Yield stability
Table 1 showed stability analysis for locations (E) and years (Y). It revealed 9 out of the selected 100 accessions were stable (≤ 1 stability index) in the expression of their yield potential. In the three years (Y) and locations (E) of the experiments, accessions TVSu-1241, TVSu-1242, TVSu-2102, TVSu-2106, TVSu-579, TVSu-644, TVSu-667, TVSu-83 and TVSu-838 had less than one (£1) stability index, which indicated that these accessions were stable and were relatively insensitive to locations mean yield in the years and suited to producing reliable yields in low yielding sites and seasons.
This further indicated that yield stability of stable Bambara groundnut accessions might be genetic and less influenced by factors responsible for instability, hence, produce reliable yields with respective changing environmental factors overtime within given location. This was supported by
Muniswamy et al., (2022) who reported yield stability in some genotypes of pigeon pea.
Tahir et al., (2015) also reported yield stability in some genotypes of wheat;
Clarke et al., (2011); Mutava et al., (2011); Annicchiarico (2002); Becker and Leon (1988); Lin et al., (1986) and Shukla (1972) reported on yield stability of crops. Accessions TVSu-268, TVSu-273, TVSu-351, TVSu-363 and TVSu-366 had less than one (≤1) stability index in the locations only, which indicated that these accessions had stable yield in the locations but unstable in the years of observation, which further reiterated that stability in locations does not ascertain stability in the years. This further indicated that accessions may be stable in environments within the year but considerable changes in the environmental factors in years may result to unexpected yield fluctuations. This was also supported by
Becker and Leon (1988); Lin et al., (1986).
The instability observed on some of the accessions yield in the years was also confirmed by
Toure et al., (2012) who reiterated that yield of Bambara groundnut varies widely, depending on the accession. Accessions with instability indexes had also been reported by
Hammer et al., (2001) who reported that traits, expected seasonal conditions and agronomic management create diversity in crops.
Mkandawire (2007) also reported that Bambara groundnut can grow and produce reasonable yield on laterite soils and made better use of the elements of weather including thermal duration or day length to produce more flower for higher yields.
Yield contributing traits
Correlation coefficients of yield and yield components were shown in (Table 2). Positive and significant correlation showed eight morphological traits were associated with plant height, which indicated that an increase in plant height might definitely lead to significant increase in the other, in other words, an increase in plant height might lead to an increase in internodes length or petiole length or plant spread, terminal leaflet length or width simultaneously. Similar positive and significant correlation was also reported by
Bonny et al., (2019); Olukolu et al., (2012). Yield per plot also had positive and significant correlation with seed length, seed weight per plot, chaff weight, 100-seed weight, yield per plant and yield per hectare, similar results of positive association of traits were also reported by
Kebede et al., (2001). This affirmed that selection based on these characters may be effective in improving yield.
Number of trifoliate leaves had negative and significant correlation with number of days to first flowering and number of days to 50% flowering, meaning that increasing days to flowering might lead to delay in crop yield harvest. Shelling percentage had negative and significant correlation with shelled harvest per plot. This indicated that an increase in shelling percentage decreases or reduces shelled harvest per plot in Bambara groundnut. This may be due to variation in shell thickness, seed weight per plot, seed length, seed width and yield per plant among the accessions.
Yield in locations and years
Table 3 showed means observed in the locations and years which showed variability and instability in the expression of traits in the production of Bambara groundnut. In the locations and years, number of days to first flowering, number of days to 50% flowering, seed length, yield per plant, number of pods per plot, yield per plot, yield per hectare, pod length, seed weight per plot, shelling percentage, chaff weight, shelled harvest and 100-seed weight showed varying mean responses in the locations and years.
Massawe et al., (2005) reported that timing is an important factor in the production of Bambara groundnut.