TOMATO YELLOW LEAF CURL DISEASE IN TANZANIA: CHARACTERIZATION, ALTERNATIVE HOSTS AND TRANSMISSION
TOMATO YELLOW LEAF CURL DISEASE IN TANZANIA: CHARACTERIZATION, ALTERNATIVE HOSTS AND TRANSMISSION
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Date
2003
Authors
KASHINA, Boniface David
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Abstract
Tomato farms in Arusha, Morogoro, Dodoma, Iringa, Kilimanjaro and Coast regions of
Tanzania were surveyed to assess the incidence of the yellow leaf eurl disease, and to
collect infected tomato leaf and weed samples for diagnosis and identification. Results
indicated that disease incidence and severity were significantly higher (P < 0.05) in
Dodoma region, but low and least severe in Iringa region. The disease-causing agent was
identified to be a geminivirus by electron microscopic examination of the geminate
particles in diseased samples. Squash and dot blots of extracts from the samples
hybridized to DIG-labelled viral DNA probes under high strigency conditions. Similarly,
Southern hybridization of genomic DNA extracted from the samples by phenolchloroform
procedures, revealed viral bands in their open circular, closed circular and
single-stranded forms. The putative viral DNA was amplified by polymerase chain
reaction using primer pairs designed to yield up to 1.4 kb amplicons. The amplified viral
DNA was digested with Alu\ and clectrophorcsed in polyacrylamidc gel. Restriction
fragment length polymorphisms analysis showed similar banding patterns for all the
Tomato yellow leaf curl Tanzania virus isolates. Furthermore, the amplified viral DNA
was ligated to pBluescript II KS' and transformed into Escherichia coli strain JM 83
cells by electroporation or Calcium chloride-mediated transformation. The viral DNA
was extracted from colonies containing the insert and sequenced using a Li-Cor DNA
Automatic Sequencer. The BLAST programme was used to search for viruses with
similar sequences, and phylogenetic relationship was established using the CLUSTAL
function of the Vector NTI.5 software. Sequence comparison and phylogeny showed
that Tomato yellow leaf curl Tanzania virus was closely related to African tomato leaf
curl virus and to Tomato yellow leaf curl Sardinia virus. However, the isolates of
Tomato yellow leaf curl Tanzania virus were biologically and genetically similar. More
than 90 % homology in the Rep and/or coat protein was found between Tomato yellow
leaf curl Tanzania virus and some crop- and weed-infecting geminiviruses.
Representative samples of the Tomato yellow leaf curl Tanzania v/rw.s-infected tomato
plants collected from the regions were maintained in the screenhouse by grafting and
through whitefly-mediated inoculations. The biological properties of the virus relating to
acquisition and inoculation time, persistence, graft transmission, mechanical
transmission and host range were studied. Results obtained indicated that the virus was
transmitted persistently by Bemisia tabaci Genn., and by grafting, but it was not
mechanically transmissible. Minimum acquisition and inoculation times were 30 min for
all the virus isolates, except the Kilimanjaro and Iringa isolates, which had minimum
acquisition feeding time of 1 h. For the first time, the present study demonstrated that the
following weed species are non-cultivated hosts of TYLCTZV: Commelina erecta,
Amaranthus spinosus, Erigeron floribundus, Ageratum conyzoides, Bidens pilosa, Sida
acuta, Ipomea batatas, Amaranthus viridis, Portulaca oleracea, Cassia oblusifolia,
Euphorbia hirta, Calopogonium mucunoides, Crotalaria retusa, Trianthema
portulacastrum, Alternanthera sessilis, Celosia trigyna, Commelina diffusa,
Chromolaena odor at a, Kclipta pros (rata, Syne dr el la nodi flora, Cassia occidental is,
Spigelia anthelmia, Boerhavia diffusa, Physalis angulata, and Acanthospermum
hispidium. Kxperimental studies using screenhouse cultures of the Tomato yellow leaf
curl Tanzania virus representative isolates resulted in the infection of five plant species
(Capsicum annuum, Datura stramonium, Lycopersicon esculcntum, Nicoliana glutinosa
and N. tabacum). Phaseolus vulgaris, Gossypium hirsutum, Solanum melongena,
Solanum tuberosum. Glycine max, and Arachis hypogea were not infected. Field and
sereenhouse experiments were conducted to determine the resistance of tomato
genotypes to Tomato yellow leaf curl Tanzania virus by comparing the yield and yield
components between inoculated and un-inoculated plants of each genotype. With the
exception of the resistant genotype TY172, both sereenhouse and field inoculated plants
of all the genotypes showed statistically significant (P<0.001) reductions in plant fresh
weight, fruit number, fruit weight and relative total yield when compared with the uninoculated
plants. On the overall, tomato genotype TY172 was the most resistant
followed by Tengeru 97, Cal-J and Marglobc. It is recommended that the resistance in
TY172 be introgressed into the Tengeru 97, Cal-J, Marglobc and Moneymaker, which
are commonly cultivated by farmers in Tanzania, to achieve high resistance to the virus.
Meanwhile, the cultivation of the tolerant tomato cultivar, Tengeru 97 should be
popularised among farmers in Tanzania while the search for sources of resistance among
wild Lycopersicon relatives continues.
Description
A DISSERTATION SUBMITTED IN FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY OF SOKOINE UNIVERSITY
OF AGRICULTURE. MOROGORO, TANZANIA.
2003
Keywords
TOMATO,, YELLOW LEAF,, CURL DISEASE IN TANZANIA,, CHARACTERIZATION,,, ALTERNATIVE HOSTS,, TRANSMISSION