Germplasm enhancement, development and distribution

Activities concentrated on local germplasm collection, introduction of genetically broad-based populations and evaluation under diverse agro-ecologies in member countries.

Kenya:
One hundred and eleven local cultivars are under maintenance and about 50,000 seedlings and 90 clones evaluated. Approximately 30% of the families evaluated had CGM incidence of less than 10%. Clones KB95/0062, KB95/0059, KB95/0029, KB95/0026 and KB95/0042 combined tolerance to mosaic, CGM and good morphological characteristics. Percent dry matter content were generally high, ranging from 37.2% in CK02 and CK01 to 43% in Serere 12200. Varieties Mucericeri, KME1, KME61, Guzo 46106/27, Mwakazanga, Kibandameno Serere, 12200, Adhiambolera, Kibandameno have been released to farmers. A total of 776 clones and about 100,000 seedlings are under evaluation at different sites.

Uganda:
A total of 380 local accessions have been assembled. About 200,000 seeds generated from elite local cultivars and introduction from IITA, Tanzania, Rwanda and D.R. Congo have been distributed to network countries. A total of 71, 20 and 12 clones were evaluated in preliminary, advanced and uniform yield trials, respectively. Clone, 89/1988-UYT-PDB-2 shows high stability. Other promising clones included: 30572-16, 30572-81, CL-EV 98, CL-EV 85, SS4, 89/91934-92, 89/30786-11. Ten clones were evaluated across four locations and two growing seasons in a GxE study. Significant differences were found among genotypes and genotype x environment interactions. Genetic components of variance were smaller compared to error variances. Interaction variances involving locations and years indicated that the former is a more important source of variation than the latter. Cyanogenic potential showed high sensitivity to environment. Broad sense heritability were moderate for storage root yield (0.44) and high for cyanogenic potential (0.69). Correlation coefficients indicate significant negative associations between cyanogenic potential against percent dry matter, storage root yield and storage root number (r = -0.725, -0.127 and -0.111), respectively. Due to highly sensitive responses to environmental factors by the genotypes, selections should be tested in target environments to be effective and efficient. A study to compare picric and enzymatic methods of CNP determination showed highly significant (r2 = 0.66) squared regression relationship between the two methods.

Rwanda:
A total of 280 clones were retrieved after the civil unrest and being evaluated. About 26,000 seedlings are being evaluated at two locations. Two advanced yield evaluations showed that the hybrid TMS 30001/7/4 x UYT Bulk 85023/11/11 had a fresh storage root yield of 45.31 t/ha, followed by the clones MIS-88-25, 90257 op/5 MIS-88-UYT Bulk 1977/11/39 and MIS-88-UYT Bulk 83022 op/7/5, with yields of 40.99, 43.37 and 40.00 t/ha, respectively. EARRNET's participation in the Seed of Hope (SOH) initiative focused on multiplication and distribution of planting material and training extension personnel and farmers. Varieties Rutamizi, Machunda, Eala 07, Creolinha Maguruyinkware were multiplied and transferred to Rwanda for further multiplication under the initiative.

Burundi:
Gitamisi, Creolinha, TMS 16013, Maguruyinkwale and Mpambayabashengera were recommended for multiplication and distribution. Ten clones out of 71 have been advanced for further evaluation.

Madagascar:
Evaluation of local germplasm were acomplished. A total of 133 clones are under a preliminary yield trial (PYT), 20 entries being evaluated in a uniform yield trial (UYT) while 65 were maintained for further characterisation. A set of 47 genotypes introduced from IITA were placed in a clonal evaluation trial. Seedlings from 110 families were evaluated out of which 1786 plants selected for further evaluation. Another set of sixty clones received from IITA were released from the quarantine station and planted at three locations. Currently, 675, 75, 35 clones are being evaluated in clonal, PYT, and UYT, respectively, while 10,000 seedlings are being evaluated at two locations.

D.R. Congo:
The country has 300 local germplasm collection. A total of 13 varieties have been released, multiplied and distributed with spill over effect into Rwanda and Cameroon. Eleven of these were introductions from IITA and the rest are local varieties.

Market driven regional cassava germplasm enhancement/development activities: The regional germplasm enhancement activities started in 1994/95 in Uganda and Kenya to cater for mid-altitude and lowland cassava growing ecologies of the region. Approximately 400,000 seedlings were evaluated against major diseases and pests, agronomic characteristics, cyanogenic potential and dry matter. Reaction to the biotic stresses normally increased between 6 and 9 months after planting. At Mtwapa, the incidence and severity of the East African cassava mosaic disease (EACMD) was low but cassava green mealybug (CM) was widespread. The distribution of CNP among 727 clones were 39%, 51% and 10%, (high, medium and low, respectively) with 20% of the clones having lower CNP than the check. The highest dry matter obtained was 51% from clone 97NML/620.

Currently, 447, 181 and 100 families are under evaluation in Serere, Namulonge and Mtwapa, respectively. A total of 6,600 plants were identified for clonal characterization. About 11,240 clones were evaluated in a clonal characterization trial and 2,000 clones in performance I trial. Clones MM96/8061 and MM96/7745 had the highest DM of 52%. Out of 152 genotypes introduced from IITA, 31.5 and 77.6% exhibited high levels of resistance to CMD and CGM respectively. Clones I89/00159B, TOKUMBO, 91/00459, OKO-IYOWO, 91/SN02322, 93/044(2), ABBEY-Ife, I89/02195, 92/0417, TMS820447, 82/00058, I89/00159, 90/00099, 93/0070, 82/00661 and I92/0342 had score of less than 2 in the major biotic stresses; mosaic diseases, green mite, bacterial light and anthracnose. Another set of 147 clones including 41 polyploids and early bulking diploids were introduced and being evaluated.

Performance trials:
About 124 clones were tested in performance trilas at two locations; 36 clones were common across both locations. The mean fresh tuber weights were higher than checks at both locations. Data collected at three monthly intervals on 116 clones indicate that maximum dry matter accumulation (approximately 40%) was attained in 9 MAP, while leaf CNP score peaked off at 5.15 at 6 MAP. Currently a total of 1943 are being evaluated (1450 Serere and 493 Namulonge, respectively). Correlation coefficient between number of storage roots per unit area and average storage root weight indicates that the expected negative relationship between the two components does not hold. Clones with higher number of storage roots per unit area and bigger weight per storage root are attainable. Clones MH95/0283 and MH95/0295 combine high number of storage roots with heavy root weights. A multiple regression analysis of dry yield on number of storage roots per unit area, weight per storage root and dry matter show that the latter two components are the driving selection indices in the mid altitude ecologies. Multiplication of a set of genotypes to be used in investigating GxE interaction within the region was initiated in member countries.

Plant Quarantine Services (Kenya/Uganda):
The establishment of an open quarantine facility at KARI station in Alupe to receive germplasm from EARRNET/ESARC regional nurseries was realized. Currently about 600 clones are being scrutinized by the Plant Quarantine Service (PQS) - Muguga, Kenya. In Rwanda, 600 clones are under evaluation by their national program in collaboration with the PQS in Kigali. The Uganda national program is evaluating 74 clones in multilocational advanced yield trials. PQS, Muguga can now receive limited numbers of germplasm from different countries for cleaning, virus indexing, tissue culturing and distributing to NARS for regional trials.

Ecological adaptation:
A programme was initiated to evaluate the physiological basis of adaptation using two genotypes from each of five different sources and three different altitudes 600, 1200, 1800m asl, (Masindi, Namulonge and Kapchorwa respectively). Results show that tuberization commenced 6 weeks after planting (WAP) in the mid altitude ecology in clones SS4, I91/02324 but starch was not detected until 8 WAP. Significant differences were detected among locations, sources and clones for plant height and storage root number. Tuberization was observed at Masindi and Namulonge at 3 MAP but not at Kapchorwa. Namulonge had the highest storage root number while Masindi had the highest storage root weight, probably associated with low altitude and high temperatures. Generally, the clones from the West African lowland were late bulking compared to the East Africa mid altitude materials.

The Regional / National collaborative research:

Objectives
· Develop improved, adapted populations and varieties acceptable for(to) different end use(r)s
· Distribute varieties and seed populations among network member countries

Background information and methodology
More than half of the world's production of cassava come from the African cassava belt, stretching from Madagascar to Senegal, where it is used almost exclusively as food. The crop has the ability to grow under conditions considered sub-optimal for the majority of other food crops and in ecosystems where food supply is constantly threatened by environmental constraints such as drought, pest and disease outbreaks. As a low cost carbohydrate source, cassava plays a food security role with potential for livestock and industrial application. COSCA data have shown that cassava generates cash income for the largest number of households in comparison with other staples.

The positive response of cassava production and utilization to improvements in environmental, biological and socio-economic conditions has influenced the strategies used in the germplasm enhancement program for the ecologies of East and Southern African region. These constraints include;

· Untapped market opportunities:
Production of cassava is demand-limited. Increased reliance on it as an energy food, its entry in the animal feed and in other industrial applications will provide incentives that will motivate farmers and processors/consumers to expand production and utilization, respectively.

· Post-harvest handling technologies:
The high perishability of harvested storage roots and the presence of cyanogenic glucosides in cassava require immediate processing into more stable/safer products. Availability of high quality dry products with long shelf life is necessary to support the development of cassava-based agro-industries. Increased utilization in animal feed, starch, confectionery, textile and pharmaceutical industries can reliably be ascertained with improved and constant supply of cassava. Cassava leaves are a preferred vegetable in many countries but lack of continuous assessment for its food/feed quality attributes has slowed efforts to improve it.

· The cyanide scare:
Recent studies have clarified cyanogenesis and the mechanisms of removing cyanogenic compounds during processing. The confusion around the toxic potential of cassava, which has limited expansion of production/utilization, has been eliminated. Genetic information on cyanogenesis is now required for the production of cassava varieties suited for specific end-uses.

· Declining soil fertility/shortening fallow periods:
Farmers' ability to respond to declining soil fertility/fallow periods by replacing more susceptible crops with cassava is constrained by its long cropping cycle. The currently available improved varieties attain their maximum yield at 12-15 months as opposed to 22-24 months for local cultivars. These early maturing varieties are likely to promote more cropping cycles for a given period of time leading to a faster decline in soil fertility. Shortening fallow periods require varieties selected for efficient nutrient assimilation, better ability to be intercropped with legumes or other soil fertility conservation strategies.

· Pre- and post-harvest pests and diseases:
The major cassava pests and diseases including arthropods, pathogens and weeds can reduce production by an estimated 50%. The major pests of concern are CGM, variegated grasshopper, root mealybug, ACMD, CBB, CAD, and root rots. The role of termites, nematodes and certain weed species particular to specific eco-zones has been reported as constraints but has not received adequate attention.

· Need for more adapted germplasm:
COSCA data indicate that farmers are abandoning old cultivars and introducing new ones signifying farmers' need for better varieties and highlighting the danger of loss of genetic diversity. The available improved germplasm are mostly adapted to the lowland humid tropics, while it is becoming more evident that cassava is expanding to other ecologies. Germplasm adapted to these agro-ecological zones are needed. Expansion of utilization base of cassava to new industrial uses requires germplasm with high yield as well as high quality for specific end-uses.

In the ECA sub-region, cassava is mainly grown in the mid-altitudes and coastal areas with differing growing (soil/climatic) conditions. Considering the high level of interaction between genotypes and their environments, site-specific selection and multi-site testing is required to improve effectiveness of breeding programs. However to efficiently develop varieties adapted to specific ecologies, characterization and rationalization of selection and evaluation sites are important. Sourcing from the broad based germplasm from IITA, Ibadan, market driven germplasm enhancement programs has been initiated at Serere, Uganda, and Mtwapa, Kenya, to cater for the two major ecologies.

The objectives of the programs are to:
· generate improved and adapted populations with desired characteristics for the agro-ecologies targeting different end-uses/markets
· avail populations to network member countries for evaluation and selection under specific agro-ecosystems
· establish special backup populations
This program follows a five-stage scheme: The first stage, comprising sib family nurseries, clonal characterization and performance evaluation assures that selected genotypes do have the necessary resistance/tolerance to major biotic stresses, good agronomic and quality characteristics. The second stage involves the super-imposition on selected genotypes of production inputs (high, low) required for commercial and subsistence production. The resultant two groups would be evaluated for their potential to satisfy various end-uses (food, feed or industrial raw material) during the third stage. Selected parental lines would be used in an improvement program to develop specific or special backup populations/germplasm for distribution (based on needs) to the different national programs during the fourth and fifth stages, respectively. EARRNET will provide an enabling environment to NARS to make effective use of broad-based genetic stocks with multiple pest and disease resistance, important food quality traits for the diverse stakeholders and ecological adaptation. Improved germplasm can be introduced to member countries from any of the stages once a clone is thought to satisfy the requirement of stakeholders in the production to consumption continuum.

Cassava genetic resources in ECA sub-region are under the threat of erosion. Old traditional cassava cultivars must therefore be collected to prevent further loss of desirable genetic diversity. National programs continue to assemble local landraces, which are normally maintained in the field. Uncertain weather conditions, disease, civil unrest and pest attacks have resulted in the loss of some of these materials or their passport information. Systematic evaluation and characterization is needed to remove duplicates and maintain only a core national collection in respective germplasm banks. National core collections would then be constituted into a regional collection, which would be evaluated and characterized. From the characterization process, a set each of the regional core collection would be maintained at the Plant Quarantine Station, Muguga, Kenya and IITA, Ibadan for regional and international use.

Additional variability needs to be tapped, particularly if adapted to harsh environments. The wild relatives of cassava are repositories of genetic potential that should not be ignored. The early cassava introductions were not sufficient to transfer the wide genetic base existing at the centre of origin of the species. Introduced progenies from Latin America hold promise to further broaden the germplasm base of cassava, by providing unique sources of variability not currently available in Africa.

Most National Root Crop Improvement Programs now have capabilities to evaluate germplasm with expanded facilities and capacities to receive/transfer tissue cultured clones and seed population from/to other international, regional and national institutions. Strategies and approaches to streamline future genetic improvement activities within the region have been institutionalized. Large numbers of seeds from selected IITA populations have been received planted. A number of clones are at various stages of evaluation in all EARRNET member countries. These achievements will be consolidated and other constraints identified in the sub-sector studies will be addressed. Sub-ecologies will be defined using the Geographic Information System (GIS) to target population improvement programs to specific environments and focus introduction of genetic variability from ecological homologues within the centre of origin through IITA. National programs are encouraged to undertake evaluation and selection of improved and adapted clones suitable for the farming systems and ecologies within their countries and acceptable to the different stakeholders from seed populations and tissue cultured material received from IITA, Uganda and Kenya. The national root crop programs in East Africa could benefit immensely from a system of in vitro micro propagation, virus elimination and indexing of cassava propagules.

The recurrent drought and reduced resource base of many farmers coupled with restricted movement of improved cassava germplasm within the ECA sub-region has been a major drawback in expansion of production and utilization of cassava as food and industrial raw material. Cassava is propagated by cuttings and the risks of carrying virus diseases without easy detection is high. Since 1951, PQS-Muguga has been in the forefront in protecting the African agriculture from pests and diseases. With the increasing roles that cassava play as a food security, cash and industrial raw material, the need for ensuring availability of clean planting material as well as ease of movement of improved cassava germplasm in the region has become greater than before.

It had not been possible for varieties or advanced genotypes developed in one country to benefit other countries in the region which impeded the spill-over effects of cassava improvement activities in the region until recently. The open quarantine permission provided by PQS, Muguga permitted the transfer of a number of clones from the regional germplasm enhancement program in eastern Uganda to western Kenya and Rwanda.

No changes in methodology are advocated. Local germplasm collection improved germplasm (seeds and tissue culture) introductions, evaluation, selection and utilization in broadening the germplasm base within the region will continue. The search and utilisation of new sources of resistance to all the major pests and diseases need to be intensified, with the aim of diversifying resistance that would prove difficult for the pathogens and pests to circumvent. Problems, which are recalcitrant to conventional methodologies, need to be addressed using the tools of biotechnology. Clones with adequate superior performance will be multiplied and distributed to producers. Multinational, multi-site trials are planned as an integral activity of the network considering the limited adaptation of varieties. Results will be incorporated into the GIS information management system to ensure optimal benefits and enable rationalization of testing sites at national and regional levels.

A Tuber and Root (Crop) Information System dubbed "TRIS" has been developed. TRIS employs the FAO physical resource coverage's to provide crop suitability maps for cassava, sweet potato and yams. Features are a) agro-ecological homologues to assist decision making for germplasm deployment and b) assessment of relative potential of lands (best to least suitable) for expansion of root and tuber crops. Its geo-referenced databases include national statistics (people, land, and crops); national systems, root and tuber crop capacity; germplasm availability; production systems (main characteristics); production constraints; end-uses; germplasm description; vulnerability and response capacity. The program is interactive and updateable.

Kenya and Uganda have good tissue culture facilities that could be supported through the provision of laboratory supplies to engage in in-vitro micro propagation. The technology for virus diagnosis could be used to index the resulting plantlets. Such materials could then be made available for international exchange in collaboration with the plant quarantine institutions. The tissue culture laboratories available within the region will facilitate in-vitro dissemination of germplasm after virus indexing and through collaborative arrangements with the Quarantine Department of the National Agricultural Research Laboratories in KARI, Kenya and the Quarantine Service located at Kawanda Research Station, NARO, Uganda. The comprehensive core germplasm collection would be maintained in-vitro at PQS. Muguga, for future utilization in enhancing improvement once the virus indexing capacity and capability has been developed to enable germplasm movement. Protocols for identifying and eliminating pests, diseases, and poor plant vigour in cassava cuttings are needed by NARS involved in plant quarantine and plant protection activities, and for selection, propagation, and management of clean cuttings by extension agents and farmers in a sustainable manner.

Due to cost and personnel constraints, it is crucial that the genetic materials furnished be consistent not only with the specific needs of NARS but their absorptive capacities as well. The small and less endowed national programs would be encouraged to undertake wide multi-location testing of almost-finished varieties and technologies from which materials will be selected for extension. The stronger or relatively more endowed national systems could use early generation materials from regional nurseries for their own adaptive breeding work.

Sub-themes
¨ Local germplasm collection, evaluation, characterization, maintenance, documentation and utilisation
¨ Introduction, selection, generation and evaluation of genotypes with specific end-use(r) desired characteristics
¨ Exchange of improved germplasm

Expected output

¨ Assembled, documented and conserved core local germplasm collection
¨ Exchange of germplasm enhanced
¨ Improved open quarantine and laboratory facilities established
¨ Clones with specific end-use characteristics identified and distributed
¨ Cassava growing environments characterised based on GxE interaction studies

Indicators for monitoring progress and impact

· At least 50 local cassava germplasm assembled, evaluated and characterised in each member country
· At least 10 local superior clones identified, released or used in breeding programs
· At least 50% of national core collection maintained at regional and international gene banks
· Number of populations with multiple pest resistance and preferred end-user characteristics
· At least 10,000 botanic seeds representing at least 40 families introduced to each collaborating country biannually
· At least 10 improved genotypes available for on- farm trials in at least four countries by the year 2002
· At least 3 clones identified for leaf production
· Rationalization of selection and evaluation sites based on GxE information
· At least 900 clones certified clean by quarantine
· Number of germplasm exchanged in tissue culture form
· At least 50,000 seed from superior parents exchanged among member countries.