118 SPORE DISSEMINATION 



Seed-borne fungi. In 1733 Jethro Tull recorded seed disin- 

 fection by the use of brine. Wheat being shipped to England 

 became wet in the hold. Some of it was planted, and the resulting 

 crop was observed to be free from stinking smut. From this ob- 

 servation came the use of salt-water steeps to prevent seed-borne 

 diseases. Moreover, before this earlv period some of the tribes 

 in Asia Minor passed their seed grain through flames and thereby 

 removed the highly inflammable smut spores. Thev did this, 

 however, as a religious ritual, because fire has long been regarded 

 as a means of purification. 



Subsequent studies have shown that many grass smuts are seed- 

 borne. In addition, such other pathogenic agencies as certain 

 viruses, bacteria, many fungi from nearly every important tax- 

 onomic e^roup, nematodes, and insects are known to be carried 

 with the seed. Orton (1931) assembled a bibliography of seed- 

 borne diseases which should serve as a basis for studies by others. 

 In his long list are such important pathogens as Gibberella sau- 

 binettiij C oil etotri chum lindemuth'iamim, Phovia Ihigam, Septoria 

 apii, Diplodia zeae, Glomerella gossypii. Collet otrichwn lagena- 

 riitm, Phomopsls vexans, Sclerospora grcnninicola y Urocystis 

 cepnhe, Ascochyta pisi, Tilletia tritici, and Ustilago avenae. 



Soil-borne fungi. Vascular and root-rot parasites, including 

 species of Fusarium, Verticillium, Cephalosporium, Thielaviopsis, 

 Sclerotium, Phytophthora, Pythium, and Rhizoctonia, commonly 

 persist in the soil and are distributed by numerous agencies. 

 These include movement of the infested soil by washing rains or 

 its transport by streams, carriage of infested soil on seedlings, 

 rooted cuttings, bulbs, corms, or roots, and transport on imple- 

 ments, machinery, tools, hoofs of farm animals, and shoes of man. 



Observations in the East Indies and in the United States leave 

 little doubt that fields which are flooded or overflowed after rains 

 may become infested with Phytophthora nicotianae, causing to- 

 bacco black-shank. The rowward spread of Fusarium wilts is a 

 matter of common observation. Carriage of fungi with soil or 

 on seedlings may not be an unmixed evil. Evidence assembled 

 by Hatch (1936) shows that in afforestation the planting of seed 

 may fail, whereas the transplanting of seedlings may succeed. 

 The reason for this anomaly is the dependence of tree species 

 upon certain fungi which become associated in the mycorrhizal 

 relationship. 



