Can Crop Diversity Reduce Disease Pressure? The Case of Maize in China
August 4th, 2011
Small holder farmers are constantly fighting with pests and diseases and every year they need to bet on which options, in terms of varieties and crops, will reduce the loss caused by pests and diseases. This is a real challenge for them as the type of pests and pathogens in any given year or cropping season will be partly determined by climatic conditions.
One possible option for them is to use varieties that differ in their resistance to pests and diseases in order to be ensured against damage made by a broad range of pests and pathogens. In a previous post we reported on the findings made by John Mulumba and colleagues on how crop diversity can reduce pests and diseases pressure in beans in Uganda.
One case is not enough, though, to prove that agricultural biodiversity is a crucial component of an integrated pest management (IPM) strategy and more evidences are needed to make the case. Here we report on the findings made by Hua Xia Peng on maize in China. The methodology used by Peng and colleagues was the same as the one used in Uganda. A team of trained farmers and assistants led by Peng inspected farmers field to assess disease pressure. The assessment was done in the site of Zhao Jue in Sichuan province. Over 14 pests and diseases were indicated by the farmers as a threat in the site of which Northern Leaf Blight (NLB), maize rust and maize borer were the major ones. The relevance of the others depends on the year.
Farmers in the site use to plant from 1 to 4 varieties, each variety playing a different role in their in their livelihood strategy (home consumption, animal feeding) and also in controlling pests and diseases, as results showed. Overall, the two parameters used by the project to measure how farmers use varieties, richness and evenness, are both very strongly related to pests and diseases management. As a matter of fact, not only higher richness is associated to reduces diseases pressure, but also higher evenness. It is important to consider not only the amount of diversity kept but also how it is deployed in the field. The next 2 figures from Peng et al., unpublished clearly show the strong relationship between richness and evenness and the disease pressure (figure 1, richness vs disease index; figure 2, evenness vs. disease index).
This is the second time that an interaction between farmers and scientists produce important results that can affect farmers life. In the first case in Uganda we found that the way farmers manage diversity is very relevant to an effective diseases control in their field. In China, under very different conditions, using a very different crop (maize is open pollinated and bean is self pollinating crop) the results are the same.
This has very serious implications for the smallholder farmers and it shows the value of traditional varieties not only for farmers’ livelihood but also as a source of resistance for breeders. As far as farmers’ livelihood is concerned, the potential of the diversity in farmers’ fields to control pests and diseases and genetic vulnerability if managed appropriately, came out clearly. As a matter of fact, we identified resistant varieties in maize in China (and previously in bean in Uganda) that when fully available to farmers, can be manipulated in different ways to optimize the use of crop genetic diversity in reducing pest and disease damage.
From the breeder perspective, this material can be a primary source of resistance for new germplasm. Traditional crop varieties are a primary source for the new resistant germplasm, providing about 39% of the resistant germplasm used in the breeding programmes of major crops such as maize, wheat, soybean, sorghum and barley.