SEED IMPROVEMENT MEETING. 20g 



will become badly affected. A notable example of this is the 

 Iron Cowpea (3) which is resistant to the attacks of the wilt 

 and of the root knot, two diseases caused by soil organisms 

 that very severely attack most other varieties. This variety 

 when grown upon soil badly infested with either disease 

 retained its vigor and produced a normal crop, but other varie- 

 ties as the Black and the Wonderful, grown in rows on either 

 side of the Iron became badly infested and produced no crop at 

 all. In succeeding years this Iron Cowpea has retained its 

 disease-resistance quality and has proved to be a valuable vari- 

 ety on infested soil. In case the resistant variety does not 

 .possess other desirable characters it may be crossed with a 

 desirable related variety in a manner pointed out later. 



Now and again individual plants of a desirable, though 

 susceptible variety may be found resistant or entirely immune 

 to the disease ordinarily affecting the plant. Seed from these 

 resistant plants sown the following year where the plants may 

 be subject to inoculation from the parasite, have produced 

 plants showing high disease-resistant qualities. This indicates 

 that disease resistance is an inheritable quality and after a few 

 years' selections in which non-resistant plants are weeded out, 

 individuals possessing a high degree of resistance may be 

 obtained which may be depended upon to transmit this quality 

 to succeeding generations. 



A very important point must be kept in mind. To be cer- 

 tain that a plant possesses the quality of resistance it must be 

 free from disease after having been subjected to the parasite 

 under conditions favorable for infection to take place. One 

 may be reasonably sure that a plant possesses such a quality 

 if it appears resistant to a disease that has badly affected 

 neighboring plants of the same variety. To be certain, how- 

 ever, that disease resistance in each case has been transmitted 

 the progeny of the plant should be subjected to the disease in 

 succeeding years. If the disease is not prevalent in succeeding 

 years it may be necessary to artificially inoculate the plants 

 with the organism causing the disease. 



3. Orton, \V. A. Plant Breeding as a Factor in Controlling Plant 

 Diseases. Am. Breed. Assoc. Rept. / : 69-72, 1905. 



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