| dc.description.abstract | Abiotic and biotic stresses are major constraints of vegetable production in the tropics
and climate change is expected to aggravate these problems. Depending upon the crop, the
combined effects of multiple stresses may reduce total yield, reduce product quality,
increase postharvest losses, and alter nutrient content. Consequently, vegetable varieties for
the tropics should possess tolerance to heat, salinity, and other abiotic stresses, carry an
array of disease and insect resistances, and still produce high yields of good quality produce
that meet market requirements. Meeting this challenge requires robust protocols to screen
and identify useful alleles from exotic germplasm and efficient selection methods to
facilitate incorporation of multiple stress-tolerance genes into new varieties. Development
of tropically adapted varieties of tomato (Solanum lycopersicum L.) and pepper (Capsicum
annuum) is a high priority at AVRDC – The World Vegetable Center. Tomato production in
the tropics has been devastated by increased incidence and severity of tomato yellow leaf
curl diseases (TYLCD) caused by whitefly-vectored begomoviruses. Development of
resistant varieties is complicated because the pathogen is highly diverse and almost all
TYLCD resistance genes originated from wild tomato species. Application of
marker-assisted selection (MAS) by AVRDC has facilitated development of tomato varieties
homozygous for multiple begomovirus resistance genes that are expected to offer higher
levels of resistance to a wider range of begomoviruses. Most modern tomato varieties are sensitive to heat, drought, and salinity, but sources of stress tolerance have been found
mainly in wild tomato accessions. AVRDC uses a multidisciplinary approach to map genes
conditioning heat, drought, and salinity tolerance in tomato and to identify markers linked to
targeted genes to facilitate gene introgression. Sweet pepper is a high value crop but
sensitive to heat. AVRDC’s strategy to develop a tropical sweet pepper emphasizes the
evaluation of sweet pepper lines under Taiwan summer stress (high temperatures and
humidity) for yield components (fruit number, fruit weight) and traits linked to heat stress
adaptation (pollen viability, root mass, vegetative biomass). Lines performing well for
different components or traits have been identified and our hypothesis is that crossing lines
with complementary traits and selection will lead to new lines with improved levels of heat
tolerance. Breeding varieties adapted to climate change will shift more attention toward
breeding for tolerance to abiotic stresses, which are often genetically and physiologically
complex. Manipulation of multiple genes and traits will complicate vegetable breeding and
will require effective use of conventional breeding techniques and molecular markers
involving multidisciplinary teams. | en_US |
