Hans Molisch’ Legacy

The Father of Allelopathy

Professor Dr Hans Molisch (1856-1937) was, appropriately, the son of a farmer. Both his parents had a love of gardening. Molisch lived in the German city of Brunn where several scientific institutes were located. Gregor Mendel was foundation professor of natural sciences at Brunn University and visited the Molisch family garden in 1865 (Narwal and Jain, 1994). Thus, were the seeds sown for his subsequent, distinguished career as a botanist which was under-pinned by his understanding of chemistry, in which field he also published. These two disciplines continue to underpin contemporary research into allelopathy.

Studies at the University of Vienna were followed by a distinguished academic career in which Molisch taught and carried out research in Czechoslovakia, Austria, Japan, and India. He traveled also in Indonesia, China and North America (Narwal and Jain,1994).

Molisch is, perhaps, best remembered for two books: Microchemistry of Plants (1912) and The Influence of One Plant on Another: Allelopathy (1937). This, his last major contribution to the literature, blended his disciplinary interests and is credited with introducing the term ‘allelopathy’, thus earning him the sobriquet ‘the father of allelopathy’. Molisch also espoused the now generally accepted view of allelopathy as describing both positive and negative effects of exposure to allelochemicals (Rizvi et al, 1992).

Pioneers of Allelopathy

There were, of course, pioneers in the world of allelopathy, albeit unfamiliar by that name, pre-Molisch. Bioactive compounds from plants have been harvested and deployed for a variety of purposes, not least in health and medicine, since before the dawn of agriculture more than 10,000 years ago. The fact that many of the most potent pharmaceuticals and poisons known to man are of natural, plant origin is often over-looked by the more ardent proponents of all things ‘organic’!

While it may not quite have been a case of:

“Eye of newt and toe of frog,
Wool of bat and tongue of dog,
Of the ravin’d salt-sea shark,
Root of hemlock digg’d i’ the dark,
Double, double, toil and trouble:
Fire burn and cauldron bubble.”
William Shakespeare ‘Macbeth’ 1606

Tose witches or wizards who used natural compounds to effect cures were often subjected to the ducking-stool, or worse, for their pains. Early agronomists may have fared better as they offered their proto-allelopathic remedies but advisory parchments of the period have not, unfortunately, survived.

Putnam (1985) notes that among the earliest records of the detrimental impact of what is now recognized as allelopathy in agriculture are the writings of the Greek philosophers Democritus (c.460-370BC) and Theophrastus (c.372-286BC). The former traveled widely and was the most learned thinker of his day. Fragments of his mathematical, physical, ethical and musical works survive, including his ‘atomic system’. The latter was a student of Aristotle and was responsible for preserving much of his teacher’s works. Theophrastus himself wrote two books on plants.

Willis (2000), reviewing aspects of the history of allelopathy notes that the Romans, too, recognized allelopathic phenomena. Circa 36BC, the author Varro, who wrote more than 600 books, observed the harmful effect that walnut trees could have on adjacent species. Early naturalists continued to make observations of ‘allelopathic’ phenomena throughout the ensuing centuries but Willis (1996) dates the first phase of allelopathy, proper, as the period 1785-1845 “the age of de Candolle”.

By the nineteenth century serious attempts were being made to provide a scientific rationale for observations of allelopathic phenomena. One of the best-known identities of this period was Augustin Pyrame de Candolle. As early as 1805 he wrote on the topic of root excretions and applied these studies in the context of crop rotation. The technology of the day, however, did not permit him to identify the bioactive compounds which he perceived to be present. As Willis (2002) writes: “To many, de Candolle is the real father of allelopathy…he developed a perspicacious theory of plant interaction, relevant to agriculture and natural ecosystems, based on chemical substances assumedly released from plants.” Perhaps de Candolle should be recognized as the grandfather of allelopathy?

In any event, it was appropriate that the acknowledged father of allelopathy, Hans Molisch, should feature in the first article of the inaugural edition of *Allelopathy Journal*, published in 1994. Greeting the arrival of the journal, Professor Al Putnam noted that a multidisciplinary approach, as exhibited by Molisch, was essential to successful studies of allelopathy. “Rarely,” he wrote, “does one individual possess all of the skills necessary to solve all of these problems” (Putnam, 1994). Collaboration between scientists would bring together the necessary mix of skills and would be “appropriate for publication in this Journal where it can reach a multidisciplinary international audience”.

Further Developments in Allelopathy

Such a broad interest in the chemical interactions of plants and their application in natural and managed systems became apparent in what Willis (1997a) characterizes as the second phase of allelopathy history, between 1900 and 1920. Spencer U Pickering (1858-1920) was a pioneer of allelopathy active during this period (Willis, 1994a). A physical chemist by training, Pickering is known for his work on the effects of grass cover on fruit trees; the effect of crops on other crops, and the effect of heat on soils (Willis, 1994a). His work was greatly facilitated by the patronage of the Duke of Bedford on whose Woburn estate, in southern England, Pickering worked for a quarter of a century. Interestingly, the noble duke appears not to have hesitated to exercise aristocratic privilege, appearing as senior author in many of the Pickering papers (for example, Bedford and Pickering, 1914)!

Profiles of a total of fourteen pioneers of allelopathy have appeared in issues of *Allelopathy Journal*, to date. These include the distinguished American taxonomist and ecologist Cornelius Muller, who investigated allelopathy in the context of dominance and suppression in natural communities (Willis, 1995); Oswald Schreiner of Germany, the first person to isolate and identify phytotoxins associated with unproductive soils (Willis, 1996), and Gerhard Grummer, who “was the first to consolidate allelopathy as a phenomenon in plant ecology” (Willis, 1997b).

The Legacy of Allelopathy

‘Allelopaths’ (a term very loosely translated from the Greek and meaning ‘those who suffer together’) were active, also, in the southern hemisphere. Fernando Almeida (1924-1993), for example, a Portuguese immigrant to Brazil, was a pioneer in the study of allelopathy resulting from mulch biomass decomposition in reduced cultivation systems (Passini and Rodrigues, 1999), bringing allelopathy studies firmly into the context of contemporary management in farming systems.

Hans Molisch’ death occurred shortly before the outbreak of the Second World War. The sixtieth anniversary of the end of that conflict has been celebrated this year. But, although the world war concluded in 1945, its legacy saw many communities of scientists working in comparative isolation for more than four decades, until the conclusion of the so-called ‘Cold War’.

Contributions from Soviet and Eastern Bloc Scientists

Andrei Grodzinsky (1926-1988), the father of allelopathy in the Soviet Union, was at his most scientifically active during this period and, accordingly, is less well known than is warranted by his contributions. Unlike Molisch, he was not able to travel widely but, nevertheless, made a major contribution to the science of allelopathy through his observations of bioactives (allelochemicals) released by plants and their stimulatory and/or inhibitory effects. He published in the western literature, for example, a paper on the phytosanitary effects of cruciferous crops in crop rotation appearing posthumously (Grodzinsky, 1992). Like his contemporaries in North America, he espoused a wide role for allelopathy as a factor in ecology (Golvko, Roschina and Narwal, 1995). Indeed, Willis (1994b) writes that “Grodzinsky has long tried to present a much less restrained view of allelopathy and has also bravely alluded that plants may even be able to react to energy fields of other plants”. Grodzinsky’s role as ‘father-figure’ influenced the work of other Soviet allelopathy scientists, who are reported as contributing more than 5000 scientific papers and 20 monographs on allelopathy between 1931-1990 (Roshchina and Narwal,1998).

Future Directions and Sustainability

In conclusion, allelopathy remains an area with vast potential that has not yet fully translated into practical agricultural applications. However, new studies and ongoing global interest in plant chemistry and sustainability provide a hopeful outlook for future breakthroughs.