PHYTOLOGIA BALCANICA 12 (2): 143–147, , 2006 143

Prof. Michail Hristov (1895–1960) – founder of cytological, genetic and embryological studies in

Dimitur Terziyski

Department of Botany, Agricultural University, 12, Mendeleev St., 4000 Plovdiv, Bulgaria

On 21st December 2005 were commem- and his pure patriotism. His life philos- orated 110 years since the birth of the ophy, eloquently expressed in his behav- prominent Bulgarian scientist, Prof. iour, can be summarized in three words: Michail Hristov, the founder of cytolog- motherland, family and work. For him, ical, genetic and embryological studies these were sacred words and he never in Bulgaria. His legacy in these impor- made a compromise with them until the tant biological fields of study is so pro- end of his life. found and up-to-date that, although 45 Prof. Hristov’s childhood was marked years had passed since the end of his life, by poverty. His father, a patriot and par- it is still difficult to speak of him in the ticipant in the April uprising fell grave- past tense. His name is not only crowned ly ill and in order to make the ends meet with the glory of a pioneer teacher, but with his meagre disability pension, the with his high scientific accomplish- family moved into Perushtitsa, the na- ments, too, many of which have inspired PProf.rof. MM.. HHristovristov tive village of his mother. Young Michail ((21.XII.188521.XII.1885 — 99.V.1960).V.1960) admiration ever since and have made received his basic education there and in us feel proud. He is one of Bulgaria’s scientists with a 1914, after years of deprivation, finished high school manifest national and international presence. in Plovdiv. Had we been able to turn back he clock Prof. Michail Hristov was born in the town of of time to that period, we would have seen a thin Plovdiv to a teachers’ family. Both on his fathers’ and and silent, simply dressed, not very tall youth, with а mothers’ side he was descendant of heroic National high forehead and large black eyes, looking with sup- Revival families. Prof. Hristov’s grandfather was broth- pressed anguish. The times were harsh and the coun- er of the Bulgarian national hero, Kocho Chestimenski, try was poor and in ruins. the Balkan war had just in the 1876 April Uprising. His mother was sister of ended and the people suffered badly from the conse- Petur Bonev, the leader Perushtitsa rebels. His famil- quences and frustration brought about by the national ial memory emotionally charged with the glory of his catastrophe. The bright and studious youth wanted to ancestors, who gave their life for Bulgaria, influenced continue his education. He was deeply convinced that strongly his personality. He grew up as bright, patriot- by doing so, he would serve his motherland best. He ic young man, who loved deeply his motherland and wanted to study literature, but had no money. Young was painfully sensitive to any injustice. He managed Michail Hristov was well aware that there were nei- to retain these features throughout his life. All who ther any available job opportunities for him to sup- had the honour of being his students or had worked port himself, nor was his family able to provide such with him knew his high moral principles, straightfor- a support. However, destiny suddenly interfered with wardness, unaffected manner and lack of selfishness, an announcement of the Ministry of Agriculture and 144 Terziyski, D. • Prof. Michail Hristov (1895–1960)

State Property for a Government scholarship compe- improved solely by the conservative method of con- tition for agricultural studies abroad. Being a dynamic tinuous natural selection. After the first field vis- and purposeful person, he did not hesitate. The coun- its, opinion polls and analyses, the young Assistant try needed badly educated people to develop mod- Professor drew some important conclusions: first, the ern agriculture and young Michail Hristov was suffi- tobaccos spread in Bulgaria were of the extensive type, ciently motivated to make such a sensible compromise well adapted to the soil and climatic conditions of the with his heartfelt desire. He won the competition and regions, but unable to achieve high yields or techni- in 1915 went to as a student of agriculture. A cal properties, and second, owing to their genetic het- fact from that period showed what a selfless and well- erogeneity, the Bulgarian tobaccos were invaluable as meaning person he was: two major personal qualities a genetic pool and stock material for effective genetic in his system of values. He used his small scholarship and selection work. These conclusions were to under- to support his brother’s studies for a chemical engi- lay a new, rationalised programme for more profound neer in Vienna. In 1921 Michail Hristov graduated as theoretical and experimental studies into the biolog- agronomic engineer. ical, physiological and reproductive tobacco charac- Back in Bulgaria, the highly qualified agricultur- teristics with a set of modern cytological and genetic al specialist lovingly began work on updating the ex- methods, which Michail Hristov implemented in the tremely primitive national agriculture ruined by the years to follow. Without these theoretical and experi- war. The well-informed agronomic engineer was well ential analyses it would have been impossible to car- aware that, in the absence of industry, the only chance ry out any exact taxonomic identification of the tobac- to revive quickly the economy of the country was to co types and to improve their variety composition and use the fine natural potential of Bulgarian agriculture. economic properties. Thanks to his analytical mind, Michail Hristov under- The scientific and experimental work of Prof. stood that the process would require some wide-rang- Michail Hristov can be conditionally grouped and di- ing educational, organizational and scientific efforts. vided into three main periods. The first, from 1921 Already then a major personal quality of his char- to the end of 1925, is a period of upgrading his sci- acter came to the fore: the ability to think over, plan entific, methodological and educational expertise, a and organize in detail every problem he was dealing period of final decision-making for further scientif- with. Wherefrom to start? He found the rational so- ic work. Supported and encouraged by the head of the lution and focused his attention on lines and culti- Department, Ivan Stranski, and the prominent spe- vars in which the country had greatest experience and cialist in animal cytology and embryology, Prof. Todor traditions, namely tobacco and vegetable production. Morov, in 1923-1924 Michail Hristov went to special- Two fortunate circumstances played a decisive role ize in , at the Institute for selection and genet- for his future development and for the fulfilment of ics with the High school of agriculture in , and set objectives: one was the opening of the Faculty of at the Institute of Agriculture in the town of Halle. For Agronomy at the University of Sofia, the second was a the purposeful young scientist that training opened meeting with the eminent soil scientist, Academician up new vistas in the achievements of world botani- Ivan Stranski, then Associate Professor and head of cal and agricultural science. He improved his German the newly opened Department of General agriculture and practiced contemporary methods for the cytolog- at the new faculty. That experienced university profes- ical, caryological, genetic and embryological analysis, sor and scholar was impressed by the expertise, ideas as well as modern selection methods. Specialisation and emanation of the young specialist. He approved in Berlin and Halle increased his willingness to gain his intentions and advised the young man to concen- maximum experience and knowledge in microstruc- trate on priority studies into the distribution and vari- tural botany, which attracted him very much, because ety composition of Bulgarian tobaccos, owing to their Bulgaria lacked such specialists. On the following year economic importance. In the autumn of the same year he won a scholarship from the Rockefeller founda- he invited him to work as his Assistant Professor. The tion and continued his education in one of the world’s tobacco cultivars grown then in the country were ge- best scientific centres: the Institute of genetics and se- netically and morphologically heterogeneous popula- lection at Harvard University in Boston USA (1925- tions, resulting from uncontrolled hybridization and 1927), under the supervision of Prof. E. East. Thus the Phytol. Balcan. 12(2) • Sofia • 2006 145 ambitious youth’s dream to receive high education and sis and method of inquiry. Along with this, the spe- to carry out scientific research in some fields extreme- cies and cultivars of genus Nicotiana were perfect ly needed by his native country came true. model objects for cytogenetic experiments and anal- In the following decade he proceeded with his ca- ysis. That first stage of inventory-making and study reer in Bulgaria: Associated Professor (1926), full of Bulgarian tobacco varieties and species set up the Professor (1930) and Head of the Department of background for further in-depth studies by applica- Agricultural botany (from 1937 to 1960). He brought tion of an array of modern analytical methods: cary- new methods, terminology and techniques for cyto- ological and genetic analysis, emasculation and isola- logical, genetic and embryological analysis in Bulgaria tion experiments, meiotic analysis and progeny tests. and organized the first cytoembryological laborato- In the following years, and especially after his two spe- ry in the country. In spite of insufficient government cialisations abroad, Michail Hristov successfully im- funding, he turned the Department of Agricultural plemented that task and laid down the foundations botany and the Faculty of Agronomy into a centre of of cytological, genetic and embryological studies in cytological and embryological studies in line with the Bulgaria. world leading standards for his time. The second period of the scientific and research ac- During that period he had relatively few publi- tivity of Prof. Hristov was closely linked with his spe- cations, because his attention was focused on an in- cialisation in Germany and the USA. Already armed ventory of the diversity of local tobacco species and with profound theoretical and methodological knowl- his specialisation abroad. He embodied his aware- edge in plant reproduction, genetics and selection, ness how important it was to have a better agricul- cytology and embryology, with fluent German and tural education in a dozen of popular-science articles English, in 1925 he published two papers which at- targeting a broader audience and discussing organo- tracted the attention of tobacco specialists: “Cytological genesis and modern technologies in agriculture ap- studies on genus Nicotiana” and “Inheritance-experi- plicable to staple crops: “Seed development in cereal mental studies of some tobacco varieties”. These publi- plants”, “ What determines the production of brewery cations marked the beginning of some more detailed barley?”, etc. studies into the cytogenesis and modern genetic selec- In 1923 Prof. Hristov published his first strictly tion work on tobacco in the country. They were fol- scientific paper “Contribution to studying the locally lowed by a string of eight detailed papers, highlighting grown cabbage species”. It was based on material col- all aspects of cytology, caryology, meiosis, hybridi- lected and analysed during his probation time at the sation potential, and sterility in the species of genus Obraztsov Chiflik farm in 1919. That paper also con- Nicotiana. It is impossible to analyse here all scientif- tained his idea of how important vegetable production ic contributions and work of Prof. Hristov in this field, was for the national economy. Its publication revealed but here are some articles, to name a few more sig- the competence and erudition of the young specialist, nificant: “Cytological studies in the genus Nicotiana” but he did not go beyond the framework of technolog- (1928), “Cytological studies on some species hybrids of ical, morphological and variety analysis of the studied Nicotiana” (1929), the overview “Changes in organisms cultivars. His interest remained focused mainly on the in the light of chromosome theory” (1929), “Genetic sur- comprehensive studies into the problems of tobacco vey of Nicotiana tabacum” (1935) co-authored with G. and tobacco growing. In 1923 he summarized the re- Gentchev, etc. In these articles focused on this field sults of two years of research on tobacco into two sci- and expressing his profound interest in the species of entific papers: “A scientific tour of the tobacco-growing genus Nicotiana, Prof. Hristov drew some important centres in the Kingdom of Bulgaria” and “The tobacco conclusions and registered new findings highly valued varieties of Perushtitsa”. Gifted with an ability to ana- by the world’s leading scientists, namely, Prof. E. East, lyse, summarise and draw conclusions, the young sci- G. Stebbins, A. Gustafsson, A. Müntzing, M. Skalinska, entist confirmed the opinion of T. Goodspeed & al. etc. His high-priority findings included the identifica- that, owing to genetic heterogeneity and strongly- tion of new and confirmation or correction of the al- expressed polymorphism, it was impossible to iden- ready reported chromosome numbers in many species tify the interrelations and systematic units in genus of genus Nicotiana; identification of four new types of Nicotiana only on the basis of morphological analy- meiosis in the interspecies hybrids of the same genus; 146 Terziyski, D. • Prof. Michail Hristov (1895–1960) validation that it was possible to use the meiosis types After 1935, Prof. M. Hristov shifted his interests for for elucidation of genetic similarity, incompatibility good onto the issues of reproductive biology of plants: and taxonomic status of arguable taxa of the genus; mainly on the apomixis. A lively dispute was then un- and recorded subordination between the chromosome der way in the embryological circles about the reasons number and relationships of hybridization among the for appearance, peculiarities and evolutionary impor- genus species. He demonstrated experimentally that tance of this unique way of embryo- and seed-forma- in reciprocal crossing hybridization is more success- tion without fertilization. Emphasis was increasingly ful, if the mother organism has a bigger chromosome laid on the practical importance of this process for the number. This dependence was lately accepted as uni- selection and seed production, because of the possibil- versal. The above-listed contributions brought huge ity it offered for obtaining homozygous plants, the fast international prestige both to Prof. Hristov and to the transfer and establishment of valuable economic char- young Bulgarian science. In this connection, another acteristics and the heterozygous effect in the progeny. element in his biography merits attention. Following Alone, or in coauthorship with A. Popov, G. Papazova his first publications in English on the cytology of to- and M. A. Hristov, Prof. M. Hristov published 11 pa- bacco, and especially after his paper on polyploidy and pers in this field, which had found their place in the apomixis in genus Potentilla delivered at the 7th World history of apomixis studies and have been widely cit- Congress of Genetics, he was invited by Prof. East of ed ever since. Due to the limited numbers of trained Harvard University, who was strongly impressed by personnel, the apomixis studies were not comprehen- him, to become his assistant, but Prof. Hristov re- sive and were limited to families, genera and species fused. Bulgaria needed his knowledge and nothing, with the highest accumulation of apomicts: Rosaceae not even the attractive invitation to work in one of the (Potentilla) and Asteraceae (Hieracium). Faithful to world’s biggest scientific centres under incomparable his style, Prof. Hristov first established a collection of conditions, could tempt him make a moral compro- apomictic forms of selected model species from the two mise with his beliefs. genera (H. racemosum, H. gothicum, H. bupleuroides, The scientific interests of Prof. M. Hristov were etc.). His first paper in this field “On the reasons for not limited only to the caryology of species from ge- virgin reproduction of plants” (1936) was an overview. nus Nicotiana. Alone, or jointly with the first young In this paper, and in another overview, “Apomictic re- scientists trained by him – A. Popov, G. Gentchev, production in the world of plants” (1942), he criticised G. Papazova– he carried out cytological and caryo- in brief the developed classification of apomixis and logical studies of the species from families Vitaceae the discussion of the reasons for its evolution. In the (Ampelopsis, Vitis), Solanaceae (Petunia), Rosaceae years to follow, with a small team of associates trained (Potentilla), Asteraceae (Hieracium). That period in embryological analysis, he published the results of brought to the fore another aspect of his character: the studies on cytoembryological characteristics and benevolence to young scientists and ability for team apomictic types in the species of the two above-men- work. tioned genera. Their most important contributions in- In spite of the markedly fundamental and theoreti- cluded the papers: “Polyploidy and apomictic develop- cal line of his scientific interests, Prof. Hristov worked ment in genus Potentilla” (1939) in English, “Apomictic successfully and efficiently in the field of tobacco se- reproduction in the plants world” (1943) in German, lection. His excellent knowledge of the climatic and “Genetic studies of Hieracium aurantiacum” (1942) in soil conditions in the tobacco-growing regions, of the German, etc. These publications in some of the most biodiversity of local populations and of the contempo- prestigious international journals, such as Genetics rary selection methods helped him create several orig- and Planta, in English, German and French, attract- inal, highly-productive tobacco varieties, well adapt- ed the attention of the international scientific commu- ed to market demands, tobacco handling and tobacco nity with their insight and were widely cited by the processing industry. Two of them, “Ustinski 1” and world leading scientists in the field of cytology, caryol- “Ustinski 4”, were internationally acknowledged and ogy and apomixis, namely: A. Gustafsson, G. Stebbins, grown in other countries. They were practical expres- A. Müntzing, and M. Skalinska. Thus, the Bulgarian sion of Prof. M. Hristov’s competence as an agronom- cytoembryological school established by Prof. Hristov ical botanist, geneticist and selector. received high international recognition and in the Phytol. Balcan. 12(2) • Sofia • 2006 147

1930s was considered a leading school in the apomixis ing subjects, but would also fail to effectively apply the studies, along with the Swedish and German schools. modern agrarian technologies. He saw the agronomic Prof. Hristov had contributed strongly to the field practice as the broadest possible field of applied bot- of plant embryology and his contributions were recog- any. nised worldwide. Some of these major contributions Prof. M. Hristov read the first lectures in genetics included the discovery of the genetic basis for apomix- in Bulgaria to the students in agriculture and forest- is types in the studied species of the genera Potentilla ry. Since 1937 he had read the general course of agri- and Hieracium; identification of the relationship be- cultural botany, which included extensive sections of tween proven apomicts and their amphimict ances- cytology, anatomy, plant morphology, mycology, and tors; and determination of the proportion between the botanical taxonomy. As a knowledgeable and highly two modes of reproduction in the studied species and qualified scientist, he transferred the European stand- populations. His analyses and papers are still model ards into his teaching work: organized a training her- examples of the general principles and precision study barium and slide collection, established a training col- of the apomixis. One of his most important contribu- lection of live plants, supported the plant propagation tions to apomixis studies was the provision of persua- departments in the establishment of test plots, nurser- sive theoretical and experimental evidence that the ies and varieties. Along with his, Prof. Hristov wrote hypothesis of hybridization of Ernst (1918) and the the first textbook on genetics in Bulgaria (1946), as theory of polyploidy of Thomas (1940) were unfound- well as the first textbook on agricultural botany (1946). ed and that apomixis was genetically determined, but The concept and layout of these textbooks have been its occurrence was conducive to polyploidy, hybridiza- inspiring admiration ever since not only with their tion and sterility. Already before the genetic hypothe- detailed presentation and comprehensive informa- sis of Powers (1945), now widely accepted in embryol- tion, but also with the way they were adapted to the ogy, Prof M. Hristov had come to his own conclusion. specific requirements of various agricultural lines and An indication of the contribution and internation- the balance between the different parts. In the peri- al prestige of Prof. Hristov in the field of tobacco cy- od 1936-1951, he wrote five textbooks, each specifi- togenetics and plant embryology was the invitation cally adapted to the requirements of the relevant ed- extended to him to participate in the 7th World con- ucational profile: Genetics (1936), Agricultural botany gress of genetics (1939) and his election as Member (1946, 1947), Applied Botany (1947), and Botany for of the Genetics society of America (1937) and the Foresters (1951). International scientific society on tobacco (1939), Prof. Michail Hristov, the founder of the cytologi- where only renowned world scientist were holding cal, genetic and embryological studies in Bulgaria, in- membership. itiator of the internationally recognised Bulgarian cy- Prof. M. Hristov was not only an internationally toembryological school, did not receive in his lifetime acknowledged scientist in the field of cytogenetics and the deservedly high appraisal of a scientist of interna- plant embryology. He was also a prominent university tional renown and prestige. The period of his work as professor, one of the pioneers in the field of contem- mature scientist and teacher coincided with the time porary higher agronomic education in Bulgaria. It was of strong political tingeing of science. The fact that a happy circumstance that he was promoted as Head he had specialized in Germany and USA and that his of the Department of Agricultural botany in 1937, scientific philosophy and studies ran contrary to the which had been under his guidance in the course of “great theory of Lisenko” doomed him to unwarrant- 23 years, until the end of his life. He maintained that ed distress. However, his scientific work is highly val- botany was a key discipline, the alphabet of agronom- ued and recognized in Bulgaria now. ical science and practice, and that without profound In the history of Bulgarian science– and the histo- knowledge of the cell structure, tissues, organs, repro- ry of science in general is part of the history of every ductive cells, and biodiversity in plants and fungi, the nation– the name of Prof. Michail Hristov marks one future agronomists would not only encounter difficul- of the highest peaks reached in the field of cytogenet- ties in studying the other biological and plant-grow- ics and plant embryology.