Revista Mexicana de Fitopatología

ISSN: 0185-3309

mrlegarreta@prodigy.net.mx

Sociedad Mexicana de Fitopatología, A.C.

México

Montes Belmont, Roberto; Flores Moctezuma, Hilda Elizabet; Nava Juárez, Raúl Arnulfo

Alternate hosts of claviceps africana frederickson, mantle and de millano, causal agent of sorghum

ergot in the State of Morelos, Mexico

Revista Mexicana de Fitopatología, vol. 21, núm. 1, enero-julio, 2003, pp. 63-66

Sociedad Mexicana de Fitopatología, A.C.

Texcoco, México

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Alternate Hosts of Claviceps africana Frederickson, Mantle andde Millano, Causal Agent of Sorghum “Ergot” in the State of

Morelos, MexicoRoberto Montes-Belmont, Hilda Elizabet Flores-Moctezuma, and Raúl ArnulfoNava-Juárez, Instituto Politécnico Nacional, Centro de Desarrollo de Productos Bióticos,km 8.5 Carr. Yautepec-Jojutla, San Isidro, Yautepec, Morelos, México CP 62730.Correspondence to: rbelmont@ipn.mx

Montes-Belmont, R., Flores-Moctezuma, H.E., and Nava-Juárez, R.A. 2003. Alternate hosts of Claviceps africanaFrederickson, Mantle and de Millano, causal agent ofsorghum "ergot" in the state of Morelos, Mexico. RevistaMexicana de Fitopatología 21:63-66.Abstract. In recent years, sorghum ergot (Claviceps africana)spread out to American and Australian continents, where itmay have new potential hosts, an important component ofthe disease cycle. This is particulary important in Mexico,where there is great variation in climate and vegetation. Weedsfrom sorghum plots and surrounding areas showing ergotsymptoms, were collected and identified in Jonacatepec andYautepec, Morelos between 1998 to 2000. Macroconidiamorphology and dimensions, as well as the presence orabsence of sclerotia were determined for each weed. Cross-inoculations were also carried out using conidia isolated fromsorghum and weeds. C. africana macroconidia were found inDigitaria horizontalis, Ixophorus unisetus, Echinochloacrusgalli, Sorghum halepense, Cenchrus echinatus, andPanicum maximum. No sclerotia were found in all the weedspecies. Cross-inoculations showed that the last three speciesmentioned, serve as alternate hosts for C. africana, but onlyS. halepense has features that could make it a source of primaryinoculum.

Additional keywords: Sorghum bicolor, host range, collateralhosts, cross-inoculations.

Resumen. El ámbito de hospederos de Claviceps africana,agente causal del cornezuelo del sorgo, constituye uncomponente importante del ciclo de la enfermedad. En añosrecientes se ha diseminado a los continentes americano yaustraliano donde podría haber nuevos hospederospotenciales de este hongo; esto es particularmente importanteen el caso de México por su diversidad climática y devegetación. En el presente trabajo se colectaron e identificaronmalezas con síntomas de cornezuelo dentro y en el áreacircundante de parcelas de sorgo en los municipios deJonacatepec y Yautepec, Morelos, entre 1998 y 2000. En cadamuestra se caracterizó la morfología y las dimensiones de los

macroconidios, así como la presencia o ausencia deesclerocios; posteriormente se hicieron inoculacionescruzadas utilizando conidios aislados de sorgo y las malezas.Se encontraron macroconidios de C. africana en Digitariahorizontalis, Ixophorus unisetus, Echinochloa crusgalli,Sorghum halepense, Cenchrus echinatus y Panicummaximum. En ninguna de las malezas se encontraronesclerocios. Las inoculaciones cruzadas mostraron que las 3últimas especies sirven como hospederos alternantes paraC. africana, pero sólo S. halepense presenta característicaspara actuar como fuente de inóculo primario.

Palabras clave adicionales: Sorghum bicolor, rango dehospederos, hospederos colaterales, inoculaciones cruzadas.

Worldwide, ergot is an important disease of sorghum duringgrain development. Several species of the genus Clavicepscause ergot, including Claviceps africana Frederickson,Mantle and de Millano, which is the most widely distributed;C. sorghi Kulkarni Seshadri and Hedge in India is important;and C. sorghicola Tsukiboshi, Shimanuki and Uematsu, inJapan (Pauzotová et al., 2000). Ergot is an important problem,especially for hybrid seed production, since inbreds are usedand infection occurs in the ovary before pollination andfertilization. A fungal mass (sphacelia) follows infection. Afterovary is fertilized ergot rarely occurs. Hybrid germplasm isseriously affected when flowering of the inbreds fails to nick.If climatic conditions are less than 13°C three weeks beforeanthesis, pollen production is incomplete (Bandyopadhyayet al., 1998). Losses caused by ergot in India are 10-80%, and12-100% in Zimbabwe (Bandyopadhyay et al., 1996). Despitethe significance of this disease, epidemiological parameterssuch as the case of alternate hosts (Futrell and Webster, 1966)are poorly researched. Numerous reports on alternate hostshave been reported (Chinnadurai and Govindaswamy, 1971;Bandyopadhyay et al. 1998), but most of them are ratherquestionable, since several species of Claviceps attack a widerange of hosts (especially gramineous) and similar symptomsmay be observed. The only way to test the validity of thesedata, besides studying the fungus morphological

(Received: June 14, 2002 Accepted: September 3, 2002)

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crusgalli. This might represent an evidence of the plantresponse to the pathogen. Sclerotia were not found in any ofthe weed surveyed during the three years. Once the plantsreached senescence, sphacelia dried and remained attachedto the panicle glumes. These results agree with the report byVelásquez et al. (1998) who did not find sclerotia in S.halepense or any other weed infected with other species ofClaviceps. S. halepense, C. echinatus, and P. maximumshowed a 100% infection and reproduction of symptoms,after inoculation with C. africana obtained from sorghum.Only E. crusgalli remained free of the disease. A 100%infection was observed in forage sorghum plants afterinoculated with ergot inoculum from P. maximum and S.halepense, while this rate was 60% when the inoculumoriginated from C. echinatus. It can be concluded that P.maximum, S. halepense, and C. echinatus are alternate hostsof C. africana; however, since only S. halepense grows sideby side with sorghum all year round, it seems to be animportant source of primary inoculum. It was also the onlyspecies infected with ergot, even before the disease wasapparent in sorghum. Previous reports indicate that S.halepense, like sorghum, is infected during flowering whentemperatures are below 13°C (Holm et al., 1991). It wasobserved that panicles of S. halepense did not produce seedsbetween March to May; probably, this had to do with theminimum temperatures (below 13°C) occurring from October1999 to February 2000, which may be related to thephenological stage where differentiation of anther progenitorcells is particularly vulnerable to low temperatures (Brooking,1976). The other host species only developed during the rainyseason, and they were not infected before sorghum in any ofthe years when the study took place; therefore, it seems thatthey might be a secondary inoculum source. As for D.horizontalis and I. unisetus, although infected plants wereobserved in 1998, apparently their morphological and/orphysiological characteristics do not allow the completion ofC. africana biological cycle. In consequence, no more infectedplants of these species were found in 1999 and 2000. As acontrol measure, destruction of Johnson grass just beforesorghum is sown, could reduce ergot occurrence.

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