Farid Waliyar

Biotechnological advances for combating Aspergillus flavus and aflatoxin contamination in crops

Aflatoxins are toxic, carcinogenic, mutagenic, teratogenic and immunosuppressive byproducts of Aspergillus spp. that contaminate a wide range of crops such as maize, peanut, and cotton. Aflatoxin not only affects crop production but renders the produce unfit for consumption and harmful to human and livestock health, with stringent threshold limits of acceptability. In many crops, breeding for resistance is not a reliable option because of the limited availability of genotypes with durable resistance to Aspergillus. Understanding the fungal/crop/environment interactions involved in aflatoxin contamination is therefore essential in designing measures for its prevention and control. For a sustainable solution to aflatoxin contamination, research must be focused on identifying and improving knowledge of host-plant resistance factors to aflatoxin accumulation. Current advances in genetic transformation, proteomics, RNAi technology, and marker-assisted selection offer great potential in minimizing pre-harvest aflatoxin contamination in cultivated crop species. Moreover, developing effective phenotyping strategies for transgenic as well as precision breeding of resistance genes into commercial varieties is critical. While appropriate storage practices can generally minimize post-harvest aflatoxin contamination in crops, the use of biotechnology to interrupt the probability of pre-harvest infection and contamination has the potential to provide sustainable solution.

An efficient method for the production of marker-free transgenic plants of peanut (Arachis hypogaea L.)

Recombinant genes conferring resistance to antibiotics or herbicides are widely used as selectable markers in plant transformation for selecting the primary transgenic events. However, these become redundant once the transgenic plants have been developed and identified. Although, there is no evidence that the selectable marker genes are unsafe for consumers and the environment, it would be desirable if the marker genes can be eliminated from the final transgenic events. The availability of efficient transformation methods can enable the possibility of developing transgenic events that are devoid of the marker gene/s upfront. Taking advantage of the high and consistent transformation potential of peanut, we report a technique for developing its transgenics without the use of any selectable marker gene. Marker-free binary vectors harboring either the phytoene synthase gene from maize (Zmpsy1) or the chitinase gene from rice (Rchit) were constructed and used for Agrobacteriumtumefaciens-mediated transformation of peanut. The putative transgenic events growing in vitro were initially identified by PCR and further confirmed for gene integration and expression by dot blots assays, Southern blots, and RT-PCR where they showed a transformation frequency of over 75%. This system is simple, efficient, rapid, and does not require the complex segregation steps and analysis for selection of the transgenic events. This approach for generation of marker-free transgenic plants minimizes the risk of introducing unwanted genetic changes, allows stacking of multiple genes and can be applicable to other plant species that have high shoot regeneration efficiencies.

Utilizing Conjoint Analysis to Design Modern Crop Varieties: Empirical Example for Groundnut in Niger

Preferences for monetary and non-monetary plant traits influence modem crop variety adoption decisions of farmers. To enhance adoption probability of modem crop varieties, it is necessary to identify and focus research on traits that significantly contribute to utility while de-emphasizing insignificant plant attributes. This paper illustrates the potential for applying conjoint analysis to aid the design and targeting of client-responsive modem crop varieties. Farmers ranked eight orthogonally-derived plant trait combinations used in an illustrative example. Utilities were estimated using the choice-probability-based method of ordered probit. Results showed that conjoint analysis can differentiate significant and non-significant traits of modem crop varieties. The usefulness of applying conjoint analysis over identifiable disaggregated groups of a sample was also evident. Future application of conjoint analysis to the design and targeting of modem crop varieties should carefully consider sample composition and size to permit the estimation of relevant sub-models for desired farmer segments.

Farmer preferences for socioeconomic and technical interventions in groundnut production system in Niger: Conjoint and ordered probit analyses

Crop production decisions reflect preferences of farmers which are based on the structure of incentives and constraints that characterize agricultural systems. Therefore, an assessment of the intensities of farmer preferences for technical and socioeconomic interventions can provide useful guidance for the choice of appropriate strategies to improve productivity and incomes. Based on surveys conducted in groundnut-growing zones of Niger in West Africa, utilities of selected socioeconomic and technical interventions to farmers were derived through application of conjoint and ordered probit analyses. Across all regional and gender subgroups of respondents, groundnut farmers attach significant importance to access to credit and reliable markets for pods. The introduction of new and more productive varieties per se would not significantly contribute to utilities of farmers at the present time. This possibly implies that until market and credit constraints are alleviated, farmers have lower utility for more productive varieties. Regional diversities were observed in the significance of utilities groundnut farmers can gain from the availability of local small-scale groundnut oil processing plant, fertilizer and changes to traditional rules governing access to land. There is no evidence of genderbased diversity in utilities and, therefore, prioritization of the interventions on the basis of observed utilities will benefit both gender components.

A Case for Regular Aflatoxin Monitoring in Peanut Butter in Sub-Saharan Africa: Lessons from a 3-Year Survey in Zambia

A 3-year comprehensive analysis of aflatoxin contamination in peanut butter was conducted in Zambia, sub-Saharan Africa. The study analyzed 954 containers of 24 local and imported peanut butter brands collected from shops in Chipata, Mambwe, Petauke, Katete, and Nyimba districts and also in Lusaka from 2012 to 2014. For analysis, a sample included six containers of a single brand, from the same processing batch number and the same shop. Each container was quantitatively analyzed for aflatoxin B1 (AFB1) in six replicates by using competitive enzyme-linked immunosorbent assay; thus, aflatoxin contamination level of a given sample was derived from an average of 36 test values. Results showed that 73% of the brands tested in 2012 were contaminated with AFB1 levels >20 μg/kg and ranged up to 130 μg/kg. In 2013, 80% of the brands were contaminated with AFB1 levels >20 μg/kg and ranged up to 10,740 μg/kg. Compared with brand data from 2012 and 2013, fewer brands in 2014, i.e., 53%, had aflatoxin B1 levels >20 μg/kg and ranged up to 1,000 μg/kg. Of the eight brands tested repeatedly across the 3-year period, none consistently averaged ≤20 μg/kg. Our survey clearly demonstrates the regular occurrence of high levels of AF B1 in peanut butter in Zambia. Considering that some of the brands tested originated from neighboring countries such as Malawi, Zimbabwe, and South Africa, the current findings provide a sub-Saharan regional perspective regarding the safety of peanut butter.

Annotation of Trait Loci on Integrated Genetic Maps of Arachis Species

Peanut or groundnut (Arachis hypogaea L.) is second, behind soybean, in the world’s legume oilseed market. In 2012, global production was 41.2metric tons from an area of 24.7million hectares (FAOSTAT, 2014). Yield of peanut under stressed environments is an ultimate goal of improvement for enhanced production as it is usually susceptible to a range of abiotic and biotic stresses, such as drought, tomato spotted wilt virus (TSWV), early leaf spot (ELS) and late leaf spot (LLS), nematodes, rust, and aflatoxin contamination (Guo et al., 2012a). However, cultivated peanut is an allotetraploid (2n=4x=40) with a large genome, which greatly complicates interpretation of genomic data compared with the diploid wild relatives (2n=2x=20) (Guo et al., 2013). It is difficult to transfer alleles from wild species to cultivated peanuts (Simpson, 1991). For the last ten years, extensive efforts in the area of peanut genomics have resulted in a large number of genetic and genomic resources such as mapping populations, expressed sequence tags (ESTs), a wide range of molecular markers, transcriptome and proteomics (Guo et al., 2013; Katam et al., 2014; Varshney et al., 2013). These genetic and genomic resources have been successfully used to construct genetic maps, to identify quantitative trait loci (QTLs) of traits of Authors personal copy 164 Peanuts Peanuts, First Edition, 2016, 163-207 interest, and to conduct marker-assisted selection and association mapping for peanut improvement (Pandey et al., 2014a).