Agriculture Reference
In-Depth Information
Foolad et al.
1998
). In both of these investigations, linkages between some molecu-
lar markers and cold tolerance QTL were confirmed in the interspecific populations.
These may be useful for marker assisted selection to introgress cold tolerance traits.
The emphasis was on seedling cold tolerance as this is an issue for early planting in
many locations. Even within the
S. esculentum
germplasm, breeders have exploited
cold tolerance traits to enhance flowering and fruit set at lower temperatures for
short season regions. Cultivars such as 'Siberia,' 'Sub-Arctic Plenty,' and 'Mani-
toba' have these attributes.
Cold tolerance in melons has been achieved through traditional breeding as well.
Hutton and Loy (
1992
) identified a cold temperature germination trait in melon
and determined that both recessive genes and a cytoplasmic factor were involved.
They successfully developed lines with this important trait for regions were di-
rect seeding into sub-optimal soil temperatures is carried out. Edelstein and Kigel
(
1990
) identified some melon accessions that are able to germinate at low (14 °C)
temperature, and also have investigated the inheritance of these traits (Edelstein
and Nerson
2009
). Another investigation into mature melon plant cold tolerance
demonstrated the positive impact of heterosis on performance traits under colder
than normal conditions. Seven open-pollinated cultivars with above average cold
tolerance were intercrossed and the F1 hybrids outperformed the parents under two
cold temperature regimes. In cultivated pepper (
C. annuum
), very little cold toler-
ance exists in commercial types. The wild chile piquin (
C. annuum
var. aviculare)
has some resistance to freezing temperatures and grows as a perennial in northern
Mexico and south Texas. It may serve as a useful source of cold tolerance genes for
breeders. The authors have conducted investigations into freezing tolerance within
interspecific families derived from
C. annuum
x
C. baccatum
crosses. The latter
species has a natural range that includes high elevations of the Andes in Bolivia and
Peru. Preliminary results have demonstrated resistance to temperatures of − 3 °C for
6 h in these lines. Backcross introgression and genetic studies of the cold tolerance
genes is underway.
Breeding for Heat Tolerance
Heat tolerance may be even more important for sustainable vegetable production,
considering that many countries within the tropics struggle with food security is-
sues. Though cucurbits, solanaceous crops and many other vegetables originated in
tropical regions, not all are capable of yielding good crops in lowland areas or in the
warmest growing periods. Adaptation to higher temperatures has occurred through
human selection, but needs continued efforts. Quality of heat tolerant cultivars is
often inferior to crops grown at optimum temperatures. Heat tolerance in tomato
has been the focus of extensive breeding efforts in Texas, Florida and Taiwan. Heat
tolerant, large fruited cultivars have been released by both Texas A&M and the Uni-
versity of Florida (Leeper and Cox
1986
; Scott et al.
2006
). High temperature pollen
stability and fruit set are traits which permit these cultivars to yield even when day
and night temperatures are high.
