the young tomato seedlings grown in flats in the greenhouse with late 

 blight inoculum when the plants were only a few inches tall. After a 

 few days incubation in a cool moist chamber, the resistant plants could 

 be separated from those affected by disease. It was found that resistance 

 to late blight was partially dominant. The F^ -hybrid plants were more 

 resistant than the ordinary varieties. In the second generation, about one- 

 quarter of the progeny were virtually immune, about one-half fairly re- 

 sistant, and one-quarter of the progeny were decidely susceptible to the 

 late blight. Only highly resistant plants were saved for further breeding 

 work. Backcrosses were made to a variety received from Argentina called 

 Mikado which in itself seemed less susceptible to various tomato diseases 

 than most varieties, though it had potato leaf and large, rough, fasci/f'ated 

 fruits. 



Promising lines carrying good resistance to late blight were selected 

 from the backcross progenies, but no line having all the necessary horti- 

 cultural characteristics for a commercial variety was realized. Another 

 cross was made to the early-maturing New Hampshire Victor, and pro- 

 ductive blight resistant selections of a good size and quality were recovered 

 in the second generation. After being purified, a true-breeding line re- 

 sistant at least to those races of late blight prevalent in New England has 

 been named New Hampshire Surecrop. This new early variety has a de- 

 terminate plant productive of uniform-colored red fruits rather similar 

 to those of Victor, but in contrast New Hampshire Surecrop has tolerated 

 late blight under field conditions in New Hampshire. It is also somewhat 

 resistant to early blight, Alteriiaria, much more so than the early-maturing 

 determinate varieties of tomatoes observed at Durham, New Hampshire. 

 Since many varieties of tomatoes are adapted only to certain localities, 

 New Hampshire Surecrop may not be fully acceptable over the wide areas 

 devoted to tomato culture. This variety should prove valuable as breeding 

 material for plant breeders. Seeds have been sent already to them in widely 

 separated places throughout the world. 



Irradiation to Induce Variations in Tomatoes 



Early blight of tomato, Altcrnaria, in many years is a disease that seri- 

 ously limits the yield of ripe fruits, particularly so for early-maturing de- 

 terminate varieties. No source of complete resistance to the disease has 

 been found yet among the early determinate tomatoes observed to date. 

 Disease-resistant varieties of cereal crops have been reported, however, 

 following exposure of seeds and plants within radiation fields at the 

 Brookhaven National Laboratory for studies with atomic energy. 



Seeds of the Chatham, an early determinate variety of tomato, were sent 

 to the National Laboratory, Brookhaven, Long Island, for treatment. Both 

 X-ray and thermalneutron radiations were given the seeds. Some seeds 

 received ten thousand, twenty thousand, and thirty thousand roentgens 

 of X-rays, respectively. Other lots were exposed to thermalneutrons for 

 15, 20, and 25 hours respectively. Following these treatments, the seeds 

 were returned to Durham, New Hampshire, for starting plants that were 

 grown in the open field in 1956. 



Germination vigor of the seeds treated with X-rays varied between plants 

 from very weak to strong. However, by the end of the growing season, 

 there was little if any apparent differences among these plants. 



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