28 Journal of Agricultural Research vol. xx.No. i 



N 1039, July 17, 12 spikelets infected. 



July 24, whole head killed. 

 N 1 1 56, July ii, uppermost spikelet infected. 



July 24, 1 spikelet infected. Plant almost ripe. Infected spikelet covered 

 with Fusarium conidia. 



There has been considerable discussion as to whether the headblighting 

 of the cereal crops caused by Gibberella saubinetii and some other Fusarium 

 species is the result of a systemic invasion of the host plants by these 

 organisms. Naumov (5) , as stated before, considers the invasion systemic. 

 He finds the mycelium of the fungus in all parts of the plants and even 

 in plants showing no blighting of the heads. He showed that infection 

 of the heads can also take place externally. 



Since there is uncertainty in determining from its appearance the kind 

 and nature of any mycelium that may be present in the tissues of the 

 cereal plants, it was thought that the easiest and only reliable way to 

 show whether certain plants carry in their tissues the mycelium of 

 Gibberella saubinetii or any other Fusarium species would be to plate 

 out portions of such plants on some suitable artificial medium on which 

 the organisms are known to thrive well. If they are present in the tissues 

 of the plated plant they are sure to appear on the plates. 



Wheat and rye plants with blighted heads where the infection from the 

 heads has extended to the upper part of the upper internode, as previously 

 described in this paper, were used for plating. Such peduncles were 

 cut in portions 1 inch long, beginning from the end next to the blighted 

 heads. These portions were disinfected on the outside by dipping them 

 in 1 to 1 ,000 mercuric chlorid for two minutes. They were then rinsed 

 in sterile distilled water and plated in order on hard potato agar. In all 

 cases colonies of Gibberella saubinetii were formed over the portion next 

 to the infected head and in some cases over the adjoining portion. The 

 portion of the peduncle which was farthest from the head and perfectly 

 green and free from discoloration never developed any fungous growth 

 (PI. 3, B). This shows very conclusively (1) that the infection on the 

 cereal heads is local, and (2) that it proceeds from the head down and not 

 from the roots up. 



WEATHER CONDITIONS IN RELATION TO HEAD INFECTION 



Weather is one of the important factors for the successful parasitism 

 of Gibberella saubinetii and the various Fusarium species on the cereal 

 crops. Indeed, it is the limiting factor for the occurrence of head- 

 blight under certain conditions, and its importance was noticed early 

 by students of the subject. Dry weather with slight winds during and 

 after the period of blossoming and extending well toward the dough 

 stage will practically eliminate blight infection though all the other 

 necessary conditions may be present. It was observed in many cases 

 that in fields where there have been only few blighted heads before the 



