| dc.description.abstract | Sweet potato is an important food crop worldwide since it is drought tolerant and acts as
a famine relief crop. However, its production is limited by viral, fungal and bacterial
infections. Lack of rapid and sensitive techniques for detection of infections inhibits their
control. Use of synthetic chemicals to manage microbial infections cm.is!s is discouraged
since they ar non-biodegradable. The aim of this study was to identify viruses infecting
sweet potato in western Kenya, develop a multiplex PCR protocol for detection of major
viruses of the crop, and evaluate efficacy of medicinal plants for antimicrobial activity
against the crop pathogens. Symptomatic sweet potato vines obtained from farmers'
fields were testes for ten viruses using NCM-ELISA. The mPCR protocol for detection of
SPFMV and SPCSV was optimized through variation of test parameters under standard
PCR conditions. Extracts from Warburgia ugandensis, Elaeodendron schweinfurthianum
and Terminalia brownii, which are traditionally used to manage microbial infections,
were fractionated using chromatographic methods to obtain pure compounds. Structures
of isolates were determined using spectroscopic and physical methods. Extracts and
isolates were tested for antimicrobial activity against Alternaria spp, Aspergillus niger,
Fusarium oxysporum, F. solanum, Rhizopus stolonifer (fungi), Ralstonia solanacearum
and Streptomyces ipomoeae (bacteria). Five viruses namely SPFMV, SPCSV, SPMMV,
SPCFV and CMV were detected. Eighty nine percent of samples had viral infection with
over 80% showing multiple infectious. Occurrence of CMV in Kenya was recorded for
the first time. An mPCR protocol was successfully developed that detects SPFMV and
SPCSV. Phytochemical studies afforded 26 compounds including 7uacetylugandensolide
that was isolated from W Ugandensis for the first time. All the
methanol, ethyl acetate and n-hexane extracts of the three plants were active against one
or more of the test organisms. Methanol extract of W ugandensis exhibited significantly
higher activity (24.50 mrn) than positive controls against R. stolonifer. Eighteen out of
the twenty six compounds isolated exhibited antimicrobial activity against one or more of
the test pathogens at concentrations :S200 ug/rnl. Polygodial, warbuganal, mukaadial,
ugandensidial, ugandensolide, deacetoxyugandensolide and muzigadial, exhibited low
MIC (MIC :S 50 ug/rnl) against one or more pathogens that was comparable to those
exhibited by standard drugs. This study provided a quantitative assessment of viruses
infecting sweet potato in western Kenya and a simplified mPCR protocol for routine
rapid detection of SPFMV and SPCS V. Scientific proof for the efficacy of extracts of W
ugandensis, E. schweifurthianum and T. brownii as antimicrobial agents against sweet
potato pathogens and perhaps other crop pat~ogens was also provided. | en_US |
