46 



THE AORICULTUKAL NEWS. 



1'i;i;ki.ai:v 1, 1913. 



FUNGUS NOTES. 



RECENT WORK ON A PLANT DISEASE. 



In the Meuioin of the Imperud Department of Agri- 

 ridtwi- ill Iiidiii, Botanical Series, Vol. IV, No. (J, an acnount 

 is given by Shaw of his investigation into the existence of 

 physiological races of the fungus Ithizoct' nia whicii has 

 been found to be parasitic in India on the ground nut, 

 "Cowpea, jute and cotton. 



Before procfteding to describe the impoitant results that 

 have accrued from this investigation, it may prove helpful 

 to sketch the position regnrding the identity and parasitism 

 of lihizictonia that existed previous to the commencement 

 of Sliaw - researches. 



Rhizoctonia is a form genus which was established by 

 de Candolle in 1S15 to include certain sterile (i.e fruitless) 

 fungi occurring upon the roots of plants: though the first 

 reference to I'hizoctonia wa.5 made by Duhame, who, as 

 early as 1728, descril"ed a disease of saffron {Crorv.^ salii'its), 

 and considered the sclerotia, or spherical masses of mycelium 

 typical of Rhizoctonia, to be a special plant of which the 

 hyphae were the roots. He named the plant Tuberoides. 



Since de Candolle's time the genus lUiizoctonia has 

 received considerable attention by mycologists in Europe, 

 and various forms were described at some hngih by the 

 Tulasnes (1651) and by Kiihn (1858). The disease was 

 recorded in Denmark during ISS'i and 1902 on hosts 

 belonging to widely ditl'orent natural orders, and rfcently the 

 parasitism of the fungus has been investigated in Sweden by 

 Eriksson, in connexion with the considerable variability in 

 the susceptibility of ditlerenl varieties of one kind of host to 

 the disease. In England, Gusson has described the disease 

 on .several plants, and he considers li. soffini (Knhn) and 

 a. vio!w-a (Tulasie) to be one and the same species; whereas 

 Massee, subsec^uent on Hartig's observations, suggests that 

 Itosellinia is the fruiting stage of lihizoctonia. 



In America, Rhizoctonia is known to attack much the 

 same crops as in England, and has been investigated by 

 Duggar and Stewart; but the most interesting of the Ameri- 

 can publications on Rhizoctonia is that of Rolfs who recently 

 discovered a fruiting stage whicU he stated to be a basidio- 

 itiycete a'rcady known to science as Cortirium nrr/niK, 

 P.. and C. 



Such was the position relating to the indentity of the 

 fungus up to about 1910; and it must be admitted that 

 considerable doubt prevailed as to what were the true 

 perfect forms. 



It has been stated already that the disease has for years 

 been observed on a large ntimber of ditterent sjiecies of host 

 plants, and the following list.-^ of hosts show the remarkable 

 distribution of the disease, both geographically and biologi- 

 cally: In Europe and America, Rhizoctonia ii Hacks sugar- 

 beet, bean, carrot, cabbage, cotton, lelture, potato, radish, 

 sweet potato, pumpkin, wnftrmclon, garden pea, and alfalfa. 

 More recently, Shaw, in India, has obseived the disease on 

 the following: ground nut, cowpea, jute, soy bean, cotton, 

 bonavist bean {DoUfhos LaUali), I'lkosaiit/fs curumeriiia, 

 and mulberry. 



In view of the importance of cotton, ground nuts and 

 cowpeas in the West Indies, the remaining part of this article 

 will be concerned with Shaw's work on the Rhizoctonia 

 disease of these crops and will end with a short account of his 

 conclusions as to the identity of the causative organisms. 



COTTON. Infected seedlings have a soft yellow patch on 

 the lower ] or ion of Ihc hypocotyl, and in bad cases the rot 



is sufficient to cause collapse of the seedling. The similarity 

 will be noticed between this 'damping oS' and that cau.sed by 

 Pythium; indeed, incidentally it may be stated that most 

 investigators now consider that many of the 'damping otl' 

 diseases attributed to Pythium are really caused by 

 Rhizoctonia. 



In India, l!hiz"ctoni i does not attack Jesi cotton (a variety 

 of Gossi/jiiiiiii ne'jln-ta) in the field; it seems to be restricted 

 to pot cultures of special varieties Diseased plants may 

 recover, but a second attack on the same plant never takes 

 place. Seedlings seem to be susceutilile only when quite 

 young. 



An examination of withered seedlings shows hyphae of 

 Rhizoctonia The branches tend to lie parallel, are closely 

 sep'ate and are constricted at the base— characteristic of 

 Rhizoctonia. The sclerotia are rounded bodies, exactly like 

 the sclerotia found by Shaw on jute seedlings, but rather 

 smaller, the average diameter being about 90 microns. Oa 

 agar- meat-extract medium the sclerotia may measure as 

 much as 150 microns in diameter. After discussing the 

 views of American authors and of P)alls in Egypt, Shaw 

 comes to the conclusion that cotton is attacked by Rhizoc- 

 tonia in America, Egypt and India, and the section of his 

 paper dealing with cotton concludes with an account of 

 inoculation experiments in which it is shown that: (1) no 

 successful inoculations took place on ded cotton in the field; 

 (2) grown in pots, inoculated desi cotton showed a mortality 

 of 20 to 30 per cent : (3) 'khaki' variety grown in pots gave 

 a mortality of 90 per cent. 



GKOUND NUT. Ithizoctonia was originally observed on 

 the 'seeds' of this plant. The pericarp had a mottled appear- 

 ance showing discoloured patches. Hyphae were found in 

 the pericarp and also within the embryo. Portions of peri- 

 carp were incubated in sterile petri dishes and a vigorous 

 growth of Rhizoctonia hyphae was obtained, which resembled 

 the Rhizoctonia of cotton and jute. 



Pour of these infected seeds were sterilized with formalin 

 and kept moist, but only one failed to succumb to the disease. 

 Later in the year infected ground nut plants were found on 

 the Pusa Farm; the upper portion of ihe plants appeared 

 brown and withered, while at the ground level, the stem was 

 of a dark-brown colour; in this portion hyphae and sclerotia 

 of Rhizoctonia were particularly abundant. The morpho- 

 logical features of the Rhizoctonia of ground nuts agreed 

 exactly with those of the fungus on cotton and jute. In 

 the inoculation experiments, about 30 per cent, of the 

 inoculations were .successful. If the ground nut was first 

 wounded the percentage of deaths reached as much as fifty; 

 this plant also seemed particularly susceptible to attack at 

 the growing-point. 



cowi'K.A. Tlie syniptoms of attack in the case of this 

 plant are the s;irae as those already described for the 

 ground nut, and the fungus also resembles that of the other 

 three hosts. In the early stages of infection a red-brown 

 discoloration appears upon the stem and slowly spreads; the 

 stem ultimately becomes fiaccid and colla|>ses. Sclerotia are 

 formed abundantly. Infections from agar cultures on 

 unwounded plants gave »n average mortality of 50 per cent.; 

 by wounding, the mortality reached as high as 80 per cent, 

 of the infections. 



Leaving the^ consideration of the behaviour of the 

 fungus on various host plants, attention miy now- be given 

 shortly to the parts of the work that dealt with cross- 

 inoculations, and the identity of the fungus, 



( i;os> iNorui..\TiONs. Ericksson, working in Denmark, 

 was able to make lihizoctonia pass from the carrot to the beet. 

 Its virulence upon beet, however, was greatly increased after 



