26 BULLETIN 1195, U. S. DEPARTMENT OF AGRICULTURE, 



The 29 plants of Solarium jamesii grown from tubers and listed in 

 Table 6 represented 23 known different clons, and these were selfed in a 

 total of 169 flowers. Only five seed balls were obtained, one from 

 each of five plants. There is some pollen impotence in this species, 

 but in most cases at least half of the pollen is vigorously viable. It 

 appears that this stock is either only feebly self-compatible or that 

 abscission was very decided under the particular conditions of 

 growth. Of 12 combinations in crosses only two succeeded, which 

 suggests that cross-incompatibility is in evidence. 



The plants of Solanum maijlia which have thus far been grown at 

 Presque Isle have all been so highly pollen sterile that they could not 

 be expected to function as pollen parents irrespective of any real 

 incompatibilities that might be present. 



The compatibility between the various wild species and between 

 these and the cultivated varieties awaits the completion of investiga- 

 tions now under way. 



RESULTS OF THE STERILITY SURVEY. 



The survey has clearly shown that two types of sterility exist in 

 cultivated potatoes: (1) Sterility from nonblooming and abscission 

 and (2) pollen sterility or one-sided impotence, giving loss of maleness. 

 In wild species as grown at Presque Isle, early abscission of flowei"s 

 is rarely seen, but in certain species pollen sterility is marked, and 

 there are also evidences of physiological incompatibilities. In the 

 hybrids between the two species Solanum fendleri and *S. chacoense 

 there is very decided impotence of both pistils and stamens. 



The sterility from nonblooming to a large degree can be overcome 

 for seed-breeding work by growing varieties under cool-season condi- 

 tions such as prevail at Presque Isle. There are without doubt some 

 variations in the potency of pollen in fully developed flowers of a 

 single variety, possibly even for the various flowers of a single cluster, 

 and it may be possible that special conditions may shift the pollen 

 of a variety even from class 1 to class 3 or the reverse, but there has 

 been no indication of this in studies made thus far. 



Success in obtaining seed depends decidedly on using as male 

 parents varieties which yield the most viable pollen. But even in 

 the best pollen producers among the cultivated potatoes there is 

 much abortion oi pollen. As a group these varieties are decidedly 

 low in maleness but relatively higli in femaleness. 



Other studies of the condition of potato pollen in its relation to 

 sterility include those of Turner. Dorsey and Breeze, respectively. 

 In studies of the pollen of 11 leading commercial varieties grown at 

 Presque Isle, in 1918, Turner* found a very high percentage of the 

 grains to be imperfect. In the 01 seedlings studied he reported 

 a wide range of variability in the (|uality of the pollen, with germina- 

 tion ranging from to 75 per cent. From tests of pollen from plants 

 grown without fertilizer and with (lifferent ratios ot fei-tilizer ingredi- 

 ents he concludes that uulrition has a marked efl'ect on the via- 

 bility of pollen, l^orsey (5) found that a large j)ercentage of the 

 pollen of several of the best-know ti varieties grown xn Minnesota 

 was imperfect. Ho concludes that the development of the pollen 



» From unpublished manuscript by Thomas \V. Turner. 



