**5. Evaluation of genetic diversity in soybean germplasm at the biochemical level**

The genetic markers have made possible a more accurate evaluation of the genetic and environmental components of variation. The biochemical markers are ones of the interesting measures of genetic diversity. They include protein techniques and isozymes. The protein techniques are practical and reliable methods for cultivars and species identification because seed storage proteins are largely independent of environmental fluctuation (Sammour, 1992, 1999; Camps *et al.*, 1994; Jha and Ohri, 1996). They are less expensive as compared to DNA

tolerate drought stress which is the major factor that limiting soybean yield. The results showed substantial genetic diversity in the capacity for increased lateral root development (number and total length of roots produced) and in the responses of overall root and shoot

The extent of between- and within-species differences in the resistance of the four commonest species of Glycine (*G. canescens*, *G. clandestina* , *G. tabacina* and *G. tomentella*) to leaf rust caused by *Phakopsora pachyrhizi* was investigated by Burdon & Marshall (1981). The results of their study showed qualitative and quantitative resistance to leaf rust, and considerable variation in a number of disease characteristics both between and within

**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

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

**5. Evaluation of genetic diversity in soybean germplasm at the biochemical** 

The genetic markers have made possible a more accurate evaluation of the genetic and environmental components of variation. The biochemical markers are ones of the interesting measures of genetic diversity. They include protein techniques and isozymes. The protein techniques are practical and reliable methods for cultivars and species identification because seed storage proteins are largely independent of environmental fluctuation (Sammour, 1992, 1999; Camps *et al.*, 1994; Jha and Ohri, 1996). They are less expensive as compared to DNA

growth under water deficit conditions.

(Bennett *et al*., 1998; Chung *et al*., 1998).

accessions good candidates for crop improvement.

**level** 

populations of each species.

markers. SDS-PAGE is one of these techniques, widely used to describe seed protein diversity of crop germplasm (Sammour, 2007; Sammour *et al.,* 2007). Genetic diversity and the pattern of variation in soybean germplasm have been evaluated with seed proteins (Hirata *et al.,* 1999; Bushehri *et al*., 2000; Sihag *et al*., 2004; Malik *et al.,* 2009). SDS-PAGE (Bushehri *et al*., 2000) and discontinuous polyacrylamide slab gel electrophoresis (Sharma and Maloo, 2009) were used very successfully in evaluating the genetic diversity and identifying soybean (*Glycine max*) cultivars. Malik *et al*., (2009) evaluated the genetic variation in 92 accessions of soybean collected from five different geographical regions using the electrophoretic patterns of seed proteins. The accessions from various sources differed considerably, indicating that there is no definite relationship between genetic diversity and geographic diversity. Similar results were reported by (Ghafoor *et al.,* 2003). Based on the results of Ghafoor *et al.,* (2003) and Malik *et al*., (2009), SDS-PAGE cannot be used for identification of various genotypes of wild soybean at the intra-specific level, because some of the accessions that differed on the basis of characterization and evaluation exhibited similar banding patterns. However, it might be used successfully to study inter rather than intra-specific variation (Sammour, 1989; Sammour *et al*., 1993; Karam *et al*., 1999; Ghafoor *et al*., 2002). 2-D electrophoresis can be used to characterize the genotypes exhibited similar banding patterns (Sammour, 1985).

Allozyme markers have been used in soybean to evaluate genetic diversity in accessions from diverse geographic regions (Yeeh *et al*., 1996; Chung *et al*., 2006), wild soybean in natural populations from China, Japan and South Korea (Pei *et al.*, 1996; Fujita *et al*., 1997), and Asian soybean populations (Hymowitz & Kaizuma, 1981; Hirata *et al*., 1999). From an analysis of the Kunitz trypsin inhibitor (*Ti*) and beta-amylase isozyme (*Sp1* = *Amy3*), Hymowitz & Kaizuma (1981) defined seven soybean germplasm pools in Asia: (1) northeast China and the USSR, (2) central and south China, (3) Korea, (4) Japan, (5) Taiwan and south Asia, (6) north India and Nepal and (7) central India. Hirata *et al.* (1999) compared the genetic variation at 16 isozyme of 781 Japanese accessions with the genetic variations of 158 Korean and 94 Chinese accessions, detecting a number of region-specific alleles that discriminated Japanese from Chinese accessions. The presence of alleles specific to the Japanese population suggested that the present Japanese soybean population was not solely a subset of the Chinese population.
