HISTOLOGICAL RELATIONS OF SUGAR-BEET SEED- 

 LINGS AND PHOMA BETAE 



By H. A. Edson,' 

 Physiologist, Office of Cotton and Truck Disease Investigations, Bureau of Plant Industry 



In a former paper ^ it was pointed out that practically all sugar-beet 

 {Beta vulgaris) seed is more or less heavily infected with Phoma betae 

 (Cud.) Fr., and that a large proportion of the seedlings developing from 

 such stock suffer from incipient or severe attack of the fungus, but that 

 under favorable conditions a high percentage of the attacked plants re- 

 cover sufficiently to make a good growth. It appears that the period 

 during which the sugar beet is susceptible to infection by this fungus is 

 confined to the seedling stage, or, in the case of leaves, to old age, but 

 that when infection has once occurred, it persists. After apparent recov- 

 ery of the host, the fungus is still present, although it remains concealed 

 until conditions arise sufficiently unfavorable to the beet to enable the 

 parasite to renew its attack. Except in the seedling stage, it seldom 

 accompHshes the immediate destruction of its host, but remains inactive 

 during the first growing season and becomes destructive on mother beets 

 in storage or reappears during the second growing season on the seed 

 stalks or racemes in time to cause infection of the new crop of seed. 



Histological studies recently conducted upon seedling sugar beets in- 

 fected with Phoma betae have shown the fungus fruiting on the surface 

 of young plants that were scarcely past the cotyledon stage. They have 

 also revealed the organism living without serious injury to the host, within 

 the deeper cells of plants that had thrown off the attack and which could 

 safely be predicted to show no further sign of infection during the growing 

 season if reasonably good cultural conditions were maintained. The slides 

 show that the fungus may persist both in and on the tissues of the beet and 

 also indicate something of its modus operandi in attack on seedlings. Sec- 

 tions were prepared from material grown from pasteurized seed in experi- 

 mental pots in steriHzed soil which had been inoculated at the time of 

 seeding with pure cultures of the fungus. The material was controlled 

 by check pots and by recovery of the fungus from certain of the seedlings 

 from each pot as the disease appeared. Damped-off and root-sick seed- 

 lings selected at different stages in the progress of the disease and healthy 



1 The author wishes to acknowledge his indebtedness to Mrs. Nellie D. Morey, formerly of the Office of 

 Cotton and Truck Disease Investigations, for assistance in the preparation of sUdes. 



' Edson, H. A. Seedling diseases of sugar beets and their relation to root-rot and crown-rot. In Jour. 

 Agr. Research, v. 4, no. 2, p. 135-168, pi. 16-26. igis- 



Journal of Agricultural Research, Vol. V, No. i 



Dept. of Agriculture, Washington, D. C Oct. 4, 191S 



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