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Remarks (public):For a complete description including images see 
Remarks (internal):Leaf spot was first described as a disease of celery in Italy in 1890 and has since been recorded causing serious losses from every part of the world where the crop is grown without adequate protection. In addition to leaf damage, seed losses may at times amount to 80% (Noble et al., 1958). Until recently it was believed that two distinct species of Septoria were responsible for the disease, one causing large definite spots and the other small indefinite spots, but only one species is now recogruzed by Gabrielson & Grogan (1964), who made a comparative study of a world-wide collection of isolates. Cultural measures for control include crop rotation, the avoidance of excessive N in fertilizer mixtures, and the use of healthy seed. Hot water treatment of seed has been found to eradicate infection. Good control has recently been obtained by treating seed in 0,2% thiram suspensions at 30°C for 24 hr. (43, 2791e). Sprays with Bordeaux or other copper compounds and organic fungicides have proved effective in controlling the disease when applied early to the seed bed and in the field; dyrene has been recommended for the two final applications to prevent foliage discolouration (39: 77; 40: 504, 644; 43, 2154). None of the regular celery varieties are resistant to leaf spot though evidence of sources of resistance have been reported from Switzerland, the United States and Egypt (17: 743; 33: 135; 38: 644). Some resistant varieties of celeriac have also been reported (33: 135; 39: 365).
Description type:Non-original description 
Description:Septoria apiicola Speg., Boln Acad nac. Cienc. Cordoba 11: 297, 1887.
= Septoria petroselini Desm. var. apii Cavara, 1890.
= Septoria apii Rostrup, 1893.
= Septoria apii-graveolentis Dorogin, 1915.
An expanded synonymy is suggested by Gabrielson & Grogan (1964).
Pycnidia immersed, separate or aggregated, amphigenous, globose, becoming depressed, mid brown to black, 75-195 µm diam.; wall 3 cells thick, composed of thin-walled, pale brown, pseudoparenchymatic cells, considerably darker andsclerotioid near the circular ostiole which is slightly papillate, 15-50 µm diam. Conidiophores hyaline, non-septate, cylindrical to clavate phialides, 8-10 x 3-3,5 µm. Conidia hyaline, filiform, (1-) 3 (-5)-septate, apex slightly tapered,subacute, base obtuse, 22-56 (mean 35 µm) x 2-2,5 µm.
Hosts: On Apium spp.
Disease: Leaf spot (or late blight) of cultivated and wild celery and celeriac. On leaves, seeds and seedling roots, reducing yield and causing wastage through blemishes on the edible petioles. Leaf lesions of variable size, 1-6 mm diam., abundant, amphigenous, circular or sometimes vein-limited, confluent when severe, becoming depressed pale brown, margin diffuse.
Geographical distribution: World-wide on Apium spp.
Physiological specialization: Thomas found the pathogen was restricted to celery and celeriac and did not attack parsley (1: 8). Gabrielson & Grogan (1964) carried out successful reciprocal cross inoculation tests with isolates from celery and Apium australe and found them indistinguishable. Some celery isolates failed to attack A. australe. Bohme has reported two strains from Italy which produced severe infection of celeriac in Germany (39: 365).
Transmission: Seed-borne (Noble et al., 1958; Sheridan, 1966). Also disseminated by rain-splash, in irrigation water, by contact as well as by animals and workman's tools (Chupp & Sherf, 1960). The pathogen may remain viable in the soil for 18 months in buried celery crop refuse, but for less than 6 weeks in the absence of intact host tissue (42: 82). Viability in infected seed may drop to 2% within 8 months from harvest and both mycelium and conidia can stay alive in seed stored up to 14 months (42: 508; 44, 1332) but not beyond 2 yr.
Literature: Gabrielson & Grogan, Phytopathology 54: 1251-1257, 1964 [18 refs] (taxonomy); Noble et al., An annotated list of seed-borne diseases, 1958; Marshall, Ann. appl. Biol. 48: 27-33, 1960; Hewett, J. natn. Inst. agric. Bot. 9: 174-178, 1962; Sheridan, Plant Path. 12: 127-173, 1963; Maude, Ann. appl. Biol. 54: 313-326, 1964; Sheridan, Ann. appl. Biol. 57: 75-81, 1966 (seed infection); Chupp & Sherf, Vegetable Diseases and their Control, 1960 (control).

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