Effective selection for disease resistance in segregating populations
requires accurate, cost-effective screening methods that
permit rapid testing of thousands of plants. Common disease
screening techniques include field testing under natural disease
pressure, and greenhouse/growth room screening procedures in
which plants are inoculated with specific pathogen strains. Field
screening is appropriate when the breeding is conducted in the
region where the cultivars will be released and high disease pressure
can be expected. Greenhouse seedling inoculation can assess
disease reactions quickly, reduce some sources of environmental
variation by use of characterized pathogen strains and defined
inoculum concentrations, and avoid confounding effects from other
pests or diseases. Many disease resistance genes have been mapped
in tomato, and molecular markers linked to these genes are available
for marker-assisted selection (MAS). The choice of screening
method depends upon effectiveness, availability, cost, and convenience.
Disease resistance alone is insufficient to ensure farmer
adoption; commercial cultivars also must possess high yield potential,
early maturity, and other horticultural traits, as well as fruit
quality and nutrient content. Consequently, disease resistance
breeding must be conducted with selection for important horticultural
and fruit characters.