ON-FARM DIVERSITY AND GENETIC VARIABILITY OF COMMON BEAN (Phaseolus vulgaris L.) AND ITS VARIETAL COMPATIBILITY, PLANT POPULATION AND SPATIAL ARRANGEMENT IN MAIZE COMMON BEAN INTERCROPPING IN EAST HARARGHE ZONE, EASTERN ETHIOPIA

Abstract

Common bean (Phaseolus vulgaris L.) is an important source of food and income in East Hararghe Zone, Ethiopia. However, the extent of its on-farm diversity and conservation by smallholder farmers is not well known and no sufficient information is available on the characteristics of the genotypes for production and breeding purpose. Likewise, maize is a highly productive, multi-purpose crop and the cheapest source of calorie among the cereals and it is well-suited for diverse cropping systems. Small land size owned by resource poor farmers and the need to increase land productivity calls for suitable cropping system that maintains soil fertility and biodiversity that satisfies the nutritional demand of smallholder farmers. To this end, maize-common bean intercropping system is widely practiced in East Hararghe Zone, eastern Ethiopia. However, the varietal compatibility, planting proportion and spatial arrangement of farmers’ common bean cultivars in the maize-common bean intercropping system are not well studied and documented. Therefore, both survey and field experiments were conducted to assess on-farm diversity and genetic variability of common bean and gender roles on its production, to characterize common bean genotypes based on morphological and agronomic traits, to determine optimum plant density and suitable spatial arrangements of farmers’ common bean cultivars for intercropping with maize, and to determine the effect of the intercropping system on certain soil chemical properties. For the first study, potential common bean producing districts (Woredas) were selected purposely and peasant associations (kebeles) were selected randomly to collect the survey data. Two major agro-ecological zones ([tepid moist mid highland (M3)] and [tepid sub-humid highlands (SH3)]) were included in the survey. Three kebeles from each major agro-ecological classification, two key respondents, and twelve general respondents from each kebele were included which constituted a total of 84 respondents (72 for the structured survey and 12 for the non-structured survey). Seven farmers’ cultivars of common bean were identified and their diversity was found to be higher in the tepid moist mid highlands (M3) whereas the cropped area (ha) was significantly (p < 0.05) higher in the tepid sub-humid highlands (SH3) agro-ecology. Most production activities of common bean were undertaken by male adults. Insect pests were the prominent constraints of common bean production. For the second study, seven farmers’ cultivars collected from farmers’ fields and 18 accessions of common bean from Ethiopian Biodiversity Institute (EBI) which were collected from East xxii Hararghe Zone (a total of 25 genotypes) were evaluated for their phenotypic and genetic variability in field experiment in a randomized complete block design (RCBD) in three replications. Data collected from all quantitative characters were subjected to analysis of variance (ANOVA) using SAS version 9.0 (SAS, 2002). Shannon Diversity Index (SDI) analysis, heritability in broad sense, principal components analysis (PCA), Euclidean distance (ED) and descriptive statistics were used to compute different traits of common bean genotypes. The analysis of variance revealed that all quantitative traits of the genotypes were significantly (p < 0.001) different. Plant height ranged from 54.9 to 180.7 cm, pod length from 7.8 to 13.2 cm, number of pods per plant from 12.2 to 41.5, number of seeds per pod from 3.9 to 6.6, hundred seed weight from 10.3 to 36.6 g, grain yield per plant from 8.7 to 45.4 g, yield per hectare from 0.9 to 4.4 t ha–1 , and aboveground biomass from 4.2 to 10.8 t ha–1 . Adibosolia, Bure, Dimaashongore, 33171 and 9220 were the most promising genotypes as yield and yield components were concerned. The phenotypic variance ranged from 0.007 for harvest index-to 643.27 for plant height and genotypic variance ranged from 0.006 for harvest index to 642.18 for plant height. The heritability in a broad sense ranged from 80.0% for number of seeds per plant to 99.83% for plant height and the genetic advance as a percent of mean (GAM) ranged from 10.16 % for pod length to 118.26 % for grain yield per plant. . Seven traits of the genotypes had high GAM and the two traits (pod length and seeds per pod) showed a moderate GAM. Three principal components explained 71.94% of the total phenotypic variance in the original data set. Grain yield per plant, grain yield per hectare, aboveground biomass, and harvest index were the variables with high loadings on PCA I. The highest morphological divergence of the genotypes was observed for pod color (SDI = 1.4). The cluster analysis produced a more understandable summary of the 25 common bean genotypes by grouping them into four clusters. The maximum distance was obtained between cluster I and III (D2 = 242.25). The third study involved a field experiment conducted in 2018/2019 and 2019/2020 main cropping seasons to determine the effect of planting density of common bean cultivars intercropped with maize on yield components and yield of the companion crops, system productivity and on selected soil properties. The experiment consisted of factorial combinations of four cultivars of common bean (Gofta, Dalecha, Qeye and Nech) and three densities of common bean (25, 50, and 75% of the sole crop population) with their respective sole crops laid out in RCBD in three replications. The highest grain yield (7.78 t ha– 1 ) and aboveground biomass yield (19.19 t ha–1 ) of maize were recorded in the 2019/20. The highest number of pods per plant (27.63) and number of seeds per pod (5.7) were produced by farmers’ common bean cultivars Nech and Qeye, respectively. On the other hand, improved common bean variety Gofta produced the highest grain yield (1.32 t ha–1 ), aboveground biomass (3.25 t ha–1 ), hundred seed weight (39.97 g) and harvest index (0.45). The highest total soil nitrogen content (0.35%) and cation exchange capacity (35.8 cmol [+] kg soil–1 ) were recorded from plots planted to 25% population of common bean cultivars, namely, Dalecha and Qeye, respectively, intercropped with maize in 2019/20. The highest soil organic carbon xxiii content (1.49%) and available phosphorus content (15.37 ppm) were recorded in 2019/20 cropping year from plots planted to 25% density of Nech and Dalecha farmers’ cultivars of common bean, respectively. A higher land equivalent ratio (1.54) was recorded by intercropping maize with Gofta variety of common bean. The fourth study was a field experiment conducted in 2018/2019 and 2019/2020 main cropping seasons to determine the effect of spatial arrangement of common bean cultivars intercropped with maize on yield components and yield of the companion crops, system productivity and on selected soil properties. The experiment was laid out as a RCBD in a factorial arrangement and replicated three times. The highest aboveground biomass of maize (19.02 t ha–1 ) and harvest index (0.39) were recorded for the 2:2 and 1:2 maize to common bean row arrangement, respectively. Significantly higher number of ears per plant (1.38), kernels per ear (604.45) and aboveground biomass of maize (19.58 t ha–1 ) were recorded in 2019/20. For the common bean component, significantly higher number of pods per plant (25.48), grain yield (1.49 t ha– 1 ), and aboveground biomass (4.29 t ha–1 ) were recorded from sole common bean than intercropped common bean. The highest grain yield (1.27 t ha–1 ) and biomass yield (3.20 t ha–1 ) of common bean were obtained from Gofta variety of common bean. The highest land equivalent ratio (1.47), maize equivalent yield (7618.4 kg ha–1 ) and gross monetary return (114276 ETB ha–1 ) were obtained when Gofta variety of common bean was intercropped with maize in the 1:1 spatial arrangement. A higher total soil nitrogen (0.35%) was obtained when farmers’ common bean cultivar Dalecha was intercropped in 2:2 maize common bean spatial arrangement in 2019/20. A higher soil organic carbon (1.113%) was recorded whe n farmers’ common bean cultivar Qeye was intercropped in the 1:2 maize and common bean spatial arra ngement in 2018/19. The highest CEC (35.4 cmol [+] kg soil-1 ) and available phosphorus (14.96 ppm) contents were recorded when common bean variety- Gofta was int ercropped with maize in 1:1 spatial arrangement in 2019/2020. In conclusion, seven farmers’ common bean varieties were identified by the survey experiment of which some were endangered that need maintenance and conservation. The analysis of quantitative and qualitative data of genotypes showed significant genotypic and phenotypic variability of traits that could be used for further selection and breeding program of the common bean genotypes. Moreover, intercropping of maize with 25% population of Gofta variety of common bean increased the productivity of the intercropping system and economic benefits as well as improved selected soil chemical properties. Intercropping Gofta variety of common bean and maize in the 1:1 spatial arrangement was found to be the most productive intercropping system with the highest economic benefits for farmers in the study area.