Horticultural science has recently lost one of its unsung heroes. Dez Barbara’s death on 15 July 2012 followed a short period in hospital and came as great shock to those who had seen him at the laboratory bench just a few days previously.
Dez made a substantial and creative contribution to the plant pathology of horticultural crops during his varied and productive 35 year research career at East Malling and Wellesbourne. He was not one to seek the limelight but his research spanned diseases of fruit, hops, ornamentals and vegetables caused by viruses, viroids, phytoplasmas and fungi. He leaves a legacy in the scientific literature of almost 100 publications which almost invariably connected detailed studies on the detection, characterisation and basic biology of pathogens to their practical management in commercial cropping situations. Dez was no “ivory-tower” scientist but was always alert to that way that questions of practical significance could yield to development and application of the latest advances in technology. Dez had a love of the natural world in general and he was a committed scientist of the highest integrity who continually challenged conventional or uncritical thinking. He was always “hands-on” whether in the laboratory, glasshouse or field; and he had a healthy irreverence towards administration and administrators of science.
Dez and his wife Anne (who worked alongside him for 18 years and was a co-author on more than 20 papers) moved to Wellesbourne from East Malling in 1996 as part of the reorganisation of Horticulture Research International. Twenty years previously he had joined the internationally renowned virology group at East Malling from the University of Birmingham where he obtained a BSc in Biological Science and a PhD in plant virology. At East Malling he developed a series of serological and nucleic acid based diagnostic tests to enable the sensitive detection of viruses, viroids and phytoplasmas in hops, strawberry, raspberry, apple, pear and woody ornamentals. He worked closely with Michael Clark and Tony Adams on the development and refinement of ELISA techniques for routine and highly specific virus disease diagnosis. In the late 1980s, Dez also spent time at Purdue University in the USA working on Barley Yellow Dwarf Virus by way of adding to his tool-box of expertise in molecular biology and diagnostics. His East Malling papers read like a “who’s who” of perennial crop virology: hop mosaic, arabis mosaic, prunus necrotic ringspot, apple mosaic, raspberry bushy dwarf, hop latent, American hop latent, rubus Chinese seed-borne, strawberry crinkle and others. However, Dez was not just interested in detection and discrimination of pathogens; he always wanted to see follow-through in field application and his work on hop viroids is classic in this regard. With his wife Anne and with Tony Adams, Dez developed a nucleic acid hybridisation assay which enabled the detection of these infectious circular RNA molecules and demonstrated the occurrence in UK hops of hop latent viroid (the name implying that it was previously thought to be benign). However, challenging conventional thinking as always, Dez went on to show that infection caused very significant loss of yield in the field and to initiate the production of viroid-free planting material. The ability to produce virus and viroid-free nuclear stocks of hops (and other perennial crops) owes much to Dez’s work.
Before leaving East Malling for Wellesbourne, Dez, together with John Carder and a PhD student, Ada Okoli, had developed some new molecular approaches to the study of soil-borne diseases caused by fungal species of the genus Verticillium which cause serious wilt diseases of a range of horticultural crops including strawberry, hops, tomatoes, potatoes, chrysanthemum and brassicas. At Wellesbourne, Dez and his co-workers continued this work and revealed hitherto unexpected and biologically significant complexity in the identity of these plant pathogens particularly among types that were known to cause serious disease in oilseed rape and vegetable brassicas elsewhere in Europe (but not recorded in the UK until 2007). These brassica pathogens (classified as V. longisporum) were shown to be of several genetically distinct “biotypes” originating from hybridisation between the common wilt fungus V. dahliae and an as yet unidentified species. Work in Dez’s lab enabled the rapid confirmation that outbreaks of disease in UK oilseed rape crops at several UK locations were attributable to V. longisporum and this alerted vegetable growers to a new threat.
In addition, Dez also contributed to improved methods for the rapid detection and diagnosis of virus diseases of carrots and parsnips including the first detection in the UK of an infectious virus-associated RNA (carrot red leaf virus associated RNA – CtRLVaRNA) previously unrecorded outside California. The carrot crop featured prominently in the work Dez was actively engaged with until days before his death. His work on cavity spot disease (caused primarily by Pythium violae) is an excellent parting example of Dez’s characteristic challenge to conventional wisdom. The work has yet to be published but is summarised in a conference presentation made in February this year. Dez developed and deployed a sensitive detection technique to demonstrate that the cavity spot pathogen did not build-up with repeated cropping at the same site and he showed that there was no evident relationship between disease severity and levels of the pathogen in soil. His work indicated that soil moisture and varietal susceptibility were primary determinants of the severity of symptoms. He also demonstrated that the causal organism could grow on the roots of many other crops and weed species. These new insights, when taken together, indicated that long rotations and expenditure of time and resources on the search for disease-free fields were not profitable practices for carrot growers. The outcome of Dez’s last contribution to science was, characteristically, of genuine significance to the industry.
Dez successfully supervised seven PhD students and, aside from his own research, he was a willing contributor of his expertise to others as is evident from his co-authorship of papers on genetic fingerprinting of apple varieties, studies on the epidemiology of apple canker and scab, as well as production of transgenic fruit and brassica crops. Beyond his research, Dez had many other interests including history, music and geology. He and Anne created a fine garden at their house in Wellesbourne and he was a skilled carpenter. Dez will be much missed by Anne, and his very many scientific associates throughout the world. I cannot think of any scientist who I have encountered during my own career that I have more enjoyed scientific discussions with than Dez Barbara.
(Obituary prepared by Ian Crute and Rosemary Collier)