SCLEROTINIA WILT OF GREENHOUSE SNAPDRAGONS

Abstract

Our attention was called in October, 1927, to a serious disease of snapdragons grown in a commercial greenhouse at Temple, Texas. About 6o percent of the plants had been killed, causing a loss of about $20,000. The owner believed that the trouble was brought about by the prolonged cold, cloudy, and rainy weather then prevailing, which interfered with the proper ventilation of the greenhouse. The disease was thoroughly distributed in the three beds of the house. Plants were found in all stages of infection. Early infections appeared as water-soaked lesions overrun by thin wefts of white fungus growth. Individual branches, particularly those closest to the grounid, soon wilted (text fig. I, a). The shrunken stems were covered with a copious white wefty mycelial growth with numerous large sclerotia (fig. i, b and f). These occurred on the outside and inside of the affected roots and stems of the plants (fig. i, c, d, e). As large portions of the stems and branches became involved, entire plants wilted and fell to the ground, often within 24 to 48 hours after infection, forming mats of dead and wilting plant material which were overrun by the dense growth of white mycelium and sclerotia. The fungus apparently spread by direct contact of the collapsed, infected plants with adjoining normal plants, as well as on the surface of the soil. In an area of 64 square feet of an infested snapdragon bed, 466 sclerotia were collected. Of these, I7I were on the surface of infected stems; 92 were in the inside of these stems; and 203 were formed on the ground. The appearance of infected plants anid the numnbers of sclerotia found suggested a Sclerotinia as the probable cause of the trouble. Petri dish isolations from infected tissues and from the sclerotia yielded a growth resembling S. sclerotiorum. Healthy snapdragon planits were then inoculated with this culture and also with S. sclerotiorumn previously isolated, respectively, from apothecia produced under infected fig trees,2 from celery, and from beans. Snapdragon seedlings were planted in 8-inch pots in February, in a cool greenhouse held at about 700 to 750 F. After two months, these plants had attained considerable size and were used for inoculations. Pure cultures of the Sclerotintia strains mentioned were grown on sterilized bean pods, which inoculum was placed on the ground next to the uninjured stems, and the plants 1 Published with the approval of the Director as Contribution No. 208. Technical Series, of the Texas Agricultural Experiment Station. 2 Taubenhaus, J. J., and W. N. Ezekiel. A Sclerotinia limb blight of figs. Phytopathol. 2I: II95-II97. I93I. 8o8