Peter Posnette - A tribute.

Peter Posnette, who died on July 17 aged 90, was credited with saving
the West African cocoa industry, the source of the vital ingredient for
most of the world's chocolate.

When Posnette arrived at the Gold Coast (now Ghana) in 1937 as a
young plant pathologist with the Colonial Agricultural Service, many of
the colony's cocoa trees were dying from mysterious causes. At first
the trees were believed to be withering because of lowered humidity
after the degrading of much of the rainforest. Stem swellings had been
noticed, but had been disregarded.

After spending most of his first year on cocoa farms, Posnette
concluded that the leaf symptoms and stem swellings were not caused
by drought but a virus. He then discovered the transmission agents -
mealy bugs known as Pseudococcus njalensis and related genera.

In 1938 Posnette established a Cocoa Experiment Station at Tafo to carry
out research into control methods. The problems he faced were not all
scientific. When he wrote his first official letter requesting some very
modest equipment as an "urgent necessity" to the Director of Agriculture
in Accra, he received a reply stating that "in this country nothing is
urgent and very little is necessary".

The practical difficulties involved in control methods such as protective
inoculation led Posnette to conclude that resistance breeding offered the
best hope of a solution to swollen shoot virus and other diseases.
However, genetic diversity in the West African cocoa crop of the time
was very limited. The prevalent Amelonado type of cocoa trees were
derived from trees introduced from Brazil in the late 19th century. The
Trinitario types introduced in the early 20th century from Trinidad had left
few descendants. The need for a wider genetic base was evident if
resistance breeding was to be successful.

From time spent as a research student in Trinidad, Posnette knew that
cocoa strains from the Upper Amazon region, recently brought to
Trinidad, contained genotypes resistant to witches-broom disease
Crinipellis (Marasmus) perniciosa. In 1943 Posnette returned to Trinidad,
where he hand-pollinated seed, crossing different Upper Amazon types
and Trinitario clones.

Planted in Accra, some of the seedlings showed hybrid vigour, starting
to crop in the third or fourth year rather than the more usual fourth or
fifth, and producing higher-than-normal yields. Many of the Upper
Amazon introductions were more tolerant of the swollen shoot virus and
more resistant to infection more generally. The introduction of Upper
Amazon hybrids almost certainly saved the West African cocoa industry
from extinction and the hybrids now form the basis of most cocoa
improvement programmes worldwide.

Adrian Frank Posnette, always known as Peter, was born on January 11
1914 and educated at Cheltenham Grammar School. His main interests as
a boy were zoological rather than botanical, and he went up to Christ's
College, Cambridge, with the intention of becoming a zoologist. He also
played football for the college and flew with the University Air Squadron.

Finding genetics particularly interesting, he hoped to find work as an
animal breeder. But the generous terms offered by the Colonial
Agricultural Service, including two years' paid postgraduate study
abroad, proved an irresistible lure and in 1935 he was offered one of
only two CAS research studentships - in plant genetics. After studying
at the Cambridge University School of Agriculture, he moved to the
Imperial College of Tropical Agriculture in Trinidad, where he undertook a
research project into the natural pollinating agents of the cocoa tree
(Theobroma cacao).

After leaving Africa, in 1949 Posnette moved to the East Malling
Research Station to work on viruses of strawberry and other berry
fruits, and later on diseases of apple, pear, cherry and plum trees.
Among other things, he discovered that mosaic, rubbery wood and chat
fruit diseases of apple trees had become prominent in English orchards
because a new variety that was sensitive (Lord Lambourne) had been
grafted on to trees of other varieties in which infection was latent.
Posnette contributed to the international research that led to the
development of new virus-free fruit tree varieties.

Posnette became head of the Pathology Department at East Malling in
1957, and served as deputy director from 1969 and director from 1972
until his retirement in 1979. He was, for many years, a visiting professor
in Plant Sciences at Wye College, part of London University.

Posnette's interest in fruit was not confined to the laboratory. At Little
Ashurst Farm, Chart, Kent, where he lived until 1970, he and his wife,
Isabelle, built up a successful fruit farm, Posnette planting every tree
himself.

The cocoa research station which he founded in the 1930s became the
West African Cocoa Research Institute. Shortly after his death, his family
discovered that the Ghanaian authorities are to name the building where
he did his work the Posnette Building in his honour. Posnette was
appointed CBE in 1976, elected FRS in 1971 and awarded the Royal
Horticultural Society's Victoria Medal of Honour in 1982.

He married, in 1937, Isabelle La Roche, who died in 1991. They had a
son and two daughters.

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