The influence of boron on the second year's growth of sugar beet affected with heart-rot

Summary 1 Heart-rot of sugar beet occurred on experimental plots at Rothamsted during 1935, the severity of the attack decreasing steadily with later sowing, but the effects of spacing of the rows and of treatment with sulphate of ammonia were not significant. Where the number of affected plants per row was high, a higher proportion of affected plants showed severe symptoms. 2 Unaffected sugar beets and others showing slight and severe symptoms of heart-rot were transplanted to sand cultures and treated with light and heavy dressings of boric acid or with none. 3 In the absence of boric acid the characteristic signs of boron deficiency appeared in the shoots, the apices of the stems and the flower buds blackening and dying. This occurred even when no symptoms were present before transplanting. 4 In the presence of boric acid all plants produced healthy shoots, with no deficiency symptoms. Where heart-rot was originally present and the main axis killed, a number of healthy, lateral shoots were produced. 5 A certain number of plants failed to survive transplanting, the proportion being greatest with the heavy dose of boric acid, with which one-half of the plants died. This suggests a possible toxic action of the heavy dose which did not come into play if the plants were constitutionally able to withstand the initial poisoning and start away into growth. 6 The later addition of boron did not improve the condition of the roots of affected plants, as irremediable damage had been done before transplanting. 7 The possibility of producing healthy shoots in the second year from affected roots is important from the point of view of seed production, as considerable loss may be saved by the use of small amounts of boron compounds.