Significant (P≤0.05) effects of general combining ability (GCA) and specific combining ability (SCA) were recorded for root yield in both drought stress and no stress conditions, indicating that both additive and dominant gene effects were important in the inheritance of resistance against drought stress. ICARDA International Center for Agricultural Research in the Dry Zones IPGRI International Council for Plant Genetic Resources (Bioversity).
Importance of sweetpotato
2. pests and diseases of major crops such as wheat and maize, 4) growing understanding among consumers that sweet potatoes are a healthy crop to eat rather than a poor man's food, and 5) the growing shift of sweet potatoes from a subsistence crop to ' a commercial crop (Stathers et al., 2005).
Constraints to sweetpotato production
Drought
Therefore, the presence of one or more of these drought resistance mechanisms in different combinations can make a variety drought tolerant at a certain stage of its growth cycle (Amede et al., 2004). In sweet potato, drought stress is detrimental during the stages of crop establishment and storage root filling (Ekanayake, 1990).
Breeding for drought tolerance
The cultivar with the lowest number of plants (that is, the least drought tolerant) also had the lowest yield of 9.65 t ha-1 (Mkandawire et al., 2008b). In La Trinidad, Philippines, Anselmo et al. 1998) evaluated seedlings from a polycross of eight local landraces of sweet potato during the dry season.
Problem statement
Drought counts were made at 79 and 100 days after planting (DAP) and yield capacity of genotypes at harvest which is also used as an indicator of drought tolerance. This will help identify the most suitable test environments for evaluating drought tolerance of sweet potatoes in Kenya.
Research objectives
Therefore, it would be important to determine the size of GEI and yield stability of sweet potato clones and advanced genotypes.
Research hypotheses
In addition, drought is highly correlated with ecological zones and thus any drought study also requires analysis of genotype x environment interaction (GEI). This will help identify the most suitable test environments for evaluating drought tolerance of sweet potatoes in Kenya. iii) Potato storage root yield performance is influenced by genotype x environment interaction. iv) Sweet potato responds to moisture stress through several mechanisms. v) The inheritance of genes for drought resistance and other agronomic traits is controlled by both additive and non-additive gene action.
Structure of the thesis
Screening sweet potato for drought tolerance in the Philippine highlands and genetic diversity among selected genotypes. Growth, yield and quality of sweet potato (Ipomoea batatas (L.) Lam..) cultivars in the southeastern Anatolian and eastern Mediterranean regions of Turkey.
Introduction
- Origin of sweetpotato
- Botany of sweetpotato
- Flowering in sweetpotato
- Growth requirements for Sweetpotato
In addition, Pacific Islanders are among the largest per capita consumers of sweet potatoes in the world today (Rossel et al., 2001). The crop is very sensitive to aluminum toxicity, which occurs at pH below 4.5 and can lead to crop death within six weeks (Ames et al., 1996).
Constraints to sweetpotato production
- Moisture stress
- Plant response to drought stress
- Water use efficiency
- Drought tolerance mechanisms
Root growth traits play important roles in drought stress tolerance in plants (Ahmad et al., 2009). Crops under water stress undergo three stages of dehydration; alarm, resistance and exhaustion (Amede et al., 2004).
Breeding for drought tolerance
- Sources of drought tolerance
- Drought evaluation and screening methods
- Identification of drought related genes
- Sweetpotato breeding
- Participatory rural appraisal (PRA)
- Gene action and heritability
Increased drought tolerance relies on finding the most suitable alleles of drought tolerance genes and pyramiding them (Sorrells et al., 2000). The diallel mating design is used to study the polygenic effect (Hayman, 1954; Hallauer et al., 2010).
Genotype x environment (GE) interaction and stability
- Additive main effects and multiplicative interaction model (AMMI)
- Genotype, and genotype x environment (GGE) biplots
- Regression
Overlapping genotypes in the biplot (Muibai and Marooko, 440015 and K135, Ejumula, Jubilee and Sponge, Sponge and Bungoma and Jewel and Salyboro) indicated cross-over interaction in the different environments (Mwololo et al., 2009). Genotype and genotype x environment interaction biplots enable assessment of yield trials in multiple environments (Kaya et al., 2006; . Yan and Tinker, 2006; Choukan, 2011).
Summary
The stability behavior of the genotypes can be determined using regression analysis (Eberhart and Russell, 1966; Becker and Léon, 1988; Ngeve, 1993). The overall impact of drought stress is a reduction in the quantity and quality of the harvestable portion of the crop.
Introduction
Importantly, farmers use almost all parts of the sweet potato as livestock feed (Claessens et al., 2008). Other diseases affecting sweet potatoes include alternaria, bacterial wilt, and fusarium wilt (Ames et al., 1996).
Materials and methods
- Study area
- Sampling procedures and data collection
- Data analysis
Four districts were selected in each region (Eastern, Central and Western Kenya) with the assistance of the extension officers. Sweet potato farmers were selected from two wards in each of the selected districts but spread across the villages of the wards with the help of extension officers in the localities.
Results
- Farmers interviewed in four selected districts/divisions
- Demographic information
- Food and cash crops grown by the farmers in the regions
- Sweetpotato varieties grown by farmers
- Cultural practices
- Sweetpotato planting material conservation method
- Sweetpotato farmers’ yields
- Sweetpotato production constraints
- Farmers’ coping strategies for the constraints
Qualities of the most preferred genotypes were; orange flesh (OFSP), favorable sugar content (FSC), favorable starch content (FSC), low fiber content after cooking (LF), not overcooked during normal cooking time (NO), high yield (HY) and improved varieties (IV). Farmers' coping strategies regarding pest constraints were mainly the use of clean planting material (20%), the use of crop rotation (15%) and early harvesting practices (15%). In terms of diseases, most farmers (24%) returned to using clean planting material to combat viral diseases, followed by crop rotation (22%) and use of resistant clones (19%) (Table 2.4b).
Discussion
- Demographic information
- Food and cash crops, and sweetpotato varieties
- Cultural practices
- Sweetpotato planting material conservation method
- Sweetpotato yields
- Sweetpotato production constraints and coping strategies
The sweet potato planting material was mostly recycled from the previous crop, as only a very small proportion of farmers indicated that they used certified planting material. There is a great need to develop a workable system of developing clean and sufficient sweet potato planting material prepared at the onset of the rains. This means that production constraints need to be addressed in order to improve sweet potato productivity.
Conclusion
Tusiime, eds, Proceedings of the thirteenth triennial symposium of the International Society for Tropical Root Crops (ISTRC) ISTRC, AICC Arusha, Tanzania. Proceedings of the thirteenth triennial symposium of the International Society for Tropical Root Crops (ISTRC). Proceedings of the thirteenth triennial symposium of the International Society for Tropical Root Crops (ISTRC) ISTRC, AICC Arusha, Tanzania.
Introduction
These drought tolerant genotypes can be identified through germplasm screening under controlled drought stress conditions. No research has yet been conducted in Kenya to determine the drought stress tolerance of sweet potato genotypes. Because only about 20% of the land in Kenya receives adequate rainfall, there is a great need for the development of drought-tolerant crops (Jaetzold et al., 2006).
Materials and methods
- Description of sites
- Sweetpotato germplasm
- Field evaluation
- Chlorophyll content determination
- Greenhouse evaluation
- Data analysis
The SPAD was calibrated by analyzing the chlorophyll content of samples collected from some of the genotypes used. Three leaves were randomly sampled in each of the following randomly selected genotypes for calibration; Prior to the start of the experiment, the growth medium was watered to field capacity.
Results
- Weather conditions
- Soil chemical properties
- Results of field evaluation
- Mean performance of genotypes
- Genotypes performance across environments
- Poor performing genotypes under drought stress and no drought stress
- Days to permanent wilting point
- Drought susceptibility index for the best performing genotypes across the
The performance of the other traits observed in a drought stressed environment is shown in Table 3.5b. Note: The abbreviations of the measured characteristics and rankings are as shown in Table 3.4. 3.3.7 Poor performing genotypes under drought stress conditions and without drought stress. The best performing clones under drought stress conditions were Kilungu, Munyilia-3, 48-Gabagaba and Marooko and had the lowest DSI (Table 3.8; Appendix 3.4).
Discussion
- Weather and soil conditions
- Performance of genotypes
- Genotype performance under irrigated and non-irrigated environment
- Days to permanent wilting point
- Drought susceptibility index for the best performing genotypes across the
The results agree with the findings of Malla et al. 2012) who reported yield reductions of 65-80% in rice grown under drought stress and non-drought stress regimes. In this study, clone 441725 was also among the best in the non-drought stress environment, indicating that it is stable and high yielding. This clone also performed among the best in non-drought stress and overall average environmental performance, indicating that it was high yielding.
Conclusion
Development of upland rice cultivars for drought tolerance through drought susceptibility index and stability parameters. Assessing the effectiveness of Dalton's weighing tapes and body measurements to estimate live weights for small East African zebu cattle in Kenya. NSR= number of stock roots, FSR= fresh stock root weight, RDM= root dry matter, FB= fresh biomass weight, MFSR= salable fresh stock root weight, HI= harvest index, DPWP= days to permanent wilting point, LCC= leaf chlorophyll content, and rank = ∑x , where x is the sum of genotype rank in each measured trait, where k = rank in trait 1, and n = rank of the last trait.
Introduction
The ability of crop varieties to withstand drought stress varies worldwide (Walters et al., 2002). Drought alters the sink-source relationship by affecting assimilate production, translocation and partitioning (Mundree et al., 2002). Genotypes continuously exposed to drought stress for some time and in different environments express their ability to tolerate drought stress (Amede et al., 2004).
Materials and methods
- Plant materials
- Locations
- Tensiometer calibration
- Statistical analysis
Where Yij is the corresponding variable for the ith genotype in the jth environment (location), µ is the pooled mean, Gi is the main effect of ith genotype, Ej is the main effect of jth environment, GEij is the effect of genotype x environment interaction . Where; Yij is the cell mean in the ith genotype and jth environment, µ is the overall mean gi. The least square estimate of the AMMI parameters λk is the singular value of the nth PCA axis, αik andyjk are the scores of the ith genotype and the jth environment. The AMMI model was adjusted depending on the number of principal components (PC) considered.
Results
- Climatic data
- Combined AMMI analysis of variance
- Genotypic yield performance in the test environments
- AMMI GE and IPCA scores biplot
- GGE biplot analysis
- Ranking GGE biplot
- Relationship between environments
- Regression analysis
Perpendicular lines were then drawn on each side of the polygon starting at the origin of the biplot. Another line called the average environmental axis (AEC) was also used to show the ranking of genotypes with their average yield and viability. The line passed through the origin of the biplot and another line perpendicular to it was drawn to represent the stability of the genotypes.
Discussion
- Climatic data
- AMMI analysis on genotype performance across environments
- AMMI GE and IPCA scores biplot
- GGE biplot analysis
- GGE ranking biplot for stability and yield
- Relationship among test environments using GGE biplots
- Regression analysis
- Comparison of yield and stability of genotypes using the different methods
Some of the genotypes with high yields under no drought stress also tended to perform well under drought stress conditions over the four cropping seasons. A polygon view of the GGE biplot revealed the highest yielding genotypes for each environment and clustered the environments. The environments can be grouped into two based on drought tolerance expression and discrimination groups of the genotypes; E2, E4, E6, E8 and E1, E3, E5, E7.
Conclusion
The GGE biplot showed G1 and G13 as stable comparable to AMMI biplot, while G8 and G24 were unstable comparable to AMMI biplot. Ranking based on GGE biplot indicated that G7, G3, G22, G20 and G1 are among the highest yielding genotypes, similar in AMMI and GGE biplot analysis. GGE biplot - Windows application for graphical analysis of multi-environment trial data and other types of bi-directional data.
- Introduction
- Materials and method
- Plant materials and experimental site
- Data analysis
- Results
- Weather conditions
- Soil chemical analysis
- Analysis of variance for yield traits
- Genotype performance for yield traits
- Performance of genotypes on the growth traits
- Performance of the genotypes on drought stress traits
- Discussion
- Weather conditions and soil analysis
- Genotype performance for yield traits
- Performance of genotypes for the growth traits
- Performance of the genotypes for moisture stress traits
- Conclusion
Pencil root length was longer in genotypes under drought stress, indicating that sweet potato responds to drought stress by increasing. Drought-tolerant genotypes had increased root yield, while the number of storage roots and vine branches decreased with increasing drought stress. Drought stress after 90 DAP) (R3) did not cause a significant difference with the non-stress regime (control) in root drought.
Introduction
Drought is the major abiotic constraint found in large parts of this region (Anjum et al., 2011). Diallele mating designs are commonly used to determine gene action for quantitative traits (Hayman, 1954; Hallauer et al., 2010). Mwanga et al (2002) reported additive gene action as dominant for SPVD resistance, Chiona (2010) reported additive gene action in the inheritance of β-carotene.
Materials and methods
- Experimental sites
- Plant materials and crosses
- Field experiment
- Screen house experiment
- Ranking the clones
- Statistical analysis
Four of the 15 families (G3, G6, G9 and G11) had negative and significant effects of SCA on fresh root yield under both drought stress and no drought. Five out of 15 families; G7, G8, G10, G12 and G15 had significant positive effects of SCA on storage root yield under drought and non-drought stress conditions. The best two parental crosses under drought and without drought stress were G15 (P3 x P5) and G5 (P4 x P5).
Results
- Analysis of variance
- Performance of F1’s and parents under drought and no drought stress
- Combining ability effects
- Combining ability effects under drought stress environment
- Combining ability effects under no drought stress environment
- Heterosis
- Heterosis under drought stress environment
- Heterosis under no drought stress environment
Discussion
- Performance of F1’s and parents under drought and irrigated environment
- Combining ability effects
- Performance of F1’s in days to permanent wilting point (DPWP)
- Estimates of heterosis
G10, G12 and G15 progeny of P5 and P6 parents had positive and significant effects of GCA under drought and without drought stress on FSR. RDM SCA effects in drought but positive without drought stress, suggesting that probably root dry matter could be negatively related to yield and drought tolerance. The storage root yield of the G15 family was ranked among the highest without drought and among the highest under drought stress, indicating that this progeny can be stable, high-yielding, and drought-tolerant.
Conclusion
Progeny G15, whose parents were P3 and P5 and were susceptible to drought, had high root yield under drought and no drought stress environment, indicating that donors of drought tolerance genes may actually be drought susceptible themselves. The high DPWP indicated that sustained but slow growth of vines was one of the mechanisms of drought tolerance. Water stress effects on combing ability and reactivity of yield and genetic traits of drought tolerance indices in maize.
Overview of the Study
- Determining the production constraints and farmers preferences on grown
- Evaluation of sweetpotato genotypes for tolerance to drought stress
- Genotype x environment interaction for storage root yield in sweetpotato
- Mechanisms of tolerance to drought stress in sweetpotato
- Heterosis and combining ability for drought tolerance
Genotype 194555.7, Unawazambane Tanzania, Chingova performed well in both drought and no drought stress environment and had DSI <1 and could therefore be further investigated for confirmation of drought tolerance. The study also highlighted a number of drought tolerant mechanisms on which breeding for drought tolerance could be based. The GCA/SCA ratios indicating the dominance of additive gene effects will enable the achievement of genetic gain for drought tolerance through mass recurrent selection under sufficient drought stress selection pressure.
