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

Abstract

Field experiments were conducted over three years to investigate the effects of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) on leaf area dynamics in sugar beet ( Beta vulgaris L.). Plants infected with BMYV showed normal leaf area growth and the leaf area index (LAI) was not significantly affected by virus infection. Up to 1.4 m 2 (leaf) m −2 (soil) of leaf area was yellow, resulting in a maximum proportion of yellow leaf area of ca. 35%. Yellowing symptoms were only found on mature leaves. Plants infected with BYV showed a reduced formation of leaf area compared to healthy or BMYV-infected plants; leaves appearing after infection remained smaller than in healthy or BMYV-infected plots. As for BMYV, only mature leaves developed yellowing symptoms. The total amount of yellow leaf area on BYV-infected plants was similar to that induced by BMYV, but due to the smaller total 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 leaves. Both viruses caused a ±20% decrease of specific leaf area in mature yellow leaves, compared to healthy leaves. As a result of a lower LAI and a greater proportion of yellow leaf area, BYV 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 proportion of yellow leaf area, but significant differences from this pattern were observed for BYV.