abstracts - INCDCSZ Brasov

Since 1995, 95% of the sever virus infections have been caused by PVY. In the last few years, many
new isolates of PVY (potyvirus Y) were characterized on potato fields in Switzerland. New
recombinations have been revealed by PCR methods (Rigotti and Gugerli, 2004). The dissemination
rapidity of the old PVY isolates and the sensitivity of the cultivars changed fundamentally. One of the
reasons is that Switzerland has regular intensive trade exchange of potato seed with different European
areas and countries. These exchanges accelerate the dissemination of the diverse predominant PVY
types originally found in different parts of Europe. Early nineties, the first PVY NTN potato tuber
ringspot disease symptoms on the new breeding variety Lido have been observed. The real
dissemination of ringspot types started in 2000 with the cultivars Nicola, Erntestolz, Ditta and Hermes.
At the beginning of this millenary, PVY Wilga has been detected.
Method
The dissemination of six different PVY isolates on six potato cultivars (Bintje, Charlotte,
Desiree, Lady Christl, Marlen, Nicola) have been carried out under field conditions. Sixteen plots of
200 m 2 containing each a total of 800 healthy seed tubers of 6 cultivars were separated by twelve
meters bands of oat to reduce the attractiveness for wing aphides to move between plots at the
beginning of the growing season. In every plot and for every cultivar two rows of 50 tubers each were
grown. In each plot 4% of PVY infected plants of the cultivar Nicola were planted on the 15 th and on
the 35 th plant-position of every 50 plant rows of a single PVY isolate and harvested one week before
the end of the trial. PVY isolates were produced under greenhouse conditions (each PVY isolate in a
separate compartment) one year before the field trial. The infection with the different PVY isolates
was made manually by abrasion of 5 leafs when the potato plants reached 30-50 cm high. In the
control plot Nicola plants were treated with water. From each cultivar and plot, 200 tubers were
harvested. The dormancy of these tubers was then broken by Rindite. Five weeks later, control of the
dissemination of PVY by wing aphids between plots was done conducting PVY O and PVY N antibody
ELISA tests separately on each tuber. A second sample of 200 tubers was also controlled visually for
ring spot symptoms just after harvest and 2 months after stocking.
Using similar oats band isolation design, two other experiments were carried out. First, the yield of
healthy Nicola plants was compared with Nicola plants infected by different PVY isolates. Secondly,
PVY ring spot necrosis sensitivity on tubers was studied for all promising varieties present in the
Swiss official cultivar field trials. Since five years, this study has been part of the variety assessment in
Switzerland. In each no infected variety plot, 4 % PVY NTN infected potato plants (Nicola and
Erntestolz) were inserted. These infected plants were harvested one week before the other plants in the
plots. The yielded tubers of promising varieties are controlled visually.
Results
The cultivar Lady Christl was surprisingly highly resistant to all PVY isolate infections; Bintje
and Charlotte were sensitive to PVY and very sensitive to PVY NTN and PVY Wilga isolates. Charlotte
was very sensitive to PVY N isolates in 2006. Spread of PVY O803 and PVY N605 was lower than PVY NTN
and PVY Wilga isolates (figure 1). Formerly, Nicola and Desiree were reputed to be well resistant to
PVY, but today, these cultivars are sensitive to the new isolates of NTN (necrotic) or PVY Wilga. . The
isolates of PVY O803 and PVY NTN854 are very phytotoxic for Nicola and Desiree. Some of the infected
plants died before harvest and did not serve as a virus source for the healthy plants during the growing
season. The cultivation of vigorous infected plants with the different isolates of PVY is very
challenging. The small PVY O803 infected plants where rapidly covered by the healthy vigorous plants.
After the harvest, ring necroses on tubers were mostly observed on Nicola and rarely on Bintje,
Desiree or Charlotte.
Under field conditions, the spread of diverse PVY isolates between plots was very low in 2005 and
2006 (figure 2). The 12 meters isolation bands of well-established oat between the plots were
sufficient to prevent isolates transfer via wing aphids.
The cultivar assessment denotes sensitivity to ring necroses on tubers for sensitive varieties like
Nicola, Ditta, Erntestolz, Verdi, Juliette, Derby, Arielle and Amandine. These cultivars should not be
selected as recommended varieties for Switzerland. The sensitivity of the cultivars tested in our study
is variable and differs from the necroses tuber-sensitivity.
121