Banana (Musa spp.) is a staple food for more than 400 million people. Over 40% of world production and virtually all the export trade is based on Cavendish banana. However, Cavendish banana is under threat from a virulent fungus, Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) for which no acceptable resistant replacement has been identified. Here we report the identification of transgenic Cavendish with resistance to TR4. In our 3-year field trial, two lines of transgenic Cavendish, one transformed with RGA2, a gene isolated from a TR4-resistant diploid banana, and the other with a nematode-derived gene, Ced9, remain disease free. Transgene expression in the RGA2 lines is strongly correlated with resistance. Endogenous RGA2 homologs are also present in Cavendish but are expressed tenfold lower than that in our most resistant transgenic line. The expression of these homologs can potentially be elevated through gene editing, to provide non-transgenic resistance.

Bananas are one of the top ten world food crops. Unlike most other major food crops, bananas are difficult to genetically improve. The challenge is that nearly all banana cultivars and landraces are triploids, with high levels of male and female infertility. There are a number of international conventional breeding programs and many of these are developing new cultivars. However, it is virtually impossible to backcross bananas, thus excluding the possibility of introgressing new traits into a current cultivar. The alternative strategy is to “modify” the cultivar itself. We have been developing the capacity to modify Cavendish bananas and other cultivars for both disease resistance and enhanced fruit quality. Initially, we were using transgenes; genes that were derived from species outside of the Musa or banana genus. However, we have recently incorporated two banana genes (cisgenes) into Cavendish; one to enhance the level of pro-vitamin A and the other to increase the resistance to Panama disease. Modified Cavendish with these cisgenes have been employed in a field trial. Almost certainly, the next advance will be to edit the Cavendish genome, to generate the desired traits. As these banana cultivars are essentially sterile, transgene flow and the outcrossing of modified genes into wild Musa species. are highly unlikely and virtually impossible in other triploid cultivars. Therefore, genetic changes in bananas may be compatible with organic farming.

Uganda is a tropical country with a population in excess of 30 million, >80% of whom live in rural areas. Bananas (Musa spp.) are the staple food of Uganda with the East African Highland banana, a cooking banana, the primary starch source. Unfortunately, these bananas are low in pro-vitamin A (PVA) and iron and, as a result, banana-based diets are low in these micronutrients which results in very high levels of inadequate nutrition. This inadequate nutrition manifests as high levels of vitamin A deficiency, iron deficiency anemia, and stunting in children. A project known as Banana21 commenced in 2005 to alleviate micronutrient deficiencies in Uganda and surrounding countries through the generation of farmer- and consumer-acceptable edible bananas with significantly increased fruit levels of PVA and iron. A genetic modification approach was adopted since bananas are recalcitrant to conventional breeding. In this review, we focus on the PVA-biofortification component of the Banana21 project and describe the proof-of-concept studies conducted in Australia, the transfer of the technology to our Ugandan collaborators, and the successful implementation of the strategy into the field in Uganda. The many challenges encountered and the potential future obstacles to the practical exploitation of PVA-enhanced bananas in Uganda are discussed.

Bananas and plantains (Musa spp.) are an important staple and food security crop in sub‐Saharan Africa. In Uganda, where the consumption of East African highland banana (EAHB) is the highest in the world, the population suffers from a high incidence of vitamin A deficiency (VAD). Since the consumption of pro‐vitamin A carotenoids (pVAC) made available through the food staple can help alleviate these ailments, we set out to identify the most suitable banana variety to use in future biofortification strategies through genetic engineering. The study focussed on eight popular Musa cultivars grown in the heart of banana farming communities and across the three major agricultural zones of Uganda. The fruit pVAC concentration varied considerably within and across the cultivars tested. These variations could not be explained by the altitude nor the geographical location where these fruits were grown. More than 50% of the total carotenoids present in EAHB cultivars was found to comprise of α‐ and β‐carotene, while the retention of these compounds following traditional processing methods was at least 70%. Storage up to 14 days postharvest improved carotenoid accumulation up to 2.4‐fold in the cultivar Nakitembe. The technical challenge for a successful biofortification approach in Uganda using genetically modified EAHB lies in guaranteeing that the fruit pVAC content will invariably provide at least 50% of the estimated average requirement for vitamin A regardless of the growing conditions.

Summary: Bananas (Musa spp.) are a major fruit crop worldwide, with the Cavendish cultivar dominating the export industries, which are based primarily in the Americas and the Philippines. The sustainability of banana production in these, and other regions, is under threat from the fungal disease Fusarium wilt tropical race 4 (TR4) which kills Cavendish and many other banana cultivars. No effective TR4 control strategies exist, and no consumer‐acceptable TR4‐resistant Cavendish replacements are currently available. Previously, we identified four genetically modified (GM) TR4‐resistant Cavendish (cv. Grand Nain) banana lines (RGA2‐2, ‐3, ‐4, and ‐5), each transformed with the MamRGA2 resistance gene derived from a TR4‐resistant wild banana. Here, we provide a comprehensive agronomic evaluation of these lines and report the regulatory approval of the top‐performing line, RGA2‐4 (QCAV‐4), in Australia. After five crop cycles of field trialling, TR4 disease incidence reached 66% and 84% in the Grand Nain and Williams non‐GM controls, respectively, while GM lines showed a significantly reduced incidence ranging from 2% (QCAV‐4) to 36% (RGA2‐5). Agronomic comparisons between QCAV‐4 and non‐GM Grand Nain controls for bunch weight, yield and cycle time indicated that, for most crop cycles, there were no differences, showing that, apart from TR4 resistance, QCAV‐4 is agronomically and phenotypically comparable to conventional Grand Nain. Molecular characterization of QCAV‐4 confirmed a single, large T‐DNA insert containing multiple copies of the MamRGA2 gene on chromosome 6 of the QCAV‐4 genome. QCAV‐4 is the first GM banana approved for commercial cultivation and consumption.

Iron deficiency anemia (IDA) is alarmingly prevalent in sub‐Saharan Africa, where populations often rely on nutrient‐poor staple crops as their primary energy source. The East African highland banana (EAHB), a staple for millions in Uganda and most of East Africa's highlands, contains insufficient iron to meet dietary needs. Based on average daily consumption and recommended iron intake, biofortification of EAHBs with upwards of 18.3 mg/kg DW of iron could significantly reduce IDA in these communities. A comprehensive analysis of 43 Musa genotypes revealed that, although iron concentrations in banana fruit pulp were generally low, significantly higher concentrations were found in the pulp of wild species and Fe'i cultivars compared with other genome groups. In other tissues, such as the peel and seeds of wild fertile diploids, iron concentrations were consistently higher, underscoring the critical role of this mineral in photosynthesis and seed development. Genomic and phylogenetic analyses across five selected banana cultivars identified 37 genes associated with iron homeostasis, spanning six distinct protein families, and revealed distinct differences between Fe'i and the commercially important cultivar, Cavendish. A tissue‐specific differential gene expression study in Cavendish further identified key regulators of iron homeostasis in this crop. These findings provide a foundational resource for the biofortification of this important fruit and contribute to addressing a persistent global health challenge.