58 TRACE ELEMENT DEFICIENCY 



but which may even affect the seeds, as in the case of the 

 garden pea. 



Grey Speck of Oats. The disease of oats most usually known 

 as grey speck, but also sometimes called grey stripe, grey spot, 

 or dry spot, is characterized by the appearance in the leaves of 

 spots of a greyish colour, small chlorotic areas, chiefly in the 

 lower half of the leaf, which tend to coalesce and form elongated 

 streaks which finally turn brown. The first sign of the disease 

 often occurs in young plants in the third or fourth leaf. Very 

 characteristically a line of withering and weakness develops 

 transversely across the leaf blade so that the distal portion of 

 the leaf hangs down (see Figs. 1,2). In the young leaves this 

 line of weakness is often about 1 or 2 in. from the base of the 

 leaf lamina, but correspondingly higher up in older and longer 

 leaves. The leaves may eventually turn completely brown and 

 die. Colour photographs of oats badly affected by grey speck are 

 given by Wallace (1943, p. 95, pi. 77; 1944, p. 37, pi. 188). 



Badly affected plants may be stunted and die early; in less 

 severe cases flowers may be produced but little grain is formed. 

 Root development tends to be poor, so that affected plants are 

 much more readily pulled out of the soil than healthy ones. 



Grey speck appears to be widely distributed. It occurs in 

 different parts of Europe, including Britain, and in America and 

 Australia. It appears to be most liable to occur on certain soils 

 with an alkaline reaction, especially if they contain much humus, 

 and in such conditions the disease may be so serious as to lead 

 to the complete failure of the crop. 



It has been recognized for many years that grey speck disease 

 could be controlled by treatment with a soluble manganese salt, 

 either as a soil dressing or by spraying the foliage, but the proof 

 that grey speck was actually related to manganese deficiency was 

 provided by Samuel and Piper (1928, 1929). They grew Algerian 

 oats in carefully controlled water cultures, using carefully 

 purified materials, and with various amounts of manganese 

 sulphate added to the culture solutions containing the usual 

 major nutrients. The initial concentrations of manganese in the 

 different cultures were 0, 1 in 50 x 10 6 , 1 in 10 x 10 6 , 1 in 5 x 10 6 

 and 1 in 1 x 10 6 . Cultures grown in solutions free from man- 

 ganese developed the symptoms of grey speck in about 4 weeks, 



