The use of radiation interception and transpiration to predict the yield of healthy, droughted and virus-infected sugar beet

dThis paper reports an analysis of the yield of sugar beet crops grown unde r experimental conditions between 1993 and 1995 in the UK. Crops were eithe r healthy (unstressed) or subjected to drought, infection with Beet yellows virus (BW) or a combination of both. The study investigated whether the la rge differences in yield between the crops grown in different seasons and s ubjected to different stresses could be accounted for by simple relationshi ps between total biomass and radiation interception (epsilon (s)), transpir ation (epsilon (w)) or epsilon (s) and epsilon (w) adjusted for mean satura tion deficit (Omega (s) and Omega (w) respectively). Mean values of epsilon (s), epsilon (w), Omega (s) and Omega (w) in healthy crops were 1.42 g/MJ, 0.89 g/kg, 6.76 g/kPa/MJ and 4.29 g/kPa/kg respectively. Variations in the dry matter yield between seasons were best accounted for by Omega (w) and less well by epsilon (w) or epsilon (s).Omega (s) accounted for least varia tion in yield between seasons. None of these relationships remained constan t in stressed plants; both drought and BW-infection decreased epsilon (s) ( and Omega (s)) but Omega (w) was increased by drought and decreased by BYV- infection. However, in common with healthy crops, seasonal variation in yie lds was best accounted for by Omega (w). Mean values of epsilon (s), Omega (s), epsilon (w) and Omega (w) for all healthy, infected and droughted crop s accounted for 61, 50, 88 and 97% of the Variation in dry matter yield bet ween experiments respectively. Accurate prediction of the yield of stressed plants requires a knowledge of their infection and drought status. If this information is unavailable then the mean value of Omega (w) for healthy, i nfected and droughted crops will provide a reasonable prediction of the yie ld of such crops.