Disease Resistance in Beans 7 



orously. Some lots that gave little promise were carried in small quantity 

 from year to year, and in a few instances yielded, on further selection. 

 types which have considerable promise. 



RESULTS 



In the summer of 1922, 58 selections remained in the test. All of 

 these families were in the sixth to the tenth generation, the exact genera- 

 tion depending upon the number of times greenhouse cultures were pro- 

 duced. None of the plants was susceptible to either race of the an- 

 thracnose fungus under the most severe conditions that could be im- 

 posed in field or in greenhouse. They had been subjected to possible in- 

 fection, from the stage of tender dispirited seedlings as grown in the 

 weak light of midwinter, through a great variety of telluric conditions in 

 the field, and had shown no infection whatever. They were immune. 

 Also, so far as could be determined, they were immune for mosaic. 

 There were lots of early-maturing and of late-maturing plants, plants of 

 determinate and of indeterminate growth, seed types of typical Navy 

 Pea and White Imperial with many intergrading types, one of which 

 approximated White Marrow in size and was of the exact shape of this 

 popular variety. 



RACE GAM ATA 



Some of the lots had reached the stage where they might be put in a 

 test for production, when race gam nut was cultured, and identified by 

 Burkholder (1923). This race was isolated from White Imperial, but 

 when it was found that it did not infect Robust it appeared that some 

 of the hybrids might prove resistant. This seemed the more likely in 

 view of the results which Burkholder (1923:322) had obtained with a 

 Robust- Wells' Red Kidney hybrid and which he subsequently pub- 

 lished. On August 11, 1922, and on September 15, a sample of each lot 

 of the hybrids was inoculated in a Large moist chamber with race gamma, 

 the culture being very kindly supplied by Dr. Burkholder. The follow- 

 ing record tor ten consecutively numbered lots of plants will show what 

 was found throughout this and subsequent tests, in these fractions, the 

 denominator represents the number of plaids inoculated, and the nu- 

 merator the number that became infected — 1/9, 3/10, 8/8, 4/5, 2 5, 

 2 5, 1/4, 0/2, 2/5, 5/5, and so on. In this test Wells' Red Kidney and 



White Imperial Were severely affected, whereas Robust and White Sickel 



were entirely \'vcr. 



All plants that showed resistance to the new race were grown to ma- 

 turity and the progeny was grown in the field in the summer of 1923. 

 All three races of the fungus were introduced early and gave good infec- 



