Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Limited but persistent genetic differentiation among biotype Q of Bemisia tabaci, the only biotype detected in protected crops in Southern France
1 INRA-LNPV, Plant Pathology Department, Montfavet, France. Correspondence: dalmon@avignon.inra.fr
2 CIRAD, UMR BGPI, Montpellier, France
Bemisia tabaci is a major pest in glasshouses in Southern France. It was first reported in the 80ies and population levels increased highly in 2001. At the same time TYLCV was reported for the first time, and subsequently several criniviruses were characterized in greenhouse crops. Genetic diversity among B. tabaci French populations was characterized, and gene flow in vector populations was studied. Eighteen populations were collected in glasshouses in Southern France from 2003 to 2005, mainly from tomato crops, but also from other vegetables and ornamentals. One population was collected on Poinsettia in a botanical garden. The 19 populations (520 female individuals) were studied with seven independent microsatellite markers, which revealed a high genetic diversity. Within populations, some heterozygote deficiency was observed, but FIS values were not significantly different from 0. Four groups were distinguished using a Bayesian clustering method (Structure software). One group limited to the botanical garden population consisted of biotype B individuals according to nucleotide sequences of cytochrome oxidase 1 gene. Despite a mixed ancestry derived from the three other groups, all individuals of the 18 crop populations were inferred to belong to biotype Q. This is the first detection of biotype Q in France. Its predominance was unexpected because only biotype B was previously detected based on silver leaf symptoms (Villevielle and Lecoq, 1992, Phytoma 440). No geographic structuring was observed among the 18 crop populations with AMOVA test (after pooling 2003 populations into 3 main geographic areas) and isolation by distance analysis, suggesting a recent colonization event of a single origin and/or large-scale migration events despite of isolation due to glasshouse protection. When all data were pooled according to the host species sampled, a host selection effect was tentatively noted for individual sampled from hibiscus.Genetic diversity was studied over time for B. tabaci populations collected two or three times in the same glasshouse from 2003 to 2005. A genetic differentiation process was highlighted in one of the four repeatedly sampled glasshouses through a decrease of allelic richness and observed heterozygosity in the B. tabaci populations collected yearly from 2003 to 2005. The populations from this glasshouse were the sole to differentiate among biotype Q. It is supposed that this glasshouse population was sufficiently isolated from other populations and has undergone sufficiently severe reductions of population size during host free periods to exhibit such a drift.
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