EFFECT OF BEET YELLOWING VIRUSES ON LIGHT INTERCEPTION AND LIGHT USE EFFICIENCY OF THE SUGAR-BEET CROP

We monitored the development of ground cover by green and yellow leave s in healthy sugarbeet and in sugarbeet infected with beet mild yellow ing virus (BMYV) and beet yellows virus (BYV). Infection with BMYV red uced light interception by green foliage by up to 40%, due to leaf yel lowing. Infection with BYV reduced light interception by green leaves by up to 55%, due to 50% cover by yellow leaves and decreased total (g reen + yellow) ground cover. Dry matter accumulation was regressed aga inst cumulative light interception by green foliage to estimate light use efficiency of the visually unaffected foliage. Healthy and BMYV in fected sugarbeet had similar light use efficiencies, indicating that y ield loss can be entirely attributed to interception of solar energy b y yellow, unproductive foliage. Infection with BW decreased light use efficiency. The results show that yield losses caused by yellowing vir uses can be assessed by monitoring the disease-induced reduction in gr ound cover by green leaves.