Mar. 3,1993 
Gray Mold of Castor Bean 
713 
practicable. Control measures, therefore, are to be wholly preventive 
rather than to any extent destructive of the disease after it once gets a 
start. 
SUMMARY 
(1) Castor beans were cultivated on a large scale in 1918, as a war 
emergency measure. A number of insect pests and diseases appeared, 
the most serious of which was a blight of the inflorescence caused by a 
new species of Botrytis, the perfect stage of which was later found and 
described (Sclerotinia ricini Godfrey). 
(2) The disease was found throughout the State of Florida, and also 
in Mississippi, Louisiana, and Texas. It was not to be found in fields 
in South Carolina, Alabama, Georgia, Tennessee, or Arkansas. From 
10 per cent up to 100 per cent loss was sustained by growers in the 
affected districts. 
(3) A succession of several continuously wet days was requisite to 
the development and spread of the pathogene. In localities where there 
was much of this kind of weather during the growing season the percent¬ 
age of loss was high; where there was less, lie loss was correspondingly 
lower; where summer rains were of brief duration and followed by long 
periods of dry weather the disease did not occur. 
(4) The disease is a typical Botrytis blight. The inflorescences or 
“spikes” are attacked, in all stages of development, with heavy growth 
of mold and complete destruction. The leaves and stems are also 
attacked occasionally* During the winter and spring following, sclerotia 
appeared in abundance, at first on the old spikes and later on the stalks 
of the plants. 
(5) The causal organism is very readily isolated, since it is a rapid 
grower on most of the common culture media and outgrows most con¬ 
taminating organisms. About 50 isolations were made from different 
sources, mostly from single conidia. Its appearance in culture is that 
of a typical Botrytis, with the usual abundance of gray mold and black 
sclerotia. It is characterized microscopically by its comparatively small 
globose spores in dense heads and the constant dichotomous divisions of 
the conidiophores. Appressoria are mostly microscopic. Microconidia 
occur. 
(6) Attempts made to induce a perfect stage to develop during the 
winter of 1918-19 were at first not successful. Early in March a limited 
number of cultures showed apothecial stalks arising from sclerotia. 
Single ascospore strains were isolated from apothecia which matured, 
and the connection with the Botrytis stage was established. Later a 
great abundance of apothecia were produced under artificial conditions 
and were found in nature. 
(7) The'fungus is homothallic. Freezing, drying, or an extended rest 
period are^not requisite to the development of apothecia from sclerotia. 
Factors necessary before this will happen are reasonably moist conditions, 
a temperature near the optimum for vegetative growth of the fungus, a 
reasonable amount of air space, and light. 
(8) The perfect stage is a true Sclerotinia, smaller than the more com¬ 
mon forms. Ascospores are discharged forcibly in a visible cloud when 
the apothecia are subjected to a sudden change from moist to dryer condi¬ 
tions. Frequently all eight spores cling together. Ascospores may ger¬ 
minate directly, with the production of a germ tube and hyphse indis¬ 
tinguishable from those of the Botrytis stage, Microconidia have been 
observed on germinating ascospores. 
