BREEDING DISEASE-RESISTANT PLANTS 415 
the various citron characters appearing to be dominant in the majority 
of plants. From among 3000 or 4000 plants ten fruits were selected on 
the basis of resistance and quality and the seeds were planted the follow- 
ing year, 1904, in isolated, infected plots. Of these ten plots two were 
found to bear melons of uniform appearance and quality one of which 
resembled the Eden parent. These were sesquihybrids from the F, 
pollinated by Eden. Again all the best melons were selected and planted 
separately the following year and further variations were found. After 
five more years of selection a variety was obtained which had great uni- 
formity and disease-resistance while the fruit had a thin, tough rind which 
enables it to endure long railway shipments. The flesh is so juicy 
that the melons are heavier than Eden melons of the same size; the 
quality and flavor are good although not equal to the finest (Fig. 168). 
These qualities have been preserved and resistance maintained at a dis- 
tance of 740 miles from the place of origin, but on the Pacific Coast the 
resistance was not maintained. 
This failure of the supposedly resistant variety when grown in a far 
distant locality is not strange when we remember that the wilt fungi are 
highly specialized in their adaptation to hosts. According to Orton 
Fusarium niveum attacks no other living plant than the watermelon and 
“in this respect, coupled with their close morphological resemblance and 
their common geographical distribution, they seem to be analogous to the 
biological strains of Puccinia and Erisyphe.”’ In combating all such 
diseases the importance of developing locally adapted varieties must not 
be overlooked. 
The specific nature and heritability of disease resistance is also evi- 
denced by the results of numerous other experiments among which may 
be cited the following. In the tomato wilt resistance was found by 
Norton to be recessive to susceptibility and varieties of Fusarium-resis- 
tant tomatoes from Tennessee were found to be susceptible in Maryland. 
Stuckey found that cherry, pear and currant tomatoes were immune to 
the blossom-end rot, a functional disease and, when crossed with com- 
mercial varieties, they transmitted resistance as a dominant character. 
Resistance to leaf blight in the cantaloupe was found by Blinn to be 
inherited as a dominant character. Jesse B. Norton when breeding for 
resistant varieties in combating the asparagus rust, Puccinia asparagi DC., 
found resistance dominant in all the F, offspring in his crosses between 
the female plants of the rust-susceptible American varieties and a rust- 
resistant European asparagus. ‘The resistance was somewhat variable 
but was fixed by selection in succeeding generations. These few cases, 
taken almost at random, together with the typical illustrations already 
discussed, amply justify the recommendation that the breeding of disease- 
resistant varieties of economic plants by hybridization and subsequent 
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