Screening for Salt Stress Tolerance, In Vitro Regenerability and Relative Growth among Selected Kenyan Sweetpotato Ipomoea Batatas L. Lam Genotypes
Nzaro, Gona Makenzi
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Salinity affects about 40% of the global area mainly the arid and semi-arid regions. In Kenya the ASALs cover approximately 80% of the total area where agricultural production constraints include water scarcity, salinity and sodicity. Sweetpotato Ipomoea batatas L. (Lam.) is the third most economically important root crop after potato and cassava in the world cultivated for human consumption, animal feed and industrial uses. The production of sweetpotato by smallholder farmers in the ASALs is affected by abiotic stresses including salinity. However, data on levels of salinity stress tolerance among Kenyan sweetpotato genotypes is limited. The objective of the study was to determine physiological response of sweetpotato to salinity stress and assess in vitro regeneration among selected Kenyan sweetpotato genotypes. Fifteen Kenyan selected sweetpotato genotypes Ksp 36, Ksp 20, Ksp28, Kemb 36, Kemb 10, Kemb 23, Kalamb Nyerere, Mweu Mutheki, Enaironi, Mugande, Zambezi, Spk 004, Spk 013, Spk203 and Jewel were used for the present study. In vitro shoot organogenesis using TDZ was used in detrmining regenrability while sudden shock treatment and an incremental stress regime were used for studying the physiological resposes of sweetpotato genotypes to osmotic and salinity stresses. Physiological responses was assessed by measuring the leaf photosynthetic pigment content, vine and leaf length, relative water content and yield. All data collected were analyzed using ANOVA at 95 % confidence interval using SAS statistical software. Mean separation was carried out using pairwise comparison test at 5 % probability level. Results shows that the highest number of adventitious bud; 8.00 (Kalamb nyerere) was produced in the dark at 0.25 mg/l TDZ hormone level. Regeneration frequencies of adventitious buds recovered in the dark was the highest, 83.20% (Jewel) at 0.10 mg/l NAA hormone level. The best genotypes for direct shoot organogenesis were Kalamb nyerere, Kemb 36 and Spk 004. Growth analysis shows that the sweetpotato genotypes with the highest mean growth rates were Kalamb Nyerere, Spk203, Enaironi, and Mweu Mutheki. Results show that at high in vitro osmotic and salinity stresses all genotypes had reduced amount of photosynthetic pigments. Best performing genotypes under in vitro osmotic and salinity stress were Ksp 36, Ksp 28 and Zambezi. Results of in vivo salinity stress shows that all the genotypes had reduced vine length except Spk 013, Spk 203 and Kemb 23. Yield was negatively affected by in vivo salinity stress but was lowest in Spk004 (-31.13%), Mweu Mutheki (-31.43%) and Ksp 36 (-35.29%). Using the combined morphophysological approach the following genotypes were found to be salt tolerant Spk 004, Mweu Mutheki, Ksp 36, Kemb 36 and Kalamb Nyerere and can be incooperated in breeding programs so as to introgress tolerance to sensitive genotypes.