PHYTO MEDIZIN Mitteilungen der Deutschen ... - Die DPG

ever, in Trialeurodes vaporariorum (a non vector of geminiviruses), wildtype
WmCSV was detected in the midgut only, thus suggesting that the virus
was not capable of crossing the gut wall. In contrast, in B. tabaci, the accessory
and/or the primary salivary glands apparently present the significant
epithelial barrier to virus transmission. Hence, for the begomovirus WmCSV
and its whitefly vector, a pathway similar to the luteovirus / aphid translocation
is expected. In immunolocalization studies with organs excised from
viruliferous insects carrying wild type or non transmissible virus mutants, a
specific labelling with WmCSV antiserum was obtained at the microvilli
region of the epithelial cells of the gut wall food canal, indicating for putative
virus adsorption sites or, for a putative receptor-mediated delivery to the
hemoceol. Respective experiments carried out with primary and accessory
salivary glands so far did not indicate for specific adhesion/entry sites into
these organs.
Recent developments in Augusta disease of tulip in the Netherlands
VP Bijman, AFIM Derks and GJ Blom-Barnhoorn; Applied Plant Research, section
Flower Bulbs, Lisse
Augusta disease in tulips is caused by Tobacco necrosis virus (TNV). The
virus is transmitted by zoospores of Olpidium brassicae. The host range of
this fungus includes many commonly found weeds such as annual blue grass,
annual sowthistle, chickweed, dandelion, shepherd’s purse and others. Some
of these Olpidium brassicae hosts are also hosts of TNV. Damage caused by
Augusta disease can be severe in the Netherlands. Disease incidence occurred
up to 60% in fields in some years and up to 20 % in flower forcing. There has
been a shift in tulip bulb production on sandy soils towards production on
heavy clays. Since Olpidium brassicae is spread by water and clay soils are
more sensitive to standing water, the occurrence and establishment of the
disease is enforced. As a common practice in certain areas, bulbs are grown
on soils, which have been in pasture for a period of circa 6 years. These pastures
are a favourable environment to enhance the spread of Olpidium brassicae.
The influence of soil type, plant debris and planting time are examined.
The addition of Pseudomonas to the bulb dipping bath with fungicides leads
to a significant decrease of Augusta. Preliminary results suggest that incorporating
Sarepta mustard in the soil might prevent the occurrence of Augusta
disease. Several other crops are currently under investigation. The fungus
Olpidium brassicae can be detected with the aid of PCR in soils and in closed
water supply systems. These methods will be applied in epidemiological
studies.
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