Acola, G

Orone, J

Otim-Nape, GW

Ssemakula, GN

van der Grift, YK Baguma Remco

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G. N. Ssemakula, et al. Uganda Journal of Agricultural Sciences, 2000, 5:8-11 Printed in Uganda. All rights reserved ISSN 1026-0919 ©2000 National Agricultural Research Organisation Improvement of local cassava germ plasm in Uganda G. N. Ssemakula, Y.K Baguma, Remco vanderGrift, G. W. Otlm-Nape, (r. A cola a1rd J. Orone Namulonge Agricultural and Animal Production Research ln:;titule (NAARf) P.O.B<)x. 7084, Kampala Abstract Use of local varieties in cassava gcrmplasm improvement has been intensified in the recent past as farmers demand for resistant types of their local varieties. This seems to indicate that recently released varieties may be lacking certain unique characteristics for which farmers selected and maintained the local varieties. During the evolution of the local varieties, there were hardly any biotic stresses on cassava and therefore, farmers did not consider this in their selection criteria. As a result, most, if not a ll local varieties, are susceptible to most of the important diseases and pests of cassava. Therefore, considerable breeding efforts have centred around improvement of such local cassava varieties for disease and pest resistance. Sources of resistance have been mainly the Tropical Manihot Series(TMS lines). Though it has been difficult to get resistant progeny from local cassava female parents, one successful clone yielded a resistant clone, 95/SE-0087 from a local female parent (Bao) and an improved male parent, TMS60142 (Nasc I). The clone 95/SE-0087 yields up to 24 tons/ha. It is sweet with good architectural characteristics, a low cyanogenic potential, good resistance to bacterial blight, cassava green mite and has so far not shown any symptoms of mosaic. Key words: Cassava, gennplasm, Uganda. Introduction Cassava is an important food crop grown all ov~r Uganda and recent trends indicate that it will soon be the m()St important staple in the country replacing bananas. Cassava was .introduced in Uganda as early as 1862 (Langlands, 1972) and since then it spread and gained popularity among farmers and consumers. The major reasons for the fast adoption of the crop were: (i) the ability of the crop to yield well even under marginal conditions where other crops can hardly give yield . (This abi lity was specially demonstrated during the droughts of 1931 and 1941 when it was essential to maintain local food production (Jameson, 1964)). (ii) the ability of the crop to store long in the soil and therefore its usc as a famine reserve crop. Evolution of land races When cassava was introduced in Uganda, farmers used to grow it and store it in the soil, only turn ing to it under conditions of food shortages. The long period it was left growing enabled the crop to flower and seed. Being an outcrossing crop and highly heterozygous, a lot of variation emerged as seed sprouted into seedlings. Whenever the farmers harvested their crop, they also harvested the seedlings and whatever was appealing to them waS'-kept through generations by cloning. The major route for the spread of cassava has been farmer to farmer diffusion. Those goodclones that had high stability and adaptability spread to many parts of the country to the extent that.rheir origin cannot be traced. Importance oflandraces Farmers selected cassava plants in their fields basing on unique characteristics that suited their preferences. These included underground storability, taste and compatibility with other crops in intercropping systems. During the early days of the recent mosaic pandemic re-mobilisation oflocal landraces particularly Ebwanateraka to affected areas served as a short tern1 solution to the problems of food shortages thal could otherwise have had more serious implications. What is very apparent to have been neglected in farmers ' selection criteria is resistance to diseases and pests either because they were not important at the time or the' crop itself was considered of low value compared to other crops. The recent mosaic pandemic that devastated cassava in the North and Eastern parts led to serious genetic erosion as farmers abandoned cultivation of their local varieties that had succumbed to the disease for the improved ' to lerantires istant varie ti es from the research system. Following the reduction of the disease pressure in the environment, interactions with farmers hoth rormally and infom1ally have indicated the need to restore or improve local variet ies. It is therefore very obvious that the new varieties lack some of the un ique characteristics for which farmers selected and maintained landraces. 9 Improvement or local cassava gcrmplasm in Uganda Approach to improvement of local varieties In response to the above demands, the cassava breeding programme at Namulonge initiated a hybrid isation project in order to introgress disease/pest resistance genes into local Jandraces. Particular attention was paid to Ebwanateraka and Bao because these were high ly adaptable and acceptable by farmers. The strategy of this project has been development of genotypes from local varieties with resistance to prevalent biological and environmental stresses. Other objectives of this project include: development of varieties with high yields especially in terms of dry maner content per unit area per unit time, improvement of root quality with respect to the different consumption practices among farmers, improvement of plant architecture suitable for different · cropping systems and stability and adaptability across environments. Schematic approach Local cassava variety e.g Bao Resistant cassava X (TMS series) +~~~ FI Hybrids in seedling nursery (Segregation high variability) lonal evaluation stage (unreplicated single row plots) Earlier efforts to improve local varieties in E. Africa centred upon the usc of Manihot glaziovii, a wild species of cassava. However, this was a long process that involved backcrossing to recover root qualities. All the same success was recorded with the development of the TMS series that have since then featured prominently in many African cassava breeding programmes (Sscmakula et al, 1997). The Uganda breeding program has utilised the TMS series as males and the local varieties as females in an introgression block. Seed is collected of both cross and open pollination, planted and evaluated at seedling and subsequent clonal levels. This follows the breeding and selection scheme shown in Figure I. This process has experienced difficu lties similar to those faced by earlier programmes to improve local varieties in E. Africa. Selection Criteria ·· · _. ____________ __ Preliminary yield trials (replicated x 2) Advanced yield trials (multilocational & replicated x 4) Uniform yield trials (multilocational & replicated x 4) On-farm trials (Farmer participants) Fig. I : Breeding and selection scheme for resistance to cassava pests and diseases Table 1. Performance of selected cassava clones at advanced yield trial stage planted at Serere and Ngetta 97/98 Clone Mean yield MeanCMDI (tonslha} (6 MAP) 95/SE-0050 28.11±7.13 14.92±5.89 95/SE-0290b 16.58±2.83 0.00±0.00 95/SE-0160 21.94±3.85 89.83±6.00 95/SE-0412 11.16±2.71 22.22±12.24 95/SE-0348 5.91±0.78 2.08±2.08 95/SE-0290a 14.92±5.25 53.12±15.26 95/SE-0055 12.32±3.55 6.80±4.86 95/SE-0126 9.61±1.96 29.07±15.29 95/SE-0094 21.94±2.51 0.00±0.00 95/SE-0245 8.83±2.61 44.17±1 0.91 95/SE-0312 12.68±2.85 7.14±7.14 95/SE-0230 16.67±2.74 23.04±10.74 95/SE-0044 30.12±3.25 35.36±10.37 SS4 (check) 24.62±4.21 15.64±12.21 95/SE-0087* 24.21±3.89 0.00 ±0.00 95/SE-0253 23.19±4.17 41 .09±16.25 95/SE-0088 21.06±2.12 2.50±2.50 95/SE-0356 19.13±3.81 62.19±1 0.60 Nase 2 (check) 18.11±2.22 48.29±12.56 CMDI=mosalc disea·se incidence(%) • Bao x Nase 1 cross CMOS= mosaic disease severi1y ( 1-no symptoms± 5-very severe symptoms) CBB=cassava bacterial blight (1-no symptoms± 5-very severe symptoms) 0 -MeanCMDS (6 MAP) 1.75±0.25 1.00±0.00 3.00±0.00 2.00±0.38 1.33±0.33 2.62±0.37 1.43±0.30 2.00±0.45 1.00±0.00 2.50±0.34 1.29±0.29 1.87±0.35 4 .50±1.50 1.87±0.61 1.00±0.00 2.43±0.43 1.25±0.25 3.00±0.00 2.75±0.25 MeanCBB MeanCGM Raw HCN (6 MAP) (6 MAP} taste (mg/kg dry wt) 1.87±0.35 1.12±0.12 1.50±0.33 1.75±0.37 1.25±0.16 2.00±0.33 1.75±0.37 1.25±0.16 1.12±0.12 1.62±0.32 1.12:0.12 1.62±0.32 1.50±0.34 1.17±0.17 1.00±0.00 1.62±0.26 1.50±0.33 2.00±0.26 1.50±0.22 1.86±0.34 1.67±0.42 1.50±0.22 1.17±0.17 1.40±0.40 1.87±0.29 1.37±0.26 2.37±0.32 1.55±0.34 2.00±0.36 1.60±0.40 1.57±0.30 1.14±0.14 2.00±0.45 1.75±0.31 1.25±0.16 1.75±0.31 2.12±0.35 1.62±0.26 1.00±0.00 2.75±0,92 2.00±0.27 1.25±0.16 1.75±0.31 1.12±0.12 1.37±0.26 1.42±0.20 1.14±0.1 4 2.50±1 .22 1.75±0.31 1.75±0.31 1.57±0.30 1.75±0.31 1.37±0.26 1.75±0.25 1.87±0.35 1.50±0.19 1.75±0.31 CGM=cassava green mite (1-no symptoms± 5-very severe symptoms) Raw taste 1 =sweet± 2=slightly bitter± 3=bitter MAP=months after planting 234±47 395±56 461±45 241±45 243:t34 570±45 263±56 258±45 192±34 297±41 595±67 507±67 240±34 258±41 232±43 269±32 163±27 344±18 166±21 9 ;z: en ~ ~ j» n. !!!-Improvement of local cassava gennplasm in Uganda ll Table I shows the perfonnance of selected cassava clones at an advanced yield trial stage planted at two locations. With the selection criteria adopted, only 5 clones from table 1 were promising and were selected. These arc: 95 I SE-0050, 95/Sl:-:-0055, 95/SE-0094, 95/SE-0088 and 95iSE-0087. Other clones were not selected either because they had low yield (less than 12 tonslha), had a cassava mosaic disease (CMD) incidence of more than 30 %, a CMD severity score of more than 2.5, a ta5tc score of upto 2.0 or a cyanogenic potential of up to 300mg HCN/kg dry weight. From the table, it is evident that CMD is still the major biotic constraint being addressed. Originally what hindered progress in the improvement of local varieties was the lack of genetic. variability for resistance to diseases and pests especially CMD. Also, a close association between taste, yield, cyanogenic potential and resistance to CMD has been reported by Ssemaku Ia ct al 1997. Many highly disease resistant cassava varieties always tend to have bitter taste and high cyanogenic potential, a combination that makes breeding for resistance, good taste and low cyanogenic potential almost incompatible objectives. With the close access to a large germplasm pool from the Jntemational Institute of Tropical Agriculture, a lot of variability bas been exploited in order to improve the Ugandan local germplasm. A number of cassava clones with high resistance to pests I diseases and low cyanogenic potential have been identified and are being used as male parents for improving local varieties. Recording success has not been very easy as seedlings from local varieties have in most cases been as susceptible to diseases and pests as their female parents (locals). On the other hand, seedlings from reciprocal crosses very often been resistant but with unacceptable cyanogenic potentiaL Recently, however, a progeny of Bao (female) and Nase I (male) has shown a high level of resistance to mosaic disease. This clone (95/SE-0087) is sweet, with a low cyanogenic potential and yields higher than Nase 2, a check variety that has been used in evaluating it. Table 1 shows its performance relative to others in an Advanced Yield trial. The clone has petiole and stem colours like those of Bao but sometimes branches lower than Bao. References Jameson J.D. 1964. Cassava mosaic disease in Uganda. East African Agricultural and Forestry Journal 29:208-213. Laoglands J. 1972. Cassava in Uganda. Uganda Journal 10:2?3-286 Ssemakula G.N ., Baguma Y.K., Otim-Nape G. W., Bua A. and Ogwal S. 1997. Breeding for resistance to mosaic disease in Uganda. African Journal of Root and Tuber Crops vo!. 2 (1&2); 36-42 

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Improvement of local cassava germ plasm in Uganda

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Improvement of local cassava germ plasm in Uganda

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