1 1 



THE AGRICULTURAL NEWS. 



.1 \M \ l: <• 



1915. 



FUNGUS NOTES. 



A DANGEROUS CITRUS DISEASE IN 



FLORIDA. 



References I b i recently to a new and 



serious disease of citrus trees in Florida. Since by 

 some oversighl the bulletin describing it lias nol yel 

 i. ached us, bhe magazine Mod 



Culm, an article b) I >r. J. R. Johnston, « hich gives the 

 necessary warning to West I d u citrus planters. 



\- there is a great possil ty that the citrus canker 



i into ( -il'.i. n is advisable thai 



every citrus grower should famili rize aimseli as quickly as 



possible with it- appearance. The following description is 



given K\ Stevens oi the Florida State Experiment Station: 



'Thi di mall circular spots, from less 

 than one-sixteenth to oni qi irtei of an inch across. They 

 may occur singly , o ral to hej ma} form an irregular 

 area. They the surrounding tissue, an 

 light brown, and composed ol a spong} mass ol dead cells 

 covered bj a thin (white to grayish) membrane that finally 

 ruptures and turns outward, forri ;ed margin around 



the spot. The general appearance of the spots is much the 

 same whether they are found on the leaves, fruit or twigs. 

 The older spots often become overgrown with saprophytic 

 fungi, and may be pink or black on account of secondary 

 infection by species oi Fusariv Oladosporiv/in. 



'The infections on the leaves appear first as small watery 

 bulging dots, which are usually oi a darker green than the 

 surrounding tissue. They ma} appear on either surface of 

 the leaf, but do not penetrate through the leaf tissue at this 

 stage. The spots gradually increase in size, change to 

 a light brown colour, and become visible on both sides of 

 the leaf. Each spot is surrounded "bj a narrow yellowish 

 band or zone. Later, the surface of the spot becomes white 

 to greyish, and finally ruptures, exposing a light brown 

 spongy central mass. 



'The spots "ii the fruit are similar to those on the leaves. 

 The} project from the surface and retain a circular outline. 



They d t penetrate far into the rind, and max be scat 



tered singly over the surface, or several ma} occur together, 

 forming irregular masses. 



•Tin 3pOtS on the older twigs are more prominent, and 

 Usually larger and more irregular in shape. They show the 



pong} tissue and th. ami col as those on the 



leaves. On growth more than a year old, the spots assume 

 a cankerous appearance, and the membrane covering the 



surface disappears. The spots do not pi to the y I, 



but are confined to the outer tis of tie- Karl..' 



Although this disease is said o n si mble the well Known 

 ii, it ma} be distinguished K\ its roundel and larger spots, 

 and b} it - bit< gi h col ur. The cankei doe not 

 distort the leaves, not causi the wart-like projection that 

 are so common in infections ol scab. Canker is found on 

 the older wood, while infei tion cab nevei >ci ur on the 



older tw igs and branches. 



The cause of tin disi ot been determined an} 



i v than that it is a fungus, and j infectio I I. a- 



i ards its i lature, il sidered one ol the worst 



own. 

 Up. to date it has Keen reported in Florida and the 

 ■ the ( lull, nd there it has occurred 



oiiK \ir\ recently. That it will be communicated to Cuba 

 and the other West Indies before long seems bhi} a foregom 

 conclusion, unless the utmost care is taken to prevent it. 



This disease maj be looked for especially in nurseries, 

 but also On th fruit, foliage, and stems ol grapi fruit, and 

 occasional!} it occurs on other citrus trees. 



Tin- safest and surest known way to tre.it the canker is 

 to Kuin the affected trei 



ASCOSPORIC CONDITION OF THE 



GENUS ASCHERSONIA. 

 Overshadowed b} the more abundant forms, the part 



played by the fungi of the genu- A-chci-"iiia a- scale insert 



destroyers has not attracted much attention in the West 

 Indie.-, or at an\ rate, one ma} say with confidence, in the 

 Li er Antilles. Asckersonia turbinate has Keen recorded 

 from Dominica, St. Lucia, and Antigua, and it was recently 

 found to be abundant on estates visited in the interior of the 

 first-named island, occuKring on unidentified scales on the 

 leave- and twigs of lime tree-. A species believed to be 

 A. cubensis is known to occur in considerable numbers in one 

 situation in Barbados, attacking Vinsonia stellifera on lime 

 t rees. 



In Florida two species of the genUS have had a great 

 i nl ol' attention in I iew of the control they exercise <m the 



abundance of two species of white fly (Aleyrodes) on citrus 



trees. The genus is also well known in the Eastern Tropics. 



Hitherto only the cpnidial forms of these fungi h 

 been described, and the ascosporic condition, though often 

 sought, seems to bave completely eluded notice Professor 

 Thaxter now announces ( Botanical <,'•< ette, I. VII. pp. 308-13) 

 that as a result of a special effort made during a -ta\ of some 

 months in Grenada and Trinidad, he was able to obtain the 

 perfect form of A. turbinate, in the former island, and of four 

 or five species in the latter. The ascosporic condition 

 'occurred either by itself or associated on the same stroma 

 with the pycnidial formj so that there could be no question 



as to the actual connexion of the two conditions. In some 



instances it appeared to follow the pyenidia in older speci 



mens, while in others it was as evidently primary in its devel- 

 opment, and unaccompanied by pyenidia.' The general 

 character and appearance, it is further stated, recalls that o| 

 the genus Cordyceps, to which A-chersonia is evidently closely 



relat.d. The description and figures given show the asci to 

 occur in bottle-shaped perithecial cavities embedded in the 

 stroma. The ascus is slender, and contains eight filamentous 



-pores, at first continuous, later dividing up into segmi 



which eventual!} become separated into rod like unicellulai 



.-poivs. 



Professor Thaxter finds that the variability of the species, 

 and the scanty information available regarding their hosts 

 make any attempt at systematic revision at present prema- 

 ture. In this connexion it may be said that owing to tin- 

 usual verj complete envelopment of the host b} the stroma 

 of the fungus, the identification of the former is often very 



difficult. 



Material from the Lesser Antilles available for the study 



of thi- genu- at tin IK. id Office of the Imperial Department 



of Agriculture is at present somewhat scanty, and i ■« 



would be welcomed. For the information of collectors it 

 i,i,i\ K. explained thai fungi taking the form of small pink 

 cushion-, expanded oi not into one or several cups, and 



found on li'. er} well provi 



I., long to t be genus it question. 



