Agriculture Reference
In-Depth Information
~1700
~1732
1799 811 8211825 838
1846<1850
1854
1857 1861
1868
1876
1880
<18881890 895190319051910
1720
1785
<1814
1824 1827
1842
≤
1849
1851
1856 1859
1867
1874
1878
1882
1889
1892
<1904
1908
Before the late blight epidemics
Andean cytoplasm
Chilean cytoplasm
Fig. 1.4.
Composition of potato cytoplasm based on DNA extraction of dried foliage of herbarium
specimens. (From Ames and Spooner, 2008; reproduced with permission from the
American Journal of Botany
.)
For many decades, private breeders had
sought to produce commercial blight-resistant
varieties. The Mexican specimens at the botanic
garden were a source of resistance; it was also
the beginning of publicly funded research pro-
grams for the breeding of new varieties of crop
species. Over the next
40
years, numerous blight-
resistant varieties were developed, by introducing
genes from
S. demissum
.
Crop geneticists also began to examine the
idea of returning to the center of origin of crops.
Returning to these locations and collecting crop
specimens was a positive and successful way to
expand the gene pool and introduce new var-
ieties with unique traits.
Resistances to
Potato virus Y
, PVX, and
Glo-
bodera
(Cyst nematode spp.) were found first in
collections of wild and primitive cultivar potato
taken to home countries and maintained as
collections (Ellenby, 1948; Ross, 1954, 1958, 1986).
Meanwhile, comprehensive taxonomic treatments
were emerging, due to the efforts of Americans,
Europeans, and South Americans.
The incorporation of traits from wild species
became a large component of most national
breeding and genetic programs (Ellenby, 1948;
Ross, 1954, 1958, 1986). Two reviews of resist-
ance breeding in potato by Jansky (2000) and
Pavek and Corsini (2001) provide a thorough
overview of active research fields, while numer-
ous instances of exotic ancestry in modern var-
ieties are noted by Plaisted and Hoopes (1989).
Breeding programs initially bred potatoes
towards modern needs, resulting in taming the
extravaganza of shapes in native varieties.
Similarly, the number and depth of each potato
eye was selected through breeding. The native
varieties in South America were selected in a cul-
tural context that valued diversity and eccentri-
city over convenience. The modern-bred var-
ieties are devised for an industrialized society
where ease of peeling reigns, and a controlled
size and shape is packed easily in boxes, stored,
and transported to consumers.
Douches
et al
. (1996) compared groups of
old, intermediate and modern breeds in agro-
nomic trials. First, improvement in total yield,
comparing the old to the intermediate and mod-
ern varieties, was not seen. This could be attributed
to genetic impoverishment of the breeding pool.
Alternatively, the number of traits that required
optimal performance as the potato went from a
household-prepared item to factory processed
were more important than yield itself. Yet im-
provement in overall appearance, depth of eye,
and common scab resistance was found. Extreme
pressure for higher solids achieved a high spe-
cific gravity.
The necessity for a specific variety to store
well for long periods without a rise in reducing
sugars means superior performance in yield, or a
percentage of large tuber sizes might not be se-
lected for. Tuber appearance has improved signifi-
cantly, because a uniform shallow-eyed tuber is
best for mechanical peeling, used in manufacturing
1.3 Botanical Collections
and Breeding Research
The plant collector, George Bitter, was among
the first to travel to South America, although he
was not deeply influential on potato taxonomy
(Bitter, 1912). Potato and wild potato biosys-
tematics began to take shape, with expeditions to
South America by Russian and British plant col-
lectors (Jucepczuk and Bukasov, 1929; Bukasov,
1933; Hawkes, 1941, 1990). Additional exped-
itions undertook surveys of wild potato species
that were resistant to disease and pests, which
yielded immediate results and contributed to the
publication of taxonomic compendia (Hawkes
and Hjerting, 1969; Ochoa, 1990, 1999).
