This document discusses breeding for pest resistance in vegetable crops. It begins by introducing some key insect pests that damage vegetable crops and cause significant yield losses. It then covers the different mechanisms of insect resistance including nonpreference, antibiosis, tolerance and ecological resistance. The document discusses the genetics underlying insect resistance and describes different breeding methods used for developing resistant varieties like introduction, selection, hybridization and genetic engineering. It also covers techniques for screening vegetable crops for insect resistance in the field and glasshouse. Finally, the document lists some vegetable crop varieties that have been bred for resistance to important insect pests.

1. WELCOMEDar Maajid

2. Division of vegetable science
BREEDING FOR PEST STRESS MECHANISM &
GENETICS OF RESEISTANCE, SOURCES,
BREEDING METHODS AND SCREENING OF
VEGETABLE CROPS
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3. Submitted by :- Majid Rashid
Degree programme :- Ph.D. ( Vegetable
Science)
Course title :- Advances in vegetable
breeding
Course no. :- VSC-602
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4. Introduction
 All crops are attacked by insects, but the degree of damage to as
well as the number of insect species attacking different crops
vary considerably.
 Insect pests on an average cause 25-30% yield loss in vegetables.
On the basis of host range, insects may be :-
 Monophagous:- narrow host range, Hypothenemus hampei
(Coffee berry borer).
 Polyphagous:- broad host range i.e., feed on several crop
species, e.g., Helicoverpa, Red cotton bug.
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5. Yield losses due to major insect pests in vegetables in India
Crop Pest Yield loss (%)
Tomato Fruit borer (Helicoverpa armigera) 24-65
Brinjal Fruit and shoot borer (Leucinodes orbonalis) 11-93
Chilli
Thrips (Scirothrips dorsalis) 12-90
Mites (Polyphagotarsonemus latus) 34
Okra
Fruit borer (H. armigera) 22
Leafhopper (Amrasca biguttula biguttula) 54-66
Whitefly (Bemisia tabaci) 54
Shoot and fruit borer (Earias vittella) 23-54
Cabbage
DBM (Plutella xylostella) 17-99
Cabbage caterpillar (Peiris brasicae) 69
Cabbage borer (Hellula undalis) 30-58
Muskmelon Fruitfly (Bactrocera cucurbitae) 76-100
Shivalingaswamy et al., 2002
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6. Methods of insect control
Biological method
By the use
of
Predators
and
Parasites
of Insects
By using botanical
pesticides such as
neem, Datura
Ipomea in the form
of leaf extracts
Use of
R
e
si
st
a
n
t
v
a
ri
et
ie
s
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7. Chemical Method
• Reduces population of
natural enemies
• Leads to development
of pesticide-resistant
biotypes of insects
• Pollutes environment.
Chemical control
will effectively
control, or even
eliminate insect
pests. But extensive
pesticide application
will:-
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8.  PEST MANAGEMENT:- involves ,in addition to pesticide
application, several divergent measures to minimise the losses
due to insect pests. Insect resistant varieties form an important
component of pest management.
 Maxwell (1972) has defined insect resistance as “those
heritable characteristics possessed by the plant, which influence
the ultimate degree of damage done by insects”.
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9. Losses due to insects
 On the basis of mode of feeding, insect pests can be divided into
two groups:-
i. Sucking pests:- e.g., aphids, jassids, thrips, whitefly etc.
ii. Tissue feeders:- e.g., stem or shoot borers, root borers, fruit
borers etc.
 Insect infestation can lead to Direct or Indirect damages.
i. Direct damage :- reduced plant growth, damage to leaf, stem,
branch etc. premature defoliation and wilting of plants.
ii. Indirect damage :- caused by aphids, mites, whitefly etc.,
transmit plant viruses, i.e., serve as vectors of pathogens.
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10. Aphids Fruit and shoot borer
White fly
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11. DEGREE OF RESISTANCE
•Immunity
•High resistance
•Low resistance
•Susceptibility
•High Susceptibility
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12. Immunity describes a host-insect relationship in
which the insect will not consume the plant under any
condition.
In high level of resistance, the host plant possesses
such traits that result in a small level of damage by a
specific insect under a given environment.
In low level of resistance, host suffers less than
average damage by an insect .
In susceptible response, the level of damage or
infestation is average or more than average.
In case of high susceptibility, level of damage is
much greater than the average for the crop.Dar Maajid

13. Mechanism of Insect Resistance
ToleranceAntibiosis
Ecological
Resistance
Nonpreference
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14. 1. Nonpreference/ Antixenosis
 Host varieties are unattractive or unsuitable for colonization,
oviposition or both by an insect pest.
 Includes hairiness, leaf angle, colour, taste & odour.
Crop Non preference
mechanism
Insect pest
Pea Yellow leaves Pea aphid
Brassica Low sinigrin Cabbage aphid
Potato Unfavourable odour Potato beetle
Soybean Hairiness Potato leaf
hopper
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15. 2. Antibiosis
 Adverse effect of feeding on a resistant host plant on the
development and/or reproduction of the insect pest.
 May involve morphological, physiological or biochemical
features of the host plant or, in some cases, combination of these
features.
Host crop Insect- pest Mechanism of Antibiosis
Potato Aphid Gummy trichome
exudates
Pea Aphid Low amino acid
Carrot Dacus dorsalis Lack of thiamine
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16. 3. Tolerance
 An insect tolerant variety is attacked by the insect pest to the
same degree as a susceptible variety, but at the same level of
infestation, a tolerant variety produces a larger yield than a
susceptible variety.
 In some cases, tolerant varieties show greater recovery from pest
damage than do susceptible varieties.
 Tolerance may also be due to the ability of host to suffer less
damage by the pest, e.g. aphid tolerance in Brassica spp.
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17. 4.Ecological Resistance
 Also called as apparent resistance or pseudo-resistance.
 Results from some temporary shifts in the environmental conditions
that enable a susceptible host to suffer less damage or escape insect
infestation.
 Escape of variety from insect attack results due to earliness or its
cultivation in the insect free or low insect populated area e.g. seed plot
technique in potato to avoid aphid infestation.
 Some environmental conditions may induce transient insect resistance
in otherwise susceptible strains of host e.g higher level of N decreases
while higher level of K application increases resistance of plants to
aphids (Induced resistance).
 The protein harpin binds specific receptors of host plants, which
activates natural defences of host. It protects the plants from insects,
mites and nematodes as well.
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18. Nature of Insect Resistance
Morphological features
 Hairiness:- Hairiness of leaves
is associated with resistance to
many insect pests e.g. in turnip
to turnip aphid.
 Colour of plant:- Plant colour
may contribute to nonpreference
in some cases e.g red cabbage
and red leaved brussel sprouts
are less favoured than green
varieties by butterflies and
certain other Lepidoptera for
oviposition.
Physiological factors
 Various physiological factors
e.g. osmotic concentration of
cell sap, various exudates are
associated with insect
resistance. Leaf hairs of some
Solanum species secrete
gummy exudates, aphids and
colorado beetles get trapped in
these exudates and are unable
to feed and reproduce.
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19. Biochemical factors
 Allelochemicals; Allelochemicals are natural chemicals mainly present in
higher plants that act as antinutritional, pest and disease-resistance factors
 The chemical substances responsible for plant resistance to insect pests can be
classified into three categories: substances that act on pest behavior
(glycosides, alkaloids, terpenes, phenols and essential oils); those that act on
pest metabolism, such as secondary metabolites (including some alkaloids
and quinones); and antimetabolites, which make essential nutrients
unavailable to pests, causing nutritional imbalances.
 The most important allelochemicals found in wild tomato species are acyl
sugars, sesquiterpenes and methyl ketones.
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20. Genetics of Insect Resistance
PlasmagenesPolygenes
Oligogenes
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21. Oligogenic Resistance
 Governed by one or few major genes or oligogenes, each gene
having a large and identifiable individual effect on resistance.
 Resistance may be governed by a single gene(monogenic
resistance) e.g. in pumpkin to Fruitfly, or may be governed
by two or more oligogenes, all the genes may control a single
character of the host plant or each oligogene may govern a
different trait e.g. in lettuce to leaf aphid, in cucumber to two
spotted spider mite, in muskmelon to melon aphid, etc.
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22. Polygenic Resistance
 Governed by several genes, each gene producing a small and
usually cumulative effect.
 May involve more than one feature of the host plant, transfer of
resistance is relatively much more difficult than that of
oligogenic resistance.
E.g. in cucumber to stripped cucumber beetle, in squash to two
spotted spider mite, in Brassica spp. to aphid, etc.
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23. Cytoplasmic Resistance
 Governed by plasmagenes.
E.g. resistance to root aphid in Lettuce show
cytoplasmic inheritance in addition to the
nuclear genetic control
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24. Sources of Insect Resistance
Cultivated variety
 Resistance to insect pests may be
found in a cultivated variety having
good horticultural traits.
 E.g Pusa purple long, Azcabey,
Thorn pendy, Black pendy, Arka
mahima and Banaras long green are
resistant to Brinjal shoot and fruit
borer (Dependra and sharma, 2005)
 Caleapin red and chamatkar are
resistant to thrips while kalyanpur
red is resistant to mites and aphids in
case of chilli (Tawari et al., 1985).
Germplasm Collection
 It includes collection of germplasm,
and its evaluation and maintenance.
In case of chilli NP46A, BG-4,
X226, X230, X233, X1068 and
EC119475B are resistant to
thrips,LEC-1, S-118 and 300-1-5-1
are resistant to mites and LEC-28,
LEC-30, LEC-34 are resistant to
aphids (Tawari et al., 1985).
 H-128 and H-129 are resistant to
Brinjal shoot and fruit borer
(Dependra and sharma, 2005).
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25. Related wild species
 Cucurbita asper, C. denteri, and C.
sagittatus are resistant to whitefly in
case of muskmelon (Naidu et al.,
2006).
 Some accessions of Lycopersicon
pennelli are resistant to several
important pests of cultivated tomato
(Mutschler et al., 1996).
 Clone selected from the wild diploid
species Solanum berthaultii have
been shown to possess useful levels
of resistance to the Colorado potato
beetle as well as to the insects such
as aphids, flea beetles, leafhoppers
and potato tuber moth (Plaisted et
al., 1992).
An unrelated organism
 A gene conferring insect
resistance may be transferred
from an unrelated organism into
plants by recombinant DNA
technology.
 Cry gene , encoding crystal
protein of Bacillus thuringiensis.
Other genes of importance are the
protease inhibitor encoding genes
found in many plants e.g cowpea
trypsin inhibitor (CpTI) gene.
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26. Breeding Methods for Insect Resistance
HybridizationSelection
Genetic
Engineering
Introduction
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27. 1) Introduction:- Bringing insect resistant genotype or a group of
genotypes of plants into new environment. Thus it is the quickest
and perhaps the easiest method of developing an insect resistant
variety.
1) Selection:- Insect resistant variants may be present in an existing
variety of a crop. In such a case selection for insect resistance may
result in an insect resistant version of the variety. In self pollinated
crops, generally Pureline selection is used for the purpose while
mass selection or more often recurrent selection is employed in
cross pollinated crops. For example, selection for resistance to
potato leaf hopper and spotted alfalfa aphid in two broad based
germplasm of alfalfa was highly effective in both the populations.
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28. 3) Hybridization:- Agronomically inferior variety(insect resistant sp.)
is crossed with an agronomically superior, but insect pest
susceptible, variety of crop to develop superior, insect resistant
variety. Backcross method of breeding is usually used when the
gene for resistance is present in related wild species which is
agronomically undesirable. In general 5-6 backcrosses are necessary
to recover the genotype of the recurrent parent. In addition Marker
Assisted Selection may be used to facilitate gene transfer and to
reduce the required number of backcrosses to 2 to 3.
4) Genetic engineering:- Genes conferring insect resistance in plants
have been transferred from B. thuringiensis (cry gene) and from
other plants through genetic engineering. The cry gene transfers are
the most successful and insect resistant transgenic varieties of
cotton, maize, Brinjal, etc expressing this gene are being cultivated
in U.S.A. and other countries. Transgenic broccoli plants expressing
Bt toxins confers resistant against DBM.Dar Maajid

29. Screening Techniques
Most difficult task in breeding for insect resistance is identification of
insect resistant plants during segregating generations. Screening for
insect resistance may be done either
In the field In Glasshouse
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30.  In field screening, large number of plants can be screened in field.
In field conditions the plants are exposed to other insect pests
prevalent in the area thus reducing the unintended selection for
susceptibility to them.
The various techniques designed to promote uniform infestation by an
insect pest in the field are as follows:-
 In case of air dispersed insect pests, planting of one row of a known
susceptible variety between two rows of the test material should be
done.
 Screening for resistance to a given pest should be done in an area
where it is prevalent.
 In case of soil insect pests, the plant material being tested should be
planted in such a field that is known to contain a large population of
the concerned pest.
 Screening for resistance to a given pest should be done in a particular
season in which there is occurrence of heavy natural infestation.
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31.  In Glasshouse screening, smaller number of plants can be
screened than in the field, & the results from glasshouse tests
are much more reliable than those from field tests since both the
environment and the initial level of infestation can be kept more
or less uniform for all the test plants.
 In some cases, seedlings grown in the seed boxes are infested by
the concerned pest, resistant seedlings are identified and
transferred to pots. After a period of recovery the plants are
reinfested by the concerned pest and further selection is made for
resistance. This technique has been used for many insects e.g.
screening of alfalfa for resistance to spotted alfalfa aphid.
 It may be pointed out that field and glasshouse screening are
complementary to each other.Dar Maajid

32. Pest tolerant varieties of some vegetable crops
Crop Variety Breeding Method Pest
Tomato Arka Vikas Selection Fruit borer
Pusa early dwarf Hybridization
Onion Arka Lalima Hybridization Thrips
Chilli Pusa Jawala Hybridization Thrips, mites and
aphids
Okra Pusa A4 Hybridization Jassids, fruit and shoot
borer
Pumpkin Arka suryamukhi Pureline Selection Fruit fly
Tapioca Co 1 Selection Scale insects
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33. Advantages of Insect Resistance
Insect resistant crop varieties provide an
inherent means of insect control, which does not
involve any recurring expenditure.
In contrast to chemical control, it does not pose
any hazard to environment.
Its effectiveness is not ordinarily affected by the
environment.
This is the only economically feasible means of
insect control in low value crops, in developing
countries and at low insect densities
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34. Problems in Breeding for Insect Resistance
Breeding for resistance to one insect leads to susceptibility to
another pest, thus reducing the quality of produce or may
even make it unfit for consumption.
Long term programme, requiring adequate financing over a
long period of time.
Depends on detailed knowledge of biology, feeding habits and
population dynamics of insect pests.
Screening requires close association between the breeder,
entomologist, pathologist, biochemists, physiologists etc.
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35. Thank you
stay home
stay safe
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