An overview of the research findings
8.1 Introduction and objectives of the study
Soybean was introduced to Ethiopia in the 1960s. Despite the recent introduction, (Asfaw et al., 2006) its production has tremendously increased in both small scale and commercial farms of the country, owing to increased awareness among the researchers, governmental and non-governmental institutions about the wide range of benefits it can provide to subsistence farmers in particular, and the country’s economy at large. In addition, there has been an increase in the number of oil and fortified food processing companies and increased price of soybean in the local market, which have also contributed to increased soybean production in the country. Despite its growing importance, production and productivity of the crop has been constrained in Western Ethiopia by several production constraints; among which poor soil fertility that is mainly attributed to soil acidity is one of the most important factor. Phosphorus (P) is critically deficient in acid soils due to fixation by aluminium and iron forming compounds such as that are not used by plants (Liao et al., 2006). Assessment of farmers’ perception on the various soil fertility problems and management practices, examining the extent of genetic variability, and genetic analysis of soybean for performance under low and high P conditions has not been done in Western Ethiopia, and hence, this study was undertaken.
The objectives of this study were to:-
a) Understand farmers perception and experience on the existing soil fertility problems and management practices that help make decision on plant breeding intervention in the development of low P tolerant varieties
b) Estimate the magnitude and pattern of genetic diversity of the crop using morphological data under low and high P conditions,
b) Identify low P-tolerant, and high P-responsive soybean genotypes
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e) Determine gene actions and estimate combining ability of soybean for low and high P conditions
8.2 Brief summary of the research findings
8.2.1 Farmers perception on the different kinds of soils, the fertility status of the soil and the use of inorganic fertilizers
The respondent farmers utilized soybean more in crop rotation and soil fertility improvement than in household consumption and marketing.
Most farmers kept their harvest for 3-6 months before sell, and believed that the time of sell was not appropriate. Farmers’ assessment also revealed poor demand of soybean compared to other crops in the local market.
Most respondent farmers believed that soil fertility has been declining over time.
Most farmers reported that obtaining inorganic fertilizers at the right application time was a problem; mainly due to the high price of fertilizer.
Farmers’ cooperatives were identified as the major suppliers of fertilizers.
However, farmers rated the quality of their services in supplying fertilizers as poor
8.2.2 Evaluation of soybean for performance under varying P regimes
The analysis of variance revealed significant GXP interaction for number of nodules and total nodule weight at Jimma, and Assossa, and for root weight and root volume at Mettu. Though the GXP and GXPXL interactions showed non-significant difference for the over locations
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combined analysis, the genotypes displayed significant difference for root fresh weight, root volume, tap root length, and weight of effective nodule.
Genotypes Pr-142 (26), AGS-3-1, SCS-1, AGS 234, and H 3 were identified as the best performing for the root and nodulation characteristics.
Significant GXP interaction was revealed for grain yield only at one site (Assosa); while the genotypes exhibited highly significant difference for most of the traits in all the sites. Most traits showed significant difference for G and GXL interaction in the over locations combined analysis.
Essex-1, IAC 11, and AGS-3-1 were the best performing genotypes at high P; genotypes IAC 11, AA 7138, G 9945 and AGS-7-1 displayed tolerance to low P; while genotypes AA-7138, PR-142 (26) and H3 exhibited stable performance across the three P levels.
8.2.3 Assessment of the genetic variability of soybean under low and high P conditions
Plant fresh weight, root fresh weight and root volume exhibited high GCV and PCV under both high and low P conditions
Both principal component and cluster analysis verified the presence of high genetic variations in the population
The traits 100-seed weight, plant height, roots and plant fresh weight combined high heritability and genetic advance estimates
8.2.4 Combining ability of the soybean genotypes under low and high P conditions
The GCA effects were highly significant for grain yield, pod length, days to maturity and plant height under low-P conditions; while grain yield, 100- seed weight, days to maturity, plant height, pod number, and pod length
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showed highly significant, and number of seeds per pod significant GCA effects under high P condition.
The relative contribution of SCA was higher than GCA for most of the studied traits under both P conditions, indicating that the non-additive gene actions were more important than the additive. The fact that non- additive gene actions are non-fixable, more selfing generations are required to eliminate the undesirable effects of the non-additive gene action.
Genotype Hardee-1 was the best general combiner for most of the quantitative traits under both low and high P conditions
8.3 Implications of research findings for breeding soybean for low P tolerance and acid soils
The fact that farmers’ acknowledged the crop rotation and soil fertility improvement role of soybean as a major reason for producing soybean could be considered as an important motive for scaling up soybean, and it was learnt that much needs to be done to improve the value chain of the crop both in the local and central market.
Farmers report on the deteriorating soil fertility and limited capacity to use inorganic fertilizers, can be related to the very low productivity of soybean relative to its potential productivity in the research field. This shows that there is a great challenge to enhance soybean production and productivity on small scale farmers’ field. In such conditions, breeding programs need to play a vital role in developing varieties that are adapted to and perform well on low fertile soil. Among the major plant nutrients phosphorus is critically important, as the soybean has inherent capacity to fix atmospheric nitrogen. Thus, breeding for low P tolerance should be at the
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top of the priorities for crops like soybean, and in areas, where the majority of the soil is acidic, and P is deficient.
Rooting traits play an important role in the screening of genotypes for tolerance to low soil fertility (Lynch, 2007); while genotypes with high nodule formation are important in improving the fertility of soils. The fact that genotypes, Pr-142 (26), AGS-3-1, SCS-1, AGS 234, and H 3 combined both high root and nodule formation made them some of the best suited for soils with low fertility. These genotypes can be used in breeding programs to improve root and nodulation characteristics in soybean.
The significant difference among the genotypes in each of the locations, and in the over locations and P levels combined analysis indicates that the genotypes exhibited significant variation that enable identify genotypes with superior performance. The existence of significant GXP interaction at Asssosa also indicates the existence of differential performance of the genotypes under the varying P regimes.
The fact that AMMI bi-plot reveled that Essex 1, IAC 11, and AGS-3-1 were the best performing genotypes at high P; while genotypes IAC 11, AA 7138, G 9945 and AGS-7-1 exhibited tolerance to low P, and AA-7138, PR-142 (26) and H3 were stable for varying P regimes indicates that these genotypes will have important role in breeding soybean for low P tolerance and stable performance for varying P conditions
Traits 100-seed weight, plant height, roots and plant fresh weight combined high heritability and genetic advance, indicating that the inheritance of such traits is controlled by additive gene actions under both P conditions.
The different techniques employed revealed high genetic variation among 36 genotypes which indicates that there is the possibility of improving the crop for performance under both low and high P conditions.
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The inheritance of traits that exhibited highly significant GCA effect, viz.
grain yield, pod length, days to maturity and plant height under low-P conditions, and grain yield, 100-seed weight, days to maturity, plant height, pod number, and pod length under high P conditions is controlled by more of additive gene action, and selection is the appropriate procedure to improve the segregating generation for performance under low and high P conditions, respectively.
The fact that Hardee-1 uniquely exhibited high GCA effect for several traits under both low and high P conditions indicates that it is the best general combiner, and can be used in breeding programs to improve soybean for better response to low P tolerance and applied P.
8.4 Challenges encountered and recommendations
Soybean crossing was one of the most challenging tasks that affected the progress of the thesis research. The major reasons for this were:
- Soybean flowers are very small and the stigma is very delicate. Thus, handling the female flower during emasculation and artificial pollination can easily damage the stigma and the flower itself.
- The fact that the night temperature was very low at Jima, getting viable pollen from the male parents for pollination was challenging. Therefore, strategies, such as timing the artificial crossing of soybean during the season, where the night temperature gets optimum, and constructing the crossing tunnel that has better capacity to retain the day temperature throughout the night. Future crossing programs need to target crossing blocks in warm locations, such as Teppi Agricultural Research Center, or Gojeb private farm. Other possibility is to renew the existing crossing tunnel in a way that the inside temperature can be maintained optimum under conditions of cool external environment.
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- There was severe epidemic of soybean rust around Jimma, and Mettu in the years 2008, 2009, and 2010, which caused the death of pods of a successful cross. Thus, disease control strategies, such as spraying need to be prepared; when planning a crossing program in situations of heavy rust incidence.
Future directions of soybean research and development in Jimma Research Center
- As the oil and fortified food processing companies are increasing in number, variety development programs need to work in-line with the quality requirements of these companies
- Screening for resistance to emerging diseases, such as rust, need to be prioritized
- Strengthening the soybean breeding program through introduction of soybean germplasm; screening and identification of superior genotypes; and hybridization and selection of best segregants using pedigree breeding procedure will be emphasized
- Soybean germplasm storage and maintenance requires major reform
- Improving the value chain of soybean by working closely with various stakeholders’ viz., farmers’, non-governmental and governmental organizations; processing companies and donor organizations will be dealt with.
In general the study clearly displayed that farmers’ realized that the fertility of their soil is declining, their fertilizer use is reducing over time mainly due to fertilizer price increase. This clearly shows that farmers are producing soybean and other crops under sub-optimum fertility