17i 



THE agricultuhal news. 



May 20, 1916. 



PLANT DISEASES. 



PINE-APPLE WILT. 



An affection of pine-apples occurring on trial plots at 

 lirove Botanic Station, Montserrat, has recently received 

 attention, and is discussed below. 



The plots in question were planted in .July-October 1914, 

 and the affection was first noticed about September 1915. 

 A plot at Elherton, on heavier land, also became diseased 

 after making good growth for about twelve months. The 

 plants are from local stock, classed as varieties of the Eipley. 



According to the account given by Mr, W. Kobson, 

 (. urator, the first indication is a reddening of the foliage, 

 which later becomes strongly marked, and the leaves wither 

 from the tip downwards. 



More than half of the |-acre plot is now affected, 

 and the disease continues to spread. Its progress is not very 

 rapid: e.g. in one bed twelve plants which were slightly 

 afTectBd on December 1, 191-5, took until March to become 

 seriously affected, the rest oj the bed meanwhile beginning 

 to show signs of disease. 



The writer took an opportunity of inspecting the plots 

 when passing Montserrat in ilarch. The general appearance 

 is that of a slowly progressive drooping and wilting of the 

 leaves, accompanied by loss of colour, and ending in the 

 complete drying up of the plant. Mr. Eobson feels quite 

 certain that the malady spreads to plants adjacent to those 

 first affected, and the appearance of the beds supports this 

 idea. 



Specimens forwarded later exhibit the progression of the 

 disease, and show quite clearly that it is a question of root 

 decay. The worst affected plant had hardlj' any functioning 

 roots, the least affected was fairly well provided, and the others 

 were intermediate. In all the specimeTis the actual tissues 

 of the .stems, apart from the root traces, which were dis- 

 coloured, were quite .sound, thus differentiating this disease 

 from the one .seen at La Ouerite, St. Kitts, in 1914, described 

 in the At/ricutiurdl A'eivx, Yol. XIII. p. 190 Many of the 

 more rw'cntly developed )-oots were twisted around the stem. 



The affection conforms to the condition known as pine- 

 apple wilt or blight, which seems to be well known in all the 

 principal countries in which the crop is grown. An adequate 

 description of it, referring to specimens received at this Office 

 from an uu-named source, was given as early as 1902 in 

 thf Ayrirultu7al Newa, yo\. I, p. 191. It was described by 

 Stockdale, under the names of tangle root and lilight, in 

 the West Indian BuUe'in, Vol. VI ll pp. loS-fil, and has 

 attracted considerable attention in .Jamaica. Specimens 

 similarly affected were forwaided by Mr. Kobson from (jrove 

 in 1907, and from Trants in 1913. 



In the specimens under consideration there are present 

 in the roots from an early stage of their failure, fungus 

 hyphae occupying the vessels, and the presence of hyphae is 

 referred to by most writers on the subject. Most commonly 

 the fungus is referred to as a Fumrium. L. 1). Larsen (i !■) 

 obtained T/iie/aviopnis paradoxa, Trickuderma lignorum, 

 and a Fusurium from diseased roots, but was unable to 

 reproduce the disease by inoculation. The presence of 

 such fungi on the roots is not of nmch value as evidence 

 (>f their pathogenic nature unless a particular fungus is 

 well-marked and constant, and these conditions are not 

 satisfied in this case. The evidence which is most sug- 

 gestive of a parasitic origin for the disease, is that with 

 regard to its communication from one plant to another, 

 but in this respect the evidence from different countries 

 is conflicting. Smith (i) sa}'8: 'In practice we have 



reason to believe that a diseased stock will prove a 

 centre of infection for surrounding plants.' Lucas (e) says: 

 'In a field of Eipley pine-apple plants after the wilt makes 

 a start, no matter how small the affected area might be, it 

 will in an incredibly short space of time spread over acres- 

 and in a few months will completely kill every plant, no- 

 matter whether the plants be old or young, but this disease- 

 seldom allows the plant to become of any age before it 

 completes its woik of ruin;' Henricksen andIorns(!i) and 

 Wester (i i) adopt the view that the disease is infectious and 

 trnsmissible to suckers, but do not say that this is based 

 on actual observation. On the other hand, Tryon (s) states 

 definitely that affected suckers planted uncer good conditions, 

 will produce healthy plants, and further that the disease- 

 is only exceptionally communicated from plant to plant. 

 Larsen ( i u ) also says, 'The malady as occurring in Hawaii 

 does not seem to spread from one plant to its neighbour, but 

 appears in a sporadic manner, affecting one plant here and 

 another there. Thus far it has been of most general occur- 

 rence in the wetter districts and in fields of yf>ung and 

 healthy plants.' 



Accordingly there are two sets of ideas more or less 

 opposed with regard to the nature of this disease: 



(a) That it is due to infection with a fungus capable of 

 definite parasitism, causing a disease resembling in its nnture 

 those produced by the parasitic soil Fusaria. This would 

 involve the very early eradication of affected plants and 

 their immediate neighbours, some attempt at steriliza- 

 tion of the surrounding soil (say with quicklime), the 

 avoidance for n long time (at least a year and very 

 possibly several years) of infected land for replanting, and 

 very careful precautions against infecting new land with, 

 any sort of material from the old. The most hopeful 

 measure in such a case is the search for, and adoption 

 of suitable resista)it varieties. In forwarding specimens in 

 1907, Mr. Eobson stated that the Eed Spanish variety was 

 quite immune. In the present case, in a plot of Red Spanish 

 situated between two very badly diseased plots of the local 

 (Eipley) type, nine out of fifty-seven plants show some indi- 

 cation of the same disease Lucas («) says: 'all varieties of 

 the yueen family (which includes the Ripley) are of delicate 



constitution, subject to Black Heart and Wilt The 



Red Spanish is vigorous, free from disease and easy to grow.' 



(b) That the disease is primarily due to some unfavour- 

 able condition or conditions of growth, including physically 

 unsuitable, poorly prepared, insufficiently drained and culti- 

 vated .soil (all leading to a restriction of aeration): poverty of 

 soil, lack of water, and poorly prepared planting material; 

 the.^e conditions being either sufficient of themselves to brin" 

 about the failure of the plant, or rendering it liable to attacks 

 of one or more weakly jiarasitic fungi, thus producing a disease 

 similar in nature to the root disease of sugar-cane associated 

 with JJarnsmiux. 



Taking these conditions for discussion in the order 

 named: (1) Aeration. It is universally admitted that this 

 plant is intolerant of any restriction of the air supply 

 to its roots. (2) Nutrition. Given good aeration the con- 

 sistency of the soil is of minor importance: it appears that 

 the plant will grow well in any soil rich in humus, but 

 especially in light soil it is necessary that the supply of food 

 be kept up. The plant will grow well in leaf mould until 

 the food is exhausted, and is giown in Florida in sand with 

 the addition of chemical manures. It would seem that .some 

 difficulties have arisen through the supposed aliility of the 

 pLint to thrive in any light soil having resulted in the choice 

 of land in a dried-out or exhausted condition. It is 

 imjiortant to note in this connexion that the plant has a very 



