Date: May 2021 [ProMED regrets the late posting due to delayed receipt of the story.]
Source: Wageningen University & Research [abridged, edited]
The fungus _Pseudocercospora fijiensis_ causes black sigatoka [BS] of banana, which is the most damaging leaf disease of bananas worldwide. An analysis of 592 isolates from 7 banana-producing countries on 3 continents shows how _P. fijiensis_ is evolving to insensitivity to azole fungicides due to the heavy use of pesticides. The results underscore the need to develop alternative disease control methods and new banana varieties. Cavendish bananas represent more than 50% of the global production but are very susceptible to BS.
Azole fungicides are the cornerstone for fungal disease control. This study is the 1st comprehensive analysis of reduced sensitivity to these fungicides in banana production in Latin America, the Caribbean, Africa, and Southeast Asia. In addition, [it] analyses the overall genomes of 155 isolates to study geographical clustering. All identified mutations could be associated with reduced sensitivity to the fungicides. This trend results in a vicious circle of even more fungicide applications. These alarming data call for a new view on sustainable banana production, for the benefit of producers and consumers.
[Citation: Chong P, Essoh JN, Arango Isaza RE, et al. A world-wide analysis of reduced sensitivity to DMI fungicides in the banana pathogen _Pseudocercospora fijiensis_. Pest Manag Sci. 2021; 77(7): 3273-88; https://doi.org/10.1002/ps.6372]
IBIS (International Biosecurity Intelligence System)
[Black sigatoka (BS), also known as black leaf streak, is caused by the fungus _Pseudocercospora fijiensis_ (previously _Mycosphaerella fijiensis_), which affects only species and hybrids of _Musa_. Worldwide, BS is one of the most devastating leaf diseases of bananas, with yield losses of 50 percent or more. It is present in the Americas, China, Southeast Asia, and parts of Africa. Infection occurs on the youngest leaves of the plant; older leaves are not readily infected.
BS seriously affects photosynthetic ability and plant vigour. Fruit can ripen prematurely during commercial shipment, causing further losses. It is spread by water, wind and with contaminated materials, including suckers for planting. Disease management may include frequent applications of fungicides, phytosanitary measures to reduce inoculum and cultural practices. However, the high costs of these measures make them essentially unavailable to smallholder farmers. Use of agrochemicals may also cause problems for fruit export, for example to Europe.
Related fungi cause yellow sigatoka (YS; sigatoka leaf spot; _P. musae_) and eumusa leaf spot (_P. eumusae_). Symptoms and epidemiology are similar for all three. YS is more adapted to cooler temperatures, less damage is caused to photosynthetic tissue. There are more crop cultivars with degrees of resistance to YS than to BS. A number of fungi in other genera can cause similar diseases in different regions, laboratory analysis is needed for diagnosis. BS is another example of a warm climate disease spreading due to global climate change (see links below).
Demethylase inhibitor (DMI; also called azole or sterol biosynthesis inhibitor) fungicides are the largest class of fungicides. They were introduced in the 1970s and new products continue to be introduced. Integrated disease management, including varying crops or crop cultivars in time and space, as well as rotating or mixing chemical classes of fungicides is vital to extend the useful life of host resistance genes and agrochemical compounds.
Cavendish banana varieties (_Musa_ AAA) include most of the current commercial eating bananas. Most of today's cultivated bananas are related to either _M. acuminata_ (A) and/or _M. balbisiana_ (B), with the genetic background of hybrid varieties indicated by the respective letters.
Black sigatoka symptoms:
Eumusa leaf spot, fruit symptoms:
Additional news story:
Information on black sigatoka:
Information on black and yellow sigatoka:
Information on YS, eumusa leafspot:
BS spread due to climate change:
_P. fijiensis_ taxonomy and synonyms:
Other fungal taxonomy via:
Information on DMI fungicides:
History and review of agricultural fungicides:
_Musa_ species & hybrids: