Alternaria cichorii was recorded for the first time in Brazil causing leaf spots on endive (Cichorium endivia) in 2003 based on material collected at Catalão, state of Goiás, in 2001. In 2005, A. ...cichorii was found causing severe leaf‐spotting in an escarole (C. endivia) plantation in Viçosa, state of Minas Gerais and shortly afterwards also in Viçosa, but at a different location, in the weed hosts common sowthistle (Sonchus oleraceus) and spiny sowthistle (Sonchus asper). A description of A. cichorii based on specimens collected in Viçosa is provided herein. The natural occurrence of A. cichorii on weed hosts in Viçosa indicates that it has already become naturalized in Brazil surviving on non‐cultivated composites, complicating disease management. Pathogenicity tests, complementary to those already published, were performed to better elucidate the range of potential alternative hosts in the Asteraceae of this fungus. This involved inoculation of one isolate of A. cichorii obtained from cichory and one obtained from common sowthistle on selected species and cultivars of 10 tribes in the Asteraceae, but concentrated in the Lactuceae. All species included in the test were shown to be susceptible to at least one of the isolates. A high incidence of leaf spot or blight resulted from inoculation of most individuals. All plants of six test species were killed after inoculation with one of the isolates of A. cichorii. Several of the test species have not been previously recorded as hosts for A. cichorii. Surprisingly, the known host‐range for this fungus is restricted to only few members of the Asteraceae (Acroptilon repens, C. endivia, C. intybus, Carthamus tinctorius and Lactuca sativa). Our results indicate that A. cichorii has a wide host range within the Asteraceae and that other cultivated or non‐cultivated members of this family may serve as inoculum reservoirs for this fungus in the absence of cichory, endive or escarole. An attempt to verify if contaminated seeds might be the original source for such geographically distant occurrences of A. cichorii in Brazil was made. Analysis of 24 samples of cichory and endive seeds obtained from dealers in five different Brazilian states showed that 25% of these samples carried A. cichorii with an incidence varying from 0.6% to 13.75%. Such a result highlights the vulnerable situation in Brazil for avoiding introduction of exotic seed‐carried vegetable pathogens. It is known that a very significant proportion of vegetable seeds marketed in Brazil are imported and seed inspection for pathogens is not performed regularly for such material imported for commerce. It is probable that contaminated cichory, endive and escarole seeds served as a vehicle for introduction of this fungus in Brazil and that the fungus has then become naturalized in many vegetable growing areas and is now surviving on other Asteraceae in the absence of cultivated hosts.
Full text
Available for:
BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
A foliar disease of commercially grown radicchio (Cichorium intybus) was observed in 1996 and 1997 in the Salinas Valley (Monterey County), California. Symptoms consisted of circular to oblong, ...necrotic spots ranging in diameter from 3 to 20 mm and having concentric zones of darker tissue. A fungus identified as Alternaria cichorii Nattrass (1) was observed fruiting on the spots and was consistently isolated from the margins of the spots. Conidia from leaves were obclavate in shape with slender, unbranched beaks extending from the narrow end of the spore body. Spore body dimensions measured 56 to 78 × 14 to 20 μm, and beaks measured 36 to 81 × 1 to 2 μm. Spore bodies had 7 to 9 transverse septa. Often there were no longitudinal septa, but occasionally there were 1 or 2 such septa. For pathogenicity tests, five isolates were grown for 4 weeks on potato dextrose agar under a combination of cool white and Vita-Lite fluorescent tubes on a 12 h light/dark cycle. Conidial suspensions (4.0 × 10
conidia per ml) were sprayed onto 8-week-old radicchio (cv. Rossana Rogers). Plants were incubated in a moist chamber for 48 h and then maintained in a greenhouse. After 12 days, leaf spots similar to the original symptoms developed on all plants inoculated with the five isolates, and the pathogen was reisolated. Control plants sprayed with distilled water remained symptomless. The experiment was repeated and the results were similar. When inoculated onto endive (Cichorium endivia cv. Tres Fine Maraicchere) and two lettuce (Lactuca sativa) cultivars, the isolates caused small (1 to 2 mm in diameter), necrotic, circular leaf spots on endive and Romaine lettuce cv. Green Towers, but did not cause symptoms on the iceberg lettuce cv. Alpha. This is the first report of A. cichorii on commercially grown radicchio in California. In addition, the same disease was confirmed on commercially produced greenhouse transplants of radicchio, indicating that primary inoculum can possibly be seed-borne. Reference: (1) J. C. David. Mycopathologia 129:41, 1995.
PDF
