DISEASES OF VARIOUS CROPS T377 



{Usiikgo Hilda). 



l,ength of grnins in 111111 2.0 2.25 2 50 2.75 3>-0 



Percentage of intectcd plants . . . 3.2 % 4.6 ''o i-9 *?,. i ','.. o.i '^ , 



The choice of bulky grains also allows of reducing llie number of plants 

 infested with Hehninihosporiiirn gramincum, as results from the following 

 data : 



lycrglh of gir.irs in n 111 2.0 2.15 2.50 2.73 3.1, 



Percentage ol infected plants .... 42. j ",, 43.2 >),, 35.6 "., 24.4 % 1,3,3 % 



Experiments conducted at Ultuna have shov^'n that oat plants grown 

 from small seeds are more liable to attack by Puccinia gvaminis. 



From the foregoing it follows that the sifting of seed may in many 

 cases furnish a method calculated, not perhaps to get rid completely of the 

 germs of certain diseases, but at an}- rate to diminish to a notable extent 

 the percentage of infected plants. 



1032 - Economic Data relating to the Treatment of Potatoes with Bordeaux Mixture 

 against Alternaria Solani. — Suc xo. 1014 of tiiis BuihUn. 



1033 - Di'p/odia Zeae, the Cause of Dry Rot in Maize. — vax df.r bijl Paul a., in diseases 



Union cf South Africa, Department of Agriculture, Division of Botany and Plant Pathrhn^y^ OF variov.- 



Science Bulletin No. 7, pp. 1-60, PI. 1-15. Pretoria, igi6. crops 



The disease known by the name of " dry rot " in maize is prodifced b}' 

 the fungus Diplodia Zeae (Schw.) I^ev., reported so far in Europe, America, 

 Australia, and at various points in South Africa. 



One of the most conspicuous symptoms of the disease is the appearance 

 of a dense growth of whitish mycelitim, which develops in the furrows be- 

 tween the car\^opses, makes its way to the centre of the bracts, surrounds 

 the filamentous stigmata and forces them against the internal face of the 

 bracts — which become discoloured, — and afterwards forms round the ear a " 

 large dry envelope, formed by the hyphae of the fungus. 



The caryopses of the diseased ears are stunted and light in weight, dark 

 in colour, and are easily detached. The colourless segmented h}-phae, of 

 a breadth of from 1.15 to 3.08 [.t are not capable of perforating the cell parti- 

 tions, but they generate into the interstices of the cells and vessels through 

 the areolae. The mycelium in itself is not distinguished from other fungi 

 [Fitsariitm spp.) parasitic on maize. On the other hand, a characteristic of 

 the genus Diplodia is the small black pycnidia w^hich usually grow on the 

 edge of the alveolae, as may easil}' be seen on breaking the diseased ear 

 across. They are however also found embedded in the mycelium on the 

 caryopses and bracts, and sometimes even in the culm, near the nodes or at 

 a point corresponding to some lesion. 



The shape and size of the pycnidia vary greatly ; they ma}- be pear- 

 shaped (from 187.5 to 337.5 fj.), ellipsoid (150 X 330 [jt) , spherical or spheroidal 

 (from 200 to 275 (jl). The wall of the pycnidium is formed of two layers 

 of cells, and on its internal face grow the hymenium and the spores, bilocular 

 (rar^l5• trilocular), straight or slightly curved, cylindrical, brownish- black 



