294 V. Selvanarayanan
Introduction
Since the advent of intensive agriculture, explo-
ration for pest-resistant crop cultivars and their
widespread exploitation is continually practiced.
Though successful initially, those crop cultivars
lost their glory later due to selection pressure
by the target pest as well as other factors. Con-
ventional breeding methods for exploitation of
insect-resistant traits have earlier yielded prom-
ising cultivars. Due to practical limitations such
as time and manpower requirements and cost
considerations, such methods are in wane paving
way for novel molecular approaches. This is evi-
denced by a brief perusal of the papers published
in the Annual Reviews of Entomology since
2000, wherein a major proportion of the papers
related to host plant resistance was focused on
genetically modified crops or on molecular bases
of plant resistance. Though many molecular tech-
niques are available, the field success of outputs
is less validated. Further, genetically modified
food crops still faces the consumerist enigma,
warranting for more detailed safety studies. The
success of pest resilient cultivars depend on fac-
tors including preference by the growers based
on better yield and economic parameters and
preference by the consumers based on organo-
leptic characters. This chapter highlights insect
resistance in huge germplasm of tomato, the
paradigm shifts in research approaches, attempts,
and the results therein.
Insect Resistance in Tomato
Germplasm
Tomato ( Lycopersicon esculentum Mill.), an
important vegetable is commercially cultivated
throughout the world both for fresh consump-
tion and processing industries. In India, among
the insect pests damaging tomato, the fruitworm,
Helicoverpa armigera Hubner (Lepidoptera:
Noctuidae) is a polyphagous, widely distributed
insect pest inflicting heavy loss. Its young larvae
feed on leaves or flowers, while matured instars
bore into the fruits. Occasionally, vine boring is
also witnessed (Gopalakrishnan 2006 ). Among
the other insect pests, whitefly, Bemisia tabaci
Gennadius (Hemiptera: Aleyrodidae) is also pre-
dominant in India. Besides desapping and reduc-
ing the vigor of plants, it also vectors leaf curl
disease. In addition to these two insect pests, leaf
caterpillar, Spodoptera litura Fabricius (Lepidop-
tera: Noctuidae) and serpentine leaf miner, Liri-
omyza trifolii Blan. (Diptera: Agromyzidae) are
also commonly infesting tomato. Dependence on
chemical insecticides for managing these insect
pests is discouraged and warrants for exploration
of insect tolerant or resistant tomatoes.
The gene pool of tomato ( Lycopersicon spp.)
is diverse and offers an ample scope for exploita-
tion and utilization in pest and disease resistance.
Resistance to 16 pest species has been reported
in accessions of wild lines such as Lycopersicon
hirsutum f. typicum and L. hirsutum f. glabra-
tum (Dimock 1981 ; Dimock and Kennedy 1983 ;
Kauffman 1987 ). Both physical (Gentile et al.
1969 ) and chemical (Williams et al. 1980 ) factors
have been reported in these accessions where in
the trichome mediated resistance playing a major
role. Other physical and chemical factors asso-
ciated with the leaf lamella were also reported
earlier (Quiros et al. 1977 ; Elliger et al. 1981 ).
Host plant resistance in tomato against H. armi-
gera, B. tabaci and other pests has been widely
explored and exploited. Reports on resistance of
tomatoes against key insect pests are listed below
(Table 1 to 6 ).Evaluation of Insect Resistance in
Tomato Germplasm
Considering the above, a huge tomato germ-
plasm comprising 321 accessions were gathered
from various sources. This germplasm included
few wild species, land races, hybrids, and many
cultivars (89 % cultivated species, L. esculentum,
10 % wild relative, L. pimpinellifolium and 1 %
suspected cross of this two). These accessions
were screened for resistance against H. armig-
era, both under field and glasshouse conditions at
Annamalai Nagar, Tamil Nadu, India from 1998
to 2000. In the field screening, larval population
and fruit damage was recorded while in the glass-