**4. Genetic diversity in soybean germplasm based on karyological traits**

Genetic diversity based on genome size among and within plant species has been well documented in the literature (Rayburn, 1990; Bennett and Leitch, 1995; Rayburn *et al*., 1997). The variation was pronounced in Chinese germplasm collected from diverse geographic locations. It was attributed to the environmental factors (Knight and Ackerly, 2002), cell size, minimum generation time, cell division rate and growth rate (Edwards and Endrizzi, 1975; Bennett *et al*., 1983) and polypoid species, in species with large seeds, and habits type (Bennett *et al*., 1998; Chung *et al*., 1998).

Reports of genome size variation in soybean [*Glycine max* (L.)] have ranged from 40 to 0% (Rayburn *et al.,* 2004). This wide range is highly reproducible and has resulted in doubts of the existence of intra-specific DNA variation in soybean. Rayburn *et al*. (2004) determined genome size of 18 soybean lines, selected on the basis of diversity of origin, by flow cytometry. They found that genome size variation between these lines was at approximately 4%. This amount of DNA variation is lower than was originally reported (Doerschug *et al*., 1978; Yamamota and Nagato, 1984; Hammatt *et al*., 1991; Graham *et al.,* 1994). Doerschug *et al*. (1978) is the first to determine genome size of soybean, upon examining 11 soybean lines, reporting over a 40% variation in nuclear DNA content. Graham *et al.* (1994) observed a 15% variation among soybean cultivars while Rayburn *et al*. (1997) reported a 12% variation among 90 Chinese soybean introductions. Chung *et al*. (1998) observed among 12 soybean strains a 4.6% DNA content variation. Yamamota and Nagato (1984) stated about 60% variation, while Hammatt *et al.* (1991) reported that the variation of genome size in 14 different *Glycine* species from different parts of the world was approximately 58%. These results indicated that the variability between DNA content was varied between the different scholars. The wide variation in genome size between soybean germplasm makes these accessions good candidates for crop improvement.
