**4. Some examples of exploiting genetic diversity through traditional breeding**

Above mentioned genetic diversity, preserved in germplasm collections worldwide, are the golden resources to genetically improve the cotton cultivars. There are numerous examples on the utilization of such genetic variations in solving many fundamental problems in cotton breeding and production (Abdurakhmonov, 2007). For instance, the exploration for genetic diversity for *Verticillium* wilt fungi from the exotic *G. hirsutum ssp mexicanum var nervosum* germplasm and its on-time mobilization into the elite cultivars solved wilt epidemics in 1960's and saved Uzbekistan's cotton production, and so the economy of the country (Abdullaev et al., 2009). As a result, the wilt resistant variety series named as "Tashkent" were developed (Abdukarimov et al., 2003; Abdurakhmonov, 2007). Later, salt tolerant genotype AN-Boyovut-2 was selected from Tashkent cultivar biotypes demonstrating a continuation of a 'genetic diversity imprint' introgressed from the wild landrace stock (Abdukarimov et al., 2003). This is one of the success stories on exploiting genetic diversity and its impact from the single landrace stock germplasm, *G. hirsutum* ssp. mexicanum (Abdurakhmonov, 2007). A number of other examples on the creation of natural defoliation, disease and pest resistance, tolerance to multi-adversity stresses, improved seed oil content and fiber quality parameters, utilizing the exotic germplasm genetic diversity in Uzbekistan have been well documented (Abdukarimov et al., 2003; Abdurakhmonov et al., 2005, 2007).

Successful photoperiodic conversion program in cotton was developed to mobilize dayneutral genes into the primitive accessions of *G. hirsutum.* Day-neutral genes were introgressed into 97 primitive cotton accessions by a large backcrossing effort (McCarty et al., 1979; McCarty & Jenkins, 1993, Liu et al., 2000). This converted cotton germplasm is an important reservoir for potential genetic diversity and can be used as a source to introgress genes into breeding germplasm (Abdurakhmonov, 2007).

Similarly, using genetic diversity existing in *Gossypium* genus, reniform nematode resistance, which is one of the high cost (\$100 million/year) problems in US cotton production, was addressed. Scientists succeeded in introgressing high resistance to the nematode from *G. longicalyx* into *G. hirsutum* through genetic bridge crossing of two trispecies hybrids of *G. hirsutum*, *G. longicalyx*, and either *G. armourianum* or *G. herbaceum* (Robinson et al., 2007). Later, a gene of interest was mapped (Dighe et al., 2010). Resistance to root-knot nematode was also solved with the use of genetic diversity in *Gossypium* genomes (Roberts & Ulloa, 2010). Additionally, Hinze et al. (2011) developed four diverse populations based on US germplasm collection that helped to utilize a large amount of 'still underutilized' genetic variability in cotton breeding that should be useful in sustainable cotton production with superior quality. There are many other examples recorded in different cotton breeding programs, but we limit this section with above examples and move to address the challenges behind these success stories and future perspectives in this direction.

1-9 grams per boll, 1000 seed mass varies in a range of 50-170 grams, the lint percentage varies in a range of 0-45%, Micronaire varies in a range of 3-7 mic, the fiber length varies in a range of 1-1.28 inch, and fiber strength varies in a range of 26-36 g/tex. There was also a wide range of variation in photoperiodic flowering (day neutral, weak to strong photoperiodic dependency) and maturity (Abdurakhmonov, 2007). This wide phenotypic diversity of cotton shows the extensive plasticity of cotton plants and potential of their wide

**4. Some examples of exploiting genetic diversity through traditional breeding**  Above mentioned genetic diversity, preserved in germplasm collections worldwide, are the golden resources to genetically improve the cotton cultivars. There are numerous examples on the utilization of such genetic variations in solving many fundamental problems in cotton breeding and production (Abdurakhmonov, 2007). For instance, the exploration for genetic diversity for *Verticillium* wilt fungi from the exotic *G. hirsutum ssp mexicanum var nervosum* germplasm and its on-time mobilization into the elite cultivars solved wilt epidemics in 1960's and saved Uzbekistan's cotton production, and so the economy of the country (Abdullaev et al., 2009). As a result, the wilt resistant variety series named as "Tashkent" were developed (Abdukarimov et al., 2003; Abdurakhmonov, 2007). Later, salt tolerant genotype AN-Boyovut-2 was selected from Tashkent cultivar biotypes demonstrating a continuation of a 'genetic diversity imprint' introgressed from the wild landrace stock (Abdukarimov et al., 2003). This is one of the success stories on exploiting genetic diversity and its impact from the single landrace stock germplasm, *G. hirsutum* ssp. mexicanum (Abdurakhmonov, 2007). A number of other examples on the creation of natural defoliation, disease and pest resistance, tolerance to multi-adversity stresses, improved seed oil content and fiber quality parameters, utilizing the exotic germplasm genetic diversity in Uzbekistan have been well documented (Abdukarimov

Successful photoperiodic conversion program in cotton was developed to mobilize dayneutral genes into the primitive accessions of *G. hirsutum.* Day-neutral genes were introgressed into 97 primitive cotton accessions by a large backcrossing effort (McCarty et al., 1979; McCarty & Jenkins, 1993, Liu et al., 2000). This converted cotton germplasm is an important reservoir for potential genetic diversity and can be used as a source to introgress

Similarly, using genetic diversity existing in *Gossypium* genus, reniform nematode resistance, which is one of the high cost (\$100 million/year) problems in US cotton production, was addressed. Scientists succeeded in introgressing high resistance to the nematode from *G. longicalyx* into *G. hirsutum* through genetic bridge crossing of two trispecies hybrids of *G. hirsutum*, *G. longicalyx*, and either *G. armourianum* or *G. herbaceum* (Robinson et al., 2007). Later, a gene of interest was mapped (Dighe et al., 2010). Resistance to root-knot nematode was also solved with the use of genetic diversity in *Gossypium* genomes (Roberts & Ulloa, 2010). Additionally, Hinze et al. (2011) developed four diverse populations based on US germplasm collection that helped to utilize a large amount of 'still underutilized' genetic variability in cotton breeding that should be useful in sustainable cotton production with superior quality. There are many other examples recorded in different cotton breeding programs, but we limit this section with above examples and move to address the challenges behind these success

utilization in the breeding programs as an initial material.

et al., 2003; Abdurakhmonov et al., 2005, 2007).

stories and future perspectives in this direction.

genes into breeding germplasm (Abdurakhmonov, 2007).

Fig. 1. Morphological trait diversity: (A)-pollen color, petal color and spot; (B)-matured bolls in diploid species, and (C)-matured bolls in tetraploid species.

Fig. 2. Diversity on several morphological traits in exotic and cultivar germplasm of *G. hirsutum* accessions from Uzbekistan cotton collection (Abdurakhmonov et al., 2004, 2006).

Fig. 2. Diversity on several morphological traits in exotic and cultivar germplasm of *G. hirsutum* accessions from Uzbekistan cotton collection (Abdurakhmonov et al., 2004, 2006).
