Page 209 - Encyclopedia Of World History

diseases, plant 559

turies of the Common Era were unusually wet in the the nineteenth century.True, farmers also grew soybeans
lands along the Mediterranean Sea, bringing rust to throughout Korea and China, and wheat grown along
wheat fields throughout the Roman Empire. Some his- the Indus River reached the people of central and south-
torians finger rust as a culprit in Rome’s economic ern India by trade, but soybeans and wheat were minor
decline after 200 CE and in the dissolution of the empire supplements to a diet of rice.
in the fifth century. Roughly forty diseases afflict rice making difficult the
In the seventh and eighth centuries,Arabs brought the task of sorting among them, as well as among climatic
barberry bush with them as they swept across North factors, to explain the 1,800 famines that Chinese docu-
Africa and into Spain. Neither Arabs nor Europeans ments have recorded since 100 BCE and the 70 in India
understood that the bush harbors rust fungi because the since 33 CE. Because rice needs more water than any
fungi inhabit the bush without harming it, much as the other grain to thrive, Chinese and Indian texts often
pathogens that cause malaria and yellow fever live in attributed crop failures to inadequate or impure water.
the gut of the female mosquito without harming her. A In the sixth century CE, a Japanese text mentions
barberry bush that harbors rust fungi has no symptoms stunted (short or dwarf) rice plants that bore little or no
of disease. Only in the seventeenth century did Europeans rice. The condition baffled farmers for 1,200 years. In
begin to suspect the bush to be a Trojan horse. In 1660 1733, 12,000 Japanese died of famine when stunt
France enacted the first law to eradicate the bush. Other destroyed their rice crop, yet no one was any closer to
European nations passed similar laws, as did the Ameri- understanding what stunted rice plants. Unlike Europe,
can colonies in the eighteenth century. Asia never developed science in its modern form but only
These measures were not enough to stop the spread of gradually assimilated it from Europeans during the eigh-
rust. Plant breeders in the nineteenth century began to teenth and nineteenth centuries.The people of Japan and
search for rust resistant wheat to cross with high-yielding continental Asia did, however, have a tradition of careful
but susceptible varieties, a program that accelerated that observation. This tradition led one Japanese farmer in
century as England, France, the German states, and the 1874 to study the feeding habits of leafhoppers on rice
United States poured money into agricultural science. plants. He doubted that insect bites alone could arrest
Around 1900 agronomists at the U.S. Department of plant growth and instead proposed that leafhoppers car-
Agriculture identified an Italian durum wheat suitable for ried a pathogen that they transmitted to rice plants by
pasta and a Russian emmer wheat suitable for bread. bite.The pathogen, not leafhoppers, stunted rice plants.
These were the first of innumerable resistant wheat vari- The idea was as novel as it was correct. Leafhoppers
eties that give humans the best, if incomplete, protection carry within their gut Rice Dwarf Virus just as, one may
against failure of the wheat crop from rust. recall, various species of mosquitoes carry the pathogens
for malaria and yellow fever. Rice Dwarf Virus remains
Rice Stunt Disease virulent throughout a leafhopper’s life, and female
Chinese records first mention the cultivation of rice leafhoppers pass the virus to their offspring, multiplying
4,000 years ago, though its cultivation may have begun it with each generation.When the leafhopper population
in southeastern Asia. By 1000 BCE, farmers grew rice in is large, as it must have been in Japan in 1733, the virus
China, the Korean peninsula, and the swath of land becomes widespread enough to cause failure of the rice
between modern Vietnam and India. By the first century crop even though the leafhopper is an inefficient flier.
CE, farmers were growing rice in Japan, Indonesia, and The discovery of insect transmission of a pathogen
the Philippines.The people of these regions were nearly opened a new field in the study of plant diseases by unit-
as dependent on rice as the Irish would be on potato in ing entomology, the study of insects, with plant pathology.