TURNIP ROT.

Timaru Herald, Volume XC, Issue 13280, 8 May 1907, Page 7

TURNIP ROT.

(To the Editor of the Timaru Herald.) Sir; —The farmers noiv see that the turnip crop is not to be depended on, as the ro. haj overtaken most of the crops, more or less. I have looked at a good .nany of the turnips that turned sick looking, and found most of them were illfoimed in shape, and cracked- in the outer akin, and were dwarfed and had never manured. Score of those that had been doing well fcr a time, and were not attacktd by ro':, had brown streaks down ihs st:m to the root of the turnip. In some of Llio-oe well advanced in the rotten stage the whole heart had gone, and the

.t'side ski", was all that was left. It h>>ks l : ke Ilic disease bacteriologists call, the • hits rot of turnips. An organism •i mod as Pseudomonas destructans 'ns been described recently by Potter, as -the' ca-.i-e. '" Tnc leaves of flie infected p'a.i-s iir ii \vi!i>v «'nd .drop, and the interior .oj iiii- l'Kiii ;n Uvi. or three weeks eccfes pulpy an I rottei. The bacterium s.f'ms the oc-11 walls and secretes an enemy, which dissolves the middle lamella of the cells of the turnip root. The protoplasm, separates from the cell walls, and turns brown, possibly as the result of the toxic action, of oxalic acid, which is produced by the bacterium. The organism appears: to gain an entrance into the tissues of the turnip through wounds." Since panning the foregoing I see it s'lated in the papers that the diser.se- is caused by : a By, which deposits eggs in the centre of the shaw. ' The eggs in turn develop into an insect net unlike a weivil, and is protected by a web not unlike: that spun by a spider, and so for h. TOiat may be so. but seme five : weeks ago'there was''; a telegram in all the papers in the colony stating that in the Xorth Island the black rot had attacked the. turnips. About that time "a neighbouring farmer pointed out to me that the diamond-back, moth was cutting the leaves of the turnips. This they did to some' extent, but it came on to rain for a day, and there was no more damage, done by them. Now that damage ;;is.>;pnrthe turnips to this. day.. At the same" tinie these myriads of flies, like grass-hopp?rs were flying about. I had a mixed let of turnips in my field—swedes land all the different hard and soft turnips. I kept a good lookout on what was going :onj arid after I saw the paragraph referred to in the papers I made further investigations. I found-that where any'of the ;leaves had fallen on the turnip, and there was any broken skin on the turnip, the rot had started its work. In some of the turnips I found the ro^: had started in the root)of. the ground. Some of the turnips that were well shaped, with no deformed parts.-that had lost all their leaves were starting io put on fresh leaves. Thai showed.that-"as" the bacteria had not obtained an entry into any part of the p 1 antits root was prepared to send forth p. frc<'h lot of leave". . Tn all parts affected entrance was obtained through a cut or .a hole or some opening in the skin. I cut some' of the turnip into small pieces to see if I could get some insect inside ihe turnips, but I could find none. 'As sthe swede turnips were not affected 1 have come to the conclusion that the disease is " white rot," as black rot. can effect an en'ranee into th? tissues of plants through normal channels, and is ab-e directly lo' set up disease in the infected plant. John Fercival, in his work on '" Agrir-"'* —-" Botany," on this sub ; ect writes: '.'Ei ca, ■::, of plants caused by bacteria: During the last few years a number of ailments of plants have been a'tributed to the agency of bacteria, but only in few cases has any satisfactory proof been forthcoming for the belief that bacteria alone are the direct cause of these diseases. In many cases of plant disease, where the tissues are found to-be undergoing decay, and in which bacteria are present, the trouble is primarly due to other causes, such as insect attack, the attacks of parasitic fungi, or the action of frost, heat, or adverse soil .conditions.- The production of w-ounds; and the death of the plant- tissues by~ there means allows of the entrance of bacteria, and provide the latter wi'h dead organic material upon which they can live and carry on various processes of putrefaction and decay. It must be noticed, however, that even in these complicated case's it is quite possible that the bacteria may be the chief cause of the destructive effects observable upon the plants, although their entrance can only be made after injuries previously inflicted by other agents. There is little doubt that a considerable number of common ailments are of this nature, but recently it has been convincingly shown by Erwin T. Smith, H. F. Russell, and others that some species of bacteria can. effect an entrance into the tissues of plants through normal channels, and are able directly to set up disease in the infected plant. ' Black rot' of cabbage—one of the best examples of bacterial plant diseases—is that known as ' brown rot' or ' black rot' of cabbage. The disease is not uncommon in this country, and is sometimes met with upon 'turnips, swedes, kale, cauliflower, and other eiueiferous plan.s. first stages of the disease the affected cabbages show pale yellowish-green patches, near the edges of the leaves or around holes or places torn or eaten by

insects. The patches turn brown. TTk' leaf wilts and shrinks, becoming tough sornewhat like parchment. Plants badly affected 1 becoma ■stunted, lose their leaves, anil may die altogether. In such cases the dark colour of the vascular tissues of the leaves is continued from the leaf into the stem, and on cutting across the latter the wood of tho vascular cylinder is stained a dark brown or blackish tint. Infected cabbages form no heads or only very small ones, and the roots of turnips develop very poorly. The disease is caused by a bacterium named Psewdomonas compestris Pammel. It is a yellow, rod-shaped motile organism with a single ciliuin. I'he bacterium frequ?nily enters through the waterpores which are present on the teeth at the edges of the leaves, and most easily gain admittance in damp, warm weather when drops b'f water are excreted by these pores and stand like dew -drops along the leaf margins. Slugs and the larvae of insects carry them from the soils, and from one infetced plant to another, the bacteria eventually entering into the vascular tissues exposed at the parts gnawed and bitten hy thes? pests. Tho bacteria live and multiply in alkaline solutions present in. the vessels r,r traehae.of the vascular bundles, and do not- invade tha prenchymatov.s tissue of the leaf. Ihe vessels become blocked with a brown substance which prevents the proper conduction of water, henco the withering of the diseased leaves. It is advisable to remove and burn diseased plants as soon as these are noticed, and on ground where the trouble has been prevalent cruciferous plants should not be- grown for a time. Now this disease has no symptoms of the disease known as "ciubroot," " finger-and-tos." "anibuiy,"' and " canker," so far a" I have seen, and I have seen no roots of th 3 turnips with any nodules on them. Some- of them were well grown and healthy and some were dwarfed, but had an opening in the skin where tho trouble made a start from. I am almost certain that the black rot and the white rot is at work en the turnip, but you have many readers of the. " Timaru Herald" who are farmers, and soma of them might give their experience. I am, etc;, DAVID MAXWELL. Cave, May 'sth.