New Horizons in Insect Science Towards Sustainable Pest Management

300 V. Selvanarayanan

selected accessions and their hybrid derivatives
were found varying (Table 10 ) (Selvanarayanan
2011 ). The major biophysical factor namely tri-
chome density and the major bio-chemical factor
namely phenol content was found varying in the
F 1 and F 2 generations. This suggested the possi-
bility of segregation of the defense traits among
the generations and hence a promising hybrid
with higher yield potential could not be devel-
oped.

Exploiting Insect Resistance in Selected

Tomato Accessions Through Backcross

Breeding

Upon realizing that the conventional hybridiza-
tion approach is proving futile in developing in-
sect tolerant/resistant tomato varieties, backcross
breeding strategy may be adopted, provided the
segregation of desirable traits is well ascertained
and exploited. The most promising insect tolerant
accession namely Varushanadu Local was back-
crossed with the most popular cultivar namely
PKM 1 (Manikandan 2012 ). The resultant F1
and the backcross progenies were evaluated for
resistance under semi-field conditions against
key insect pests. Both the selected accessions
and the hybrid derivatives varied widely among
themselves with regard to resistance potential.
Significant variation was observed in the pre-

liminary semi-field screening. The accession VL,

(PKM1 × VL) × PKM1 (BC 1 ) and (VL × PKM1)

× PKM1 (BC 1 ) recorded lesser population of

H. armigera and S. litura larvae, lesser popula-

tion of whitefly as well as lesser damage by leaf

miner (Table 11 ). Further studies on the hybrid

derivatives may unravel the nature of segregation

and stabilization of the desirable traits.

Mutation Breeding of Selected Tomato

Accessions

If the natural variability available in the germ-

plasm could not be exploited through conven-

tional breeding methods, mutation breeding may

be attempted to increase variability in morpho-

logical and physiological characters besides in-

ducing new plant ideotypes. Mutation breeding

is relatively a quicker method for crop improve-

ment and it has an added advantage over hybrid-

ization since the basic genotype of a variety is

slightly altered (Gopalakrishnan 2010 ).

Keeping the above approach in view, chemi-

cal mutagens namely Ethyl Methane Sulfonate

(EMS) and Di Ethyl Sulfate (DES) and physi-

cal mutagen namely gamma rays were used for

inducing mutation in the selected tomato acces-

sions (Gopalakrishnan 2010 ). EMS and DES

at various doses were evaluated and the LD 50

dose was fixed at the dose recording 50 % seed

Table 10 Preference of major insect pests toward selected tomato accessions and their derivatives
Accession Helicoverpa armigera (Hubner)
damage

Spodoptera litura Fab Liriomyza trifolii Blan

Foliage (%) Fruit (g) Percent leaf damage Percent infestation
Ac 238 14.54 (22.40) 3.28 99.09 (85.89) 39.90 (39.11)
Roma 14.54 (22.40) 2.53 100.00 (90.00) 31.04 (33.72)
Seijima Jeisei 12.80 (20.96) 1.82 23.63 (29.08) 39.99 (38.87)
Varushanadu Local 13.86 (21.85) 1.59 25.56 (30.35) 46.66 (43.05)
HY1F1 12.59 (20.79) 2.23 100.00 (90.00) 41.33 (39.67)
HY2F1 12.20 (20.44) 1.35 100.00 (90.00) 49.66 (44.89)
HY3F1 10.19 (18.64) 1.28 100.00 (90.00) 6.66 (14.94)
HY1F2 12.80 (20.96) 2.04 100.00 (90.00) 36.66 (36.92)
HY2F2 12.10 (20.36) 1.38 99.99 (87.87) 44.28 (41.64)
HY3F2 11.20 (19.55) 1.32 98.63 (83.45) 13.33 (13.82)
I 979 26.45 (30.96) 6.26 93.40 (75.14) 37.61 (37.46)
C.D. ( p = 0.05) 0.26 0.47 2.45 13.68
Each value is a mean of five replications
Values in parentheses are arcsine transformed