Aflatoxin is considered a “hidden poison” due to its slow and adverse effect on various biological pathways in humans, particularly among children, in whom it leads to delayed development, stunted growth, liver damage, and liver cancer. Unfortunately, the unpredictable behavior of the fungus as well as climatic conditions pose serious challenges in precise phenotyping, genetic prediction and genetic improvement, leaving the complete onus of preventing aflatoxin contamination in crops on post-harvest management. Equipping popular crop varieties with genetic resistance to aflatoxin is key to effective lowering of infection in farmer’s fields. A combination of genetic resistance for in vitro seed colonization (IVSC), pre-harvest aflatoxin contamination (PAC) and aflatoxin production together with pre- and post-harvest management may provide a sustainable solution to aflatoxin contamination. In this context, modern “omics” approaches, including next-generation genomics technologies, can provide improved and decisive information and genetic solutions. Preventing contamination will not only drastically boost the consumption and trade of the crops and products across nations/regions, but more importantly, stave off deleterious health problems among consumers across the globe.
SummaryAflatoxin contamination in peanuts poses major challenges for vulnerable populations of sub‐Saharan Africa and South Asia. Developing peanut varieties to combat preharvest Aspergillus flavus infection and resulting aflatoxin contamination has thus far remained a major challenge, confounded by highly complex peanut–Aspergilli pathosystem. Our study reports achieving a high level of resistance in peanut by overexpressing (OE) antifungal plant defensins MsDef1 and MtDef4.2, and through host‐induced gene silencing (HIGS) of aflM and aflP genes from the aflatoxin biosynthetic pathway. While the former improves genetic resistance to A. flavus infection, the latter inhibits aflatoxin production in the event of infection providing durable resistance against different Aspergillus flavus morphotypes and negligible aflatoxin content in several peanut events/lines well. A strong positive correlation was observed between aflatoxin accumulation and decline in transcription of the aflatoxin biosynthetic pathway genes in both OE‐Def and HIGS lines. Transcriptomic signatures in the resistant lines revealed key mechanisms such as regulation of aflatoxin synthesis, its packaging and export control, besides the role of reactive oxygen species‐scavenging enzymes that render enhanced protection in the OE and HIGS lines. This is the first study to demonstrate highly effective biotechnological strategies for successfully generating peanuts that are near‐immune to aflatoxin contamination, offering a panacea for serious food safety, health and trade issues in the semi‐arid regions.
Aflatoxin contamination, caused by fungal pathogen Aspergillus flavus, is a major quality and health problem delimiting the trade and consumption of groundnut (Arachis hypogaea L.) worldwide. RNA-seq approach was deployed to understand the host-pathogen interaction by identifying differentially expressed genes (DEGs) for resistance to in-vitro seed colonization (IVSC) at four critical stages after inoculation in J 11 (resistant) and JL 24 (susceptible) genotypes of groundnut. About 1,344.04 million sequencing reads have been generated from sixteen libraries representing four stages in control and infected conditions. About 64% and 67% of quality filtered reads (1,148.09 million) were mapped onto A (A. duranensis) and B (A. ipaёnsis) subgenomes of groundnut respectively. About 101 million unaligned reads each from J 11 and JL 24 were used to map onto A. flavus genome. As a result, 4,445 DEGs including defense-related genes like senescence-associated proteins, resveratrol synthase, 9s-lipoxygenase, pathogenesis-related proteins were identified. In A. flavus, about 578 DEGs coding for growth and development of fungus, aflatoxin biosynthesis, binding, transport, and signaling were identified in compatible interaction. Besides identifying candidate genes for IVSC resistance in groundnut, the study identified the genes involved in host-pathogen cross-talks and markers that can be used in breeding resistant varieties.
1 groundnut (Arachis hypogaea L.) in Mali, West Africa 2 3 ABSTRACT 13 Groundnut is a major source of livelihood for the rural poor in Mali. However, the crop is 14 prone to pre-and post-harvest aflatoxin contamination caused by Aspergillus flavus and A. 15 parasiticus. Therefore, to minimize health related hazards from exposure to aflatoxin 16 contaminated food, information on the prevalence and distribution of aflatoxins (AFB1) in 17 the groundnut value chain in Mali is needed for timely interventions. To this end, a study was 18 undertaken in three districts (Kayes, Kita and Kolokani) to assess aflatoxin contamination in 19 the field and storage. Ninety pod samples in each district were collected from fields (30 20 villages/district and 3 samples/village) during 2009 and 2010. Pre-harvest contamination was 21 estimated at harvest, whereas samples for post-harvest contamination were collected from 22 granaries of the same farmers at a monthly interval for 3 months. The villages in each district 23 were categorized into safe, acceptable, moderate risk and high risk areas based on pre-harvest 24 AFB1 levels. Kayes recorded more pod samples (77%) within 20 µg/kg of pre-harvest 25 aflatoxins followed by Kolokani (55.6%) and Kita (45.6%) based on 2009 and 2010 mean 26 values. Toxin concentrations at harvest were comparatively less in Kayes during both years. 27 Further, Kayes had more villages under safe and acceptable limits when compared to 28 Kolokani and Kita. Overall, 46 out of 90 villages in the three districts had acceptable pre-29 harvest toxin limits. Further, 12 villages in Kolokani were in the high risk category. An 30 increase in toxin levels was noticed with period of storage during both years. Comparatively, 31 toxin levels after storage were least in Kayes during 2009. Kayes also recorded less AFB1 32 levels in 2010 after Kita. Our results indicate that Kayes is relatively safe over Kita and 33 Kolokani in pre-harvest aflatoxin contamination. The reasons for district-wide variations in 34 pre-harvest contamination; and the reasons for post-harvest flare up of the problem are 35 discussed. Further, proper storage of pods at farmers' granaries in Mali is suggested to 36 overcome the problem from reaching alarming levels. 37 38
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