Comparison of selection indices for screening maize (Zea mays L.) germplasm for cold tolerance
The comparisons among the 6 selection indices S1, S2, S3 (simultaneous selection indices comprising of X1 only; X1+X5 and X1+X2+X3+X4 respectively as their component traits), S4 (Rank summation index), S5 (Baker’s standard deviation index) and S6 (Elston’s weight free index) were made involving 4 primary cold tolerance traits namely field emergence per cent (X1), fresh seedling root mass (X2), seedling dry weight (X3), days to 50% silk emergence (X5) along with grain yield ha-1 (X4). Highly significant rank correlations of proposed selection indices conferred the suitability in use of one index if substituted for other, to score the genotypes for selection. Selection differentials for all the indices were generally positive with respect to the traits X1, X2, X3 and X4 except S2 which, was accompanied with negative differentials for X2, X3 and X4. S1 was found to be an important cold tolerance trait depicting not so less differentials compared to other traits and had positive differentials under each selection criteria. Index S6 was efficient in selecting early silking varieties with high yield and tolerance to cold. The populations NDSM 8 WN, NDSAB (MER), NDSLC and land races GL20W and Dawar-2 showed high degree of cold tolerance among 67 genotypes evaluated and showed at par results with the C15 check which was top ranking under 5 out of 6 selection used.
KeywordsMaize (Zea mays L.) cold tolerance selection indices
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