Correlation analysis studies

Yield is an important and complex trait difficult to manipulate for crop improvement (Shi et al., 2009), however yield such as seed number per plant, seed yield per hectare, pods number per plant and 100 seeds weight could be correlated to other characters. This will then allow an indirect selection of yield based on those characters.

Relatively low correlations were found among most of the traits among 1384 bambara groundnut accessions at the International Institute of Tropical Agriculture (IITA) Nigeria, by Goli et al., (1995). They found a strong correlation of seed yield per plant to a number of characters which they identified as potential characters to select for bambara groundnut improvement. They recorded correlations of seed yield per plant to number of seeds per pod of(r = 0.88), and to pods per plant (r = 0.30). A positive correlation of r =0.13 was observed between 100 seed weight andseed yield per plant which is a good indication that these two characters could be used effectively in the selection of bambara groundnut. Number of stems per plant was positively correlated with days to maturity, which was an indication that plants with more stems matured late, a negative correlation was found between days to maturity and cercospora virus index, which could indicate that fast maturing plants have a lower probability of infection; however no heritability studies were undertaken.

103 Table 4.1.1: A comparison of correlations between yield components; seed yield per plant, number of pods per plant, seed yield per hectare and 100 seed weight and a number of characters , sourced from Karikari and Tabona, (2004); Misangu et al., (2007); Ouedraogo et al., (2008); Goli et al., (1995); Jonah et al., (2010); Karikari, (2000), and Oyiga and Uguru, 2011.

No. Characters Materials used in the study Correlation character Correlation Values Reference

1 Seed yield per plant 12 landraces Number of pods per plant 0.764 Karikari and Tabona, 2004 9 landraces 0.83 Misangu et al., 2007 310 accessions 0.852 Ouedraogo et al. , 2008 1384 accessions 0.3 Goli et al., 1995 12 landraces 0.33 Jonah et al., 2010 12 landraces 100 seed weight per plant 0.415 Karikari and Tabona, 2004 9 landraces 0.16 Misangu et al., 2007 310 accessions 0.257 Ouedraogo et al., 2008 12 landraces 0.06 Jonah et al. , 2010 12 landraces Shelling percentage 0.587 Karikari and Tabona, 2004 310 accessions 0.275 Ouedraogo et al., 2008 12 Landraces -0.1 Jonah et al., 2010 9 landraces Plant height 0.38 Misangu et al., 2007 310 accessions 0.026 Ouedraogo et al., 2008 1384 accessions 0.08 Ouedraogo et al., 2008 12 Landraces 0.42 Jonah et al., 2010 9 landraces Days to maturity -0.41 Misangu et al., 2007 1384 accessions -0.01 Ouedraogo et al., 2008 9 landraces Seed width 0.11 Misangu et al., 2007 310 accessions 0.224 Ouedraogo et al., 2008 12 Landraces -0.23 Jonah et al., 2010 9 landraces Seed length -0.08 Misangu et al., 2007 310 accessions 0.295 Ouedraogo et al., 2008 12 Landraces -0.05 Jonah et al., 2010 9 landraces Number of leaves per plan 0.34 Misangu et al., 2007 1384 accessions 0.12 Goli et al., 1995 9 landraces Leaf width 0.11 Misangu et al., 2007 1384 accessions 0.13 Goli et al., 1995 9 landraces Leaf length 0.5 Misangu et al., 2007 1384 accessions 0.14 Goli et al., 1995 310 accessions Pod length 0.194 Ouedraogo et al., 2008 1384 accessions 0.1 Goli et al., 1995 12 Landraces 0.13 Jonah et al., 2010 310 accessions Pod width 0.092 Ouedraogo et al., 2008 1384 accessions 0.08 Goli et al., 1995 12 Landraces 0.15 Jonah et al., 2010 310 accessions Canopy spread 0.231 Ouedraogo et al., 2008 1384 accessions 0.15 Goli et al., 1995 12 landraces Number seeds per pod 0.202 Karikari and Tabona, 2004 1384 acessions 0.04 Goli et al., 1995 12 landraces Number of seeds per plant 0.882 Karikari and Tabona, 2004 12 landraces Seed yield per hectare 0.8 Jonah et al. , 2010 2 Number of pods per plan1384 accessions 100 seed weight 0.12 Goli et al., 1995

12 landraces -0.71 Jonah et al., 2010 12 landraces Shelling percentage 0.35 Jonah et al., 2010 310 accessions -0.172 Ouedraogo et al., 2008 9 landraces Plant height 0.55 Misangu et al., 2007 1384 accessions 0.23 Goli et al., 1995 13 genotypes 0.66 Oyiga and Uguru, 2011 12 landraces 0.25 Jonah et al., 2010 310 accessions Seed width 0.023 Ouedraogo et al., 2008 12 landraces -0.74 Jonah et al., 2010 310 accessions Seed length 0.073 Ouedraogo et al., 2008 12 landraces 0.51 Jonah et al., 2010 9 landraces Number of leaves per plan 0.31 Misangu et al., 2007 1384 accessions 0.36 Goli et al., 1995 13 genotypes 0.663 Oyiga and Uguru, 2011 9 landraces Leaf length 0.56 Misangu et al., 2007 1384 accessions 0.27 Goli et al., 1995 12 landraces Pod length 0.67 Jonah et al., 2010 310 accessions 0.03 Ouedraogo et al., 2008 1384 accessions 0.25 Goli et al., 1995 12 landraces Pod width -0.67 Jonah et al., 2010 310 accessions -0.079 Ouedraogo et al., 2008 1384 accessions 0.18 Goli et al., 1995 12 landraces Seed yield per plant 0.33 Jonah et al., 2010 310 accessions 0.852 Ouedraogo et al., 2008

104 Table 4.1.2(Continued)

Karikari, (2000) when studying the variability of Botswana and Zimbabwean landraces in a field experiment he found a significant correlation of days to flowering (0.84), 100 seeds weight(r = 0.88), and shelling percentage (r = 0.82), to grain yield kg ha-1 of bambara groundnut. A negative correlation was recorded between grain yield kg ha-1to both canopy spread at (r = -0.85), and days to maturity at (r = -0.63). He also carried out a heritability analysis to identify the best traits for selection in the Botswanan environment. He recorded heritability (h2) values of 0.72 for grain yield, 0.25 for 100 seed weight, 0.38 for shelling percentage, and 0.36 for plant dry matter at harvest. Ouedraogo, et al., (2008) characterised and evaluated 310 accessions from Burkina Faso, yield per plant was correlated against a number of characters and revealed a positive correlation todays to flowering (0.06),100seeds weight(r = 0.257) but low correlations. In contrast canopy spread had a positive correlation(r = 0.231) while shelling percentage had a negative correlation (r = -0.199) to yield per plant. The characters were not subjected to heritability analysis.

Karikari and Tabona (2004) undertook a study on 12 bambara groundnut landraces to identify characters associated most with adaptation to drought in the Botswanan environment. Their results showed canopy spread, 100 seed weight,

No. Characters Materials used in the study Correlation character Correlation Values Reference

3 Seed yield per hectare 9 landraces 100 seed weight 0.88 Karikari , 2000

12 landraces 0.16 Jonah et al., 2010

9 landraces Shelling percentage 0.82 Karikari , 2000 310 accessions -0.054 Ouedraogo et al., 2008

12 landraces -0.11 Jonah et al., 2010

4 100 seeds weight 310 accessions Number of pods per plant -0.054 Ouedraogo et al., 2008 1384 accessions 0.12 Goli et al., 1995 310 accessions Shelling percentage 0.187 Ouedraogo et al., 2008

9 landraces 0.88 Karikari, 2000

12 Landraces 0.1 Jonah et al., 2010

310 accessions Plant height 0.096 Ouedraogo et al., 2008 1384 accessions 0.11 Goli et al., 1995

12 landraces 0.27 Jonah et al., 2010

9 landraces Days to maturity -0.8 Karikari, 2000 1384 accessions -0.14 Goli et al., 1995 310 accessions Seed width 0.524 Ouedraogo et al., 2008

9 landraces 0.85 Jonah et al., 2010

310 accessions seed length 0.529 Ouedraogo et al., 2008

12 landraces 0.79 Jonah et al., 2010

310 accessions Pod length 0.44 Ouedraogo et al., 2008 1384 accessions 0.29 Goli et al., 1995

12 landraces 0.81 Jonah et al., 2010

310 accessions Pod width 0.491 Ouedraogo et al., 2008 1384 accessions 0.48 Goli et al., 1995

12 landraces 0.62 Jonah et al., 2010

310 accessions Canopy spread 0.23 Ouedraogo et al., 2008

9 landraces -0.86 Karikari, 2000

105 root-shoot ratio, and number of seeds per pod as the most suitable characters. A highly significant correlation was found between seed yield per plant with number of pods at r = 0.76, and between seed yield per plant with number of seeds per plant at r = 0.88. They emphasised the importance of root-shoot ratio in the semi- arid environment of Botswana, and they found that the root-shoot ratio has significant correlation with shelling percentage and seed yield per plant at r = 0.296 and r = 0.398, respectively.

Jonah et al., (2010), investigated the genetic correlations between yield and yield related characters in 12 bambara groundnut landraces in Nigeria. Highly positive correlations were found between seed yield per hectare and pod yield per plant (r =0.87), and between seed yield per hectare and seed yield per plant (r = 0.91), and between seed yield per plant and plant height at 8 weeks after sowing(r =0.77). A high correlation was also identified between pod length and pod width at (r =0.89) and seed length and seed width at (r =0.82), which is potentially useful for selecting genotypes with bigger seeds. However they found a negative correlation between pod number per plant with 100 seed weight at (r= -0.74) which implies that selecting landraces for higher pods numbers could lead to, leaner pods produced in turn.

Wigglesworth, (1996), undertook a field trial on six bambara groundnut landraces in Botswana in order to study the genotypic variation and heritability of pod numbers, 100 seed weight, seed weight per plant and to find some correlation between the traits. The results recorded a significant phenotypic correlation between pod numbers and seed weight per plant (r = 0.77), and between 100 seed weight and seed weight per plant (r = 0.52). Heritability values recorded were lower for seed weight per plant (0.25), pod number (0.39) and higher for 100 seed weight at (0.94). Therefore 100 seed weight was singled out as an important trait to select for, among the local landraces.

Thirteen bambara groundnut populations were evaluated for floral structure in Nigeria in a field experiment byOyigaet al., (2010). They recorded an anther diameter correlation with number of pods per plant (r =0.41), and to seed weight per plant (r =0.51) which is an indication of the relationship between seed number and the biomass synthesized during the growth stages of seed formation (Jeuffroy

106 and Chabanet, 1994). Selection for anthers with larger diameter was identified as a strategy for yield improvement in bambara groundnut. They also found a negative correlation between stigma anther separation with seed weight per plant at (r = -0.59), which they thought the stigma-anther separation is an important factor in the production of low seed weight in bambara groundnut.

In another study, Jonah et al., (2010), carried out a phenotypic diversity study on 12 bambara groundnut landraces. They undertook some broad sense heritability and genetic advance estimates and recorded high heritability and genetic advance in pod yield per plant (0.75; 16%), for seed width (0.85; 16%), and for 100 seed weight (0.70; 12%) the high heritability and genetic advance suggest that these are selectable traits. However, they reported moderate value for seed yield per hectare at 0.54, which indicate a limitation to the improvement of this trait.