Diversity protects the bean harvests of poor farmers in Uganda

Poor farmers in Uganda use agricultural biodiversity to protect themselves against pests and diseases, according to a recent paper published in the journal Agriculture, Ecosystems and Environment  [2]. Farmers who grow more varieties of bananas and plantains (Musa spp.) and common beans (Phaseolus vulgaris) on their plots lose less of their harvest and the effect is particularly strong when pressure from pests and diseases is high.

These results are the first to be published from a four-country global exploration of links between agricultural biodiversity and the impact of pests and diseases. Implemented by Bioversity International and local partners, and funded by UNEP/GEF  [3], FAO  [4] and the Swiss Agency for Development and Cooperation  [5], the project worked in China, Ecuador, Morocco and Uganda.

“The aim was to assess how poor farmers make use of local variety diversity and their knowledge about it to reduce the damage caused by pests and diseases,” said Devra Jarvis, senior scientist at Bioversity and project leader.

Bananas and beans are important crops in Uganda, where more than 7 million people depend on them for carbohydrates and proteins. Losses to pests and diseases, such as angular leaf spot, anthracnose and bean stem maggots on beans, and black sigatoka, weevils and nematode worms on banana, are considerable. Poor farmers cannot afford the synthetic chemical treatments available to wealthier farmers, and there are also concerns about the damage to workers’ health and to the environment.

In four different eco-agricultural zones the project scientists, including partners at Uganda’s National Agricultural Research Organisation  [6], worked with farmers to identify the pests and diseases that damaged their beans and bananas and gathered the different varieties, traditional and modern, for experimental tests of their resistance. They also assessed the damage caused by the different threats, using a standard methodology to facilitate comparisons across the study sites and across countries in the project.

Two measures of diversity are richness and evenness. Richness counts the number of varieties, while evenness is an estimate of the area sown to each variety. If all varieties occupy roughly the same area, evenness is high, whereas if one variety dominates, evenness is low. Focusing on beans, households averaged 2.4 bean varieties, and these were pretty evenly distributed. Although bean diversity did not protect against angular leaf spot, it did protect against anthracnose at two of the sites.

“The really interesting point,” said Carlo Fadda  [7], the Bioversity scientist who coordinated the project in the field, “is that the correlation between richness and evenness and damage was greatest where the pest and disease pressure was greatest. So when disease pressure is low there is no big difference between farmers who grow more varieties and farmers who grow fewer varieties. But when disease pressure is high, farmers who grow more bean varieties will benefit from the diversity in their fields by experiencing less overall crop damage.”

The other main element in this study is the more rigorous examination of farmers’ beliefs about their varieties, which the project did by examining how the varieties performed in experimental fields and in glasshouse trials. Farmers have clear ideas about the resistance of their varieties to pests and diseases, and their five top-ranked varieties for resistance are all traditional varieties. In field trials, the farmers’ beliefs were borne out in some cases, not in others, and the most resistant variety was in fact a traditional variety.

In the glasshouse trials, where conditions for the development of disease were ideal, not even the most resistant modern varieties fully withstood angular leaf spot, and one of the traditional varieties, Nshemenoha, was as good as the modern varieties.

“The glasshouse trials and the cross-site on-farm experiments, where we grew varieties from each site at the other sites, have shown us that there is very useful resistance diversity in the host plants, and this is already being taken up by the local farming communities and by national bean breeders,” said Jarvis.

More generally, Bioversity scientists hope that their research results will help the use of agricultural biodiversity to gain a more prominent place in integrated pest management strategies. Results from the four countries will be synthesised and used both as widely applicable practical guides and as the basis of further research to understand better the use of agricultural biodiversity to ensure food security.

“The use of agricultural biodiversity is not only available even to the poorest farmers, it is also future-proof, because as climate change affects the activity patterns of pests and diseases, diversity can be brought in and deployed to continue protecting harvests,” said Jarvis.

Read the abstract:

A risk-minimizing argument for traditional crop varietal diversity use to reduce pest and disease damage in agricultural ecosystems of Uganda  [8]

Read more:

 Tackling pests and diseases with biodiversity (382 KB)  [9]
taken from Bioversity International Annual Report 2010  [10].