48 EXPERIMENT STATION BULLETIN 351 



PLANT PATHOLOGY 



Bacterial Ring Rot of Potatoes 



Ring-rot-free tubers planted in soil infected with the ring rot patho- 

 gen, Corynebacter'mm. sepedonicwii, failed to show symptoms of infec- 

 tion. The soil was infested by mixing macerated diseased tubers w^ith the 

 soil. The tests were conducted both in the field and in the greenhouse. 

 Tubers from the original plantings were saved and planted in the green- 

 house to see whether the tubers were infected, although the vines did not 

 show disease symptoms. 



As results from the two plantings were negative, that is, no infection 

 occurring from the soil inoculations, it is believed that under natural con- 

 ditions in the field inoculation does not occur when clean seed is planted 

 in a field contaminated the previous year by ring rot plants. It is possi- 

 ble that volunteer plants may be a factor in overwintering of the pathogen 

 but in the tests conducted such plants did not survive the winter at 

 Durham. 



M. C. Richards 



Spraying for Apple Scab 



Mcintosh apple trees were given the following spray or dust treat- 

 ments: Pink, - Flotation paste. May 4; Bloom, - dust from north side, May 

 16; Late calyx, -dust on both sides, June 3: first cover, - Lime sulfur, June 

 18. In the second and third cover sprays, the following treatments were 

 given: Ro'io 1, Mike and Bordeaux; Row 2, Bordeaux and Bordeaux; 

 Row 3, Mike, Mike, and Mike; Row 4, Lime sulfur plus arsenate of lead 

 and Mike; Row 5, Lime sulfur and Mike; Row 6, Mike and Mike; Row 7, 

 Bordeaux and Mike; Row 8, Mike and Lime sulphur. The concentrations 

 of the materials were as follows: iMike 6% -100, Bordeaux mixture, 8-40- 

 100, Lime sulphur, 2-100. Data taken at picking time showed little dif- 

 ference in scabby fruit for the various treatments, also little difference in 

 fruit russeting. There was a slight increase in pin point scab on the fruit 

 from Rows 4, 5, and 8 both at harvest time, September 21, 1942, and after 

 storage, February 11, 1943. In these three rows lime sulfur had been 

 used in the treatments. The spraying and dusting was carried out by the 

 department of Horticulture, 



M. C. Richards 



Developing Disease Resistance in Early Tomatoes 



A survey of the prevalent diseases of tomatoes in New Hampshire in 

 1941 showed that Alternaria blight (early blight) is by far the most im- 

 portant. The fungous pathogen Alternaria solani, \\'hich causes Alter- 

 naria blight, blights the leaves, resulting in lower food producing capacity 

 of the plant, in sunscald of the fruits, and in a poorer quality crop. 



An investigation was begun of the disease and its causal organism in 

 order to prevent losses. Previous findings (1942) have shown that no se- 

 lection of tomato, either wild or cultivated, is immune to the disease. 

 However, there is a wide range in the field in the time and amount of 

 defoliation of various varieties of tomatoes. This difl^erence is being in- 

 vestigated and is related to the physiological maturity of the plant. Among 



