113 

 The Detenniuation of Plant Diseases Transmitted by Seed. 



BY 



G. GENTNER, MUNICH. 



Besides the testing for purity and germinating capacity, it is a very 

 important task of the seed testing stations to investigate the state of 

 health of the seed. In many cases the pests and the causal organisms can 

 be detected in the purity and germination test or by means of special 

 methods. 



In the purity test it is possible to find Aplanobacter Rathayi on Dactylis, 

 Ustilago laevis in Avena, Ustilago Jensenii in Hordeum, Tilletia tritici in 

 Triticum, Ustilago perennans in Arrhenatherum, Ustilago hromivora in 

 Bromu.s, Tilletia Hold in Holcus, sclerotia of Olaviceps in Secale, Phleum, 

 Holcus, Poa, Agrostis, Typhula trijolii in Trifolium and Lotus species, 

 sclerotia of Sclerotinia trifoliorum, and of Botrytis cinerea and indeter- 

 minable species in Trifolium, Anthyllis and Medicago. 



The examination of the state of health of the seed in the germination 

 bed is made as follows : — The seeds are placed in the bed some distance 

 from each other, and are not removed when the germination has finished. 

 The fungi mycelium are then able to continue their development, and 

 conidia, pyknidia or perithecia can be formed, by which it is possible to 

 identify the fungi. The most simple way is to place the seeds in Petri 

 dishes on moist filter paper or in cardboard dishes. The development of 

 the fungi is favoured when the seeds are kept as moist, warm and dark 

 as possible. It is necessary to keep under observation the decayed seeds 

 in the germination bed, as these often show the causal organisms particularly 

 well developed. Inspections on from 6 to 10 days suffice in most cases. 



When the attacks by fungi, especially by Fusarium, are to be determined 

 in figm?es. Director Hiltner's " brick dust " method in which the seeds are 

 placed in large grained sterile brick dust (size of grain 2 mm.) should 

 be used. In this way the mycelimn partly develops on the surface 

 around the seedlings, and partly on the sheaths, giving them a brown colour. 

 As Helminthosporium and Cephalosporiiun Acremonium may cause a 

 similar colouring, it is recommended, in cases of doubt, to place the seedlings 

 taken from the brick dust on to moist filter paper in glass dishes for several 

 ■days. Botrytis diseases in the seed are easy to determine in percentage 

 by this method. 



Phoma oleracea in Brassica species and Phoma lini in Linum are 

 «asy to recognise by means of the attacked cotyledons when the seeds 

 are placed to germinate in soil. 



By these means I have been able to determine the following causal 

 ■organisms on the seed : — ■ 



Bacteria. — ^BaoUlus cerealium on Hordeum, Triticimi, Secale, Zea, 

 Pisum, other bacteria species on Avena, Cucumis, Vicia Faba, Brassica, 

 .Solanum Lyeopersicum. 



Helminthosporium on Hordeum, Avena, Lolium, Agrostis. 



MacrosporiiMn and Pleospora on Avena, Hordeum, Medicago sativa, 

 TiifoUum pratense, Lotus, Onobryehis, Omithopus, Glycyrrhiza, Galega, 

 Pisum, Brassica, Spinacia, Cannabis, Daucus, Apium, Petroselinum, 

 Lactuca, Cichorium. 



Altemaria on Triticum vulgare, Phleum, Spinacia, Brassica, Sinapis 

 alba, Onobryehis, Vicia Faba, Daucus, Petroselinum, Cucumis, Lactuca, 

 Scorzonera, Cichorium. 



Fusarium on Secale, Hordexjm, Triticum, Avena, Zea Mais, Medicago, 

 Trifolium, Lotus, Omithopus, Lupinus, Pisum, Phaseolus. Atriplex 

 hortense, Brassica, Linum, Daucus, Nicotiana, Borrago, Cucumis, Lactuca, 

 .^Scorzonera, Cichorium. 



