Sixteen progeny lines of common beans obtained from single crosses made between two parents, GLP2 and KAT B1, were grown in randomized complete block design in a rainout shelter at the Agricultural and Mechanization Research Institute, Machakos, Kenya. The experiment was conducted to study inheritance of traits associated with drought stress adaptation and to establish if significant variation for those traits was existing in order to carry out selection for drought tolerance. The calculated mean values were used to estimate heritability, genetic advance, and correlation study for each trait. Water stress had a significant (
Common bean is the single most significant source of dietary protein for majority of households in Kenya. However, the annual demand for this commodity far outstrips its availability. The shortage is especially occasioned by low productivity due to genotypes with low yield potential and unfavorable growing conditions due to low and poorly distributed rainfall [
According to Alvares et al. [
An intraspecific cross between two common bean genotypes, GLP2 and KAT B1, was carried out to develop F2 progenies. The two genotypes have contrasting drought tolerance characteristics; GLP2 is drought susceptible while KAT B1 is drought tolerant based on their productivity under drought stress conditions. A total of 16 F2 progenies that were developed through the single seed descent method were evaluated for phenological, physiological, yield and yield-related components traits, and drought tolerance along with parental genotypes during 2017/2018 in a rainout shelter at the Agricultural and Mechanization Research Institute, Katumani, Kenya.
The experimental materials comprising sixteen progenies and two parental lines were sown in plastic pots and arranged in a randomized complete block design (RCBD) with four replications. A total of 72 pots were used each measuring 22 cm high and 20 cm in diameter, and they were filled with Lixisol soils (textural class of loams 50.3%, silt 26.4%, and 23.3% sand). Five seeds were sown per pot, and two weeks after sowing, seedlings were thinned to three. Irrigation was done daily for a period of three weeks. A week after establishment, half of the plants were subjected to stress continuously until physiological maturity, whereas others were well watered (control). Water levels were maintained at a field capacity of 75% in the well-watered treatment while the stress treatment was kept at the range of 30% of field capacity. Artificial water deficit was created through withholding irrigation. This was done to simulate the water stress conditions experienced by the plant in the field. Hand weeding was carried out occasionally to ensure the crops were healthy.
For plant characters, data were recorded on five random plants in each replication at the end of flowering season. Ten days after withholding water, data sampling for plant traits was done between 10.30 and 11.30 a.m. using three randomly selected plants of each line per plot in the four replications. The characters measured include days to flowering, days to maturity, number of branches per plant, number of pods per plant, number of grains per pod, 100-seed weight, harvest index, stomatal conductance, water use efficiency, and leaf water potential.
The performance of genotypes under drought is determined by the grain yield and yield-related components under drought. At the midpod filling stage, the number of branches and number of pods per plant were counted and recorded from each of the randomly selected plants per plot. At physiological maturity, the plants from each pot were cut individually at the base and placed in separate bags. Samples in each bag were partitioned into stem, leaves, grains, and pods and packed separately. Measurements for each component was made and recorded. With the exception of the seeds, all the other plant components were oven-dried at 85°C for 72 hours and pod weight, stem weight, and leaf weight were determined. The measurements were subsequently used for analysis for yield and associated traits, viz., aboveground biomass, number of grains per plant, grain yield, 100-grain weight, and harvest index.
Days to flowering (DF) was estimated as the number of days between the date of sowing until when 50% of the plants in the plot had one fully open flower, whereas days to physiological maturity (DPM) was defined as the number of days between the date of sowing and when 50% of the pods had lost their green colour.
Measurements for stomatal conductance were carried out on both surfaces of the fully expanded uppermost leaf of three plants per plot using a LI1600 steady state porometer (LICOR, Lincoln, NE). Sampling was done on the 14th, 21st, 28th, and 35th day after emergence. To determine leaf water potential, leaf samples were taken from each plot in the four replicates of both treatments 14th, 21st, 28th, and 35th day after emergence.
Data obtained for the different characters in both individual and combined moisture treatments were analyzed using analysis of variance (ANOVA) with SAS software version 9.1.3. A combined analysis was performed assuming a random model for treatment and genotypes [
The genotypic and phenotypic components of variance for the traits were calculated according to a formula by Burton and Devane [
The genotypic, phenotypic, and environmental variances were used for the estimation of phenotypic and genotypic coefficient of variation as suggested by Burton and Devane [
The GCV and PCV values were classified as low, moderate, and high according to Robinson et al. [
Broad-sense heritability was calculated according to the method in [
The heritability values were ranked according to Robinson et al. [
The expected genetic advance or gain (GA) of selection for the trait was computed as
The genetic advance is given as percentage of the mean:
The GAM were classified as low, moderate, and high according to Robinson et al. [
Table
Analysis of variance for eleven traits of common bean population.
Trait | Level | Replication mean squares (RMS) | Population mean squares (PMS) | Error mean squares (EMS) | Coefficient of variation (CV%) |
---|---|---|---|---|---|
DF | Watered | 7.59 |
|
0.42 | 7.75 |
Stressed | 4.56 |
|
0.29 | 5.83 | |
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DM | Watered | 70.7 |
|
0.40 | 5.43 |
Stressed | 17.4 |
|
0.40 | 3.70 | |
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BP | Watered | 2.76 |
|
0.35 | 12.37 |
Stressed | 0.44 |
|
0.60 | 28.03 | |
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PP | Watered | 12.91 |
|
0.70 | 10.02 |
Stressed | 0.33 |
|
0.76 | 26.95 | |
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STML | Watered | 3.11 |
|
0.48 | 13.29 |
Stressed | 0.29 |
|
0.25 | 21.02 | |
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LWP | Watered | 10.93 |
|
1.03 | 6.51 |
Stressed | 2.78 |
|
0.15 | 10.51 | |
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HSW | Watered | 7.68 |
|
6.41 | 10.79 |
Stressed | 0.14 |
|
0.34 | 9.77 | |
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BG | Watered | 0.47 |
|
0.29 | 14.54 |
Stressed | 0.92 |
|
1.19 | 38.06 | |
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GP | Watered | 0.18 |
|
0.09 | 5.71 |
Stressed | 0.53 |
|
0.33 | 21.85 | |
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YP | Watered | 0.023 |
|
0.08 | 11.40 |
Stressed | 2.89 |
|
1.09 | 16.86 | |
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HI | Watered | 0.075 |
|
0.09 | 7.53 |
Stressed | 1.07 |
|
1.77 | 24.80 |
Variance of components estimations revealed that environmental variance strongly influenced most of the traits of common population (Table
Estimates of phenotypic and genetic parameters for the studied traits.
Traits | Level |
|
|
|
GCV% | PCV% |
|
GA | GAM% |
---|---|---|---|---|---|---|---|---|---|
DF | Watered | 3.10 | 0.42 | 3.52 | 17.61 | 19.20 | 88.07 | 2.46 | 22.41 |
Stressed | 2.45 | 0.29 | 2.74 | 15.65 | 11.23 | 89.42 | 2.19 | 19.92 | |
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DM | Watered | 2.03 | 0.4 | 2.43 | 14.25 | 15.63 | 83.54 | 1.99 | 18.13 |
Stressed | 7.55 | 0.4 | 7.95 | 27.48 | 25.58 | 94.97 | 3.85 | 34.97 | |
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BP | Watered | 0.56 | 0.35 | 0.91 | 1.48 | 1.52 | 61.5 | 1.05 | 9.52 |
Stressed | 2.00 | 0.60 | 2.60 | 14.14 | 14.33 | 79.92 | 2.02 | 18.35 | |
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PP | Watered | 9.60 | 0.70 | 10.30 | 30.98 | 27.17 | 73.20 | 4.34 | 32.16 |
Stressed | 21.26 | 0.76 | 22.02 | 36.11 | 36.70 | 96.54 | 6.45 | 22.32 | |
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STMLC | Watered | 3.02 | 0.61 | 3.44 | 20.45 | 21.89 | 77.65 | 1.85 | 17.28 |
Stressed | 8.76 | 0.6 | 9.03 | 36.13 | 33.47 | 84.25 | 2.06 | 19.87 | |
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LWP | Watered | 0.05 | 0.09 | 0.17 | 2.37 | 2.28 | 43.40 | 0.29 | 2.86 |
Stressed | 2.73 | 0.21 | 2.29 | 16.80 | 14.37 | 60.14 | 4.27 | 25.46 | |
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HW | Watered | 13.01 | 6.41 | 19.42 | 36.07 | 32.37 | 66.99 | 5.05 | 27.72 |
Stressed | 0.96 | 0.34 | 1.30 | 2.80 | 2.17 | 73.85 | 1.37 | 12.47 | |
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BG | Stressed | 0.96 | 0.34 | 1.30 | 2.80 | 2.17 | 73.85 | 1.37 | 12.47 |
Watered | 0.23 | 0.29 | 0.52 | 1.80 | 0.87 | 44.23 | 0.67 | 6.10 | |
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GP | Stressed | 2.20 | 1.19 | 3.39 | 4.83 | 5.65 | 64.90 | 2.08 | 28.88 |
Watered | 0.07 | 0.09 | 0.16 | 2.65 | 2.27 | 43.75 | 0.37 | 3.37 | |
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YP | Stressed | 2.98 | 0.33 | 3.31 | 17.26 | 15.52 | 90.03 | 2.42 | 21.97 |
Watered | 0.03 | 0.08 | 0.11 | 1.73 | 1.18 | 67.27 | 0.24 | 2.20 | |
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HI | Stressed | 14.85 | 1.09 | 15.94 | 28.54 | 26.57 | 93.16 | 5.39 | 26.32 |
Watered | 0.09 | 0.09 | 0.04 | 1.00 | 2.01 | 50.00 | 0.06 | 5.57 |
There was a relatively large coefficient of variability among the genotypes with regards to all the studied traits that were considered (Table
The estimates of heritability obtained from the study varied between 43.40% and 96.54% (Table
The genetic advance (GA) estimates for eleven traits of the common bean population studied are shown in (Table
The highest values of correlations were between yield per plant with DF (
Phenotypic correlations among different traits measured on progenies as result of crosses between GLP2 and KAT B1 under drought stress and nonstress.
DF | DM | BP | PP | STML | LWP | HSW | BG | GP | HI | YP | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|
DF | a | 1 | −0.41 | −0.30 |
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−0.21 | 0.33 | −0.29 |
|
−0.41 | −0.26 | −0.41 |
b | 1 |
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|
0.41 |
|
−0.15 |
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| |
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DM | a | −0.43 | −0.21 | −0.20 | −0.43 | −0.18 | −0.23 | −0.28 | −0.34 | −0.23 | ||
b |
|
|
0.49 | 0.32 |
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−0.41 | |||
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BP | a | −0.40 | 0.28 | 0.17 | −0.24 | −0.32 | −0.17 | −0.21 | −0.39 | |||
b | 0.14 | 0.45 | 0.37 |
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0.67 | ||||
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PP | a |
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0.40 | −0.36 | −0.34 | 0.38 | −0.44 |
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b |
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0.47 |
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STML | a | 0.33 | 0.45 | 0.44 |
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0.46 | 0.38 | |||||
b |
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LWP | a | −0.23 |
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0.41 | ||||||
b | −0.28 |
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HSW | a |
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0.49 | |||||||
b |
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BG | a | 0.43 |
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b |
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GP | a | −0.33 |
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b |
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HI | a | −0.35 | ||||||||||
b |
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DF: days to flowering; DM: days to maturity; BP: number of branches/plant; PP: number of pod/plant; STMLC: stomatal conductance; LWP: leaf water potential; HSW: 100-seed weight; BG: biomass aboveground; GP: number of grain/pod; YP: yield/plant; HI: harvest index.
Day to maturity exhibited a generally negative and low correlation with BP (
Significant differences were observed within the common bean population for all the traits suggesting the presence of high level of genetic diversity among them. The relatively large population mean squares obtained for the number of pods per plant, harvest index, stomatal conductance, leaf water potential, and yield per plant under stressed conditions revealed that the progeny lines differed in their potential for these traits. Significant amount of phenotypic variability obtained indicated that all the progeny lines varied with each other. This implies that further improvement of the traits is likely through individual selection of plants. According to Beebe et al. [
The close correspondence of the genotypic and the phenotypic variance for almost all traits indicated less influenced by environmental conditions, hence a wider scope for plant breeders to select common bean genotypes tolerant to drought. This agrees with Abebe et al. [
These results lead to the conclusion that traits which had a high amount of genetic variability, estimates of broad-sense heritability, genetic advance, and a high degree of positive and significant correlation coefficient under stress conditions would be very effective tools to be used in selection of high yielding common bean genotype under drought stress. Such traits in this study were number of pods, days to maturity, and yield per plant.
The numerical data used to support the findings of this study are included within the article.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors appreciate the technical and financial assistance given by the Agricultural and Mechanization Research Institute, Katumani, Kenya in support of this research.