SCREENING FOR SALT STRESS TOLERANCE, IN VITRO REGENERABILITY AND RELATIVE GROWTH AMONG SELECTED KENYAN SWEETPOTATO Ipomoea batatas L. Lam GENOTYPES
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Date
2018-12
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Abstract
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.