Carey, EE

Mwanga, ROM

Turyamureeba, G

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U~:anda Journal (if Agricultural Sciences, 2000, 5:40-42 Printed in Uganda. All rights reserved ISSN I 026-0919 ©2000 Nationa l Agri~ultural Research Organisation Evaluation of promising sweetpotato genotypes for high altitude, cool, moist agroecologies of Uganda Turyamureeba G. Mwanga R.O.M, and Carey E. E. Abstract Eighteen genotypes from the NationalSweetpotato Programme were evaluated for their fresh storage root yield and reaction to stem and leafbUght (Alternaria bataticola) at Kachwckano (2000 metres above sea level) in Southwest Uganda. The trials were set up to identify sweetpotato genotypes with adaptation to highland agroecologies with special reference to resistance to Ahemaria blight Alternaria blight was scored at harvest time on a scale of 1-5 (1 =symptomless and 5= severe infection) and storage root yields were taken at harvest. Based on the evaluation made during crop growth and at harvest, four genotypes and the local check, Magabari, bad high levels of resistance toA/Jemaria blight. Eight genotypes had total storage root yield higher than the local check indicating higher yield potential of the new genotypes. The differences in yield and susceptibility to Alternaria from the breeding programme offer great advances in breeding varieties for highland tropical environments where the disease is of major importance. Keywords: Alternaria bataticola, genotypes, resistance, sweetpotato. Introduction Sweetpotato (Convulvulaceae:lpomoea batatas (Lam)L) is the third most important food crop in Uganda after bananas and cassava (Bashaasha et a! 1995). Annual production is 2.2 million tons from about 500,000 ha. of land (FAO 1996). They are a major starch staple (Bashasha et a/ 1995, Smit I 997) for the majority of the smallholder communuties of Uganda and to some extent source of income. Sweetpotato cultivation is throughout the country in all the three major agroecologicru zones ofU ganda (Table I}. There are several pests and diseases that reduce yields in addition to abiotic facotors like temperature, and low soil fertility. Among these are virus complexes, leaf and stem blight caused by Alternaria bataticola, weevils and catterpillars and several mammals. There are three major agroecological zones in Uganda, ranging from cool highlands to the warm sub-humid environments in Eastern Uganda. Severity of Alternaria blight depends on environmental conditions 'getting more severe as conditions get cooler and moist. Disease and , lesion size increaese with altitude with high relative humidity or free water necessary for infection and sporulation (Ames et a/1996). Stem and leaf blight on sweetpotatoes caused by the fungal pathogen Alternaria bataticola has been reported in East and Central Africa (Skoglund et a/1992, Lutaladio 1995) and has become a serious threat to dissemination of improved sweetpotato genotypes in Uganda. Reports about Alternaria disease and breeding for resistance has been reported by several authors. Ted Carey 1997 quating Janseen 1982 and Ndamage et al 1992 reported that two high yielding varieties with good taste and resistance to SPV D and Alternaria blight were identified and dissem inated by the Rwanda Sweetpotato Programme. Host resistance to Alternaria blight in sweetpotato is reported to exist (Ames 1998) while its control can be achieved through integration of various control practices such as cultural methods as well as host resistance (Ames 1996). Evaluation of potent ial clones developed by Namulonge Agricultural and Animal Production Research fnstitute (NAARI) sweetpotato programme for resistance to Alternaria blight was carried out in 1995 and 1996. Screening and breeding for resistance to Alternaria is an integral part of these efforts with the overall objectives of developing resistant varieties (Turyamureeba et a/1997) . Materials and methods Seventeen genotypes were evaluated for adaptation to the Southwest highl and agroeco logy alt itude at Kachwekano, 2,000 m above sea level during 1995A rainy season. One locally important variety, Magabari known for adaptation to cool environments was included in the trial as a check. The trial was established in a RCBD replicated three times. Plot size was 5.4 m long, spaced I m between ridges. Spacing between ridges wa 1 m apart with intra row spacingof30 em from vine to vine (33,333). Vine tips 30cm long were used for planting the trial. Planting was done on November 7, 199 5 and harvesting was on January 31, 1996. The second trial was planted in 1996 second rainy season at the same location. Twelve.clom:s and six released varieties were planted in randomised complete block design replicated three times. Plots were 3 m long with 1 m between rows and 30cm from vine to vine. 41 Turyamureeba G. Planting was done on November 30, 1996 and harvesting was on June 26, 1997. During crop growth, data was collected on establishment and Alternaria blight disease severity. A scale of 1·5 was used to assess severity where l was symptomless 2 showed mild symptoms, 3 had intermediate attack, 4 had severe symptoms and 5 highly diseased. Yield data was taken at harvest from the entire plot on marketable root yield and total root yield. Dry matter content was recorded after drying the samples at 650C to stable weight at Namulongeforthe 1995 planted trial. Results and discussion Yield data, Alternaria disease severity and dry matter content of the clones evaluated during I 995a and 1996b se.ason is presented in Table 2 and 3. There was high significant differences (p=0.05) in storage root yields and Alternaria disease in the two trials. During I995a, total fresh root yields ranged from 8. 7 tlha to 0. 9 tlha. The main reason for the low yields was largely due to Alternaria blight andprobably low soil fertility (Table 1 ). There is an association between increasing severity of Alternaria blight and declining soil fertility (Low 1997). Four clones namely 137, 192,218, and 324 showed high levels of resistance to Alternaria blight and high yields than the local check Magabari. Yields during 1996b season ranged from 10.0 tl ha for genotype 324 which was also resistant to Alternaria blight to 2.5t /ha for genotype 69 with slight Alternaria attack. Clone 69 had high severity during 1995a season. Allternaria disease severity was more during l995a than I 996b season among most genotypes evaluated. Genotypes 324, 218, 316, and 137 had no symptoms at this location during both seasons indicating high levels of resitance to Alternaria blight disease.Dry matter content was high during 199 5A seasons trial ranging from 29.2 % Table 1. Major sweetpotat.o ag roecological zones in Uganda, their distribution, and associated constraints. Agroecological zone Warm, Moist tall grassland environments(bimodal rainfall) Warm subhumid short grassland environments Cool, Moist highland environments (bimodal rainfall) Major area of zone Central Uganda North and Northeast Uganda Highland zones of south west Uganda, Mbale west Nile Principal constraints SPVD Weevils ( Cy/as punticolis, Cy/as bnmneus) Drought Scarcity of planting material Alternaria disease Low soil fertility Root rats Table 2. Perfonnance of sweetpotato genotypes in and advanced yield trial at Kachwekano DFI during 1995A season. Clone Total root Marketable Alternaria DMC yield root yield score (1-5) (%) (tlha) tlha 192 8.7 5.9 3.0 34.0 202 8.1 5.9 3.3 31.6 218 7.2 5.6 1.0 32.8 324 6.9 5.7 1.0 31.0 SOWOLA 5.7 4.4 1.3 37.7 137 5.0 3.3 1.0 31.1 271 4.5 3.4 4.7 30.9 WAGABOLIGE 4.2 3.3 4.0 29.2 MAGABARI 4.2 2.8 1.0 37.5 69 4.1 2.8 4 .'0 29.9 BWANJULE 3.9 2.3 1.0 30.9 TANZANIA 3.8 2.7 1.3 33.8 282 3.7 2.0 4.7 30.3 NEWKAWOGO 3.4 2.6 4.7 30.0 148 2.7 1.5 4.7 30.5 52 2.1 0.8 5.0 31.8 TOROR0-3 1.5 0.6 3.7 178 0.9 0.4 4.7 Mean 4.5 3.1 $.0 C.V % 58.9 67.7 20.61 LSD 0.05 4.4 1.5 r.o Evaluation of promising sweetpotato genotypes for high altitude, cool, moi:;t agroecologies of Uganda 42 Table 3. Perfonnance of sweetpotato genotypes in an advanced yield trial at Kachwekano DFI during 19968 season. Clone 324 202 52 277 271 218 316 192 137 178 282 69 SOWOLA NEWKAWOGO TANZANIA WAGABOUGE TOROR0-3 BWANJULE Mean CV % LSD 0.05 Total root yield (tlha) 10.0 9.9 8.8 8.2 7.5 6.8 6.5 4.7 4.2 3.5 3.4 2.5 6.1 5.5 4.7 4.6 4.0 3.7 5.8 45.4 4.4 for variety Wagabolige to 37.7% for variety Sowola. Local check Magabari with already established consumer preferance had a dry matter content of37 .5%. Conclusion The major constraints to sweetpotato at high elevation is mai~ly leaf and stem blights caused by Alternaria bataticola, few adapted cultivars, and low soil fertility. A vail ability ofhealthy planting material is sometimes critical especially after outbreaks of caterpillars and or drought. Four clones which have been identified as resistant to the Alternaria blight disease, 218, 324, 316, and 192 will further be evaluated in on-farm trials and selections will be recommended for cultivation in high altitude environments. More. genotypes will be evaluated at Kachwekano to identify more suitable clones for this specific agroecological zone. It should be noted that such varieties could be appropriate and adapted to tropical highland environments with similar agroecological conditions and constraints like Rwanda, Burundi, Ethiopia, and Congo. References T. Ames, N.E.J.M. Smit, A.R. Braun, J.N.O'Sullivan, and L.G. Skoglund 1996. Sweetpotato: Major Pests, Diseases and Nutritional Disorders. International Potato Center (CIP). Lima, Peru. 152p. Bashasfla B, R.O.M.Mwanga, C. Ociti p'Obwoya, and P.T. Ewelll995. Sweetpotato in the fanning and food systems Alternaria score (1-5) 1.0 2.0 2.3 2.3 1.0 1.0 1.0 1.0 1.0 2.3 2.0 2.0 1.0 2.3 1.3 2.3 2.3 1.0 1.6 21.3 0.6 of Uganda: A farm survey report. NARO, Uganda and CIP Sub-saharan Africa Region, Nairobi,.Kenya, 60 pp. £ .£Carey, S.T. Gichuki, P.J. Ndolo, G.Turyamureeba, R. Kapinga and N.B. Lutatladio 1997. Sweetpotato breeding for Eastern, central and southern Africa:An Overview. APA Conference, South Africa. F .A.O Production handbook, 1996. Low J. W. 1997. Prospects for sustaining potato and sweetpotato cropping systems in Southwestern Uganda. In International Potato Centre Program Report, 1995-1996, pp 22-28. Lutaladio N.B and Ewell P, 1995. Potato and· sweetpotato research and development in Eastern and Central Africa-Proposal for PRAPACE network phase III: 1995-2000. PRAPACE working document No. l, 1995, 34pp. Skoglund L.G, Gatumbi R.W,KihuraniA W. Resulys of a suervey. of non-viral pathogens and disorders of sweetpotato in Kenya. Regional Workshop, Mom bas a, Kenya, 3-7 August 1992. E J M Smit 1997. The effect of indigenous cultural practices of in-ground storage and piecemeal harvesting of sweetpotato on yield and quality losses caused by sweetpotato weevils in Uganda . Agriculture, Ecosystems and Environment 64(1997) 191-200). Turyamureeba G, Mwanga R.O.M, Carey E, and Gichuki S 1997. Sweetpotao clonal evaluation for yield and resistance to pests and diseases in Uganda .. APA Conference, Pretoria South Africa 23-28 Feb"l997 , .. ' ' .. 

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Evaluation of promising sweetpotato genotypes for high altitude, cool, moist agroecologies of Uganda

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Evaluation of promising sweetpotato genotypes for high altitude, cool, moist agroecologies of Uganda

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