142 



THE AGRICULTURAL NEWS. 



May 3, 1919. 



PLANT DISEASES. 



THE 



SUSCEPTIBILITY OF RUTAOEOUS 

 PLANTS TO CITRUS CANKER. 



Some important data cf the results of field observations 

 knd iooculations witli citrus canker {/^sew/omonus citri) upon 

 plants belonging to genera more or less related to citrus are 

 ^iven in a paper published in the Journal of Agrkultuial 

 Meumch, Vol. XV, No. 12. The author, Mr. H. Atherton 

 Lee, Assi.?tant Pathologii^t, Bureau of Plant Industry, United 

 States Department of Agriculture, shows from these observa- 

 tions that a wide range of hosts exists for citrus canker, and 

 that the po.«sibility of lesions upon plants other than Citrvs 

 spp. serving a.s sources of new infection becomes emphasized 

 in the work of citrus caokfr eradication. 



Over 2,000 inoculations were made in the course of the 

 investigation on twenty-four species representing twenty 

 genera of the Rutaceae. In making the inoculations, an 

 infusion of the citrus canker organism was painted upon the 

 leaf blade, midrib, jiptiole, or stem, as the case might be, with 

 a small camel.s hair brush, and then the ti.sauee was punctured 

 through the coating of infusion with a needle. The inocu- 

 lated twig was maintained in a; moist condition by wrapping 

 it ia parafin paper containing a small piece of mi listened 

 eottoD. 



Tlie investigations were carried on largely at the Lamao 

 IRxperiment Station of the, Philippine Bureau of Agriculture. 

 Many of the plants studied, related to citros, grow wild in the 

 Philippine Islands. It may be noticed that two of the plants 

 investigated are widely known in these West Indian islands, 

 namely i/urraj/a {Vhn\caa)e.\otica, grown a.s an ornamental 

 shrub, and locally called 'cilronella', and Triphasic trijoliata 

 ene of the best hedge plants in these i.slands, locally called 

 'sweet or myrtle lime'. Another genus experimented with (Xan- 

 thoxylum) ha.s several West Indian representatives, although 

 the special species investigated does not occur in these i.slands. 

 The investigations show that these West Indian species 

 possess immunity to citrus canker. This iuimunity possibly 

 arises from the fact that the species referred to possess thick, 

 •oriaceous, brittle leaves, which suggests the possibility that 

 resistance to citrus canker may be influenced in some measure 

 bj' histological or morphological dUferc-nces. 



The results of the investigation may be summarized as 

 follows: that inoculation tests with citrus canker {/'sevdontnas 

 citri) upon twenty four species representing twenty genera of 

 the order Jiutaceae show that nineteen of the species are 

 Busceptible in a greater or less degree. It thus appears that 

 citrus canker is not limited tf) the genus Citrus, but has a 

 wide range of hosts among the Hutaceae. The abundance of 

 •ankers occurring naturally on some of the native Hutaceae of 

 the Philippines and South (Jhina gives rise to the theory that 

 •ne or otlier of them may have been sn original wild host from 

 Vhich citrus canker spread to eultirated .species. 



LIME CULTIVATION IN DOMINICA. 

 {Continued.) 

 III. BUDDING OF LIMES, PKOl'AGATION ilY L.VYERINU^ 

 .\X1) I'KUXIXC:. 



The following continues Mr. J. Jones'.s report on 

 his experiments with lime trees at the Experiment. 

 Station, Dominica. The first part of this report will 

 be found in the two previous issues of this Journal: — 



Budding of limes. In recent annual reports reference 

 was made on two occasions to the experiments now being 

 carried on with limes budded on the sour orange, citron, and 

 M'gergeb stocks, the last named being a variety of citroa 

 received from Algeria, where it is used as a stock for oranges. 



Experience has shown that, while lime trees are blown, 

 over by thousands during the occurrence of hurricanes, the 

 sour orange and sweet orange trees, if growing on fairly deep 

 soils, are never uprooted under like circumstances. This led 

 to these experiments being made in the budding of limes, the 

 chief object of which is to test the root-holding power of 

 the sour oranfie when carrying a lime top, which, in the ca.se 

 of a well grown tree, is much larger and heavier than aa 

 orange top. Many years may elapse before the budded 

 plants are put to test. In the meantime the planting of this 

 class of plants will probably be continued on a small scale. 

 It is important to remember that budded plants should 

 always be placed out in soils of a good depth, in order 

 that the tap root may be allowed to develop. The object 

 aimed at would be nullified by planting on shallow soils over- 

 lying a hard subsoil. 



It is also known that several thousands of sweet orange 

 trees grown upon the sour orange stocks in a forest district 

 have proved immune from the root diseases which cause a 

 con.siderable loss of trees amongst lime cultivations in newly 

 cleared areas If this immunity continues, the loss of lime 

 trees which now occurs under these conditions would be pre- 

 vented by using the sour orange as a stock. 



The trials now beins,' made with limes worked upon sour 

 orange stocks are sufficiently advanced, both on estates and 

 at the Experiment iStation, to show that under careful culti- 

 vation the plants will attain to a good size in four years. 

 Like all budded citnis plants, progress is slow during the first 

 year after planting in the field. Fair growth is made in 

 course of the second year, and during the third and fourth 

 years the rate of progress is excellent, especially so whea 

 green dressings are used, and shelter afforded. 



Should the budded limes come successful through the 

 root-holding trials, vhenever Nature may impose the test, it 

 is probable that this class of plant will appeal to planters who 

 like to do things well, and who posess the capital to carry 

 out their ideas. That seedling limes will continue to be 

 largely used is certain, owing to their cheapness, and to tke 

 fact that though easily overturucd during storms, they can be 

 renewed by suckers within two or three years, and that once 

 renewed by suckers they are not likely to be again disturbed, 

 as far as the roots are concerned. 



Should the budded plants in due course prove able t«»- 

 re.sist the high winds, and accompli.sh all that ia wished of 

 them, it would h.ave to be admitted that the grower of 

 seedling limes, in spite of initial cheajmess, has tn pay in the 

 end a much higher rate, in order to secure immunity from 

 uprooting, than the purchaser of budded limes. But it may 

 be argued that many planters are better able to meet this 

 cost when in possession of an established though damaged 

 property, than they were to pay for the high cost of budded 

 stock at the commencement of planting operations. 



