Results and Discussion

Genebank Material

Characterization of 22,469 wheat accessions revealed skewed distribution for certain qualitative as well as quantitative characters. Among the qualitative traits the gene bank accessions were skewed for absence of glume pubescence, presence of awns, straw coloured awns, white glume colour and tapering spike shape. Among the quantitative characters, the skewness was observed for traits such as grain length (GL) and grain width (GW) that exhibited highly biased distributions.

Core Set Development

Many approaches for selecting core collections have been proposed and used e.g. M-Strat (Gouesnard et al. 2001), Genetic distance sampling (Jansen and Van Hintum 2007), Power Core (Kim et al. 2007) and Core Hunter (Thachuk et al. 2009). Similarly core has been developed using several kinds of data ranging from

Table 4.1 Species wise description of the core collections developed by different approaches out of entire wheat collection

Species

No. of accessions

Entire

Core-P

Core-G

Core-M

T. aestivum

18,101

64

1,215

1,770

T. durum

3,871

53

489

386

T. dicoccum

497

31

209

52

Total

22,469

148

1,914

2,208

Core-P core developed by Powercore default approach, Core-PG core developed by Powercore with grouping approach, Core-PM core developed by Powercore with modified stepwise approach

genealogical data in the Czech spring wheat (Stehno et al. 2006), agronomic data in groundnut (Upadhyaya 2003; Upadhyaya et al. 2003) and molecular data or integration of data in bread wheat (Balfourier et al. 2007) and in rice (Borba et al. 2009; Yan et al. 2007). PowerCore is a new and a faster approach for developing core collection, which effectively simplifies the generation process of a core set with reduced number of core entries but maintaining high percent of diversity compared to other methods used. In this study, core set was developed with agronomic traits using power core with some modifications. The PowerCore could produce only 64 accessions out of entire wheat accessions (22,469) with default programme without any manual classification and forced selection of entry into the core. Therefore, a modified strategy was followed to make around 8–10 % of entire collection including maximum diversity and minimum redundancy. The method was stepwise random selection using PowerCore with cut-off fixed at around 10 %. With this strategy the core set of 2,208 accessions was developed comprising 1,770 T. aestivum, 386 T. durum, and 52 T. dicoccum accessions (Table 4.1).

Evaluation of Core

Evaluation of core was done by comparing with the other approach, classification and grouping of wheat accessions based on passport data and geographical information (stratified random sampling). The accessions without passport data were classified by hierarchical method of clustering using Euclidean distance and Ward's clustering method. Subsequently all the groups were analysed using PowerCore and then the selected accessions were merged to make the core collection. PowerCore successfully selected 1,914 accessions of the entire wheat germplasm. This consisted 1,215, 489, and 209 accessions of T. aestivum, T. durum, and T. dicoccum, respectively (Table 4.1).

 
< Prev   CONTENTS   Next >