THE A.GKICCLTT:RAL NEW5 



Av..;usT 2-t, 1916. 





PLANT DISEASES 



KiiSISTANCE AND SUSCEPTIBILITY. 



Th.^ American Joiiriiai of Botany, June 1918, contains 

 two papers bearing on the above subject. W. A. Orton 

 (■Breeding for I>isease Resistance in I'lants ) reviews some of 

 «he salient instances of success along these lines. 



The common asparagus was cultivated in America up to 

 1 896 without any notable lots from disease Si.x years after 

 that date the Kuropean asparagus rust had spread across the 

 continent An English variety, Reading Giant, was found 

 to be so resistant as to escape serious damage, and from this 

 and other similar imported types the American continent is 

 now being restocked. It is found that where the susceptible 

 types have been eliminated, and the reservoirs of infection 

 thus removed, the disease can be reduced to negligible propor- 

 tions. 



Selection has been notably successful in the well-known 

 cases of Fusariurn wilt of cotton, and the similar disease of 

 cowpea>: and in the more recent cate of cabbage yellows, 

 another Fusariurn disease, great success has been attained, 

 and varieties are n-w being propagated which will prevent 

 the devastation experienced on infected soil. The Fusarium 

 ■wilt of tomato is being dealt with on similar lines, with 

 results that are already good in regard to a late variety, 

 while satisfactory early varieties are in sight. Strains of 

 flax f esistant to /•'iisariiim liiii have made possible the con- 

 tinued culture of this crop in regions where it was being 

 abandoned. 



ITie writer discusses the addititional risks, as a result 

 of extending commerce, cf the importation of new diseases, 

 and makes a suggestion that explorers in search of new 

 ■varieties should in all case.- be accompanied by pathologists 

 to note the diseases f>ccurring in regions from which intro- 

 ductions are made. 



The second paper, by I •. I '. .(ones, deals with the segre- 

 gation of .-u-ceptibility to para^titism in maize, as studied 

 in the inheritance of this character in relation to the corn 

 •mut (Ustilago Zeae). 



Six inbred strain?, ilerived froni one original variety, 

 and two from a different variety, and the first and second 

 generation hybrids of these strains were studied. 



In the comparison of nearly 1,000 individuals grown 

 bide by side, there wa.- a ditf'erence in two of the strains 

 between complete freedom and 10 [>er cent, of infection. 

 The strain from which infeition was absent was the mo.-5t 

 vigorous of the tour inbred line^ from the .same parent, having 

 a darker green colf'ur. and being larger and more productive 

 than the other three. The author considers it doubtful, 

 however, that vigour in this case is more than a minor 

 factor in resistance. .since many naturally crossed varieties 

 are 'several times fis vigorous and productive, and yet are 

 quite .sueceptib'e. 



The result.^ 'show without a doubt that segregation of 

 ftosceptibility to infection by the smut fungus has taken 

 place during the reduction to hotcozj-gosity accompanying the 

 inbreedirg process.' 



A recent pr.jgress report, on tL - trial- conducted by 

 the British Board of Agriculture cf varieties of potatoes 

 resi.=tant to the black scab disease, shows that numerous 

 immune straic? of considerable prc-dr.ctiveness are now avail- 

 able for u<e in infected districts. ^V'here cases of the apparent 

 breakdt wri o' immunity have occurred, they have usually 

 been traceable t<:' impurities in the strain. The production of 

 the^e resistant ani immune varieties is of high importance ia 

 connexion with the war-time prciucticn of food, as some of 

 the principal potato-growing areas had become infected with 

 this highly destructive and persistent disease. 



WILD TAMARIND-A PEST OR 

 A BENEFIT ? 



A leaflet published by the Department of Agriculture, 

 Ceylon, on the uses of Leiiiaena ■jmi/ch. has recently been 

 received at this Office. As will be noticed below, this plant 

 is utilized in several ways not only in Ceylon, but in other 

 parts of the East. In reference to the above question, we 

 have received a communication from Mr. .Joseph Jones, 

 Curator of the I'.otanic Station, Dominica, in which he sounds 

 a note of warning as to this plant for planters in the West 

 Indies. It may also be remarked that Mr. .(oness opinion 

 that the wild tamarind is regarded as a pest on or near to cul- 

 ti%'ated land, on account of the great difliculty in eradicat- 

 ing it when once established, is fully shared bj- planters in 

 St. Croix. Antigua, and Barbados, all of which are among 

 the drier islands of the West Indies. This corroborates 

 Mr. Jones's conjecture that the characteristic of persistency, 

 so evident in the plant in drier situations, may have been 

 modified under damper conditions. Mr. Jones says:— 



'From time to time notes a[)pear in the publications of 

 the Agricultural Departments in the Kastern Tropics on the 

 uses of /.(//(((tv/tf ;■/(?«(■((, a small leguminous tree native to- 

 Tropical America. In some of thi- West Indian islands this 

 plant is known as the Horse Tamarind or Wild Tamarind. 

 The value of its food for fuel is well known, and the leaves 

 are eaten by cattle and goats. It is, however, regarded in 

 some parts of the West Indies as a pest. Unce established 

 in the land it is almost impossible to eradicate it except at a 

 very great cost of labour. No amount of cutting back will 

 kill the plants. < >nly by digging out the roots, which is a 

 most tedious operation, can the land be cleared. It comes 

 therefore as a surpri.se to find that this plant is recommended 

 for use as a soil renovator, thi.s i.-., as a green dressing, in the 

 Kastern Tropics, when so many other plants, the roots of 

 which rapidly decay or aie easily eliminated from the soil, 

 would accomplish the same result. 



'In Dominica the plant thrives in places in which the 

 rainfall -tverages 80 inches annually, that is, in the drier 

 paits of the island. It does not occur in the wet districts, 

 and it is possible that when grown in wet places in the East 

 as shade for coft'ee, the characteristic of persistency which is 

 so dominant in the West may be luodified. It may even 

 require some care to grow it under damp conditions, and 

 when grown it may not spread as it does in dry places in the- 

 West Indies. 



'No doubt l.tiittHiia f^laucn ha.s its uses in dry districts aa 

 a fuel plant, and also for fodder. But under the latter condi- 

 tions in the East, unless some great change has taken place 

 in the habit of the plant, it is bound sooner or later to come 

 to be regarded as it is in the West, that is, a pest oc or near 

 to cultivated lands.' 



In the leaflet referred to above, information is given 

 with recard to I.iuiaena glauca as a green manure, and as 

 fuel. 



