84 TRACE ELEMENT DEFICIENCY 



The connexion of heart rot with boron deficiency was shown 

 by Brandenburg by means of controlled water cultures, first of 

 mangolds (1931) and later of sugar beet (1932). Similar results 

 were obtained by Bobko and Belvoussov (1933) and by Rowe 

 (1936). In the experiments of Bobko and Belvoussov, seedlings 

 provided with no boron developed symptoms of heart rot after 

 about a week. Renewed root development of boron-starved 

 cultures resulted on the addition of boric acid to the culture 

 solutions. Too high a concentration proved toxic, the most 

 satisfactory range of boron concentrations being from 0-5 to 

 5 mg. of boric acid per litre. These findings were confirmed with 

 sand cultures and field trials carried out by Brandenburg and 

 others. 



Canker and Internal Black Spot of Red or Garden Beet. 

 Pathological conditions of garden beet attributed to boron 

 deficiency have been described both here and in the United 

 States. A full description of the disease as it occurs in the 

 United States has been given by Walker (1939), who terms it 

 internal black spot in reference to its most prominent symptom, 

 the presence of internal hard black necrotic masses which render 

 the beet unfit for canning. These masses, irregular in size and 

 shape, are not characteristic of any particular part of the root, 

 for although they may be confined either to the central region 

 or the peripheral region, they may also be scattered throughout 

 the root. When the black spot occurs near the periphery a rift 

 in the surface tissues may occur, soil micro-organisms may enter 

 and attack the root and a surface canker may result. But when 

 the necrotic areas are well inside the root there may be no 

 external symptom of the disease. 



In this country the lesions on boron-deficient garden beet 

 appear always to be superficial and are known as canker. Thus 

 Wallace (1943) states that 'rotting occurs on the sides of the 

 roots and may not penetrate into the more central tissues', and 

 he gives some good colour photographs of cankered garden 

 beet (op. cit. plates 106, 107, pp. 109, 110). The absence of the 

 internal necrosis in red beet grown in this country is not ex 

 plained, but it may be related in some way to varietal differences 

 in growth. Walker states that the necrotic areas are most 

 obvious between the prominent rings marked by the thick- 



