Disease Eesistance in Beans 11 



The hybrids in the present work have been tested to a limited extent 

 in the greenhouse for root-rot toleration. The data show that some of 

 the families are very susceptible and that others are decidedly resistant. 

 It was inadvisable to inoculate plants in the field when the number was 

 rather small, but now that the original purpose of the work has been ac- 

 complished the tests for root-rot tolerance can be executed although to 

 do so means the introduction of the organism into land where it does not 

 now exist. 



Rust. In some sections of the United States the bean rust, caused by 

 Uromyces appendiculatus, has been a serious factor in production. This 

 disease seems never to have been important in New York. Random 

 cases have been detected, especially on snap varieties and on Navy Pea. 

 In two different years a trace of rust has been found on a few plants in 

 the hybrid plots. In each case the infection probably came from Ken- 

 tucky Wonder Wax or Golden Cluster Wax, both of which varieties 

 have usually grown in close proximity to the hybrids and on both of 

 which rust has been observed late in the season. 



Anthracnose. That other races of Collet otrichum lindemuthianum 

 exist has been demonstrated already by Leach (1923) and by Muller 

 ( 1926). Unfortunately the varieties of beans employed by Leach in his 

 work are not varieties that have been used by other workers nor are 

 they known in the trade, so that there is no way of knowing at present 

 whether or not the eight races that he describes are distinct from the 

 three already known. Muller, on the other hand, obtained American 

 material for comparison with four races which he isolated in Holland, 

 and shows that the Dutch forms are different from those in New York. 

 He also inoculated the seven differential varieties which were supplied 

 him by Leach, and finds that two of his races behave alike on all seven 

 varieties and therefore are like Leach's race VIII. But, from his tests 

 with other varieties, he knows that they are biologically different. It is 

 to be noted that Barrus found and recorded some variations in his work, 

 but concludes (1918: 597) that "we have been concerned here with only 

 two strains of the pathogene." Leach (page 10 of reference cited) 

 "docs not consider this justifiable, because, if we consider difference in 

 parasitism a sufficient basis for distinguishing biologic forms, a difference 

 cannot justly be disregarded even if manifested on one host only. Fur- 

 thermore, these forms may act differently on many oilier bean varieties 

 which were not inoculated." Midler, in turn, quotes Leach's objection 

 and uses it as a criticism of Leach's work. Just what the true situation 

 is remains to be determined. Barrus points out that there may be varia- 

 tion within the host variety itself, and that a certain amount of cross- 

 pollination which occurs naturally also may account for some of the 

 valuations which occurred in his tests. Of Leach's work it is to be noted 



