A study was made oí the reaction of F1 progenies from crosses between selected clones and oí the selfed progenies oí the parental clones. The relation of tuber reaction to the vine reaction, firmness of tuber and season of maturity was included in the study.
The selfed progenies of two susceptible clones and one resistant clone gave, in arate of tuber reaction resistant to susceptible, from 1 to 4 means of 3.04 ± 0.07, 2.98 ± 0.06 and 2.46 ± 0.07, respectively. The means of the crosses of the two susceptible clones with the resistant clones were 2.08 ± 0.06 and 1,97 + 0.06, respectively. The crosses had significantly lower means than the mean of the selfed progeny of the more resistant parent.
Significant positive correlation coefficients were obtained between tuber and vine reaction in a selfed family of the resistant clone 96-56 and in two crosses in which this clone was one of the parents. The correlation coefficients were 0.54, 0.57, 0.56 respectively. In one selfed family from a susceptible clone a non-significant value of r was obtained.
The correlation coefficients obtained between tuber rot reaction and firmness of tuber were significant for two progenies with r value of 0.53 and 0.56, and non-significant in the other three progenies studied. In the two cases of significant correlation the variation in maturity was much smaller than for the three cases where thare was no correlation between tuber firmness and tuber rot. There was no very clase association between stage of maturity of the plants at harvert and tuber rot reaction under controlled laboratory conditions. In the selfed progeny 95-56 the late maturing group of plants the resistance was greater than that of the other maturing groups.
The results of this study indicate that tuber reaction of seedlings can be determined with greater accuracy than vine reaction. This reaction deserves wider use by the breeder.

1 Ing. Agr.