Journal of Applied Biosciences (J. Appl. Biosci.) [ISSN 1997 - 5902]
Volume 15: 820 - 828. Published March 4, 2009.
Morphological markers cannot reliably identify and classify sweet potato genotypes based on resistance to sweet potato virus disease and dry matter content
Karuri HW*, Ateka EM*^, Amata R,** Nyende AB.* and Muigai AWT*
*Jomo Kenyatta University of Agriculture and Technology P.O. Box 62000, 00200 Nairobi, Kenya; **Kenya Agricultural Research Institute. P.O. Box 14733, 00800 Nairobi, Kenya.
^Corresponding author: emateka@yahoo.com
ABSTRACT
Objective: To characterize Kenyan sweet potato genotypes for resistance to sweet potato virus disease (SPVD) and dry matter content using morphological markers.
Methodology and results: Three hundred and fourteen genotypes were evaluated in the screenhouse for their reaction to sweet potato virus disease (SPVD) followed by serological analysis. Severity of SPVD was determined following graft-inoculation using a severity scale of 1- 5. Results showed that the genotypes responded significantly differently (P<0.01) to SPVD infection. Twenty genotypes were resistant to SPVD in the screenhouse. The 314 genotypes were planted in the field and characterized using 42 morphological characters. Tuber dry matter (DM) content was determined 5 months after planting in the field. The tuber DM content varied significantly (P<0.01) among the sweet potato genotypes. Phylogenetic analysis using morphological descriptors grouped the genotypes into two major clusters. None of the clusters clearly distinguished the 20 resistant genotypes from the 294 susceptible ones. Genotypes with highest and lowest tuber DM content were not distinguished from each other using the UPGMA phenogram generated.
Conclusions and application of findings: Our results indicate that morphological markers are not reliable in identifying and classifying sweet potato genotypes based on response to SPVD and dry matter content of the tubers. Morphological markers therefore need to be supplemented with molecular markers in identification of sweet potato germplasm with SPVD resistance and high dry matter content. This study has further shown that there is a significant amount of morphological variability among the SPVD resistant and high dry matter genotypes, which could be utilized in breeding to diversify resistance to the disease and generation of novel/new genotypes.
Key words
SPVD, severity, markers, phylogenetic analysis, serological analysis.
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