Source: Open Access Government [summ., edited]
In East Africa, xanthomonas wilt (BXW) is considered one of the most serious limitations for banana cultivation. It has destroyed whole plantations in many of the affected areas. Controlling BXW and developing resistant banana cultivars is a priority in the region. No source of resistance has been found against BXW in any cultivated banana varieties so far. However, the wild-type diploid species _Musa balbisiana_ exhibits resistance to the pathogen. Transferring disease resistance traits to crop cultivars through conventional breeding is difficult and time consuming since most cultivars are sterile due to their polyploidy. Biotechnology is the most promising and effective approach for this purpose.
Transgenic bananas expressing the capsicum (_Capsicum annuum_) hypersensitive response-assisting protein (Hrap) or plant ferredoxin-like protein (Pflp) genes showed enhanced resistance to BXW through successive crop cycles and agronomic performance comparable to uninfected control non-transgenic bananas in field trials. Since single gene-based disease resistance can break down quickly due to pathogen evolution, the 2 genes were also stacked to enhance durability of the trait. Resistance levels and yield of stacked gene cultivars were equivalent to single gene cultivars. Specific biological and environmental safety checks showed no adverse effects due to consumption or cultivation of the stacked gene cultivars and no interference with soil or other environmental microbiomes. A potential release to farmers may be expected in a few years. Research using other biotechnological approaches is ongoing internationally.
[Most of today's cultivated bananas and plantains are related to either _Musa acuminata_ (A) and/or _M. balbisiana_ (B), with the genetic background of polyploid hybrids indicated by the respective letters. _Xanthomonas vasicola_ (previously _campestris_) pv. _musacearum_ is the causal organism of bacterial wilt of Musaceae in central and eastern Africa (BXW; bacterial wilts due to _Ralstonia_ species are present elsewhere). BXW was first reported in Ethiopia in 1968 and has been spreading in the region since then. Symptoms of BXW may include wilting of leaves and plants; premature ripening of fruit; fruit rot; bacterial ooze on cut surfaces. An incidence of 70-80 percent in many plantations and yield losses of up to 90 percent have been reported.
The bacteria survive in soil and plant debris. They are mainly spread with infected planting material, by human or insect activities, mechanical means, and contaminated tools. A range of alternate hosts may serve as pathogen reservoirs. An integrated approach is needed for disease management. Removal of male buds immediately after fruit set has been found to prevent transmission of bacterial ooze by flying insects. Other control measures may include crop rotation; disinfection of orchard tools; use of certified clean material for replanting; phytosanitation to reduce inoculum and prevent re-introduction or plant-to-plant spread of the pathogen. However, these measures may be difficult to implement with smallholders. No resistant banana cultivars have been identified. Research is being carried out on transgenic lines of banana for field resistance to BXW. The story above provides the current state of research on this aspect.
BXW symptoms on _Musa_:
https://www.musarama.org/dl215?display (bacterial ooze)
Extract of the story at:
BXW disease information:
BXW management and control:
BXW resistance research
https://doi.org/10.1111/pbi.13614 and via
_X. v._ pv. _musacearum_ taxonomy:
_Musa_ species & hybrids: