M. A. WAHID, R. J. STEIB, S. J. P. CHILTON REFERENCES. In the absence of the authors the following paper was laid on the table.

Transcription

1 M. A. WAHID, R. J. STEIB, S. J. P. CHILTON REFERENCES 1 ABBOTT, E. V Red rot of sugarcane. U S D.A. Tech. Bull pp. 2 CHONA, R. L. and C. W. PADWICK More light on the red rot epidemic. Indzan Farming 3: EDGERTON, C. W The red rot of sugarcane La. Agvzc. Expt. Sta. Bull pp. 4 PADWICK, G. W The red rot epidemic. Indzan Farmzng I: STEIB, R. J. and S. J. P. CHILTON Infection of sugarcane stalks by the red rot fungus, Physalospora tucumanenszs Speg. Phytopath. 41: In the absence of the authors the following paper was laid on the table. THE LIFE HISTORY OF THE CAUSAL ORGANISM OF LEAF BLIGHT OF SUGARCANE* W. Y. YEN and C. C. CHI Taiwan Provincial College of Agriculture, and Taiwan Sugar Experiment Station, (Pingtung Station), res$ectively INTRODUCTION The leaf blight of sugarcane had been reported by MATSUMOTO and YAMAMOTO*" in 1934 as a new disease caused by a new species of Cercospora. It was identified as Cercospora taiwanensis Mat, et Yam, while the perfect stage of this causal organism remained unknown. The authors had made some investigations on leaf blight disease in Taiwan last year, and obtained the perfect stage of Cercos$ora taiwanensis in cultures in laboratory as well as in plantations under natural condition. The present paper deals especially with the perfect stag; of Cercosfiora taiwanensis. From the field survey, the authors found that the leaf blight disease occurred throughout the whole year and was prevalent in some districts of Taiwan. The sugarcane varieties such as Co. 285, Co. x, F. 109, F. 134, P.O. J. 2883, P.T , and F were found to be the most susceptible to this disease; F. 107, F. 108 and F. 132 slightly resistant while the varieties of P.O. J and F were highly resistant. The disease is chiefly infected on the leaf blade as well as on the leaf sheath, especially in the later stage of the affected plants. They present the typical lesions almost a reddish purple colour to the naked eye (Plate I). At the later stage of the disease there are many minute black dots arranged in the marginal portion of the lesions and immersed in the dead tissue of the heavily affected leaves. These black dots are the fruiting bodies of the perfect stage of the causal organism. By way of isolation of the fungus, some small pieces, about 2 mm. in length and I mm. in width, of leaf tissues were cut off from the initially diseased spot areas and sterilized in solution of corrosive sublimate (I : 1000) for half a minute. After that, they * Partial abstract of a manuscript wlth the title "Studles on Leaf Bllght of Sugar Cane", now in press. ** MATSUMOTO, T. and YAMAMOTO, Y Three Importailt Leaf Spot Diseases of Sugarcaile n Taiwan (Formosa). Jour. Soc. Trop. Agri. 6 (3):

2 940 PATHOLOGY SECTION were washed thoroughly with sterile water for 3 times and at last transferred to the nutrient agar media in Petri dishes. These dishes wereplaced in the incubator maintained at a constant temperature (25" C. or 28O C.). Two or three days later, the primitive colonies of fungus were obtained. Plate I. Symptoms : A. on leaf blade ; B. on leaf sheath (left: Co. x; right: F. 134). U THE IMPERFECT STAGE OF THE CAUSAL ORGANrSM On the lower surface of the leaves, around the lesions there are many external hyphae which are hyaline, s@h-, branched, p (mostly p) in diameter. The conidiophores &;is'; di'k'ctfi from the kxternal hyphae at right angles to the latter, pale olivaceous brown to tli& b&el and m;,$ipor less paler toward the end, singly and unbranched, straight or sligk?tly geniculate, Aontinuous or 1-7 septate (mostly 2-4 septate), generally p in length (rarely 156 p in length) and 3-4 p in width. The conidia are of the type of cercospora, filiform, more slender toward the end and obclavate on the base, straight or slightly curved, hyaline to subhyaline, 3-5 septate for the small ones and 9-15 septate for the large ones (mostly 5-10 septate), p in length and 2.4-4p in width (mostly x p). THE PERFECT STAGE OF THE CAUSAL ORGANISM

3 W. Y. YEN, C. C. CHI or amphigenous, spherical to subspherical or ovoid, glabrous, dark in colour to the naked eye and dark-brown under the microscope, p in length and p in width (mostly x p) ; perithecial wall membranaceous, formed by polygonous cells, deep brown in colour ; ostiole raised, protursive, mammiform (papilate), p in length and p in width (Plate 11, A) ; asci hyaline, ovoid to oblong-ovoid, straight or slightly curved, x p (mostly x p), roundish on the end and attenuated toward the base, containing eight ascospores; ascus wall thin and hyaline, gelatinous and thick (mostly 3-5 p in thickness) to the top in the young stage (Plate 11, B) ; ascospores oblong-fusiform, slight curved, 3 septate (rarely 4 septate), distinctly constricted at septa, brownish in colour for the immature and dark-brown for the mature spores, p in length and ,u in width (mostly x p) (Plate 11, C) ; paraphyses hyaline, filiform, slender, unbranched, and as long as the asci (Plate 11, B). Plate 2. Perfect stage of Leptosphaerza tazwanenszs: A. Section of leaf blade showing the natural appearances of penthecmm x 100; B. Mass of cultural asci and paraphyses x 300; C. TWO individual ascospores from field x , TAXONOMY OF THE FUNGUS In the course of the studies on sugarcane diseases, the authors have observed six different species of Cercospora which caused different diseases on leaf blade or leaf sheath of sugarcane. (I) Cercospora vaginae caused "Red spot on leaf sheath"; (2) Cercospora kopkei caused "Yellow spot" on the leaf blade; (3) Cercospora stage of Lefitosphaeria sacchari caused "Ring spot" on the leaf blade; (4) Cercospora stage of Erios$haeria sacchari caused "Purple spot" on the leaf blade; (5) Cercospora stage (namely Cercospora taiwanensis) of the authors' caused "Leaf blight" on the leaf blade as well as on the leaf sheath; and (6) Cercospora sp. caused "Small-spot type leaf blight" on the leaf blade. The former two species of Cercospora (C. vaginae and C. kofikei) are quite different from the authors' fungus in the appearance of the diseased spots, in the genital mode of their conidiophores and in the type of their conidia. The other three species of Cercospora are very similar to the imperfect stage (C. taiwanensis) of the authors' with the conidiophores produced directly from the external hyphae with presence of the filiform conidia. When these four species of Cercospora are growing on sugarcane (for example F. 134)~ the appearances of the diseased spots are different and can be distinguished from one another. I

4 942 PATHOLOGY SECTION In Taiwan, there is a very common species of Leptosphaeria (L, sacckari) which caused "Ring spot" on the leaf blade of sugarcane. Its perfect stage is somewhat similar to that found by the authors to the nalted eye, but it can be easily distinguished from each other by the position from which the perithecia grows, by the shape of ascus (cylindric fusiform), by the ascus and ascospore measurements (39-62 X 6-9 p and x 5 p, respectively) and by the colour of ascospores (yellowish brown). Accor~lin$ to the above systematic characters the present fungus is considered as a new Leptosphssria and given the name of Le$tos$kaerial taiwanensis (Mat. et Yam.) Yen et Chi. The Latin diagnosis of the fungus is as follows: Le$'tos$kaeria taiwanensis ~ (Mat. et Yam.) Yen et Chi. Maculis amphigenis, in foliis, raro in foliis vaginarum, initio minutis, anguste fusiformis, flavis, 5-26 x mm., postea expansis, late fusiformis, rubro-sanguinis, x mm. ; caespitulis hypophyllis vel amphigenis, vix visibilibus; hyphis sterilibus, hyalinis, p diametris (plerumque 1-13 p) ; conidiophoris erectis, non fasciculatis, haud ramosis, pallide brunneis, sursum attenuatis et subhyalinis, geniculatis, 1-7 septatis (plerumque 2-4 septatis), non constrictis, p longis, 3-4 p latis (plerumque p longis) ; conidiis anguste filiformi-obclavatis, sursum attenuatis, leniter curvulis, raro rectis, hyalinis, non constrictis, 3-15 septatis (plerumque 5-10 septatis), p longis, /u latis (plerumque x p). Peritheciis numerosis, sparsis, immersis, in laminis folirum, haud in foliis vaginarum, amphygenis, globosis aut subglobosis, glabris, atris vel nigrobrunneis, ostiolis elevatis pertundentribus ( x p), membranaceis, x p (plerum- que x p) ; membranacee fusce contextis ; ascis ovoidis vel oblongo-ovoidis, brevissime pedicellatis, filiformi-paraphysatis, rectis vel leniter curvulis, x y (plerumque x p), apice rotundatis, basique attenuatis, octosporis; membranacee hyalinis ( p crassitudia); sporidiis oblique quadrustichis aut polystichis, oblongo-fusoideis, utrimque attenuatoobtusis, plerumque leniter curvulis, x p (plerumque X p), 3 septatis, ad septa constrictis, brunneis aut castaneo-brunneis. Hab. in foliis putrescentibus Sacckarum oficinarum L. in Whalien, Taiwan, China, Leg. W.Y. Yen, 1952, 11, i3 (F. 134, Co. x); in Taichung, Taiwsn, China, Leg. W.Y. Yen et T.W. Chen, 1952,111,10 (P.O. J. 2883) ; in Pulee, Taiwan, China, Leg. W.Y. Yen, 1952, IV, 3 (P.O. J. 2882). CULTURAL CHARACTERS OF LEPTOSPHAERIA TAIWANENSIS Five kinds of media had been used in the cultural studies; namely corn agar, bean agar, onion agar, carrot agar and potato dextrose agar. All these media were prepared by the usual method. All tests were repeated three times using five replications for each trial. In the test, the corn agar medium was found to be the most favourable for the growth of the fungus, followed by bean agar, onion agar, carrot agar and potato dextrose agar in descending order. The colony covered the whole plate (88 mm. in diameter) on the corn agar medium within 11 days at 30" C. The maximum temperature for the growth of the fungus was about 35" C., and the optimum temperature, 25" C. to 30" C. The minimum temperature has not yet been ascertained in the laboratory. According to the fieid observations of different districts over this island, this fungus was active even in winter. It was estimated that the mini-

5 . - W. Y. YEN, C. C. CHI INOCULATION OF LEPTOSPHAERIA TAIWANENSIS The inoculations were made by different methods in the present studies. Some small pieces of mycelial mat of new culture of 7 to 10 days old were transferred on the leaf blades of sugarcane seedlings of the variety P.O. J. 2883, kept in a glass jar under the condition of saturated humidity and constant temperature (28" C.). After 3 days, the young leaves presented some small yellow diseased spots. Seven days later, the spots developed in size and became oblong-fusiform lesion or large spots with irregular borders, Plate 3. Typical lesions produced on leaf blade after inoculatioil with cultural ascospores. and the colour of the lesion changed from yellow to reddish brown. After 10 to 13 days, the conidia of Cercospora type appeared. The symptoms were exactly similar to that pro- 1 duced under natural conditions. When the seedlings of P.O. J inoculated with the same method as leaf blades mentioned above were placed in the corridor of the laboratpry, the humidity and temperature were not controlled, the young leaf of sugarcane showed typical diseased spots which were similar to that produced in natural condition both in shape and in colour. If the leaves of seedling of P.O. J were inoculated with the perithecia or the mature ascospores found from the tissues of diseased and dead leaves in the field, the typical symptoms might also be produced from inoculated leaves after two weeks (Plate 111).

6 934 PATHOLOGY SECTION 1 FORMATION OF PERITHECIA IN CULTURAL MEDIA The fructification of the perfect stage of Leptosphaeria taiwanensis had been obtained from different cultural media, such as potato dextrose agar, carrot agar, bean agar and especially the sterilized green leaf blade. A great deal of black dots was produced easily in 2-3 weeks at 25 to 30" C. while the latter was used as a medium. According to the microscopri: examinations, the black granul'ations were the true formation of perithecia of the fungus. The perithecia which the asci and paraphyses produced in the usual manner were spherical, ~ub~spherical or oblong-ovoid and dark brown in colour. The asci and ascospores were morphologically similar to that formed in the tissue of the diseased leaves of sugarcane in the field. DISCUSSION AND CONCLUSION The perfect stage of the causal organism of leaf blight of sugarcane has not yet been secured since this disease was reported by MATSUMOTO and YAMAMOTO~~ 1934 In 1951 the authors obtained the perfect stage of C. tazwanenszs in the laboratory as well as 111 the field. For the morphology of this fungus was clifferent from those other five Cercospora species caused sugarcane d~seases in Taiwan, and from the repeated inoculations it was proved that this fungus is, no doubt, the perfect stage of C. taiwanensis. Therefore the name of this fungus - ~e~tos~hae$ia taiwanensis (Mat. et Yam ) Yen et Chi - was given. The perithecia of this fungus were occurred scattered and immersed in the margin of the lesions of diseased leaves. They may be obtained also on different media when the cultivation of this fungus was made. They produced more abundantly on the sterilized green leaf blade which was used as a medium. In the medlal test, the corn agar was found to be the most favourable for the growth of this fungus. The opt~mum temperature of this fungus was 25-3o C, maximum temperature about 35'C., minimum temperature has not yet been ascertained but from the field investigation, the minimum temperature was estimated about 10" C.. i: