American. SugarcaneJ>eague, New Orleans, La. and Louisiana Agricultural Experiment Station, Baton Rouge, La.

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1 524 Pathology Section Mr. Hughes showed a sel;ies ofphotographs which are to appear in a Technical Communication in the near future. He pointed out that these spectacular photographs-the black setae were very obvious in the larger magniflcatdons-c-would be the firatncw illustrations of the imperfect stage of the Physalospol'a tucurnanensie for more than 40 years.. Mr. Martin, in congratulating Mr. Hughes on the- excellence of the photographs said he had always thought that papers were not illustrated sufficiently. He could not. recall having seen any illustration of red rot in the same class as the photographs shown. n reply to Mr. Robinson, Mr. Hughes said that a resistance trial was to be planted this year. The site was on a dry ridge at the pathology plot of the Bureau of Sugar Experiment Stations near Brisbane. n all probability natural infection only would be relied on, and counts would be made late in the season when the canes were overmature. :ro laboratory trials would be done as these did not give a reliable indication of field resistance. He inquired whether anyone present had information or had done work on the resistance to red rot in relation to the amount of certain phenolic aubsnancos present in the cane. As no information was forthcoming, the discussion was closed.. The paper on Phytophthora rot was presented to the meeting by Mr. Hughes. Paper THE PHYTOPHTHORA ROT OF SUGAR-CANE SEED PECES N LOUSANA... R. J. STEB AND S.J. P. CHLTON.. American. SugarcaneJ>eague, New Orleans, La. and Louisiana Agricultural Experiment Station, Baton Rouge, La. n the spring of 1947, it was found that certain fields of sugar cane whi~h had been. planted the previous fall, gave very poor stands. These were in rather wet places. solations gave a few cultures of fungi which were identified as belonging to-the genus Phytophthora. The poor stands were of particular interest, si~ce one of the varieties (C.P )was very resistant to Physalospora tucumanensis Speg. (Oolletotrichum falcatum Went), the fungus causing the disease known as red rot. n 1948, further isolations were made from dead and dying seed cane which had been planted in the fall of 1947, and consistent isolations of Phytophthora were obtained. An examination of the literature indicated that this group of fungi apparently had not been reported as pathogenic to sugar cane. t is the purpose of this paper to describe the symptoms and to present evidence that a disease of sugar cane, named the Phytophthom rot, occurs in Louisiana.. SYMPTOMS The disease, Phytophthora rot, is very similar in the advanced stages to red rot. However, when a cane is first attacked by this fungus, the split stalk shows water soaking of the tissue. As the disease progresses', there is a salmon-pink to orange-red discolouration appearing in streaks throughout the interior of the stalk. With yellow-stalked varieties such as C. P , these salmon coloured streaks, when close to the; surface, will show through the rind of the cane in a very characteristic manner. With varieties having a purple rind, -these streaks may also be seen, but the colour is darker and the streaks not so clear cut. nthe

2 R. j. Steib and S.]. P. Chilton 525 advan~ed stages of the disease, the whole cane becomes water soaked, there is a darkening of the salmon-pink to a reddish-brown, and an odour similar to that of fermenting fruit is rather characteristic, if the disease. is not too far advanced. SOLATON OF THE FUNGUS When isolabions were first begun with canes showing these symptoms, very few cultures were obtained. However, it was found that if the cane stalk were split open and a sterile cork borer with a diameter of 7-10 mm, were used to obtain tissue for transfer, a large proportion of the diseased stalks gave cultures of Phytophthora. Further work showed that the fungus could be isolated from the, nodes if well sterilized and large pieces of tissue were removed with a sterile scalpel and placed on agar. ' DSTRBUTON OF THE FUNGUS N LOUSANA A large number of isolations, which are summarized in Table 1, were made in the spring of t can be seen that this fungus was isolated from: a high percentage of the internodes and nodes of diseased stalks. The distribution of the disease seems widespread since the fungus was found in 12 of the 14 parishes from which collections of diseased specimens were made. Table 2 shows that the fungus was isolated from many of the varieties released for commercial use in this State. TABLE 1 OCCURRENCE OF Phytophthom N DSEASED SEED PECES OF SUGAR CANE N THE SPRNG OF Parish No. nodes and internodes plated Per cent. giving Phsttophthora. Ascension Assumption Avoyelles East Baton Rouge beria Lafayette Lafourche Pointe Coupee Rapides.. St. JalleS St. John.. St. Mary.Terrebonne West Baton Rouge... '1 30 \ Total 2, DENTTY OF CULTURES Three distinct cultural types were isolated from the various seed pieces. All three were at times obtained from the samediseased stalk. One strain was clearly Phytophthora erythroseptica, forming zoospores within thezoosporangia and amphigenous antheridia. The other two strains at present can only be assigned to the genus Phytophthora. Although erratic, zoosporangia and zoospore formation.. typical of Phytophthom could be induced by placing the cultures on nutrient medium and then transferring to ~istilled water.

3 ,526 Pathology Section TABLE 2 RE,SUL~S; 0; SOL4TONS OF Phy'tophthm;ct FROM '8 VARETES OF E:UGAR CANE G~OWN N LOUSANA,,. Variety.. Phytophthom from leaf scars and buds Phqjtophihora' from interior nodes No. hodes Pel' eent., giving No. nodes P~r cent. giving plated fungus plated fungus Co. 290 ' ;." C.P.2!U20, C.P ,, 52 ' C.P , C.P C.P , C.P , C.P Totals.., PROOF OF PATHOGENCTY n the first test, made in the spring of '1947, single-eye pieces of O. P: were planted in 2-gallon crocks of sterilized soil to which Petri dish cultures of the three strains were added. Two crocks, with three single-eye pieces of cane in each crock were used for each isolate. Two crocks were left uninoculated as.controls: At the end of two months, the pieces were dug up and the seed pieces from the inoculated crocks showed typical pink streaks from which the fungi used to inoculate the soil were reisolated. The seed pieces planted in the uninoculated soil were free of the disease. n the second test, begun in the fall of 1948, 4-gallon crocks of sterilized soil were used. Each of fifteen isolates, comprising three cultural strains, coming 'from single hyphal tip isolations, were grown in Petri plates and added to two crocks of,soil. Four' crocks were used as controls. Ten two-eye 'seed pieces of were planted in each crock inoculated with an isolate of the fungus, and also in two of the control crocks. The other 17 were planted with two-eye pieces of O.P The crocks were kept in a room at 70 F. and were well watered. Two and a half months later, the seed pieces were examined. Tissue was plated from all discoloured nodes to make certain the fungus was present. Typical symptoms were produced. Figure 1 shows the seed pieces from the control and inoculated pots. n a third experiment, large tubs of sterilized soil were used. Two tubs were inoculated with a culture of each of the three cultural types, and two tubs were used as a control. Fifteen stalks of with four or more nodes were planted in one tub with each strain. Fifteen stalks of this variety of the same length were. planted in one tub in which the soil had not been infected with Phytophthora; The same was done using the variety O.P This gave two tubs for each strain and, two control tubs. The tubs were placed outside and were watered as needed. The experiment was begun November 22, 1948, and the canes dug up three months later and examined. The canes from the infested soils. all showed typical disease

4 R. f Steib and S. P. Chilton 527 TABLE 3 RESULTS OF TESTS WTH THREE STRANS OF Phsftophthora. WHEN NOCULATED NTO STALKS OF SUGAR qane AND PLANTED. (NOCULATED NOVEMBER 20, 1948.), ExaminedDecember 28, 1948 Average rating. of each variety *, Strain C.P.36,13 Co. 290 C.P C.P C.P t Average 4.1 t Average 3.9 1t Examined February 21, Examined March ~ \ , ') ' Average * 0 0;= no spread of disease. 5 = much spread through stalk. t Phytophthom e1 yth1'oscptica Figure.-Pathogenicity of Phytophthora to sugar-cane seed,pieces in sterilised soil. Left: check. Right: planted in inoculated.sotl.

5 528 Pathology Section ' ( symptoms and the three strains of Phytophthora were isolatedfromthl diseased tissue on platings. The canes from the uninoculated tubs were an free offymptoms. n a fourth experiment, 15 stalks of each of five varieties of sugar cane were inoculated with 15 cultures of Phsjtophthora, This was done by cutting two holes in each stalk with a cork borer and placing a piece of mycelium in eac~ hole. The cultures.were the same as used in the second test given above. ThesJ canes were then buried and dug up at three different tdmes, split and examinedfor the development of the disease. No development of disease was rated as 0 and nearly complete destruction of the stalk as 5. The'results given in: Table 3 show that the cultures were pathogenic and that varieties tended to differ in their resistance to' the cultures used. DSCUSSON From the aboveresults, there seems little doubt that members of the genus Phytophthora play an important role in the rotting of seed pieces in Louisiana, particularly when planted in wet areas. The relative importance of this disease as compared to red rot and that reported as caused by species of Pythium can only be determined by further observations and study. Preliminary tests indicate the presence in sugarcane of resistance to this disease. Techniques for evaluating resistance will be necessary. and must be developed. DSCUSSON Mr. Hughes expressed the opinion that this disease might have occurred in Queensland on C.P.36~62,although no isolations were possible at'the time the plants became affected.' Mr. Martin thought that the disease could be present in Hawaii, as he had seen symptoms' similar to those described here, but had never found the' causal organism... Dr. Hes said that in 1935 Miss Bolle had isolated a species of Phytophthom from cane in Java. t was, he thought, obtained more often on roots than on other parts of the cane plant. n reply to Mr. Martin, Mr. Hughes said that the so-called sour rot in D.1l35, symptoms of which included tissue breakdown and a sour conditiol, was mainly caused by rind disease. (i,'!