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PCCORD OFFICE

Peference -

LC.O.882/12

PUBLIC RECORD OFFICE, LONDON |

ALLY WITHIQUI PERMISSION OF THE RE REPRODUCED. PHOTOGRAPHIC-)

COPYRIGHT PHOTOGRAPH-NOT TO'

REPORT OF MR. S. F. ASHBY ON HIS VISIT TO MAURITIUS, 1929.

TO THE DIRECTOR, IMPERIAL BUREAU OF MYCOLOGY.

I left England on the 9th October and Marseilles on the 10th, and arrived at Mauritius on the 16th November. After spending four weeks ashore, I left on the 13th December, had five days ashore at Réunion and reached Marseilles on the 25th January and England on the 26th.

Object of the visit.

My purpose in going to Mauritius was mainly twofold :---

1. To see the most important diseases which were injuring the varieties of sugar-cane in general cultivation and to obtain information, at first hand, about their severity and the means of controlling them which have been or may be put into operation.

2. To note the practical interest which the planters were taking in the newer seedling canes, because, apart from the probable superior yielding powers of some of them over the varieties now mostly grown, the cultivation of resistant kinds is everywhere recognized as one of the most effective ways of controlling diseases.

The crop of 1929 had been, for the most part, reaped on my arrival, but, with the aid of the itinerary prepared in advance by the Director of Agriculture, I was able, without delay, to visit about a score of representative estates in all the districts and at most of them to see mature standing cane, and at all, of course, immature virgins (plants) and young ratoons. The work of observation was greatly facilitated by the fact that the diseases of any consequence in the Island had been studied and described by the Botanist and Mycologist in the course of his six years' service, so that I knew already what there was to see, and as he was with me on all occasions there was no difficulty in finding and recognizing the four outstanding specific diseases-Gummosis or Gumming Disease, Leaf Scald or Java Gum Disease, Red Rot, and Smut. Instances of Root Disease were seen also, and a number of minor affections including Eyespot, Ringspot, Brown Spot, Pokkah Bong, Bunch Top, and Twisted Top, and, on one variety alone, Streak. Four serious diseases elsewhere, Mosaic, Fiji Disease, Sereh, and Leaf Stripe or Downy Mildew, do not appear to be present on sugar-cane in Mauritius.

The varieties now in general cultivation on the estates are White Tanna, Striped Tanna, the locally raised seedlings M.P. 55 and M.P. 131 and the introduced seedling D.K. 74 (the Demerara seedling D. 74). White Tanna is the dominant variety occupying from 75 to over 90 per cent. of the cultivated area on most estates in the east and south (Flacq, Grand Port, and Savanne) and on a number of estates in the central uplands (Moka, Plains Wilhelm). In the two northern low- land districts (Pamplemousse and Riviere du Rempart) where the rainfall is less and the soil frequently lighter, this variety shares the area on more equal terms with a number of other kinds including the introduced seedlings D. 109 and D. 130 and to a small but increasing extent P.O.J. 213.

Cases of the bacterial vascular disease, Leaf Scald, were seen on mature standing virgins and ratoons of White Tanna (and other Tanna canes) at all estates where the crop was not finished, and on the young ratoon shoots of that variety at every estate visited. On the infected mature stalks, the buds had sprouted as a rule at very node, giving rise to short side shoots bearing reduced leaves with white stripes; the foliage at the top of the stalk had become discoloured and withered prematurely, and the cane when split showed numerous red fibres at many or most of the nodes and some in the internodes, from which there was no ooze of gum. The young infected ratoon shoots were frequently stunted and bore leaves showing one or more long, narrow white stripes. The symptoms were characteristic of the chronic phase of Leaf Scald as described by D. S. North in Australia, and Mr. Shepherd has isolated a bacterium on several occasions from infected canes which is quite similar to the form (Bacterium albilineans Ashby) causing the disease in Australia. Although the disease is evidently widespread on the Tanna canes in the Island, cases have been found rarely on the other varieties in general cultivation.

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