50 Experiment Station Bulletin 363 



of significant increases in marketable fruits. Fermate at the recommended 

 strength of 1-100 gave higher yields of marketable fruits than any of the 

 Copper oxychloride sulphate or Bordeaux mixture treatments. 



3. Physiological umnirity. In 1944, further investigations were 

 made on the physiological maturity of tomato plants and its relationship 

 to Alternaria blight. 



Attempts to keep plants of the New Hampshire \"ictor variety phys- 

 iologically young during the fruiting period by the addition of nitroge- 

 nous and complete fertilizers were unsuccessful because of a lack of suffi- 

 cient rainfall during August to make the soil nutrients available for plant 

 use. 



It had been shown from earlier work that a plant with a heavy fruit 

 to leaf ratio reaches physiological maturity earlier and is thus more sub- 

 ject to Alternaria blight than one with a low fruit to leaf ratio. Further 

 evidence on this phase of the problem was obtained this year. When 

 only half the normal number of fruits was allo\\'ed to remain on certain 

 plants, the number of marketable fruits was increased and defoliation was 

 decreased on these plants as compared to the check plants. Certain toma- 

 to varieties, because of their high fruit loads, reach physiological maturity 

 earlier than other varieties with lighter fruit loads; thus, they defoliate 

 sooner because they become susceptible to Alternaria blight earlier in the 

 growing season. 



M. C. Richards 



Factors Influencing the Development or Suppression of 

 Leaf Roll Symptoms in Potato Foliage 



During previous years, while making tests in the greenhouse for 

 virus detection in potatoes. Green Adountain tubers known to have net 

 necrocis did not always produce plants showing leaf roll. Environmental 

 conditions were thought to influence the production or suppression of 

 the leaf-rolling symptom. In preliminary tests with Green Mountain 

 plants grown in the greenhouse during February, Anarch, April, and May, 

 it was possible by adding nitrogen as Ammonium nitrate or a complete 

 fertilizer (8-16-16) to the soil to completely mask foliage symptoms of 

 leaf roll. On the other hand, when the plants were growing in soil con- 

 taining triple superphosphate without additional nitrogen being added, 

 leaf rolling was pronounced and the leaves took on a glossy appearance, 

 a symptom often associated with this disease under field conditions. When 

 potassium chloride, only, was added to the soil, the plants were severely 

 stunted and yellowed. The leaves showed severe rolling but definite leaf- 

 roll symptoms were masked by the stunting and yellowing of the plants. 



In addition to soil cultures, healthy and leaf roll plants were grown 

 in water cultures by means of special boxes so placed that the roots were 

 permitted to enter nutrient solutions in jars below. The tops and tubers 

 were supported above in excelsior-peat mixtures. This proved success- 

 ful in securing vigorous plants and may be used in more exact work con- 

 cerned with the effects of nutrients. Consistent with soil cultures, addi- 

 tions of nitrate tended to suppress leaf-roll symptoms. 



M. C. Richards. Stuart Dunn, R. C. Jones 



