Barley yellow dwarf virus (BYDV) causes significant losses in yield
and in overwintering ability of winter cereals.
Mechanisms by which the physiology of plants is affected by the virus are
not clear. To see how carbohydrates
in the crown of winter cereals were affected by BYDV, fructan isomers of
degree of polymerization (DP) 3–5,
fructan DP>6 and the simple sugars, glucose, fructose and sucrose, were
measured before and during cold
hardening in three oat (Avena sativa L.) cultivars, ‘Wintok’,
‘Coast Black’ and ‘Fulghum’. On a fresh weight
basis fructan DP>6 decreased by 50% in infected ‘Wintok’
and ‘Coast Black’ and by 25% in ‘Fulghum’. Two
DP3, one DP4 and one DP5 isomer were significantly higher than non-infected
controls. The percentages of
simple sugars in infected crowns were significantly higher than controls
in all three cultivars in every week except
the first week of hardening. Crude enzyme extracts from BYDV infected plants
incubated with sucrose suggested
higher invertase and lower sucrose-sucrosyl transferase activity. When
incubated with 1-kestose and neokestin, no
significant difference was found in fructose fructosyl transferase or in
hydrolase activity. The activity of
unidentified enzymes catalysing the synthesis of larger (DP>5) fructan
was altered by BYDV. The decrease of
carbohydrates in the crown induced indirectly by BYDV may alter the plant's
capacity to regenerate tillers in the
spring. The ability of plants to prevent or tolerate carbohydrate fluctuations
induced by BYDV infection may be
an important genetically regulated characteristic for developing virus-resistant
cultivars.
