40 Station Bulletin 372 



The shift to more legume hay has raised problems of harvest and added 

 some conflicts in operation, so that there is more emphasis placed on grass 

 siiage. 



M. F. Abell 



PLANT PATHOLOGY 



Factors Influencing the Development or Suppression of 

 Leaf Roll Symptoms in Potato Foliage in the Greenhouse 



Green mountain seed pieces, known to be infected with the potato leaf 

 roll virus, do not always produce plants showing the leaf-roll symptom when 

 they are grown in the greenhouse during the winter months. It can be dem- 

 onstrated that the leaf-roll symptom may be suppressed, or entirely masked 

 in some cases, by adding nitrogenous fertilizers to the soil at planting time. 

 On the other hand, the symptom may be accentuated by the application of 

 phosphate nutrients. Such results are obtained under greenhouse condi- 

 tions during the winter months. They were not reproducible under field con- 

 ditions during the summer. 



When a number of infected tubers were planted (each tuber in a sep- 

 arate pot) the degree of symptom expression was not the same in all cases. 

 The leaf-rolling symptom varied from healthy to slight, moderate to severe. 

 Therefore, with the addition of nitrogenous fertilizers, there was a tendency 

 for most of the plants to be normal or show only a slight rolling of the 

 leaves. Similar symptoms were obtained when infected tubers were planted 

 in pots of different sizes and in beds. Plants developing from infected tubers 

 were larger, and a higher percentage of them showed more severe leaf roll- 

 ing when grown in eight-inch glazed pots or in plant beds than when grown 

 in six-, five- or three-inch unglazed pots. Plants in the unglazed pots were 

 smaller in size and greener in color. 



Plants with severe symptoms retained starch in the rolled leaves for as 

 long as 60 hours after being placed in the dark. Healthy plants and virus- 

 infected plants with unrolled leaves lost all starch from their leaf tissues in 

 less than 12 hours. 



The higher nitrogen content of the soil in combination with the low light 

 intensities during the winter months probably suppresses starch accumula- 

 tion in the leaves and thus prevents the rolling of leaves to varying degrees. 



M. C. Richards 



The Control of Tomato Diseases 



Alternaria blight and late blight continue to be the most important dis- 

 eases of tomatoes in New Hampshire. Investigations to discover plants re- 

 sistant to these diseases have been continued. Tomato seeds obtained from 

 the Division of Plant Exploration and Introduction, United States Depart- 

 ment of Agriculture, have been planted and tested for resistance to both dis- 

 eases; as yet no species having sufficient resistance to warrant its use for 

 plant breeding purposes has been found. 



Tests were made to determine the effects of organic and inorganic ferti- 

 lizers on the incidence of Alternaria blight on Marglobe and New Hamp- 



