It is a little effort to highlight the problems which a breeder may face during tomato hybrid seed production.

2. IMPEDIMENTS IN HYBRID SEED PRODUCTION
OF TOMATO
BY
MUHAMMAD YASIR SALEEM
M.SC. (HONS.) P.B.G
2017-AG-163
2017-2019
SUPERVISOR
DR. AMIR SHAKEEL
DEPARTMENT OF PLANT BREEDING & GENETICS
FACULTY OF AGRICULTURE
UAF

3. Contents
1. Introduction
2. History
3. Exploitation of heterosis in tomato (Hybridization)
4. Factors which affect hybrid tomato seed production
i. Effect of temperature, moisture and photoperiodism
ii. Effects during pollination
iii. Effects due to pollen carrying insects
iv. Limitations in utilizing male sterility
v. Labor costs
vi. Other problems
5. Conclusion

4. INTRODUCTION
English Name Tomato
Botanical Name Solanum lycoperscium L.
(formerly Lycopersicon esculentum L.)
Chromosome Number 2n=2x= 24
Family Solanaceae (Nightshade)
Centre of Origin South America (Mexico City)
Introduced in Subcontinent 19th century by Britishers

5.  Tomato belongs to the Solanaceae family, which includes ≈ 3000 species
including potato, eggplant and pepper (Knapp, 2002; Wang et al., 2005, He
et al., 2003).
 It is second-most important vegetable crop after potato (FAO, 2016).
 Tomato was globally cultivated on an acreage of 4.79 million hectares
overall production of 176.82 million tons (FAO, 2016).
 China was the leading producer followed by India and USA (FAO, 2016).
 In Pakistan tomato was cultivated on 0.06 million hectares with production
of 0.58 million tons (FAO, 2016).

6.  In 2017 Pakistan imported improved tomato seed costing PRs. 300 million with
an increase of 10 percent (Syed, 2017).

7. HISTORY
 Phylogenetic classification of the Solanaceae has been recently revised and the
genus Lycopersicon is re-integrated into Solanum which includes ≈1500 species
(Hunziker, 1979; Spooner et al., 1993; Bohs and Olmstead, 1997; Olmstead and
Palmer, 1997; Knapp, 2002; Spooner et al., 2005, 2003; Peralta et al., 2008).
 Solanum section Lycopersicon includes the cultivated tomato (S. lycopersicum)
in addition to 12 wild relatives (Peralta et al., 2006; Peralta et al. 2008;
Rodriguez et al., 2009).
 Tomatoes were domesticated in America; though, the original site was doubtful
(Peralta and Spooner, 2007).
 However it is believed that tomatoes are native to South America [Mexico City]
(Bergougnoux, 2014).

8. EXPLOITATION OF HETEROSIS IN TOMATO (HYBRIDIZATION)
 Wild tomatoes have large genetic diversity, especially within the self-incompatible
section (Rick, 1988).
 In single accession of self-incompatible tomato species, more variation was present
as compare to all self-compatible species (Miller and Tanksley, 1990; Breto´ et al.,
1993; Sacks et al., 1997; Villand et al., 1998; Egashira et al., 2000).
 Genetic variation from wild species, for specific traits, was utilized in tomato
breeding (Walter, 1967; Rick and Chetelat, 1995; Larry and Joanne, 2007).
 F1 varieties of many horticultural crops were pioneered by Japanese in 1930’s-40’s
(Yamashita, 1973) and first 'Single Cross' hybrid tomato cultivar was released in
1946 (Dorst, 1946; Liedle and Anderson, 1993).

9. Continue…….
 F1 hybrid tomato cultivars are now one of the most popular vegetable crops
worldwide (Tay, 2002).
 Increasing trend in the adoption of hybrid seed technology in vegetables was
seen like in tomato 40% (Sudha et al., 2006).

10. FACTORS WHICH AFFECT HYBRID TOMATO SEED
PRODUCTION
(i) Effects of temperature, moisture and photoperiodism
 In tomato temperature severely effect critical growth stages, i.e., the seed filling
and developmental stage (Kameswara Rao and Jackson, 1996; Spears et al.,
1997; Craufurd et al., 2002; Thomas et al., 2003; Greven et al., 2004; Demir et
al., 2004).
 A plant growing at 16°C produces four times more flowers than a plant growing
at 24°C, whereas below 10°C, causes premature flower abscission (OECD, 2017).
 Flower opening is also temperature dependent. Longer flowering periods occur at
lower temperatures (Henry, 1952).
 Above 32/26°C during day/night, pollen viability and number reduces.

11. Continue…….
 Temperature alters carbohydrate metabolism during anther development
(Pressman et al., 2002; Firon et al., 2006).
 High temperature cause various undesirable effects such as low pollen fertility,
poor fruit set or necrosis (Soost, 1959; Laterrot, 1973; Philouze, 1976;
Lapushner and Frankel,1979).
 Temperature is also known to affect the pollen tube growth (Levin, 1996).
 Extremely poor pollen germination occurs at both 10° and 38 °C. Optimum
germination is between 21°-27 °C (Henry, 1952).

12. Continue…….
 Occurrence of low quality seed was more prominent particularly when high
temperature was combined with high humidity (TeKrony et al., 1980).
 Air humidity less than 55% and greater than 70% affects the pollen production
and pollination, and more than 60% during fruit development increases the
chance of disease infestation (OECD, 2017).
 Photoperiodism of less than 12 hours or more than 14 hours effect tomato fruit
setting (Nightingale, 1927; Nightingale et al., 1928).

13. (ii) Effects during pollination
 Currently, most of the hybrid tomato seed is produced manually.
 Fruit set highly dependents upon gap between emasculation and hand pollination
(Daskaloff, 1937).
 Fruits from immediate pollinations were smaller and contained less seed (Henry, 1952).
 Another challenges is to avoid self-pollination of the female-parental line to ensure
high genetic purity of produced hybrid (Singh, 2001).
 Lack of male/female flower nick is a common problem that’s why pollen parent is sown
and transplanted 10 days earlier to get sufficient amount of pollen (Watkins, 1998).
 Pollen source impurity is also a problem (Liu et al., 2007).

14. (iii) Effects due to pollen carrying insects
 Complex interaction was seen between tomato flowers and pollinators (Levin
1971; Bertin and Peters 1992; Grant 1994).
 In tomato, flower/pollinator interaction exists (but minute) [Levin 1971; Bertin
and Peters 1992; Grant 1994].
 Pollen-collecting bees tend to work the male-fertile inbreds and spend little time
on male sterile plants (Riggs, 1988).
 There is also sometimes a tendency for insects to stay on the inbred on which
they first alighted (Riggs, 1988).

15. (iv) Limitation in utilizing Male Sterility
 In general, male sterile plants are morphologically not easily distinguishable from
the sister fertile plants (Sawhney, 1997).
GMS:
 As tomato is a highly self pollinated crop, free out crossing is prohibitive, thus
leading to poor seed and/or fruit set (Dhall, 2010).
CMS:
 Cytoplasmic male sterility can be utilized for producing hybrid seeds in those
vegetables where the vegetative part is of economic value so it is of no use in
tomato because the hybrid progeny will be male sterile (Dhall, 2010).
CGMS:
 CGMS system in tomato is derived from sterile cytoplasm of S. peruvianum
(Petrova et al., 1999). However, the practical utility of these CGMS lines depend
upon the identification of restorer genes in tomato clade (Dhall, 2010).

16. (v) Labor Costs
 It is generally perceived that hybrid technology is costly and need high skill.
 The production process is complex and relies upon intensive manual labor for
emasculation and hybridization of individual flowers (Benziger, 1996; Rosset et
al., 1999; Sudha et al., 2006).
 In tomato hybrid seed production, labor expenditure for manual emasculation
process is about 40% of the total expenditure (Yordanov, 1983).
 Likewise, expenditure for manual pollination is also a considerable amount
because of lesser insect pollinators (Kumar et al., 2002).
 The necessity of hand pollination makes the production of first generation hybrid
tomato seed a costly enterprise.

17. Continue…….
 Failures of fruit set and seed development in artificially pollinated tomatoes are
also two contributing causes for the increased cost of F1 seed (Henry, 1952).
 Another problem of seed production in hybrid cultivars, relate to the inbreeding
necessary to produce parent lines (Wills and North, 1977).

18. (vi) Other problems
 To a smaller extent seed weight is influenced by the mode of pollination and
competition effects (Hatcher, 1940; Pet and Garretsen, 1983).
 Although not only environmental factors, harvest time is known to be a major
factor responsible for physiological maturation level, size and quality of seed
(Delouche, 1980).
 Fresh hybrid seed has to be produced every year.
 Male sterility exists but not very popular practically because of lesser data and
knowledge (OECD, 2017).
 High cost of hybrid seed because it requires technical skills for hybrid
production, rising labor costs and/or competition with manufacturing job.

19. Continue…..
 Political or trade instabilities.
 Local disease issues (bacterial, fungal and viral).
 Insect/Pest infestation (nematodes, white fly, aphids, thrips etc.).
 Cultural practices (Fertilizer, Irrigation, Soil pH etc.) also affect seed crop.
 Timing of production vs market demand.
 Lack of inputs at public sector level.
 Lack of collaboration between public and private sector.

20. CONCLUSION AND RECOMANDATIONS
 Strengthening of public sector in R&D is needed.
 Collaboration of both public and private sector help in quality vegetable seed
production.
 There should be exchange of germplasm and other inputs between public and
private sectors.
 Studies should be carried on male sterility and to identify restorer genes (Rf
factor) in order to restore CGMS.
 Insect pollinators should be provided in order to attain higher fruit set.
 Proper cultural practices should maintained.

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