Effects of beet yellows virus and beet mild yellowing virus on leaf area dynamics of sugar beet (Beta vulgaris L.)

Field experiments were conducted over three years to investigate the effect s of beet yellows virus (BW) and beet mild yellowing virus (BMYV) on leaf a rea dynamics in sugar beet (Beta vulgaris L.). Plants infected with BMYV sh owed normal leaf area growth and the leaf area index (LAI) was not signific antly affected by virus infection. Up to 1.4 m(2) (leaf) m(-2) (soil) of le af area was yellow, resulting in a maximum proportion of yellow leaf area o f ca. 35%. Yellowing symptoms were only found on mature leaves. Plants infe cted with BYV showed a reduced formation of leaf area compared to healthy o r BMYV-infected plants; leaves appearing after infection remained smaller t han in healthy or BMYV-infected plots. As for BMYV, only mature leaves deve loped yellowing symptoms. The total amount of yellow leaf area on BYV-infec ted plants was similar to that induced by BMYV, but due to the smaller tota l leaf area index, the proportion of yellow leaf area was greater, up to ca . 50%. Infection with BYV substantially reduced the life span of infected l eaves. Both viruses caused a +/-20% decrease of specific leaf area in matur e yellow leaves, compared to healthy leaves. As a result of a lower LAI and a greater proportion of yellow leaf area, BW causes a greater reduction of crop light interception on green leaves than BMYV. In BMYV-infected plots, proportion of soil cover by yellow leaves was generally similar to the pro portion of yellow leaf area, but significant differences from this pattern were observed for BYV. (C) 1999 Elsevier Science B.V. All rights reserved.