CHAPTER III 



TRACE ELEMENT DEFICIENCY 

 DISEASES OF PLANTS 



At the end of Chapter I a list was given of species which have 

 been shown to be dependent for growth on one or other of the 

 micro -nutrients, or which at least have benefited by treatment 

 with a micro-nutrient. It has been established that certain 

 well-recognized pathological conditions met with in the field 

 are associated with deficiency of a micro -nutrient, and some 

 of these are so widespread or of sufficient economic importance 

 to be designated by common names. Such, for example, are 

 the grey speck disease of oats, and heart-rot of sugar beet. In 

 this country diseases due to a deficiency of manganese and 

 boron are both widespread and of economic importance; else- 

 where shortages of zinc and copper have been shown to be 

 responsible for diseases causing considerable damage to fruit 

 crops. So far no well-defined diseases attributable to lack of 

 molybdenum or other trace elements have been recognized. 



The more important of the deficiency diseases attributable to 

 shortage of trace elements are described in this chapter. 



1. Diseases Attributable to a 

 Deficiency of Manganese 



The most general effect of manganese deficiency appears to be 

 in the first place the development of small chlorotic patches 

 localized in intervenal areas of the leaves. The form these patches 

 take in different species is no doubt largely dependent on the 

 anatomy of the leaf, so that in grasses with their parallel 

 venation they tend to take an elongated form, producing 

 'stripes' or 'streaks', while in reticulate-veined dicotyledons 

 they produce a spotted, speckled or mottled effect, as in potatoes 

 and sugar beet. Other symptoms may follow, including reduc- 

 tion or cessation of growth and the development of necrotic 

 areas which may not be limited to the affected regions of the leaf, 



