Farmers' perceptions of the importance of two bruchid species to beans both in the field and in storage were established using a participatory rural appraisal (PRA) in three extension planning areas (EPAs) in the Lilongwe Agricultural Development Division (ADD). Arcelin A seed defense protein that accumulates in the seed cotyledon identified in wild bean accessions and confers resistance to dry bean against Zabrotes subfasciatus.
Importance of dry beans in eastern and southern Africa
Bean production statistics for Malawi
Status of bean research in Malawi
Involving farmers in cultivar development through participatory plant breeding is likely to increase the adoption of newly developed technologies, including new crop varieties (DeVries and Toenniessen, 2001; Bänziger, 2004).
Constraints on bean production
Bruchids, their importance and control methods in Malawi
Host plant resistance and gene action for bruchid resistance
Justification for the study
No effort has so far been made to screen local germplasm to identify effective sources of resistance to bruchid strains found in Malawi. This diversity can be used to identify possible sources of resistance to the bean bruchid.
Thesis structure
Introduction
This chapter provides an overview of bean genetic diversity and major gene pools and their breeding implications. The strategies that have been used to breed bruchid resistance in dry bean, the key role of germplasm collection and its use to provide sources of such resistance are also reviewed.
Origin, gene pools and genetic variation in dry beans
The common bean presents a remarkable range of diversity of phenotypic traits (Debouck, 1999; Singh, 2001), ranging from its morphology, cultivation, use to its ability to adapt to different environments (CIAT, 2001). The world average yield of common bean remains as low as <900 kg ha-1 and bean production continues to suffer from many biotic and abiotic constraints.
Bean genetic diversity in Malawi
The greatest bean diversity was observed in the northern and central regions of Malawi, with less genetic diversity reported in the south (Martin and Adams, 1987a). A follow-up collection was made in 1983 following the initiation of the Bean-Cowpea Research Support Program (CRSP) at the Bunda College of Agriculture.
The genus Phaseolus
Further analysis revealed that this diversity was produced both biologically (Martin and Adams, 1987b) and socio-culturally (Barnes-McConnell, 1989). Significant regional variation in the number of bean varieties grown by smallholder farmers has been documented (Ferguson and Mkandawire, 1993).
Inter-specific and intra-specific hybridisation in dry beans
Bean bruchids and their importance
Composition and distribution of the two bruchid species
Ecology and biology of the two bruchid species
There is some variability in the length of their life cycles and the number of eggs laid, depending on the geographic region (Kornegay and Cardona, 1991). Understanding the biological differences and distribution of the two bruchid species is critical to develop management strategies through improved cultivar development, targeted distribution of resistant cultivars, cultural control methods or integrated pest management (IPM).
Bruchid management and control strategies
- Cultural and interference control methods
- Chemical control methods
- Biological control methods: Use of parasitoids
- Host plant or varietal resistance
These field crops may not provide effective control of bruchids, which are primarily storage pests. Ecological and environmental benefits arise from increased species diversity in the agricultural ecosystem, in part due to reduced use of insecticides.
Breeding for bruchid resistance
For example, plant resistance to insects is compatible with insecticide use, whereas biological control is not. Host plant resistance to insect pests offers a potential and sustainable option to be exploited in insect pest management.
Bruchid resistance testing methods
The no-choice test method involves measuring the antibiosis and measuring the development period, the number of emerging insects and the percentage of grain weight loss. In this study, field contamination was carried out according to the free-choice system and the no-choice test method under laboratory conditions was used to verify bruchid resistance.
Mechanisms of bruchid resistance
These methods have previously been used to screen genotypes for weevil and/or bruchid resistance (Tipping et al., 1989; Cardona et al., 1990; seed coat tannins (Deshpande, 1992) and trypsin inhibitors (Savelkoul et al., 1992) have been implicated in seed resistance to bean weevils.
Resistance factors to storage pests
Understanding the factors influencing a brucid bean attack in the field can help breeders develop appropriate intervention strategies (Teshome et al., 2001). Certain characteristics of the cellular structure of the seed coats of some pea (Vigna unguiculata L.) varieties partially prevented the entry of the first instar larvae of Callosobruchus maculatus (F.) (Shade et al., 1996).
Role of arcelin in bean bruchid resistance
The presence of arcelin, a seed protein of the phytohemagglutinin-arcelin-α-amylase inhibitor gene family, has been associated with bean resistance to Z. However, the introgression of arce into cultivars resulted in the replacement of α-amylase inhibitor 1 (AI-1) with α -amylase inhibitor 2 (AI-2), which makes the arc ineffective against Z.
Factors mediating the expression of resistance and durability of
A preliminary study of the nutritional properties of RAZ-2, a recently developed bean line containing arc 1, fed to rats showed anti-nutritional effects on rat metabolism (Putzai et al., 1993). However, it has been argued that most of the anti-nutritional effects of RAZ-2 beans can be eliminated by boiling fully hydrated beans at 100oC for 10 minutes.
Gene action and inheritance of bruchid resistance
A recent review of phenotypic variation in hybrids indicates that transgressive segregation is common in segregating plants (Rieseberg et al., 1999). In another study on the inheritance of resistance to oviposition by corn weevil, Tipping et al. 1989) reported that additive gene action was important.
Mating designs and the usefulness of the diallel
The consequences of maternal effects for the response to selection can be further complicated by the correlation between maternal and offspring environments (Singh and Murty, 1980; Rossiter, 1996). Actual influence of maternal effects on response to selection will depend on the type of maternal effect involved.
Assumptions of the diallel mating design
Christie and Shattuck (1992) concluded that diallel analysis is a sophisticated form of progeny testing from which information unavailable from any other analysis can be obtained and which can be used in plant breeding to aid selection. The parents used in the study were randomly selected based on degree of resistance or susceptibility, and it is recognized that a small sample of six parents was used and therefore it may be difficult to validate this assumption.
Summary
Proceedings of the International Symposium on Methodologies for the Development of Host Plant Resistance to Corn Insects. Evolutionary relationships among proteins in the common bean arcelin alpha amyl family of phytohemagglutinin inhibitors and its relative.
Introduction
Smallholder farmers, especially those in marginal areas, are known to have low adoption of new crop varieties (Cooper, 1999; Cleveland et al., 2000; Ceccarelli et al., 2001). DeVries and Toenniessen (2001), citing Ahmed et al. 2000), also showed that adoption of sorghum and millet varieties was very low in most countries in eastern and southern Africa.
Materials and methods
- Features of the study areas
- Data collection and analysis
- Indigenous bruchid control methods validation study
A summary of the information obtained from the bean traders in the various markets is presented in Table 2.2. The purpose of the study was to confirm what some respondents stated about the effectiveness of some bruchid control methods in controlling two species of bruchids in storage.
Results
- Secondary data
- Damage caused by bruchids
- Bruchid control methods used by farmers
- Appraisal of farmers’ bruchid control methods
- Varieties grown and farmers’ preferences
- Perceptions of bruchid incidence and severity
Super-actelic dust was effective on both species of bruchids (Tables 2.8 and 2.9) as it was lethal to almost all bruchids that emerged. Farmers' ratings of bean variety trait preferences were slightly different from those of traders (Table 2.12).
Discussion and conclusion
These findings support the hypothesis that there is little adoption of improved bean varieties in Malawi. An evaluation study showed that some control methods used by farmers are more effective against Z.
Introduction
Breeding resistance to bruchids in bean varieties would be valuable in providing a sustainable method to reduce bean losses. In America, an effort has been made to develop bean varieties containing arcelin, a protein that confers resistance to Z.
Materials and methods
- Bean germplasm collection
- Bruchid laboratory culture
- Bruchid resistance testing
- Bruchid resistance rating
- Classification of genotypes for resistance to bruchids
- Testing the resistance mechanism
In the no-choice test, the insects were allowed to lay eggs and develop on the supplied bean samples. In the field experiment, insects could feed and/or oviposit on bean genotypes of their choice.
Results
- Resistance of bean germplasm to Zabrotes subfasciatus in the laboratory test
- Resistance of bean germplasm to Acanthoscelides obtectus in the laboratory
- Resistance of improved genotypes to Acanthoscelides obtectus in the
- Confirmation of genotypes’ resistance to Acanthoscelides obtectus under
- Resistance of genotypes under field infestation
- Comparison of genotypes’ resistance to Acanthoscelides obtectus under
- Relationship between phenotypic traits in the field and adult bruchid
- Role of seed coat in influencing resistance of bean genotypes to
Overall, the ranking of genotypes for resistance showed that most genotypes were ranked differently in the field free-choice test (with the exception of those previously rated as superior in non-choice laboratory trials). The seed coat has been shown to play an important role in expressing the resistance of bean genotypes to attack by two bruchid species (Table 3.9).
Discussion
- Expression of resistance in landraces to the two bruchid species
- Bruchid resistance mechanisms: role of arcelin and the seed coat
- The influence of morpho-physiological traits on bruchid resistance
- Field resistance of bean genotypes
This explains the decline in the number of insect offspring that appeared when it was the seed coat. In the present study, resistance was not affected by any of the morphophysiological traits that were measured.
Conclusion
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Introduction
The inheritance of resistance to the bean pod weevil (Apion godmani W.) in dry beans is conditioned by two genes that segregated independently (Garza et al., 1996). No inheritance studies of resistance to bruchidee have been conducted in Malawi with the Malawian dry bean landraces.
Materials And Methods
- Germplasm
- Field procedures and diallel mating scheme
- Resistance testing of the F2 and F3 generation seed
- Parameters used to differentiate bruchid resistance of genotypes
- Determination of combining ability estimates
- Segregation analysis
- Confirmation of the adequacy of the additive-dominance model
- Estimation of components of variation and genetic parameters
The F2 seeds were harvested and pooled for each of the 30 crosses (ie, 30 bulk samples, one for each population). The frequency distribution of the Dobie susceptibility indices (DSI) for the genotypes in each of the F3 generation seeds was plotted.
Results
- Bruchid resistance in the F2 generation seeds
- Combining ability estimates for adult bruchid emergence in F2 generation 135
- F3 population segregation analysis
- Frequency distribution of bruchid resistance of the F3 genotypes
- Adequacy of the additive-dominance model
- Estimation of the components of variation and the genetic parameters
- Relationships among resistance measurements in the F3 generation seed 144
- Resistance of genotypes
- Combining ability estimates for bruchid resistance
- Role of maternal inheritance or the cytoplasmic effects for resistance
- Transgressive segregation
- Gene action and the genetic parameters
Variances for the number of bruchid emergence and the Dobie susceptibility indices varied among the populations in the F3 generation seeds. Estimates of the genetic parameters were made in the F2 population and the results are shown in Table 4.13.
Summary and conclusions
Correlation between the phenolic acid content of maize and resistance to Sitophilus zeamais, the maize beetle in the COMMIT collections. Inheritance of resistance to the bean weevil (Apion godmani Wagner) in common beans from Mexico.
Introduction
Summary of the major findings
- Smallholder farmers’ perceptions of bean bruchid damage and varietal
- Dry bean germplasm screening for sources of bruchid resistance
- Genetic analysis of resistance to A. obtectus of the Malawian dry bean
These results confirm previous findings that arcelin is found only in wild beans and not in the cultivated beans. Although not tested in the current study, some previous studies suggested that bruchid resistance was negatively correlated to yield.
Breeding implications
Resistance to bruchids should therefore be bred into the medium- to large-seeded bean varieties. In any case, seed size was not correlated with resistance in the current study, suggesting that selection for bruchid resistance will not affect seed size.
Challenges in breeding for bruchid resistance in dry beans
Bean improvement programs in Malawi should therefore focus on large-seeded (Andean-type) bean varieties to increase adoption. Therefore, there is a need to develop reliable evaluation techniques that are highly reproducible to increase the heritability of resistance in breeding populations.
Directions for future research
This and other factors could have discouraged scientists from breeding for resistance to storage insects. Thus, screening for resistance must be delayed and performed on the late generations, after much of the variability has been lost.
