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Trans. Br, mycol. Soc. S9 (2), 313-349 (1972)

Printed in Great Britain

NOTES AND BRIEF ARTICLES

(With Plates 39-43 and 6 Text-figures)

VERTICILLIUM WILT OF COTTON IN TAMIL NADD

IVOR ISAAC

Unioersity College ofSwansea

AND T. T. PANADIAN, L. SARASWATHI-DEVI AND H . C. DUBE

Uniuersity Botany Department, Madras

Verticillium wilt of irrigated winter cotton plants (Gossypium hirsutum)during the cooler months of the year (October-February) has beenreported by Natarajan, Sivaprakasam & Ramakrishnan (1968) in somecotton-growing tracts ofCoimbatore district ofTamil Nadu (Madras State).The disease has attained serious proportions, losses of 70-90 % in seedcotton having been recorded by Srinivasan er971}. These earlier workers,however, found it difficult to isolate the pathogen from field-wilted cottonplants. For their experiments they had used an isolate of Verticillium,obtained from egg plant (Solanum melongena), raised in potted wilt-sicksoil and which they named V. albo-atrum R & B.

During a field trip to the abo ve wilt-affected areas of Coimbatore districtin January 197I, samples of field-wilted cotton plants were collected andbrought to Madras for isolation and pathogenicity studies. The results arebriefly reported here.

Vascular portions, showing the typical browning symptom, from surface­sterilized root and stem pieces of th e wilted plants were aseptically trans­ferred to Czapek-Dox agar in Petri plates and incubated at about 23 °C. Aspecies of Verticillium, producing the characteristic verticillate conidio­phores , grew out from these tissues by the third day in almost pure culture.Dark resting structures were also formed within another 3 to 4 days. Thisculture was used for pathogenicity trials.

Twelve-day old cotton plants (G. hirsutum var. MCD 5) raised in sterilepotted soil were inoculated by injecting a spore suspension of the fungusin distilled water into the stem I to 2 em above soil level. The controlplants received plain distilled water injection. The plants were maintainedat 25° in a growth chamber. Plants in the inoculated series started showingthe typical Verticillium wilt symptoms within a week after inoculation,beginning in the cotyledonary leaves. In some plants there was a unilateraldevelopment of the syndrome. The symptoms included marginal flagging,irregular yellow patches, browning of the veins, cupping, wilting, dryingup and falling of leaves. The fungus was re-isolated from the roots, stems,petioles and laminae of the wilted plants. The control plants remained

2 0 MY C 59

314 Transactions British Mycological Societyhealthy. The re-isolated fungus was identical with the original isolate usedas inoculum.

This Verticillium species, verified according to Koch's postulates to bethe causal organism in this wilt disease, produced dark resting structuresin culture within a week. These were found to be microsclerotia, typical ofV. dahliae according to the classification of Isaac (1949). Based on thedevelopment and structure of these microsclerotia, the pathogen involvedin this cotton wilt is identified as Verticillium dahliae Kleb.

The junior authors thank Professor T. S. Sadasivan for much interestand encouragement.

REFERENCES

ISAAC, 1. (1949). A comparative study of pathogenic isolates of Verticillium, Annals ofApplied Biow!'l32, 137-157.

NATARAJAN, M. K., SIVAPRAKASAM, K. & RAMAKRrsHNAN, K. (1968). Record of Verti­cilliumwilt of cotton in Madras State. Madras Agricultural Journal 55, 455.

SRINIVASAN, K. V. Verticillium wilt of cotton - some observations on resistance. Inter­national Symposium on Pathological Wilting in Plants, Madras 1971. (In the Press.)

OOOHLIOBOLUS STATE OF CURVULARIA CTMBOPOGONIS

JOYCE A. HALL AND A. SIVANESAN

Commonwealth Mycological Institute, Ferry Lane, Kew

After reconstitution and germination oflyophilized spore suspensions ofsix isolates of Curvularia cymbopogonis (Dodge) Groves & Skolko, ascocarpswere observed in three isolates from Sorghum but not in the other threefrom Oryza. Mature ascocarps formed on both potato-carrot agar and tap­water agar +wheat straw after 12 days exposure to near ultraviolet source(Leach, 1962) and incubation at 23-25 °0. Plating of these strains main­tained under oil also produced ascocarps under similar conditions in thesame media.

The perfect state can be placed in Cochliobolus Drechsler. Cochliobolusperfect states have been reported for Curvularia intermedia Boedijn by Nelson(1961), for C. geniculata (Tracy & Earle) Boedijn by Nelson (1964) and forC. lunata (Wakker) Boedijn by Nelson & Haasis (1964)' These were allfound to be heterothallic and described as having unitunicate asci. Thefungus described here was homothallic, as a single spore isolate derivedeither from a conidium or an ascospore produced both conidial and asco­carp states. The ascospores germinated both terminally and laterally I hafter incubation at 23-25 °0 and produced the conidial state after 3 days;the ascocarp initials began to appear after 4-5 days.

The nature of the stromatic locule with its branched pseudoparaphysessuggests the fungus belongs to the Pleosporales in the Loculoascomycetes,and this is further supported by the nature of the asci, which may betermed vestigial bitunicate. The structure is typically bitunicate but on

Trans. Br. mycol. Soc. 59 (2), (1972). Printed in Great Britain