SATrends Issue 80 July 2007
  • Managing Striga in Niger and Mali
  • Low-cost, high-throughput marker services for SAT crops
  • Thermal cameras screen drought-tolerant chickpea
  • Basins strengthen partnerships among poor farmers!

  • 1. Managing Striga in Niger and Mali

    Striga is a parasitic weed whose main hosts are cereal crops in the semi-arid tropics (SAT) of sub-Saharan Africa. It causes huge reductions in yields of sorghum, millet, maize and rice. The area and intensity of infestations have increased, especially in areas where agriculture is extensive, fallow periods are reduced and soils are deficient in nutrients.

    The last decade has seen the development of a wide range of potential control methods. However, in the extensive agricultural systems of the Sahel, appropriate measures are scarce and technology transfer has thus not made much progress. It is important to simultaneously search for new technologies, as well as assess, and implement technologies readily available in farmers’ fields. Also, since farmers will not accept control techniques that are solely aimed at reducing Striga, a technology that serves additional goals such as direct income increase through the introduction of potential cash crops has more chance for adoption.

    A proud trainer farmer showing the poster he prepared on millet growth and the Striga life cycle.

    ICRISAT has a two-fold approach to this problem. The first approach involves quantifying the effects of individual and combined control methods on crop yields, Striga performance and population dynamics on-station in Niger and Mali. This information is also used for modeling Striga seed bank dynamics.

    Secondly, ICRISAT has started a project in collaboration with Catholic Relief Services and the Institut d’Economie Rurale for implementation of farmer field schools (FFS) on Striga in the region of Douentza, north Mali. Participatory village mapping and interviews were used to analyze the agricultural systems in the area. Based on the interviews, six villages were selected, and each village was asked to choose 25 participants. Of about 300 farmers, 30 were chosen as farmer trainers. Practical and do-able steps to remove Striga are communicated to these farmer trainers.

    One village was chosen as the training of trainer site, where trainer farmers come together each week to do observations in the field and get training on subjects such as weeds, biology and control of Striga, insect pests, intercropping and botanical extracts to combat insect damage on cowpea, and other such activities. Thus the lessons in the labs were transferred to the farmers.

    The future activities envisaged include:

    1. Continuing FFS activities and addressing multiple goals like Striga seed bank dynamics, soil fertility and income generation
    2. Studying effects of integrated systems’ components on (a) the seed bank dynamics of Striga (b) yield aspects of host and non-host crops (c) economical revenues to farmers
    3. Introduction and use of sorghum varieties from marker assisted selection for Striga resistance at ICRISAT into integrated management practices

    For further information, contact

    2. Low-cost, high-throughput marker services for SAT crops

    Molecular markers have substantially influenced plant breeding in the past two decades. However, markers are not widely integrated into many breeding programs, especially in developing countries often because of complicated techniques and high costs. Genome-wide marker information and locations of key loci for both desirable and undesirable characters are now available for many major crops and this information can be judiciously integrated with conventional breeding strategies.

    Unfortunately, such information is still lacking for many crops of resource-poor farmers in the semi-arid tropics, essentially due to inadequate global investment on marker development for these crops, where the direct returns on investment are often meager. ICRISAT is committed to bridging these gaps through the exploitation of cost-effective molecular marker techniques for such orphan crops and making them readily available to researchers.

    With support from the Government of India’s Department of Biotechnology, ICRISAT has established a Center of Excellence in Genomics (CEG) at Patancheru. The CEG is currently adopting the Diversity Arrays Technology (DArT) platform as a low-cost alternative marker system.

    DArT is a generic, hybridization-based, cost-effective whole-genome fingerprinting method. DArT markers are scored for polymorphism (difference among individuals in genetic makeup) in parallel rather than serial analysis as done in gel based marker systems. A DArT assay simultaneously genotypes hundreds to thousands of Single Nucleotide Polymorphisms (SNPs) and insertion/deletion polymorphisms (InDels) across the genome. In other words, DArT can score differences in genetic makeup in multiple locations in one run thereby reducing the time and cost for genotyping. This technology can be applied to virtually any organism for a range of applications.

    DArT can reduce the time and cost of analyzing the genetic makeup of plants.

    With the high-throughput and low cost (a few US cents per data point), the number of markers and genotypes will no longer be a limitation for assessing diversity in germplasm accessions and breeding lines. Construction of high-density linkage maps will be possible even for previously marker-less crops. Association studies, which require large number of markers distributed across the entire genome, can be accomplished with DArT, as it profiles the whole genome and yields data for hundreds of loci in a single assay.

    The most significant application of DArT will be screening for recovery of recurrent parent genotypes in backcross progenies, saving time and resources in moving new traits into elite cultivar backgrounds. In addition to DArT marker services, the CEG will provide sequencer-based SSR genotyping services and high-throughput allele determination via TILLING (Targeting Induced Local Lesions in Genomes) and EcoTILLING (a variation of TILLING) for various crops. This ‘DNA to data service’ will be available to SAT researchers in late 2007, substantially reducing the need for investments in instruments and technical expertise to generate molecular marker data for crop improvement at many SAT research sites.

    For further information, contact

    3. Thermal cameras screen drought-tolerant chickpea

    To improve the plant growth and final seed productivity of chickpea, it is important to screen the chickpea germplasm that has mechanisms to minimize the adverse effects from water stress on the plants under drought conditions. Maintaining the transpiration via stomatal (the pores on the leaves through which the plants lose water through transpiration) sensitivity under drought conditions is one of the relevant traits. The transpiration can be estimated by polometer, however, the measurements in this system are time consuming, and therefore it would be difficult for large-scale germplasm screening and characterization, especially under the field conditions.

    Measuring the canopy temperature is one of the potential solutions to know the transpiration status of the plants. Higher canopy temperatures, a result of an early stomatal closure under severer drought conditions, would indicate drought susceptible genotypes. This will result in grouping of the chickpea germplasm for the magnitude of drought tolerance through a gradient of canopy temperature differences.

    In 2006 post rainy season, 16 chickpea genotypes which have different drought responses were cultivated under two irrigation schemes, irrigated and rainfed in ICRISAT field. The thermal images of plant canopy captured by handy infra-thermo camera were used to estimate the plant canopy temperature in chickpea (Figure 1). It was a very convenient device allowing us to capture a thermal image less than minutes, and easy to work in the field conditions. Chickpea was suitable material for this investigation because it has suitable height to take the thermal images from the above without any help of stand or stepladder.

    In several measurements taken in a day, the maximum difference of canopy temperature between the irrigation treatments was observed during mid day (1100 - 1400). The canopy temperatures in the irrigated condition was 7 oC lower than those in the rainfed conditions in average. The temperature differences among the chickpea genotypes were 2 to 3 oC under the rainfed conditions, which indicate that the canopy temperature difference between the irrigation treatments could be captured easily by this device but more accurate analysis is needed for capturing the genotypic difference in the canopy temperature.

    Infrared pictures of chickpea canopy show the heat variation in
    different parts of the leaves.

    Some drought tolerance genotypes, e.g. ICC 4958 showed lower canopy temperature than the drought susceptible one. Some other drought tolerant genotypes, however, did not always show much difference in the canopy temperature from the drought susceptible genotypes, which indicate that maintaining lower canopy temperature, viz., maintaining high transportation, is not the only trait to improve the drought tolerance, and there would be some other traits relating the drought tolerance improvement in these genotypes.

    The infra-thermo camera systems tested here potentially allowed ICRISAT scientists to score the canopy temperature differences among field-grown chickpea genotypes instantly and visually. However, the camera doesn’t have a function with each pixel to contain the numerical temperature data. Now, based on the color scale function indicating the temperature, we are finding the way to convert the color image into numerical temperature data, and will continue the optimization in 2007. Also it will be applied on other ICRISAT mandate crops.

    For further information, contact

    4. Basins strengthen partnerships among poor farmers!

    In the SATrends story ‘Boost from Basins’ (April 2006) we reported on how farmers who had tested the planting basin technology for one season were excited about the higher yields they obtained compared to their conventional system. The basin technology – a conservation agriculture option suitable for poor farmers – is simple:

    • Seed is placed in small pits that are dug in the field without ploughing
    • Manure and fertilizer are precisely applied
    • Soil is covered with crop residues to protect it from erosion and to conserve moisture

    For the past two seasons, 13 non-government organizations (NGOs) and the Zimbabwe Agricultural Research and Extension Services (AREX), with technical support from ICRISAT, and financial support from DFID, have scaled out the basin technology to 16 districts in the dry areas of southern Zimbabwe. Many lessons and impacts have been realized from this collaboration, but higher crop yields, strong partnerships and empowered farmers are the highlights.

    Better crop with basins (right) compared to ploughing (left)

    For three consecutive seasons, farmers have realized 20-75% higher yields in their basin plots compared to the conventional system. As a result, the number of farmers practicing the basin technology has increased 10-fold over the three seasons. Use of small doses of nitrogen fertilizer has been shown to enhance the benefits from basins.

    Farmers were facilitated to form and run conservation agriculture groups, ensuring sustainable implementation without outside support. The farmers meet periodically to learn from each other about basins and work as a team when undertaking some of the labor-intensive operations, such as digging basins for the first time.

    However, these farmer groups have gone beyond basins. Financial savings clubs, small livestock rearing as well as emotional support to bereaved members are some of the extra benefits to group members. In communities where HIV/AIDS is a major problem, these benefits are very much needed.

    Challenges, such as achieving soil cover using crop residues in these mixed crop-livestock systems, identifying profitable rotations and developing markets for inputs and products, still remain. But the partners believe these challenges can be tackled through the diversity of ideas and opinions, which has so far been the reason for success. All the stakeholders including farmers attend periodic interactive reflective learning workshops, which have proved to be useful fora for tackling constraints to technology development and for learning about drivers of success.

    For further information, contact