Plant Sanitation. 



m 



[February, 1909. 



He suggests crossing the different resis- 

 tant sorts, especially resistant varieties 

 ol* different races, with the hope of 

 obtaining varieties which will combine 

 the good qualities of both laces. 

 Mr. Orton's investigation of cotton 

 resistant to the wilt fungus revealed 

 a very important fact. He found 

 that even with the most resistant 

 sort grown on infected land, infection 

 occurred in the rootlets, but the fungus 

 was not able to gain entrance to the 

 main root system, and therefore could 

 not spread in the plant. The resistance, 

 then, in cotton to the wilt fungus is not 

 caused by some peculiarity of the root 

 which prevent the entrance of the 

 fungus into the tissue, but to some 

 undetermined character which prevents 

 the spread of the fungus to any extent 

 after it has gained entrance to the 

 tissue. 



Water-melon. 



Vu account has already been given of 

 the success of Mr. Orton in obtaining a 

 wilt-resistant variety of the water-melon 

 by hybridization with the citron. 



Cantaloupe or Musk-melon. 

 The work, previously mentioned, of 

 Mr. P. K. Blynn, special agent of the 

 Colorado Station, in developing the 

 Pollock strain of the cantaloupe resistant 

 to leaf spot disease due to Macrosporium 

 is especially notable, as it is, perhaps, 

 the most successful attempt yet made in 

 this country to develop a variety resis- 

 tant to a leaf parasite. The strain is a 

 result of careful selection of seed from 

 resistant vines. 



Asparagus. 

 It is well known that the Palmetto 

 variety of asparagus is especially resist- 

 ant to rust. It is, however, not a 

 desirable variety for canning. In Cali- 

 fornia, R. E. Smith of the State Experi- 

 ment Station, is engaged in developing 

 a variety which will combine rust 

 resistance with the qualities desired 

 by canners found in the Conover's 

 Colossal. 



Violet. 



Violets grown in greenhouses are 

 especially subject to a leaf spot disease 

 known as Alternaria vialw. It is known 

 among violet growers that the Lady 

 Hume Campbell variety is the most 

 naturally resistant variety in culti- 

 vation. This natural resistant has been 

 greatly increased by carefully selecting 

 the most resistant plants from which to 

 propagate. 



Fruits. 



Little work has been attempted to de- 

 velop disease-resistant varieties among 



the fruits. As I have previously stated, 

 the development of disease resistance is 

 a comparatively new undertaking for 

 plant-breeders. That is, it has been a 

 relatively short time since horticul- 

 turists and plant-breeders have under- 

 taken, with a definite idea in view, to 

 develop varieties resistant to specific 

 diseases. Perhaps this is why little 

 work has been accomplished among the 

 fruits. Obviously it would take a longer 

 period to obtain results in developing 

 varieties of perennials than annuals, and 

 the plant-breeder will naturally select 

 for study those problems which give 

 promise of solution in the shortest time. 

 It is, however, a matter of common 

 observation that some varieties of 'air 

 tree fruits are more resistant to certain 

 of their maladies than others. For 

 example, in Delware, it is known that 

 among apple varieties the Lily of Kent 

 is above all others most resistant to scab 

 and bitter rot, while the Jonathan is 

 especially susceptible to rot. The whole 

 Winesap group is said to be relatively 

 resistant to rot but susceptible to scab, 

 while the York Imperial is resistant to 

 scab. Among pears the Keiffer is known 

 to be resistant to fire blight, while the 

 Bartlett and others are very susceptible. 

 A host of such observations might be 

 cited to show that among our tree fruits 

 there is varietal variation as regards 

 resistance to disease. 



There are some diseases of tree fruits 

 which are especially troublesome and 

 impossible to combat satisfactorily, for 

 which it would be highly desirable to 

 have resistant varieties. I refer parti- 

 cularly to the peach yellows. The 

 observations of Professor E. W. Morse, 

 reported in the Bulletin of the Bussey 

 Institution, indicate that individual 

 peach trees from which to "propagate 

 may be found which are resistant to 

 yellows. Since no satisfactory method 

 has ever been found to combat this 

 dread disease, the study of the problem 

 of prevention from this standpoint is 

 highly desirable. 



Another disease of great importance 

 is the crown gall of raspberry and black- 

 berry. This is a very serious trouble 

 in infested districts. In Sussex County, 

 Delware, the raspberry industry, once 

 very large, has been practically wiped 

 out by this trouble. Since the organisms 

 of the disease are retained in the soil 

 and attack the roots or crown only, no 

 preventative measures are practicable. 

 It seems highly desirable to attack the 

 problem of the treatment of this disease 

 by the selection or breeding of disease- 

 resistant varieties. 



(To be continued.) 



