Agriculture Reference
In-Depth Information
have been documented as salt tolerant by several investigators (Fredrickson and
Epstein
1975
; Cuartero et al.
1992
). Several salt tolerant tomato lines have been
developed through inter-specific hybridization and backcrossing between cultivated
tomato and these species (Rush and Epstein
1981
). Additionally, some salt-tolerant
tomato lines have been selected from open-pollinated cultivars over multiple gen-
erations of production under saline conditions (Shannon
1997
). Recently, candidate
genes and QTL (quantitative trait loci) for salt tolerance traits at the seedling and
vegetative stages have been discovered (Foolad
2004
). Thus, DNA sequence data
may be useful for marker-assisted selection to improve the efficiency of introgress-
ing salt tolerance genes from wild species into cultivated tomato.
Peppers are frequently produced in arid regions to achieve optimum fruit quality
with minimal pests and diseases. However, soils and irrigation water are frequently
saline. Salt tolerance in cultivated pepper,
C. annuum
, is considered moderate, but
variation for this trait exists within the germplasm. Aktas et al. (
2006
) screened 102
pepper germplasm accessions for salinity resistance and found 6 lines with only
slight symptoms. Further tests revealed significantly less sodium accumulation in
shoots of the 6 tolerant lines compared to 6 sensitive ones. In west Texas and New
Mexico, salinity is a constant threat to pepper production, and tolerance is a valu-
able attribute within the germplasm. In another experiment, 20 diverse pepper lines
of
C. annuum
and
C. chinense
were irrigated with a saline solution in pots for 4
weeks as a rapid screen for salt tolerance. Shoot dry weights were not significantly
reduced compared to control plants for 6 of the 20 entries and final height was not
significantly reduced for half of the entries (Niu et al.
2010
). Total plant survival of
several entries was also 100 %, while the most salt-sensitive entries had between 33
and 0 % survival. The most salt tolerant entry, 'AZ 20,' was selected in Arizona and
New Mexico, under conditions of high salts in both irrigation water and field soils.
In addition to breeding salinity problems can be overcome by different conventional
ways as reviewed by Plaut et al. (
2013
).
Breeding for Cold Tolerance
Open-field vegetable production is often subject to extreme temperatures which can
inhibit growth, reduce quality and even destroy crops. Tolerance to low and high
temperatures is determined by species adaptation, plant health and genetics. Breed-
ing for cold and heat tolerance has been successful in both vegetable and agronomic
crops to a limited extent. Tropical origin crops such as cucurbits, peppers, tomatoes
and beans have almost no resistance to freezing or frost conditions. By contrast,
onions, brassicas, spinach and carrots can withstand periods of exposure to sub 0 °C
temperatures. Within species, progress has been made to select cultivars with great-
er degrees of cold tolerance, even for some tropical vegetables. In onions, Japanese
germplasm has been utilized for its inherent cold tolerance, compared to other short
day onions. Many of the European brassicas, such as cabbage and kale have greater
tolerance to freezing conditions than East Asian brassicas. In tomato, cold tolerance
from wild species
S. hirsutum
and
S. pimpinellifolium
, has been introgressed into
