ANNUAL REPORT, 1947-48 25 



Both causes produce chlorotic, narrowing leaves, even to filiform. Rosetting 

 also occurs. Frenching from high soil-temperature is usually obtainable within 

 20 days and has been obtained in as little as 5 days. In these experiments, the 

 shortest time in which pinhead mottling was obtained from a nitrogen-deficient 

 soil was 38 days. 



Plants with frenching due to nitrogen deficiency have always resumed normal 

 growth after the application of nitrogenous material to the soil, but affected 

 leaves did not completely recover. Frenched plants resulting from a high soil- 

 temperature do not respond to applications of nitrogen, but resume normal 

 growth if the soil moisture is reduced so that the plants wilt, or if the soil tem- 

 perature is reduced to about 70° F. Frenched plants with chlorotic leaves due 

 to nitrogen deficiency remain chlorotic till nitrogen is supplied. On the other 

 hand, the chlorosis resulting from a high soil-temperature frequently disappears 

 and newly developing frenched leaves, even the filiform type, may develop with 

 a normal green color. 



The theory that a lack of available iron is the cause of the type of frenching 

 induced by a high soil-temperature is further substantiated by an experience 

 "with chlorotic rose plants in a greenhouse. The temperature in the greenhouse 

 was high (August). A manure mulch supplied ample nitrogen, which was veri- 

 fied by the diphenylamine test on foliage tissue. An application of a mixture of 

 iron sulfate (copperas) and peat followed by a heavy w^atering brought recovery 

 to the plants. Discs made from the chlorotic leaves and floated on a solution of 

 ferrous sulfate (Fe 6 p.p.m.) recovered a normal green color, while the checks 

 remained chlorotic. 



Tomato Leaf Mold Caused by the Fungus Cladosporium fulvum Cke. (E. F. 



Guba, Waltham.) All the effort since the last report has been concerned with 

 the further improvement of Improved Bay State tomato with respect to quality 

 and yield of fruit and resistance to leaf mold. This tomato is essentially similar 

 to the Bay State tomato described in Massachusetts Agricultural Experiment 

 Station Bulletin 393, 1942, with the factor for resistance to all forms of the fungus 

 Cladosporium fulvum Cke. added. The variant of the pathogene to which Bay 

 State, Globelle, Vetomold-121, and Vetomold are highly susceptible does not 

 trouble Improved Bay State, which is resistant to all forms of the pathogene and 

 has been reported to be highly resistant w^herever in the world it has been grown. 

 This tomato is grown extensively under glass in Ontario, New York, Nova Scotia, 

 and the New* England States, and the financial benefit to growers has been great. 

 Similar resistance to Cladosporium has been bred into several English forcing 

 tomatoes such as Carter's Sunrise, Kondine Red, Hundredfold, Best-of-AU, and 

 Market King. The study of these hybrids is in progress in the desire to develop 

 a range of commercially acceptable resistant types. 



Search for Inherent Resistance to Tomato Late Blight Fungus. (E. F. Guba, 

 Waltham.) Approximately 200 types of tomatoes have been tested for their 

 behavior to the late blight fungus, Phytophthora infestans (Mont.) de Bary. 

 The tomatoes were grow^n to maturity in the field in the summer of 1947, but be- 

 cause of unfavorable weather conditions for the fungus it was not possible to 

 promote the disease. 



Growth and fruiting habits of the plants were recorded. Epideniic conditions 

 for the fungus were established among stands of seedlings of these tomatoes in 

 the greenhouse in the early season of 1948. Included in these tests were Lycoper- 

 sicum esciilentum , pimpinellifolium, hirsutiim, peruvianwn, and numerous plum, 

 cherry, and currant fruiting types in red, orange, and yellow colors and plant 



