LITERATURE ON BUNT OF WHEAT. ) 
three general heads: (1) Physiologic and ecologic factors, (2) varietal 
esistance or immunity, and (3) seed treatment. 
f PHYSIOLOGIC FACTORS AFFECTING THE DEVELOPMENT OF BUNT. 
HISTORY. 
__ Throughout the pre-Tillet period, from Theophrastus down, the 
cause of bunt, as well as that of other smuts and the rusts, was 
ought almost entirely in physiologic and environmenta! factors, 
_ Bradley’s supposed discovery that the bunt spores were insect eggs 
being the only notable exception. Theophrastus, and evidently 
Pliny. believed this smut to be due to moisture entering the young 
head, causing putrefaction under the action of the sun’s heat. In 
all the literature of the early part of the eighteenth century we find 
the cause attributed to such things as dew, honeydew, fog, rains 
ollowed by hot sunshine, damp soil, interference with flow of sap, 
_and failure of fertilization. 7 
_ The experiments of Jethro Tull (7S) furnished strong evidence 
that certain climatic and soil conditions were contributory factors. 
He cites the fact that a large amount of bunt appeared in certain 
‘ ears. He believed that excessive soil moisture was conducive to 
bant production and finds strong support for this belief in the results 
‘of what seems to have been the earliest controlled physiologic experi- 
ment on record dealing with the bunt problem. He took up several 
seedling wheat plants from a field and transferred them to the window 
of his chamber, where they finished their growth in excessively wet 
soil, a part of their roots being at all times in water. These plants 
were entirely bunted, while bunt heads were very rare in the field 
from which he took up his experimental plants. Others observed 
that late sowings were more subject to bunt than crops sown earlier. 
_ While Tillet’s experiments proved bunt to be an infective disease, 
evidence has steadily accumulated to show that the occurrence of 
bunt in the crop is largely dependent on ecologic factors, not only at 
the time of sowing but to some extent during subsequent growth. 
_ Ferle (116) says that dampness, protected locations, impermeable 
soil, and fresh stall manure favor bunt production. Ivanoff (178), 
working with Tilletia laevis in Tiflis, Transcaucasia, found an ap- 
_ parent relation between bunt prevalence and either altitude or mois- 
cure, — 
The first recorded observations on the relation of temperature to 
spore germination in Tilletia were those of Prévost (372) about 1807. 
He states that in water they germinated at 17° to 18° C. after 24 to 
3 days, at 14° to 15° after 3 to 4 days, at 11° to 12° after 5 to 6 days, 
at 7° to 8° after 9 to 10 days, and at 4° to 5° after 11 to 12 days. 
Hoffmann (164) and Schindler (336) investigated the thermolethal 
points of spores. 
_ Tubeuf, in his comprehensive investigations of all phases of the 
~bunt problem (372, 374), concludes that at a temperature of 3° to 
4° C. the spores will not germinate, and that even at temperatures 
_ of 5° to 11°C. they may remain ungerminated in the soil and, conse- 
_ quently, a source of danger. He finds the optimum temperature for 
_ their germination to be between 16° and 18° C. He is in agreement 
with Appel that high temperatures promote bunt production. 
62675—24——_2 
(RSL Mere ee SER RT o A PE BPD 
ee? sao |) Ow | UO” ae i’. 
~ oa a. waa Pe 
es a a i ae 
