Alfalfa leaf curl virus is efficiently acquired by its aphid vector Aphis craccivora but inefficiently transmitted
Résumé
Alfalfa leaf curl virus (ALCV) is the first geminivirus for which aphid transmission was reported. Transmission by Aphis craccivora was determined previously to be highly specific and circulative. Using various complementary techniques, the transmission journey of ALCV was monitored from its uptake from infected plant tissues up to the head of its vector. ALCV was shown to be restricted to phloem tissues using fluorescence in situ hybridization (FISH) and electropenetrography (EPG) monitoring of virus acquisition. Furthermore, the virus is heterogeneously distributed in phloem tissues, as revealed by FISH and quantitative PCR of viral DNA acquired by EPG-monitored aphids. Despite the efficient ingestion of viral DNA, about 10(6) viral DNA copies per insect in a 15h feeding period on ALCV-infected plants, the individual maximum transmission rate was 12%. Transmission success was related to a critical viral accumulation, around 1.6x10(7) viral DNA copies per insect, a threshold that generally needed more than 48 h to be reached. Moreover, whereas the amount of acquired virus did not decrease over time in the whole aphid body, it declined in the haemolymph and heads. ALCV was not detected in progenies of viruliferous aphids and did not affect aphid fitness. Compared to geminiviruses transmitted by white flies or leaf hoppers, or to luteoviruses transmitted by aphids, the transmission efficiency of ALCV by A. craccivora is low. This result is discussed in relation to the aphid vector of this geminivirus and the agroecological features of alfalfa, a hardy perennial host plant.
Mots clés
Aphididae
Capulavirus
epidemiology
Hemiptera
luteovirus
nanovirus
nanovirus MSV
maize streak virus
Na2HPO4
sodium phosphate
PBS
Phosphate-buffered saline
PCR
Polymerase Chain Reaction
pd
potential drop
PEMV1
pea enation mosaic virus 1
PFA
paraformaldehyde
PlLV
plantago latent virus
PLRV
potato leafroll virus
qPCR
quantitative PCR
rm
intrinsic rate of increase
R-pd
repetitive pd
SDS
sodium dodecyl sulfate
SGBL
salivary gland basal lamina
T
mean generation time
i.e. the mean length of aphid generation
TR
theoretical transmission rate
TYLCCNV
tomato yellow leaf curl China virus
TYLCV
tomato yellow leaf curl virus
WDi
Waveform Duration by Insect
WDi-E2
variable WDi related to E2 pattern
WDV
wheat dwarf virus
WmCSV
watermelon chlorotic stunt virus
Domaines
Phytopathologie et phytopharmacie
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