Past Successes 293created by deliberately crossing two distinct lines which have been inbred through
several generations by self-pollination. The resulting hybrids combine the best fea-
tures of both lines and usually have added a certain hybrid vigour.^8 At the time the
Mexican programme began, about half of the cornland in the US was planted to
hybrids. However, the disadvantage of hybrids is that new seed for each season has
to be produced by repeating the cross, since the seed gathered at the end of the
season from the hybrid crop will have lost the hybrid vigour and become contami-
nated. An alternative approach, adopted by Edwin Wellhausen, was to grow four or
more inbred lines in an isolated field and let them cross naturally. These so-called
‘synthetics’ yielded better than the best existing varieties by 10–25 per cent and the
farmers could simply save seed from their best plants from year to year.^9
Success came very quickly. In 1948 1400 tons of seed of the improved maize
varieties were planted. The new seed, good weather that season and the ready avail-
ability of fertilizer resulted in a record harvest and, for the first time since the revo-
lution of 1910, Mexico had no need of imports. By the 1960s over one-third of
Mexico’s maizeland was being planted to new high-yielding varieties and maize
yields were averaging over 1000kg per hectare. Total production had increased
from 2 to 6 million tons.
Although maize was the main staple crop, Mexico was importing about a quar-
ter of a million tons of wheat per year. Yields were very poor – ‘most varieties were
a hodge-podge of many different types, tall and short, bearded and beardless, early
ripening and late ripening. Fields usually ripened so unevenly that it was impos-
sible to harvest them at one time without losing too much over-ripe grain or
including too much under-ripe grain in the harvest.’^10 In northern and central
Mexico the soils had lost most of their fertility. On the newer, well-irrigated lands
in the Pacific north-west the soil was generally fertile enough to produce high
yields but stem rust was very destructive. Epidemics in three consecutive years,
1939–1941, in Sonora had caused many farmers to reduce their wheatland or stop
growing the crop altogether.
The wheat programme, under the direction of Norman Borlaug, began by
testing over 700 native and imported wheat varieties for rust resistance.^11 While
some of the imported varieties were both more resistant to rust and higher yielding
than the Mexican varieties, they had the disadvantage of late ripening. They needed
the longer days of the northern summers to mature. But by crossing the imports
with the best Mexican varieties, Borlaug produced, in 1949, four rust-resistant
varieties each adapted to a particular ecological region of Mexico. Wheat is a self-
pollinating crop, so that crosses have to be made by hand, but once made the new
varieties will breed true and farmers can use their harvested seed for the next year’s
crop. By 1951 the new varieties were being grown on 70 per cent of the total
wheatland and, five years later, Mexico was producing over a million tons of wheat,
with an average national yield of 1300kg/ha. Imports of foreign wheat were no
longer required.
The next step in the wheat programme was to improve yields through greater
use of fertilizers. Experiments on properly irrigated soils showed that 140kg/ha of