Bean golden mosaic virus (BGMV) is transmitted by the whitefly Bemisia tabaci in a persistent, circulative manner, causing the golden mosaic of common bean (Phaseolus vulgaris L.). The characteristic symptoms are yellow-green mosaic of leaves, stunted growth, or distorted pods. The disease is the largest constraint to bean production in Latin America and causes severe yield losses (40 to 100%). Here, we explored the concept of using an RNA interference construct to silence the sequence region of the AC1 viral gene and generate highly resistant transgenic common bean plants. Eighteen transgenic common bean lines were obtained with an intron-hairpin construction to induce post-transcriptional gene silencing against the AC1 gene. One line (named 5.1) presented high resistance (approximately 93% of the plants were free of symptoms) upon inoculation at high pressure (more than 300 viruliferous whiteflies per plant during the whole plant life cycle) and at a very early stage of plant development. Transgene-specific small interfering RNAs were detected in both inoculated and non-inoculated transgenic plants. A semiquantitative polymerase chain reaction analysis revealed the presence of viral DNA in transgenic plants exposed to viruliferous whiteflies for a period of 6 days. However, when insects were removed, no virus DNA could be detected after an additional period of 6 days.

Exploiting the biolistic process we have generated stable transgenic bean (Phaseolus vulgaris L.) plants with unlinked and linked foreign genes. Co-transformation was conducted using plasmid constructions containing a fusion of the gus and neo genes, which were co-introduced with the methionine-rich 2S albumin gene isolated from the Brazil nut and the antisense sequence of AC1, AC2, AC3 and BC1 genes from the bean golden mosaic geminivirus. The results revealed a co-transformation frequency ranging from 40% to 50% when using unlinked genes and 100% for linked genes. The introduced foreign genes were inherited in a Mendelian fashion in most of the transgenic bean lines. PCR and Southern blot hybridization confirmed the integration of the foreign genes in the plant genome.

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As the global population continues to expand, utilizing an integrated approach to pest management will be critically important for food security, agricultural sustainability, and environmental protection. Genetically engineered (GE) crops that provide protection against insects and diseases, or tolerance to herbicides are important tools that complement a diversified integrated pest management (IPM) plan. However, despite the advantages that GE crops may bring for simplifying the approach and improving efficiency of pest and weed control, there are also challenges for successful implementation and sustainable use. This paper considers how several GE traits, including those that confer protection against insects by expression of proteins from Bacillus thuringiensis (Bt), traits that confer tolerance to herbicides, and RNAi-based traits that confer resistance to viral pathogens, can be key elements of a diversified IPM plan for several different crops in both developed and developing countries. Additionally, we highlight the importance of community engagement and extension, strong partnership between industry, regulators and farmers, and education and training programs, for achieving long-term success. By leveraging the experiences gained with these GE crops, understanding the limitations of the technology, and considering the successes and failures of GE traits in IPM plans for different crops and regions, we can improve the sustainability and versatility of IPM plans that incorporate these and future technologies.

Begomoviruses cause major diseases of sweet potato worldwide impairing considerably the yields of this important food staple. Since sweet potato plants are vegetatively propagated and globally transported, they are prone to accumulate and disseminate geminiviruses. Effective diagnostic tools are, therefore, desirable. We studied the genomic diversity of geminiviruses present in naturally-infected sweet potato accessions belonging to a Brazilian germplasm bank collection. Fifty-five samples from different sweet potato accessions displaying geminivirus-like symptoms were analyzed by combining rolling circle amplification (RCA) with restriction fragment length polymorphism (RFLP) and sequencing. The restriction enzyme MspI (HpaII) revealed diverse band patterns in 55 samples and digestion with BamHI, SstI or PstI resulted in full-length sweet potato geminivirus DNAs of about 3 kb in 46 samples. In addition, smaller fragments were identified as either viral "Defective DNAs" (D-DNAs) or mitochondrial plasmid DNAs. The diversity of sweet potato-associated geminiviruses was found to be very high under Brazilian conditions. Representative viral full-length DNAs have been cloned and sequenced yielding two new tentative species, three strains and several variants of previously described sweet potato geminiviruses. Sequence comparisons identified footprints of recombination in their genomes underscoring the risk of generating new geminiviruses in vegetatively propagated germplasm bank material. The sites of recombination were found in conjunction with predicted hairpin structures. We propose diagnostic routines to screen germplasm bank material for geminiviruses by the rapid and reliable RCA/RFLP as the technique of choice.