Pa"C iJ 



BETTER FRUIT 



JanUiirv 



Crown Gall, Black Knot, Plant Tumor or Plant Cancer 



11> C.hi 



THK (liscMse c;ille<l crown gall, 

 black knot, plant tumor or plant 

 cancer has f^or many years been 

 well known to the horticulturist and 

 plant pathologist. It is only within a 

 lew years that the cause of the trouble 

 has been thoroughly investigated by Dr. 

 Erwin F. Smith and his associates of 

 Ihe United .Slates Department of Agri- 

 culture, and their bulletins are avail- 

 able to any who may be especially in- 

 terested in this trouble. 



Crown gall is nearly world-wide in 

 its distribution, being found in all parts 

 of the United .States, in Canada, South 

 Africa, Asia, countries of Europe, New 

 Zealand, Australia, Mexico and prob- 

 ably also in South America. The 

 malady is a serious one on many of our 

 (trchard trees, as it not only decreases 

 their vigor and pi-oductiveness, but at 

 length is a frequent cause of their 

 death. A large number of different 

 species of trees are susceptible. In 

 fact the organism causing the disease 

 is almost omnivorous as to its choice of 

 its host, but it is especially severe in 

 the more important econon)ic trees, 

 such as the apple, almond, apricot, 

 cherry, grape, |)each, i)lum, prune and 

 walnut. 



The disease, when once seen, is eas\ 

 to identify, as it is characterized by an 

 enlargement or growth of soft, spongy 

 tissue of a more or less spherical shape. 

 These growths are usually situated just 

 below the surface of the ground in the 

 trunk or body of the tree, often ex- 

 tending d<iwnwar(l some distance on 

 the larger roots, and may be found on 

 them at some distance from the trunk. 

 The galls cimtinue to increase in size 

 from >eai- to year until a large ex- 

 cresence may be formed. The tissue 

 produced is abnormal and easily de- 

 cays, making an esjjecially favor;ible 

 place for wood-destro.\ ing fungi to gain 

 an entrance to the tree. While the galls 

 are usually below the ground, occasion- 

 ally aerial ones are formed on the trunk 

 and large branches. These are hard 

 and cause little or no serious efl'ects on 

 the tree, except when they may be nu- 

 merous, as on grapes of the Vinifera 

 varieties. 



.vlon O. Siiiitli, Experiment Sliition, Whiltioi-. Ciili 



Trees alfected with the disease may 

 not die for some years, indeed will not 

 until the ti'unk is entirely girdled with 

 diseased gall tissue. The alfected trees 

 usually do not make as rapid growth 

 as healthy ones, but for a time produce 

 a large amount of fruit. The cause of 

 the abnormal number of fruit is the 

 same as in twigs that have been ringed 

 to make them produce. The root of 

 the tree sulTcrs most and soon ceases 

 to make further growth because of the 

 lack of elaborated food supplied it 

 from the leaves. Severely diseased 

 trees may show improperly developed 

 trunks, in that they are flattened oi" 

 have deep grooves directly above the 

 galls. In our study of crown gall we 

 have found these two characteristics a 

 sure indication of the presence of 

 crown gall. 



All abnormal growths of trees arc 

 not caused by crown gall. (1) Some of 

 these other enlaigements are caused by 

 insect stings or by the placing of the 

 eggs in the ])lant tissue. (2) Some of 

 the galls in the roots are caused by 

 small worms called nematode worms. 

 These closely resemble small crown 

 galls and are found on the roots of trees 

 and vegetables. (3) Certain .sjjecies of 

 fungi are capable of causing galls. One 

 line example of this is the gall inoduced 

 on citrus twigs in Cuba and Porto Rico 

 by a fungus called .Sphaeropsis tume- 

 faciens. (4) Tubercles are found on 

 many leguminous plants. (5) A gall 

 caused by a dilTerent species of bac- 

 teria from that of crown gall is found 

 on sugar beets, ((i) The knot or gall of 

 the olive is caused by a distinct species 

 of bacteria. In addition to these there 

 are other aerial galls on the twigs of 

 several difl'erent kinds of trees the 

 cause of which is not yet fully under- 

 stood. Citrus trees occasionally have 

 these aerial galls, also eucalyjitus seed- 

 lings have small knots that never cause 

 any serious injury. The galls of quince 

 are not very well understood and do 

 not seriously harm the affected trees. 

 There are also natural galls on certain 

 varieties of olive that should not be 

 confused with crown gall. Locust trees 

 sonielinies have large galls on the trunk 



lijlli iliillWMW I ■»!■ Pliii 



.\rlificial Tiiin ul;il inns mi Apiicol 



Seedlings \\itll a Pure (■.ulliirt 

 Itaelerium Tliniefafiens 



)f the ('idwn Ciall Or{i;niisin 



fornia 



which pidbablx are no! the same as 

 crown gall. 



The cause of crown gall has been 

 fully demonstrated to be a species of 

 bacteria by the name of Bacterium 

 tumefaciens, a tumor-forming organism. 

 The germs are extremely small and 

 probably live in the soil or organic 

 matter as saprophytes, and from here 

 enter into the tissue of living plants 

 through some injury in the bark. Arti- 

 ficial galls have been re|)eatedly made 

 to develop by simply |)ricking the 

 healthy bark with a steel needle pre- 

 viously touched to a pure culture of the 

 causal organism. In Ihe gall or tunxir 

 tissue comparatively few bacteria are 

 present, and the microscope does mil 

 conclusively demonstrate the cause of 

 the trouble under ordinary histological 

 methods. The germs live inside the 

 cells of the host and b\ the products 

 produced during their developmenl 

 cause new cells to be foiinetl with un- 

 usual rapidity. The abnormal ti.s.sues 

 thus formed show cells with very thin 

 walls, at first soft and often with no 

 well-delined bark or epidermis. The 

 germs can often spread through the 

 plant by the developing of a narrow 

 portion of tissue into a tumor strand. 

 This strand is invisible externally, but 

 from it secondary tumors very often 

 develop. 



Strong evidence has been presented 

 !)>■ Dr. Erwin F. Smith showing man> 

 similar characteristics to exist between 

 human tumors and those of plants, but 

 to present these would be outside the 

 scope of this article. All attempts, how- 

 ever, to produce tumors on the lower 

 animals, fishes, frogs, etc., by inocu- 

 lating them with the crown-gall organ- 

 ism have been failures, or at least un- 

 certain in their results. It is therefore 

 safe to conclude that the organism 

 causing plant gall tumors cannot pro- 

 duce tumors in animals. The crown- 

 gall organism, however, is a virulent 

 plant jjarasite and is capable of pro- 

 ducing galls in a large number of plants 

 when placed in their tissue by artificial 

 inoculations. Calls have thus been 

 produced artificially on several kinds 

 of trees upon which they have never 

 been found to occur naturally. The 

 most interesting of these are the differ- 

 ent species of citrus, as the orange, 

 lemon and lime. Negative results have 

 always been seemed from inoculating 

 the avocado and Ihe olive. The fig and 

 lo(|uat are onl\- with dillicullx infected. 

 Often the inoculations when made do 

 not at once show ])ositive gall informa- 

 tion, but may, as in the ([uince, remain 

 in a dormant condition. In our quince 

 inoculations the injur\- made by the 

 puncture inoculations healed, and it 

 was neaily a year before the small, 

 gall-like formations appeared. Tlu'sc 

 eventually, however, grew into largi' 

 galls. The condition of the tree growth 

 affects Ihe rapidilx of gall Inrmation — 

 no growth of free, little oi- no develop- 

 menl of gall. Inoculalioii liile in the 



