 'Montmorency'. Three trees of each cultivar were included as controls at each date of inoculation. Inoculation. Seedlings were inoculated when 2- to 3-months old in three separate experiments. Progeny from each cross were divided into three approximately equal-number groups. Group one from each cross was inoculated on March 11, 1981; group two was inoculated on March 19, 1981; and group three was inoculated on March 27, 1981. Previous studies have demonstrated that components of resis- tance to g, hiemalis in Prunus species are affected by leaf age (15). Therefore, a single leaf, 7- to l4-days old at the time of inocula- tion, was inoculated with a modified Schein quantitative inoculator as previously described (15). All plants were randomized prior to inoculation. An average of 6360, 2150 and 2870 conidia per leaf were applied in the March 11, March 19 and March 27 experiment, respec- tively. Plants were placed into a mist chamber at 18-21 C for 48 hr after inoculation, and then incubated in a cheesecloth tent in the greenhouse (15) at 20 i 6 C. 77 Components of resistance. Infection efficiency, lesion area, spores per lesion and reproductive efficiency were determined 20 days after inoculation as previously described (15). Spore production was estimated from the absorbance at 700 nm of spore suspensions (10). A standard curve of hemacytometer counts of conidia to absorbance was established for each experiment. Examination of residual pat- terns and correlation coefficients indicated that spore counts in all three experiments were best estimated by the linear and cubic terms of absorbance measurements. Data analysis. Analysis of variance for each component of resistance were performed on parent and progeny data from each experi- ment as well as the combined data for all experiments. Equal numbers of progeny per experiment was assumed for a given cross in the analy- sis of the combined progeny data (16, p. 477). Estimates of general combining ability (GCA) and specific combining ability (SCA) were made for each component of resistance in individual experiments by Gilbert's procedure (7) for incomplete diallels with unequal numbers of progeny per cross. Broad-sense heritability estimates for each component of resistance were calculated on an individual-plant basis from the analysis of variance for parents and progenies in each experiment. Parent estimates were calculated as follows: 2 _ x2 2 2 BS - Obc/(abc I awc) h 78 2 be between-clone component of variance and 63c is the within-clone where hgs is the broad-sense heritability estimate, 6 is the component of variance. Progeny broad-sense heritabilities were calculated using 65c as an estimate of environmental variance by the following equations: 2_2 2 2 2 2 “as ’ (a p l 6wp)/(6bp + 6up 1 wc) 2 hi) the within-progeny component of variance. Coefficients of average where 6 is the between-progeny component of variance and 65p is progeny number in the expected mean squares were calculated assuming random effects for samples of unequal sizes (16, p. 289). Broad-sense heritabilities of the combined data from all three experiments were corrected for clone by experiment and cross by experiment interactions. The component of variance due to the interaction of experiments with clones and experiments with crosses was included in the denominator of the equations for broad-sense heritabilities of parents and progenies, respectively. Results Cultivars differed significantly in all 4 components of resistance (Table l). Cultivar by experiment interactions were not significant, but significant (p = 0.01) experiment to experiment variation was detected for each component. Although the relative ranking of cultivars differed from experiment to experiment, the components of infection efficiency, lesion area and reproductive efficiency were lowest overall in 'Kansas Sweet'. 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wewe: wewe m.e w.m m.ew m.me eew ewewweewe ee weweweeewww wewe. ewee. mmeewe mw.e ew ewwwwwew eeewezv eweee eweewe. wwwewe. «wewmewwe «www.e we ewwwwwew ewwzwwev _wwwe wwwewe. ewewwe. wwmwmweee wwww.w w eeweee< ewwev emcee eewweeee eev aocwwowwww cewmwp ewe ewee aocwwowwww zeppeeee> w>wuo=eeeewe wweeem newmww neeeowwew .w.e we.wopeem woeeumemwe we ucwceeseu .N unwewewexw we acweeee cw meweswwn mwoeseoemw en woeeemwmwe we muewneeeeo eew mweeeew new211.e mnmweowemwe .wo.o u.m we uceowwwnewm ene .mo.o n.m we uneowwwemwm .uceoewwcmwm wen u we .« ..m.c~ .N55 e 1 wewe: wewe w.m e.e _.mw e.w~ eew eweeeeewe ee weweweeewww ewee. ewee. wmmee ew.e we ewwwwwew eeewezv eweew wwwmee. eweeee. «Neewee .w.e em.m __ ewwwwwew ewwzwwev ewwwe .w.e ewee. .w.e ewee. .w.e ewwme .w.e we.e e e w>weoeeeeewe mweeem newmwp neeuowwew .w.e we.wop=em woeeumwmwe we unweeeseu we xnweeee cw wwweswen mwoeseooeu e» woceumemwe we menweeeeeo .m unwewewexw eew mweeeem newz-1.e mnm1, 'I- “U UCA SUD, 'U'I-O QUI— Loy-v Q“- (DQ- CKQJ C O Ul-r- Q10)" 5.0105 OI—O Q '— mLV Q) Q C A DION IPmE m5- may .4 >5 >3 EU 0: 'F’Q’ “-1-," DOS? mot-V III-W- :9- HQ) 4..) C Q) L M O. 4.9 C M E OF S— 0) D. x L” NMNNQ’ OOOOO 00000 +1 +l +1 +1 +l oooom-e- LOQ'LDQ'Q’ NMMNQ’ 00000 0000:: +1 +1 +1 +1 +1 FQFFO mmmmm o o o o o NNNNN .039 Q'Q'NN Lnd’d'N OOOO OOOOO +1 +1 +I +1 +1 N 00501 OMr-OOl I—o—u—v—v— OOOOO +I+I +1 +1 +l noomoo NNNNO F'l—I—f—f— O F F 0144 L0 $- CG) M 23 «H (I) LOU) .C O LUIUI VIC-Pm l-I-PQJr-UI 0&4JUI: I—OQJCM IZZLIJM 87 MVMMO 00000 00000 +1 +1 +1 +1 +1 SSSSS ##### NMNNQ’ OOOOO OOOOO +l +1 +l +I +1 +1 +1 +1 +1 +l NONI—ND (\l—Or—Q' Q‘QONN Coy—CO ermmmu— r-Nr-r-m 00000 +1 +1 +1 +|+I MNr—Olm [\NNNN O 1—1—01—0 O P F {D44 e S 8 a! £3 +4 m LOU) I: 0 Lin!!! Q'SO'I-IU I-I-‘QJr-Ul OLdl-JUIC I—‘OGJCI‘U IZZLIJ)‘ N Nd’NMLO 00000 06000 +1 +1 +1 +1 +1 Q’l-OMOSLO mmrwtoto ##### Nemmm 00000 00090 +1 +1 +| +1 +1 [\l—VNN came-mm NNNNN NOLONM MNMVN OOOOO OOOOO +l +1 +1 +1 +l 100N030 l-er-Nm ooooo +l+l +1 +1 +1 cord-mo QMOSNQ: (“NI—“EN O P P QI-H LG) 5- OCD «U 23 +3 U) LOU) .C O me GLOW-CU 1+4um 0&4405: I—OGJCVO IZZUJ)‘ m yNumber of lesions/number of inoculum x 100. 2Number of spores/number of inoculum. 88 Broad-sense heritability estimates for both parents and progenies varied considerably from experiment to experiment (Table 9). Overall estimates on a single-plant basis are less than 0.5 for all components except lesion areas in progenies (h:S = 0.68). Most of the genetic variance for lesion areas in all three experiments was attributed to the within-family rather than between-family variance component. Discussion Selection for components of resistance has been suggested as a means of increasing the level of partial resistance in cultivated cherries to C. hiemalis (15). Reproductive efficiency, which is the combined effect of the components of infection efficiency and spore production, is highly correlated with measurements of field resistance to defoliation in cherry. Reproductive efficiency can be measured rapidly by inoculation of individual plants with a quantitative inoculator and measurement of spore production from absorbance of spore suspensions. It is estimated that the total time required to measure leaf age, inoculate, and measure spore production is less than ten minutes for each plant. Susceptible genotypes, if identified by such a procedure, could be eliminated early in the breeding cycle, thus increasing efficiency of land utilization in the breeding pro- gram. The adoption of this procedure to screen for partial resis- tance to Q. hiemalis in cherry depends not only on deve10pment of methods that rapidly eStimate components of resistance that contribute 89 .meewpoeewucw mmeeo en pewswewexw ece wce#o An ucwseewexw eew eweoweeeo .m e» # mecwswewexw Eeew ewee ewcwnseo Eeew ewpeswumme .mwweweeee ece wueweee neon :w wocewee> #euewe:eew>ew we weeswuww :e we ewe: we: wocewee> weepo12wnnwz "mewen u=e#e1w#eeww e :e ewee#=o#eo mweuewenepwewn ##<» Nw. ee. we. we. wwwwwee we. we. we. we. weweww wwwweweeew wsewweeweeww we. ww. 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