CONTROL SERIES No. 77 



It will be noted that in spite of the fact that every seedling In the germinator 

 that showed a primary disease lesion on root or shoot was pronounced ab- 

 normal, the total of which averaged 17.5 per cent, yet the average percentage 

 of nr^rmal germination in the laboratory series remained considerably above 

 that tor the field germination test; 7.6 per cent higher. This perhaps might 

 be explained in part by the greater depressing effect of both the seed-borne 

 diseases and the otherwise weak seedlings on total emergence and normal 

 germination in the field planting than in the laboratory where conditions for 

 germination are more suitable; and in part by the additional depressing effect 

 on field germination of soil-inhabiting parasites. 



Effects of Molds and Other Seed-Borne Fungi on Germination 



Some of the more common seed-borne fungi were observed to have a marked 

 effect on germination in both the laboratory and the field. In considering groups 

 of seed-lots that were affected by some one outstanding disease in the germina- 

 tors, Diplodia appeared to cause the greatest reduction in normal germination 

 in the laboratory test, with Rhizopus, Penicillium, and Fusarium (and Gib- 

 berella) ranking next in order of importance. In the field, however, Rhizopus 

 was the most important single factor in reducing both the total emergence and 

 normal germination, with Penicillium, Diplodia, and Fusarium (and Gibberella) 

 following in the order indicated. The following table indicates the comparative 

 effect on germination of those seed-borne fungi: 



Average germination Average germination 



Outstanding Diseases in Laboratory Number in Laboratory in Field 



Germinator of Lots 



None; all diseases light 39 



Diplodia 23 



Rhizopus 34 



Penicillium 11 



Fusarium (and Gibberella) 24 



Since many more seed-lots were severely affected by the two molds (Rhizopus 

 and Penicillium) than by Diplodia or other seed-borne disease fungi, they 

 constituted in the aggregate by far the greatest depressing factors on germina- 

 tion, especially in the field. Other seed-borne fungi, such as Alternaria, Basi- 

 sporium, Hormodendron, and Cephalosporium, were observed commonly in 

 the laboratory germinator, causing dead kernels or weak seedlings, but were 

 less important than the organisms mentioned in the preceding paragraph. 



ElTett of Seed Treatment on Germination in the Field 



Following the laboratory germination test, 35 seed-lots were selected for 

 the presence of particular seed-borne diseases, and 10 for relative freedom from 

 diseases. Each lot was divided into three series, one of which was treated in 

 mercuric chloride for 10 minutes, one dusted with ethyl mercury phosphate 

 (Semesan Jr.), and the other left untreated for a check. The seeds were planted 

 in June in rows 36 inches apart, 4 inches apart in the row, and were covered by 

 hand. The three series of a lot were planted side by side in adjacent rows, with 

 the untreated one in the middle. The corresponding series of a second lot 

 followed in the same rows with a short interval between lots; and so on, with 

 7 lots end to end in each three-row group. The effect of the treatments is 

 summarized as follows: 



