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SUMMARY The utilization of amino acids by Diplocarpon rosae Wolf was investigated and compared with amino acid compositions of leaves of resistant and of tolerant roses. No amino acid appeared to determine resistance of roses to blackspot on a nutritional basis, but phenylalanine marginally increased resistance when taken up by wounded leaves of resistant or tolerant varieties. There is an accumulation of phenolic compounds in response to infection by D. rosae. Most phenolic compounds are toxic to D. rosae in vitro, particularly ellagic acid and p-coumaric acid, but their presence and quantity in healthy rose leaves could not be related to disease resistance. Inhibition of germination on rose leaves of conidia of the fungus was determined in a manner that suggested production of a phytoalexin. It is suggested that resistance of roses to D. rosae may be related to accumulation of polyphenols and possibly to the production of a phytoalexin.

Perhaps no plant disease has been more widely observed or is more generally known, both in Europe and the United States, than the black spot of roses caused by the parasitic fungus Actinonema rosae (Lib.) Fries. The spots, which are more or less circular in outline, are characterized by a very irregular, fibrillose border. This fibrillose character is due to the radiating strands of mycelium which occur beneath the cuticle. Appearing among the mycelial strands are numerous dark specks, the fruit bodies of the fungus. The spots may be isolated and confluent, or so numerous as to involve the entire upper surface of the leaf. Plants which are attacked become defoliated early in the season, and the leaf buds, which should remain dormant till the next year, often open late in the season. As a result, the plant is weakened so that it blossoms poorly or not at all in the following season. Since very little is known concerning the life history of the fungus and the development of the Actinonema stage, an attempt has been made by cultures on artificial media and on the host to furnish a more satisfactory knowledge of this interesting organism. Before giving an account of this study it may be well to state briefly the characters of the vegetative and fruiting structures of the rose Aclinonema. The vegetative body of the fungus consists of two parts, the subcuticular mycelium and the internal mycelium. The subcuticular mycelium is immediately underneath the cuticle, being above the outer wall of the epidermal cells. It consists of branched, radiating strands of mycelium which anastomose, making a network. Each strand consists of several filaments united together, either side by side or sometimes superimposed. At the right of the acervulus in fig. i is shown a cross-section of one of these strands. The internal mycelium penetrates the mesophyll of the

SUMMARY Germination of conidia of Diplocarpon rosae Wolf is inhibited in a solution made by dissolving 35 p.p.m. sulphur dioxide in water. Inhibition is permanent after exposure for 3 hr. Gaseous SO2 in air under controlled conditions at 100μg./m3 markedly reduces infection of rose leaves after exposure for 2 days. Blackspot of roses is checked or eliminated in areas where SO2 pollution of air exceeds 100/μ./m.3.

SUMMARY Conidia of Diplocarpon rosae Wolf are dispersed mainly by water-splash. Within a crop the spread of the disease can be traced from primary foci. Infection follows the ‘compound interest’ pattern, sensu van der Plank (1963), which is typical of most leafspot diseases. Accumulation of inoculum, together with certain conditions of rainfall and temperature in August, led to a characteristic, rapid development of the disease in September 1963 and 1964, after an incubation period of 2–4 weeks.

The present paper describes 6 foliicolous fungi from Jabalpur (India). These includeAsterina lawsoniae Syd. on leaves ofLawsonia alba, Diplocarpon rosae Wolf. onRosa sp.,Cercospora jujubae Chowdhury onZizyphus jujuba andCercospora subsessilis Henn. NAsterostomella strophanti Henn. on leaves ofFlacourtia ramontchii, a new fungus for the country andCorynespora cassiicola (Berk. &Curt.)Wei. onClerodendron inerme, a new host record.

One who attempts to grow hybrid roses in this part of the country is apt to find sooner or later some of them being defoliated by the black spot fungus, Diplocarpon Rosae. For example, at The New York Botanical Garden it has been observed for several years that certain varieties among our most beautiful roses such as Los Angeles, Mrs. Henry Bowles, Felicity and Padre, always show some spotting in spite of the fungicides which have been applied rather frequently. On the other hand, there are those roses like Red Radiance, Ethel Sommerset, Mrs. C. W. Edwards, La France, Radiance and others, which under the same treatment scarcely ever show black spot. The writer has been asked frequently why it is that the Red Radiance, for example, is comparatively resistant to this parasite. Is it because, as some say, the leaves probably have a cuticle which the fungus cannot penetrate? Or is it due to something more fundamental and inherent in the cytoplasm so that the fungus is unable to live even though it may readily penetrate the cuticle and so cause only a mere flecking. This is among the problems being studied, and some information on this question obtained as a result of preliminary experiments is also presented at this time.

Populations of two-spotted spider mite ( Tetranychus telarius (L.)) and severity of blackspot disease ( Diplocarpon rosae Wolf) Were negatively correlated to the amount of winter injury to rose bushes. The number of surviving rose canes was greatest in plots with the most effective mite and blackspot protection during the previous season.

A single apple shoot examined in July showed one leaf with a lesion caused by Venturia inaequalis (Cooke) Wint. Five more leaves were shown to be heavily infected after periodic acid-Schiff staining. Microscopical examination of the area near the sporing lesions showed not only germination of conidia produced by the lesions on four leaves, but also re-infection of two leaves. Adhesion of scab conidia to the leaf surfaces was localized near the lesions. Spore counts from a belt transect illustrate the complex microbiological picture at the leaf surface and the need for better sampling methods. The lesions are described and compared with those of Diplocarpon rosae Wolf and with the growth of certain soil fungi within cellophane.