A LEAF SPOT OF PELARGONIUM CAUSED BY ALTERNARIA TENUIS NEES ex PERS.

Abstract

VARIOUS workers have reported a leaf spot disease of cultivated pelargoniums {Pdargomwn species), the earlier. European, records naming tiK fungal pathogen Macrosporium [>elargomi EU. & Ev. or M. macalpineanum Sacc. et Syd. Neegaard (1945) combined M. pelargcmi with Alternaria tenuis, and Munnecke (1956) has recorded A. tenuis as the causal agent of a leaf spot of pelargonium in the U.S.A. During 1%5. specimens of a regal pelargoniutn {P. X dome.sticutn Bailey) were received from Bidford-on-Avon. Warwickshire and of a zonal pelargonium (P. X hortorum Bailey) cultivar Master Crampel from a Lea Valley nursery, both lots showing leaf spot. In both cases A. tettuis was isolated from the spots. There are no published records of this fungus attacking Pdargottium spp. in this country but Atternaria tenuis, associated with leaf spot, was recorded in ninishire in 1963 by Dr. D. C. Gwynne. NAAS. Bangor. SYMPTOMS AND PATHOGENICITYZonal and regal pelargoniums were inoculated with conidial suspensions of ihe fungus and incubated in a high relative humidity.On the zonal pelargoniums, symptoms were observed five days after inoculation. Small water-soaked spots with a necrotic fleck in the centre, appeared on the undersides of the leaves. The lesions usually increased in size up to i in. diameter and were then sunken, necrotic and visible on the undersides of the leaves only (Plate IV. 2). Occasionally numbers of spots formed together producing larger irregular lesions. Tliere was no evidence of any further spread of the disease when tlie infected plants were kept in a glasshouse maintained at 15-21°C. Spread vvas observed on plants kept in the open during the summer months and A. tenuis was found sporulating on the lesions.Regal cultivars showed leaf spot symptoms most severely on the oldest leaves on which irregular brown lesions with reddish margins were conspicuous (Plate IV. 3). There was a tendency for coilescence of spots and some were concentrically zonated with the fungus sporulating on the lesion. On younger leaves necrotic brown areas were infrequent but " pin-head " lesions could be seen and these sometimes enlarged with leaf senescence.In further experiments marked leaves on plants of a number of different cultivars were inoculated and symptoms recorded five and 20 days after inoculation. The following cultivars were used:Pelargonium X hortorum-uonaX cuttivars. . Pelargoniutn X domestictjm-iegail cultivars. Duchess of Edinburgh. Hilda Jefford. Carnival. Bridesmaid.Pelargonium peltatum (L.) Ait.-ivy-leaved cultivars. Galilee and L'Elegante.Only the zonal cultivar Dr. McNanan and the ivy-leaved cultivars did not show leaf spot symptoms. Some zonal cultivars developed numerous pin-head

Records of fungi parasitic on plants in New Zealand 1966–68

“…In the literature there are references to A. alternata occurring as a primary pathogen. Munnecke (1956) and Fletcher and Ryan (1966) report it on geranium (Pelargonium spp. ); Wilcox (1963) reported it on Lobelia sp.…”