Study identifies banana varieties resistant to black Sigatoka and provides further insights into the disease pathogen
Black leaf Sigatoka, one of the most widespread and damaging banana diseases—causing yield losses of 20–50%—is widespread in Uganda and Tanzania, posing a challenge to banana production as bananas grown in East Africa are susceptible to the disease.
However, the good news is that five hybrids of East African Highland banana hybrids named NARITA, after their developers—the National Agricultural Research Organisation (NARO) of Uganda and IITA—are resistant to the deadly disease.
These are among the key findings of a four-year comprehensive study on sustainable ways to control black leaf Sigatoka in Uganda and Tanzania conducted by Janet Njeri Kimunye as part of her PhD studies at Stellenbosch University carried out under the IITA project Improvement of banana for smallholder farmers in the Great Lakes region of Africa (Breeding Better Bananas) funded by the Bill & Melinda Gates Foundation.
Njeri was supervised by Prof. Altus Viljoen and George Mahuku from Stellenbosch and IITA, respectively. In October, Janet Njeri Kimunye successfully defended her thesis: “Distribution and genetic diversity of Pseudocerospora spp. associated with banana Sigatoka diseases in East Africa” and is set to graduate in December.
Commercial farmers manage black Sigatoka disease by spraying fungicides weekly. However, this method is not suitable for smallholder farmers who represent most banana producers in Africa. Hence, finding banana varieties with resistance to black Sigatoka is the most effective solution for resource-poor farmers.
”NARITA hybrids 2, 7, 8, 21, and 23, developed through conventional breeding, performed well across sites and had low disease pressure compared to susceptible local checks. These can be provided to farmers for managing black Sigatoka in the region,” said Kimunya.
“In addition, we identified the site Mitarula in Mbeya, Tanzania, as the most ideal and representative site for the disease evaluation and can save on resources by reducing multi-location disease evaluation,” she adds.
Understanding the pathogen
The basis for developing effective and sustainable disease management strategies is a sound understanding of the pathogen distribution, genetic diversity, and population dynamics. As part of the study, a survey was conducted in five banana-growing regions in Tanzania and Uganda to identify the Pseudocercospora spp. associated with Sigatoka leaf spots and determine disease severity.
Sigatoka-like symptoms were present in all localities and on all cultivars. Black Sigatoka caused by P. fijiensis was the most predominant species in all areas except Kilimanjaro, where Mycosphaerella musae was associated with Sigatoka-like leaf spots. Black Sigatoka was also found more severe in Uganda than in Tanzania.
Furthermore, P. fijiensis was detected at altitudes of up to 1877 m above sea level, suggesting an expansion in habitat range from the previous threshold of < 1350 m above sea level in East Africa. This expansion into new areas where the pathogen was previously not present is a major threat to the sustainability of banana production in the region.
Genetic diversity analysis revealed that P. fijiensis was reproducing both sexually and asexually. Such pathogens are difficult to manage, as they have a high potential to generate new and virulent strains that can easily overcome introduced resistance genes. Therefore, breeding programs have to broaden the sources of resistance to stay ahead of the game.
“As the most devastating pathogen, P. fijiensis is expanding its adaptation range to higher elevations, with evidence that previously resistant varieties are turning susceptible. It is important to identify new sources of resistance that can be incorporated into breeding programs and develop resistant varieties. We screened 95 banana cultivars and identified eight diploids with a similar reaction as the highly resistant Calcutta 4. These can be incorporated into breeding programs to broaden the genetic base of resistance to P. fijiensis, the cause of black Sigatoka,” Kimunya said.
Kimunya has also co-published two journal articles from this work:
- Kimunye, J.N., Muzhinji, N., Mostert, D., Viljoen, A., Bester-van der Merwe, A.E., and Mahuku, G. 2020. Genetic Diversity and Mating Type Distribution of Pseudocercospora fijiensis on Banana in Uganda and Tanzania. Phytopathology (
- Kimunye, J. N., Were, E., Mussa, F., Tazuba, A., Jomanga, K., Viljoen, A., Swennen, R., Muthoni, F. K., and Mahuku, G. 2019. Distribution of Pseudocercospora species causing Sigatoka leaf diseases of banana in Uganda and Tanzania. Plant Pathology DOI: 10.1111/ppa.13105 https://bsppjournals.onlinelibrary.wiley.com/doi/full/10.1111/ppa.13105