46 CONTROL SERIES No. 72 



of "pinks" averaged only 3.3 per cent higher germination in the laboratory than 

 another series of 50 lots with from 4 to 42 per cent "pinks. "' 



9. The same may be said in part for kernel discolorations caused by Diplo- 

 dia, Hormodendron, Basisporium, and Alternaria. In proportion to the number 

 or percentage of discolored kernels in a given lot of seed, Diplodia appeared to have 

 a greater depressing effect upon germination in both the laboratory and the field 

 than any one of the other seed-borne disease organisms except R.hizopus. It 

 appeared to infect the roots of seedlings more readily than Fusarium or Gibberella, 

 and perhaps as readily as Rhizopus. 



10. Although soil conditions might be considered ideal for growth of most of 

 the seed-borne fungi which commonly cause seedling blight and root, stalk and 

 ear rots of corn, yet they exerted no such depressive effect upon emergence in the 

 field germination test as did the presence of moderate-to-heavy mold contamina- 

 tions under the same field conditions. 



11. Since the field-maturity planting was located in the same place where the 

 corresponding test was grown last year, little dependence could be placed upon the 

 disease readings that were made during the growing season, because most of the 

 seed-borne disease organisms are able to winter over in refuse in the soil and attack 

 the second-year crop. Exception might be made in the case of Bacterial Wilt or 

 Stewart's Disease which is not definitely known to be carried over from one year 

 to the next in the field. 



12. Stewart's Disease was observed as primary infection in 25 lots, ranging 

 from 1 to 6 per cent of the stalks. Seven lots showed primary infection of bacterial 

 spot (Bacterium hold). 



13. Other diseases that may have had their orii'in with the seed were black 

 bundle iCephalosporium acremonium) \ stalk and ear rot due to Gibberella sp. 

 and Fusarium spp. and Diplodia zeae; also, a spotting or mottling of foliage 

 which was perhaps virus in character. 



In a season with copious rainfall during field germination, but not excessive 

 wetting of the soil, and with rather a heavy type of soil for the emergence test, 

 ample opportunity was afforded to ascertain the effects of molds and other disease 

 organisms carried with the seed upon normal germination. Molds, particularly 

 Rhizopus spp., reduced normal germination much more in the field than was sus- 

 pected might occur. On the other hand, although there was evidence that all such 

 seed-borne disease fungi as species of Fusarium, Gibberella, and Diplodia in partic- 

 ular, reduced emergence and normal germination in the field, yet the occurrence 

 of abnormals from, seedling infection by those fungi was not as extensive as might 

 be expected judging from the amount of kernel discoloration and root infection 

 found in the laboratory series. In many instances lots comparatively free from 

 molds but showing considerable seedling infection in the laboratory from Fusarium 

 or Diplodia gave higher normal germination in the field than in the laboratory, 

 indicating that such organisms might not affect germination in the field as much 

 as in the laboratory — even when there are few or no abnormals from other causes 

 concerned. 



Such germination tests as these conducted with sweet corn in \93?i should fur- 

 nish valuable information not only to seedsmen and growers, but also to analysts 

 and any others who are interested in the relation of laboratory germination tests 

 to emergence and normal germination in the field, as well as in the effects of various 

 seed-borne fungi upon germination in both the laboratory and the field. 



