Chapter 5: General Overview
• Participatory rural appraisals have been successful in identifying farmer constraints in various countries, similarly with participatory plant breeding with farmers.
• Gray leaf spot and PLS were important in Kenya and widely spread in all maize growing areas. Yield losses of more than 50% due to GLS and PLS were reported in several countries. Studies conducted reported GLS and PLS to be highly heritable with both GCA and SCA effects being important. For both diseases, breeding for resistance was advocated for.
• There was very little information published in Kenya in regards to GLS and PLS research. Also it was indicated from the review that very little research in Kenya has been conducted in respect to GLS and PLS.
• Heterotic systems being followed in Kenya in regards to heterotic patterns and heterotic groups of landraces, local collections are not well documented.
• Information and use of recurrent selection methods in disease improvement especially for GLS and PLS is limited.
5.3 Maize Production Constraints, Farmers Perception and Preferences
Collaboration between farmers and scientists in identification of farmer constraints, preference and perception for variety development is essential. A PRA was undertaken in 2004/2005 in two districts of western Kenya. This was through focus group discussions involving farmers, scientists, opinion leaders, administrators and local agricultural extension staff. From the PRA the following were established:
• There was a yield gap in maize production ranging from 4.7t ha-1 to 5.3t ha-1 between on-farm maize and the expected yield potential across the sites in Western Kenya. Across the sites, the constraints considered more important were low soil fertility, non viable seed and lack of seed, drought, Striga, diseases
(GLS, PLS, ear rots, streak), stalk borer and poor farming technologies. Farmers also considered constraints that directly affected yield to be more important.
Improved varieties were more susceptible to GLS and PLS and farmers had no knowledge of the causes and modes of transmission of GLS and PLS, as they perceived fertilizer or frost as the causal agents and bees as mode of spread from farm to farm.
• Farmer criteria for variety selection depended on importance of the constraints.
Those considered important were low input requiring variety, Striga resistance, drought resistance, disease resistance, early maturing and heavy grains. Local varieties were more preferred than the improved hybrid varieties because they were more tolerant to stresses than hybrids.
• Farmers recycled seed for planting from advanced generations of previous season due to high cost of seed. Criteria for seed selection considered were closed tips, big cobs, 8 row and healthy cobs. Farmers were concerned of their non participation in variety development, especially in constraint identification and on-station and on-farm evaluations.
• Across all the sites, farmers emphasised the need for training in crop management, especially in pests, weeds, diseases, seed selection and better utilization of compost and farmyard manure. Above all they echoed the need of farmer and breeders collaboration in the research and on-farm activities.
5.3 Heterosis and Combining Ability of Germplasm Collections
From the heterosis study, it was established that:
• Based on yield percentage heterosis, it was established that local collections and introductions evaluated belonged to distinct heterotic groups. Seven collections were grouped to Pool A, 17 to Pool B, 13 to KSII and six to EC 573 heterotic group. Future research should focus on identifying favourable traits in these collections and infusing them into their respective populations. More germplasm
collection and heterotic studies should be undertaken to identify useful germplasm that was not captured in this study.
• It was also possible to group collections into heterotic groups using SCA data.
Although the classification was not based on SCA as it did not contain all representative crosses for evaluation and for proper classification of all the germplasm evaluated.
• Both GCA and SCA effects were important in conditioning GLS, PLS and yield, but SCA accounted for more than 50% of the variation in these populations. This indicated high heterosis in these populations and collections. Future research should focus on development of top cross hybrids and inbred lines that are resistant to GLS, PLS and high yielding.
• Testcrosses with good GLS, PLS resistance and high yielding were identified.
These included, Embu 12 x Pool A, Taiwan x Pool A, Cheborosinik x EC 573.
These top crosses will be recommended for on-farm evaluation. Embu 12, Chalco and Reg Nur were found to possess good GLS and PLS resistance levels will be recommended for improvement of these populations.
5.4 Selection for GLS and PLS Resistance
Improvement of medium and highland populations was done in 2004/2007at Kakamega research station, and the findings were as follows:
• It was established that improvement of GLS and PLS resistance can be achieved by using SRS and RRS selection methods as two and one cycle of selection for GLS and PLS were achieved in SRS and RRS in two years, respectively. Simple recurrent selection method resulted in higher percentage gains than RRS method. For the two methods, average GLS percentage gains ranged from -61.3 to 6.4 for KSII and EC 573, respectively. These two methods should be tried on other diseases to exploit their potential in disease improvement in maize breeding.
• Heritability estimates for GLS were high and ranged from 59% to 76.8% in Pool A and KSII, respectively. This makes SRS more useful as field phenotypic variances are used for selection. Therefore, SRS method should be recommended for populations that show high heritability and where time is the limiting factor. In populations with very low heritability and time is not limiting, RRS should be recommended.
• Negative and significant correlations were observed between GLS and yield and also PLS and yield. This should be exploited in selection for either GLS, PLS or yield particularly in Pool A where r = -0.926 for GLS and yield and r= -0.947 for PLS and yield were observed.
• In these populations, high response to GLS selection was observed in KSII and lowest in Pool B. In selecting for GLS resistance in these populations, high selection intensity in Pool B is recommended.
5.5 Conclusions and Way Forward
In light with the findings of this study,
• Participatory rural appraisals and participatory plant breeding should be emphasised so as to aid breeders in the type of varieties to develop. Also use of farmers’ criteria in variety evaluation will result in varieties that address the real problems on-farm.
• Constraints and preferences identified in this study should be the basis of formulation for research agenda. This will guide in the type of varieties to develop. As it is now evident that farmers recycle seed due to high cost of improved seed, OPVs should be a priority for breeders to develop.