BREEDING STRAINS RESISTANT TO ROOT-KNOT. 71 



the sandy soils of the southern United States, the soils are already 

 deficient in potash, rather strong applications of some of the potash 

 fertilizers— for example, kainit, potassium magnesium carbonate, 

 sulphate of potash, etc. — are very helpful. Care should be taken 

 not to apply enough to prevent the germination of the seed. 



BREEDING STRAINS RESISTANT TO ROOT-KNOT. 



As already mentioned, Webber and Orton have shown ^ that the 

 Iron variety of cowpea is practically immune to root-knot and wilt 

 (Neocosmospora vasinfecfa) , wliile most other sorts are exceedingly 

 susceptible to both diseases. The latter investigator has conthuied 

 his breeding experiments, using the Iron cowpea as one of the parents, 

 and has produced several varieties more prolific than that sort in 

 wliich the resistant characteristics are present. Similarly in the 

 breeding of tobacco, Shamel and Cobey- obtained a strain resistant to 

 nematodes. Certain sorts of figs — for example. Celeste and Pou- 

 lette — are said to be less subject to injury by nematodes than other 

 kinds. Among grapes, so far as the writer's observations go, the 

 Old World species (Vitis vinifera) seems to be especially Hable to 

 injury by root-knot, although the different sorts vary greatly in their 

 susceptibihty. Thus, Zinfandel and Muscat appear very subject to 

 this trouble, wdiile Sultanina (erroneously called Thompson Seedless) 

 is apparently not so easily injured. Some of the phylloxera-resistant 

 hybrids and pure American sorts are practically immune to root- 

 knot as well as to phylloxera, although some American sorts are quite 

 badly affected by the nematode. These observations of the wTiter 

 are confirmed by Lavergne, who states '^ that the European varieties 

 are very susceptible to Anguillula vialae, as he calls the root-knot 

 nematode, while those of American origin that are resistant to 

 phylloxera are also resistant to root-knot. Of the watermelon- 

 citron hybrids bred by ^Ir. Orton with resistance to wilt as the main 

 aim, it was found by the writer that of one strain only 4 out of 333 

 plants showed root-knot, i. e., 1.2 per cent, while in two other strains 

 28 and 51.9 per cent, respectively, showed root-knot. The presence 

 of such marked differences shows that it would be entirely feasible 

 to breed a watermelon variety that would be practically immune to 

 root-knot as well as to wilt. Bouquet de la Grye * pomts out that 

 Cojfea liberica is less susceptible to root-knot than C. arabica and 

 recommends grafting the latter upon the former. To obtain a firm 

 union, this must be done hj an approach graft with seedlings. 



Simple selection can be and ought to be practiced by everyone who 

 grows his own seed; more complicated breeding work, unless per- 



1 Webber and Orton, 1902. a Shamel and Cobey, 1907. ' Lavergne, 1901. * Bouquet de la Grye, 1899. 

 217 



