Mar. 17, 1919 Fusarium- Blight of Potatoes under Irrigation 295 



PEARIv DISEASED SEED (TABLE I, L) 



In 1 91 7 one lot of seed, Pearl variety, was secured, each tuber of which 

 showed positive vascular infection by species of Fusarium, as proven by 

 isolation cultures. Conditions were generally more favorable for potato 

 growth early in the 1917 season than they were iu the 1916 season, and 

 less favorable late in 191 7 than in 191 6. Table I, I^, shows the perform- 

 ance of this badly diseased stock. 



IDAHO RURAL (TABLE I, m) 



One lot of seed from Idaho, known as Idaho Rurals, and healthy 

 throughout, were treated in the same manner. No tuber showed disease 

 or infection in the vascular system. The performance of this lot of seed 

 is illustrated in Table I, M. 



The similarity between Tables I, L, and I, M, is striking. The presence 

 of plants in the HD columns is attributed to the unfavorable late season 

 in 1 91 7. This is taken to account for the uniform health as represented 

 for the diseased. Pearl variety in Table I, L. 



There is no reason to suppose that if mere chance had operated so as to 

 have each seed fall where its twin fell, and vice versa, that the result 

 would have been the same in any table. Each seed piece was sur- 

 rounded by a different set of factors which operated to bring about 

 disease or apparent health. For that reason it is unlikely that the results 

 of a single year can be duplicated, though the average of similar years 

 ought to strike a fair average. 



DISEASE RESISTANCE 



In the fall of 191 5 a field of potatoes was chosen upon which to conduct 

 an experiment in disease resistance. It was one calculated to offer crop 

 failure if one was reasonably possible. One end of the field was white 

 with alkali, the soil was heavy, and drainage was poor. A portion of the 

 field already had potatoes on it, supposedly of the Pearl variety. It 

 presented a very ragged appearance owing to skips, diseased plants, 

 and mixture. Two of the best-looking rows' were selected to work upon, 

 and all the diseased and mixed plants were staked. After frost the staked 

 plants were taken out by hand, and the remaining healthy plants were 

 harvested with a machine. In 191 6 this seed was planted on an adjoin- 

 ing plot. All the plants came up healthy and with increased vigor. 

 Some plants succumbed to blight during the season, but at least 90 per 

 cent reached harvest. Again in 191 6 several rows were inspected, the 

 diseased and mixed plants staked, and the healthy ones harvested as 

 before. These were planted in 191 7 in a plot adjoining the one used in 

 1 91 6. In comparison with other potatoes in the field, the vigor and 

 health of the selected seed was notable. Very few diseased plants were 

 to be found, and skips in the rows were rare. These plants promised 



