Kenya ..56 Table 2.12: Susceptibility of popular cultivars to GLS and PLS in the study area. SRS in two environments in western Kenya in 2007 ..88 Table 3.8: Mean sum of squares for GLS and other maize traits SRS and RRS.
Literature Review
Introduction
Gray Leaf Spot
- Distribution
- Causal Organism
- Factors Influencing Spread and Severity
- Symptoms
- Methods of Controlling GLS disease
- Cultural Control
- Chemical Control
- Host plant resistance
- Gene action conditioning GLS resistance
- Heritability
- Selection for resistance
Most harmful epiphytotics of GLS have been observed in areas where limited tillage is practiced (de Nazareno et al., 1992). The inheritance of GLS resistance has been shown to be highly heritable and largely additive (Clements et al., 2000; Derera, 2005; Gordon and Pratt, 2006).
Phaeosphaeria leaf spot (PLS)
- Distribution
- Causal organism
- Host plant resistance and Inheritance
An experiment in Sao Paulo, Brazil, during 1996/97 to evaluate stability and adaptability of single cross hybrids from ten inbred lines from CIMMYT, hybrid L10XL11 was observed to have some resistance to PLS (Rane et al., 1966. Silva and Moro (2004) reported additive gene effects as the main source of variation.
Recurrent selection
Among periodic selection methods, RRS is a procedure that is useful in simultaneously selecting for both GCA and SCA in two genetically unrelated heterogeneous populations (Comstock et al., 1949). Similar studies have been done on improving mid-season drought tolerance in tropical maize (Pervez et al. 2004) and selection for nitrogen use efficiency in maize (Gallais and Cogue, 2005).
Heterosis and Heterotic Patterns
Heterosis was predicted based on genetic distance based on molecular markers (Warburton et al., 2002; Xia et al., 2004). Knowing the heterotic response allows breeders to group germplasm collections into heterotic groups for better hybrid development (Reif et al., 2005).
Participatory Rural Appraisal (PRA)
Participatory Rural Appraisal has been used in various social and agricultural systems studies (Joshi and Witcombe, 1996; De Groote et al., 2001). In humid mid-elevations of the Lake Victoria basin, through the PRA, farmers identified Striga as their first limitation (Odendo et al., 2001).
Conclusions
Inheritance of resistance to gray leaf spot in crosses involving selected inbred maize lines. Epidemiology and management of gray leaf spot disease, a new disease of maize in South Africa.
Participatory Rural Appraisal of farmers’ Maize Production Constraints in
Introduction
This seems to have led to low adoption of production technologies intended to improve maize cultivation (De Groote and Bellon, 2000; Odendo et al., 2001). It has been observed that farmers evaluate maize varieties with defined criteria to meet preferences, in most cases different from those of researchers (Morris and Bellon, 2004; Daniel et al., 2007; Peter et al., 2007). Farmer-researcher collaboration to develop maize varieties is a better approach than the traditional researcher-dominated one (Ashby and Lilja, 2004; Witcombe et al., 2006).
Farmers have participated in rice improvement in China (Ruifa et al., 2007) and in Ecuador on quinoa improvement (Elaine et al., 2007).
Materials and Methods
- Study Area
- Data sources
- Sampling procedures
- Data collection and analysis
Secondary data on the physical description of the study areas were obtained from the Provincial Ministry of Agriculture in Western Kenya. The family is the main source of labor on a farm where more than three members of the family work full-time (Appendix 2.7). The research team's job was to guide and facilitate farmers' discussions, while farmers took the lead in identifying problems and developing solutions.
Daily activity map, representing the daily workload of each of the sexes to highlight gender differences;.
Results
- Agricultural Enterprises
- Maize production
- Farmers’ Criteria in Selecting Varieties
- Selection criteria for farmers in Cheptulu
- Selection criteria for farmers in Esibuye
- Selection criteria for farmers in Nalondo
- Criteria of Selection across Sites
- Constraints to Maize Production
- Perceived Strategies to Counter Constraints
- Farmer Perception of GLS and PLS
- Partners in Maize Production
The variety is becoming popular among farmers in the area as Striga is one of the weeds affecting maize cultivation in the midland and lowland areas of western Kenya. As shown in Table 2.10, farmers in different areas have different preferences in the type of varietal characteristics required. Low grade = high rank and less important; High grade = low grade and very important; - = is not a criterion in the area.
Hybrid 614 was rated high, susceptible, while Katumani, local varieties Tiriki, Anzika and Sipindi were rated low, resistant in terms of susceptibility to GLS by the farmers (Table 2.12).
Discussion
Tall varieties were also not preferred as farmers claimed that they take a long time in the fields. This suggested that farmers selected for tolerance to biotic and abiotic stresses when considering the final product, as opposed to breeders who start selecting early in the field. The increase in the spread of weeds can be explained by agricultural practices in the region.
They suggested more involvement of the Ministry of Agriculture through extension staff during tillage, planting, identification and control of pests and diseases and other constraints when the crop is in the field and finally how to choose seeds.
Conclusions
Local varieties, although low yielding, were more stress tolerant than hybrids that may have been bred for only stump borer resistance or Striga resistance, but are susceptible to more diverse stresses on the farm. Farmers' participatory evaluation of pesticide, fertilizer and seed reduction in rice farming in the Mekong Delta, Vietnam. Assessment of Farmers' Reference and Constraints on Maize Production in Humid Mid-Altitude Zone of Western Kenya.
Using the right chemicals Uproot diseased plants Applying ash (stem borer) Applying cow manure (insects) Poor market (low farm prices) Lack of information Advice from KACE CBO.
Improvement of GLS and PLS resistance in medium and highland maize
Introduction
Progeny testing in the form of half-sib (HS) and full-sib (FS) selections was successful in repeated selection for general combining ability and qualitative genetic studies. Although several studies have used RRS to improve various traits in maize, so far no work has been done to select resistance to GLS and PLS using recurrent. Similarly, the RRS method using both additive and non-additive variances can be effective in population improvement for GLS and PLS.
Therefore, the objective of the study was to improve GLS and PLS resistance in Kenyan midland and highland maize populations using RRS and SRS methods.
Materials and Methods
- Maize Populations
- Reciprocal Recurrent Selection Scheme
- Crossing blocks
- Evaluation of Progenies of RRS Selection method
- Data collection
- Data analysis
- Selection
- Recombination
- Simple Recurrent Selection
- Crossing Block
- Selection
- Recombination
- Evaluation of population cycles and commercial checks
- Data analysis
- Response to Selection
- Heritability estimates
At flowering, all ear shoots were covered before the appearance of the silk with shoot bags to avoid contamination with pollen from an unknown source. The number of progeny families of the rescued S1 families evaluated in each population varied from population to population depending on seed availability. A pinch of the inoculum was placed in the whorl of the plant at knee height stages (8-10 leaves) and a second inoculation was carried out after another 14 days.
Data were collected on diseases, GLS, PLS, number of days from planting to 50% flowering (50% of plants on the plot have anthers), number of days to 50% silking, ear height in centimeters from the base of the plant at ground level to the base of the ear and diseased ears.
Results
- Reciprocal recurrent selection
- Response to Selection Using RRS method
- Simple Recurrent Selection
- Response to Selection with SRS Method
- Comparison of One Cycle of SRS and RRS
- Percentage Gain in One Cycle (C 0 and C 1 ) of Selection for GLS
- Heritability Estimates
- Correlations between GLS and Yield in Pool A and EC 573
In one selection cycle, there were significant (p<0.05) differences between gains observed with SRS and RRS selection methods (Table 3.10). For dividends, the highest percentage gains were realized in pool B and the lowest in pool A (table 3.10). Heritability estimates for GLS resistance were less variable in the three populations, except for pool A (Table 3.11).
The relationship between GLS and yield in group A was negative and significant for C0 and C1 using SRS (Table 3.12).
Discussion
In the case of ear height, there was reduction across the population in SRS method except in Pool A which had an increase in ear height. For RRS there was an increase in ear height in pool A, pool B and KSII but a reduction in EC 573. For both methods there was a reduction in days to 50% anthesis and silk as GLS was selected for all the populations.
Although the correlations were small and not significant, there was a common trend in these traits when selecting for GLS resistance.
Conclusions
There was negative significant correlation between PLS, GLS and yield in pool A in early selection cycles but reduced in advanced cycles. Yield loss potential of Phaeosphaeria leaf spot of corn caused by Phaeosphaeria maydis in the United States. Response to Recurrent Selection for Resistance to Striga hermonthica (Del.) Benth in a Tropical Maize Population.
Genetic gains from repeated cycles of complete selection for low nitrogen tolerance in a tropical maize population.
Heterotic Classification and Combining Ability of Local and Exotic Medium
Introduction
Knowledge of heterosis allows breeders to group germplasm collections into heterotic groups for the purpose of hybrid development with higher performance (Reif et al., 2005). Line of tests have also been used extensively to group germplasm into heterotic groups or patterns. Specific combining ability has also been used to classify germplasm into heterotic groups (Pilar et al., 2003).
Nine heterotic groups are used in maize breeding programs in East and Southern Africa.
Materials and Methods
- Germplasm Collection
- Multiplication Nursery
- Crossing Block
- Data Collection
- Data Analysis
- Classification of Germplasm into Heterotic Groups
- Heterosis Analysis
- Combining Ability Analysis
Given the importance of the diseases and the need to improve the population through the use of local and exotic germplasm, it is imperative to know the heterotic germplasm groups and their GCA effects for GLS and PLS as there is currently very little information on the genetic analysis of Resistance GLS and which heterotic groups farmers' collections fall into in Kenya. Therefore, the objective of the study was: (i) to characterize maize germplasm collections in their heterotic groups and (ii) to determine the effects of their combining ability for GLS. Data for GLS and PLS, number of days from planting to 50% anthesis, 50% plants in plot with anthers, number of days to 50% silking, ear height (centimeters) from plant base to ground level until the base of the ear and diseased ears were recorded.
Heterosis of the test crosses for yield and SCA was used to classify germplasm into heterotic groups, but the final classification was based on yield percentage as not all accessions were represented in SCA.
Results
- Germplasm Characteristics
- Testcrosses
- Means of Testcrosses of Pool A
- Means of Testcrosses of Pool B
- Means of Testcrosses of KSII
- Means of Testcrosses of EC 573
- Means of Testcrosses across Four Populations
- Heterosis
- Percent heterosis of Pool A testcrosses
- Percent heterosis of Pool B testcrosses
- Percent heterosis of KSII testcrosses
- Percent heterosis of EC 573 testcrosses
- Classification of accessions into heterotic groups based on
- Combining Ability effects for GLS and other five maize traits
- General combining ability effects for GLS, PLS, yield and four other
- Specific combining ability effects
- Heterotic classification of accessions based on SCA
Most of the test crosses of Group B were not significant (p<0.01) for GLS percentage and yield heterosis (Table 4.10). The percent heterosis for days to 50% anthesis and silk of most crosses was negative and significant (p < 0.05) as shown in Table 4.12. Specific combining ability was characteristic for all traits (p < 0.05), but not for days to 50% anthesis and silking (Table 4.14).
Most crosses had non-significant zero and negative SCA for yield as shown in Table 4.17.
Discussion
- Mean of six traits of test crosses
- Heterotic grouping based on percentage yield heterosis
- Combing ability
- Heterotic grouping based on SCA
Similarly, Kitale Synthetic II had more than 70% of crosses with a negative percentage of heterosis, in contrast to EC 573 with a positive percentage of heterosis. This indicated that Kitale Synthetic II was genetically more closely related to the local collections than EC 573. Most exotic germplasm were found to belong to KSII, Pool A and Pool B and showed moderate and significant heterosis with EC 573, indicating that they were genetically diverse goods. from EC 573.
Pool A and EC 573 had more variation in their classification of the accessions compared to Pool B and KSII.
Conclusions
These populations and collections are highly heterotic with each other in terms of yield, GLS and PLS in the right direction with significant heterosis from zero (p<0.05) positive and negative for yield and the two diseases, respectively. Collections Embu 12, Taiwan and Cheborosinik have been recommended for infusion in these populations to improve resistance to GLS and PLS. High heterosis was observed between collections and populations for GLS, PLS, yield, ear height, days to 50% silk and anthesis, implying that there is ample scope for expanding the genetic base of these populations.
The high variations also implied that more cycles of selection could be made in these populations by populating local collections better adapted with identified desirable traits.
General Overview
- Introduction
- Literature review
- Maize Production Constraints, Farmers Perception and Preferences
- Heterosis and Combining Ability of Germplasm Collections
Yield losses of more than 50% due to GLS and PLS have been reported in several countries. There is very little information published in Kenya regarding GLS and PLS research. It was also indicated from the review that very little research has been done in Kenya in relation to GLS and PLS.
Information about and use of recurrent selection methods in disease improvement, especially for GLS and PLS, is limited.
