Aflatoxin, a type of mycotoxin, is mostly produced by Aspergillus flavus and Aspergillus parasiticus. It is responsible for the loss of billions of dollars to the world economy, by contaminating different crops such as cotton, groundnut, maize, and chilies, and causing immense effects on the health of humans and animals. More than eighteen different types of aflatoxins have been reported to date, and among them, aflatoxins B1, B2, G1, and G2 are the most prevalent and lethal. Early detection of fungal infection plays a key role in the control of aflatoxin contamination. Therefore, different methods, including culture, chromatographic techniques, and molecular assays, are used to determine aflatoxin contamination in crops and food products. Many countries have set a maximum limit of aflatoxin contamination (2–20 ppb) in their food and agriculture commodities for human or animal consumption, and the use of different methods to combat this menace is essential. Fungal infection mostly takes place during the pre- and post-harvest stage of crops, and most of the methods to control aflatoxin are employed for the latter phase. Studies have shown that if correct measures are adopted during the crop development phase, aflatoxin contamination can be reduced by a significant level. Currently, the use of bio-pesticides is the intervention employed in many countries, whereby atoxigenic strains competitively reduce the burden of toxigenic strains in the field, thereby helping to mitigate this problem. This updated review on aflatoxins sheds light on the sources of contamination, and the on occurrence, impact, detection techniques, and management strategies, with a special emphasis on bio-pesticides to control aflatoxins.

Genetic bottlenecks may occur in virus populations when only a few individuals are transferred horizontally from one host to another, or when a viral population moves systemically from the infection site. Genetic bottlenecks during the systemic movement of an RNA plant virus population were reported previously (H. Li and M. J. Roossinck, J. Virol. 78:10582-10587, 2004). In this study we mechanically inoculated an artificial population consisting of 12 restriction enzyme marker mutants of Cucumber mosaic virus (CMV) onto young leaves of squash plants and used two aphid species, Aphis gossypii and Myzus persicae , to transmit the virus populations from infected source plants to healthy squash plants. Horizontal transmission by aphids constituted a significant bottleneck, as the population in the aphid-inoculated plants contained far fewer mutants than the original inoculum source. Additional experiments demonstrated that genetic variation in the artificial population of CMV is not reduced during the acquisition of the virus but is significantly reduced during the inoculation period.

Field surveys were conducted from 2008 to 2010 to detect and determine the incidence of viruses in the major cucurbit-growing areas of Oklahoma. In total, 1,049 symptomatic leaf samples (890 from cucurbits, 109 from weed species, and 50 from crop plants [agricultural crops]) were collected from 90 fields in four counties (Atoka, Blaine, Jefferson, and Tulsa) of Oklahoma. Samples were tested against seven viruses, including Cucumber mosaic virus (CMV), Cucumber green mottle mosaic virus (CGMMV), Melon necrotic spot virus (MNSV), Papaya ringspot virus-watermelon strain (PRSV-W, formerly known as Watermelon mosaic virus-1), Squash mosaic virus (SqMV), Watermelon mosaic virus-2 (WMV-2), and Zucchini yellow mosaic virus (ZYMV), using dot-immunobinding assay (DIBA). Results showed the highest incidence for PRSV (51%), followed by WMV-2 (14%) and ZYMV (10%) among the collected samples. SqMV, MNSV, and CMV were detected in 3.8, 3.3, and 1.1% of the samples, respectively. None of the samples collected during surveys reacted positively against the antiserum of CGMMV. Mixed virus infections were common involving two (5.18%) or three (4.61%) viruses in various combinations. New weed host species were found to be infected with PRSV when confirmed by both DIBA and reverse-transcription polymerase chain reaction (RT-PCR). Some weed species contained possible new viruses when analyzed by random RT-PCR, followed by cloning, sequencing, and BLAST analysis with sequences in GenBank.