Bio-Engineering solutions

The battle between Fusarium oxysporum f.sp Cubense and banana cultivars has been going on since the mid twentieth century. The number one cultivar, Gros Michel, was highly susceptible to the disease and created a worldwide epidemic. The lack of effective chemical controls and ineffective sanitation techniques made the disease extremely dangerous for the entire banana industry. Luckily no bio engineered solutions were needed as the Cavendish cultivar was already resistant to the fungus. This led to the complete replacement of the Gros Michel cultivar with the current Cavendish cultivar. Recently there has been an emergence of a new race of Foc that is able to infect the Cavendish cultivar. Fortunately this new race has only been found in select locations. If this new race is introduced to the main banana exporting countries, it could destroy the entire industry

One approach to this problem is to manipulate somaclonal variants and find the variants that show resistance to the disease. In 1984 Taiwan initiated a project with the Taiwan Banana Research Institute for commercial planting that involves screening Cavendish tissue cultures for Foc resistance (sciencedaily.com). A small percent of variants were found within the millions of different tissues cultured. Although the resistance can be shown, this option is not viable as the variants lack full immunity and they possess undesirable traits for commercial use.

Due to the different ploidy of different banana cultivars, bio-engineered solutions tend to be more used than traditional breeding. Everything from gene editing to gene transfer has been attempted to create new resistant cultivars. Current research has shown two resistance genes that can be genetically engineered into cultivars.

The first of these genes is the Ced-9 gene. This gene comes from the nematode Caenorhabditis elegans. Its original function is to protect the nematode from programmed cell death known as apoptosis. What prompted researchers to further explore this gene was that it was able to create resistance to Foc race 1 in transgenic Lady finger cultivars (ncbi.nlm.nih.gov). The second gene is the RGA2 gene. This gene is found in wild Cavendish cultivars. The RGA2 gene is a putative nucleotide-binding and leucine-rich repeat (NB-LRR) resistance gene. When this gene was sequenced, it phylogenetically resembled specific genes from tomatoes and melons. These genes,I2 and Fom-2, encode for Fusarium oxysporum resistance in each respective fruit. Higher levels of expression were shown in some current cultivars that promoted researchers to investigate its potential. It was then discovered that this gene is responsible for the resistance of some cultivars (Ghag).

Implementation of these genes starts with creating two binary vectors containing “either the C. elegans gene Ced9 under the control of a maize Ubi-P and a cauliflower mosaic virus 35s terminator (35S-T) or the M. acuminata ssp. malaccensis RGA2 under the control of the Agrobacterium tumefaciens Nos-P and terminator sequences”(ncbi.nlm.nih.gov).

Embryonic cell suspensions of M. acuminata Cavendish cv. GN (AAA subgroup) will need to be created. These male flower suspensions will undergo a transformation using the centrifugation assisted A. tumefaciens-mediated method. Embryos created from this are then regenerated and tested for the respective transgene using PCR with specific primers. Each transgenic line will then be multiplied through the use of tissue culture. This method ensures that the desired genes are transferred to the banana cultivar (Paul).

Although these genes have proven to create resistance in Bananas, federal regulations may make it difficult to get these new cultivars to market. The Ced-9 gene may never be fully implemented due to the gene being transferred from a nematode. The RGA2 gene stands a greater chance as it is found in wild cavendish species.