The infectivity of C. africana on pearl millet (Pennisetum glaucum) lines in Africa was studied. C. africana consistently gave 100% disease incidence on male-sterile sorghum in experiments undertaken in Zimbabwe. C. fusiformis established disease with moderate incidence on most but not all lines tested. In contrast, C. africana established a parasitic association with all the pearl millet lines tested, with incidence as high as 23% in ICMSR 260, the genotype that also supported the highest incidence with C. fusiformis. However, the disease severities were always low, between 1 and 5%. All infections on pearl millet were verified as the sphacelial stage by virtue of their conidial characteristics. After 1 passage through a pearl millet host, C. africana did not apparently become more infectious on this host

Frederickson, D E

Mantle, P G

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presented at the VI Annual Small Mil lets Workshop,May 1992, Ranchi, Bihar, India.Maloo, S.R. 1995. Small mil let as an economically alter-native poultry food ingredient. Paper presented at the 2ndAgricultural Science Congress, Jan 1995, Andhra Prad-esh Agricultural University, Hyderabad, Andhra Prad-esh, India.Sampath, T.V., Razvi, S.M., Singh, D.N., and Bondale,K.V. 1990. Small millets in Indian Agriculture. Page 32in Small millets in global agriculture. (Seetharam, A. ,Ri ley, K.W., and Harinarayana, G., eds.). New Delhi :Oxford and IBH Publishing Co.PathologyPearl Mi l let as an Alternate Hostof the Sorghum Ergot Pathogen,Claviceps africana D E Frederick son1 and P G Mantle2(1. Biochemistry Department, Imperial College, LondonSW7 2AY, UK; Present address: Biological Sciences,University of Zimbabwe, Harare, Zimbabwe; and2. ICRISAT Southern and Eastern Africa Region,Matopos Research Station, PO Box 776, Bulawayo,Zimbabwe).IntroductionThe ergot pathogen, Claviceps africana Frederickson, Man-tle and de Milliano, has been the major cause of severelydepleted yields in sorghum (Sorghum bicolor (L.) Moench)hybr id seed production in southern Afr ica (de Mi l l iano1992). In Zimbabwe the pathogen causes annual grainlosses of up to 25% fol lowing the colonization of male-sterile A- l ine ovaries, and additional losses of up to 12%also occur when contamination of seeds with honeydewcauses mold growth, spoilage, and quality reduction(Frederickson and Leuschner, in press, McLaren 1994).The host range of C. africana is poorly defined. Insome of the earlier experiments wi th C. africana by Fu-trell and Webster in Nigeria in 1966, natural inoculumfrom Panicum maximum infected sorghum. Similarly, er-got from the same grass in Thailand was transferred ex-perimentally to sorghum, as was inoculum fromDicanthum annulatum, Brachiaria mutica, and three sor-ghum species, S. sudanensis, S. almum, and S. halcpanse (Boon-Long 1992). It is assumed, from the evidence onsorghum ergot in Thailand (Frederickson et al. 1991), thatthe findings of Boon-Long all refer to C. africana. How-ever, C. africana has not been found on any alternate hostoutside the genus Sorghum in Zimbabwe. Further, thatthe Indian sorghum ergot pathogen (C. sorghi, anamorphSphacelia sorghi) can also infect Jschaemum pilosum, Cenchrus setigerous, and C. ciliaris (Chinnadurai andGovindaswamy 1971, Mughogho 1986) is not necessarilyrelevant to vegetative hyphal parasitism by C. africana since the two sorghum pathogens are taxonomically dis-tinct, and C. ciliaris could not be infected by sorghumergot in Zimbabwe, even using a high concentration ofinoculum.In Zimbabwe, pearl mil let (Pennisetum glaucum (L.)R. Br.) is grown alongside sorghum as a communal crop.Although it matures earlier than sorghum, extensive t i l -lering causes temporal overlap of the two crops. SinceSundaram (1974) found sphacelial infections of C. sorghi on pearl millet adjacent to sorghum in India, we thoughtthat infectivity of C. africana on pearl mil let should bestudied experimentally in Afr ica.Mater ia ls and MethodsAt Matopos Research Station, near Bulawayo, Z i m -babwe, pearl millet lines were sown in a 4 m x 6 m blockin six replications in 1991, and two replications in 1992.Due to seed availability only four lines were common toboth years. Upon emergence from the boot in A p r i l ,spikes were bagged and inspected daily for the onset ofstigma emergence. At approximately 20% stigma emer-gence they were inoculated with either the natural patho-gen, C. fusiformis, or the sorghum ergot pathogenC. africana, Conidial inoculum (106 conidia mL- 1) wasdirected at inflorescences until run-off. Spikes were re-bagged, and the inoculation procedure repeated over thenext 2 - 3 days until the completion of stigma exsertion.Concurrent inoculations of A- l ine sorghum wi thC. africana were performed to verify the infectivity ofC. africana inoculum.Ergot incidence and severity were assessed on pearlmil let spikes 3 - 4 weeks post-inoculation. Infected spikeswere removed to encourage further t i l lering of the mil letand to allow microscopal verification of the identity ofthe pathogen based on conidial characteristics. In 1991,C. africana inoculum from successful pearl mil let infec-tion was re-inoculated onto pearl mil let to see if its infec-t ivity changed after one passage through the host.ResultsClaviceps africana consistently gave 100% disease inci-dence on male-sterile sorghum, and in the absence of a ISMN 37,1996 83pollinator, achieved approximately 95% disease severitywi th in infected inflorescences.The natural ergot pathogen of pearl mil let (Clavicepsfusiformis) established disease wi th moderate incidenceon most, but not on a l l , of the lines tested (Table 1); butdisease severity was relatively low, not exceeding 15%.In contrast, C. africana established a parasitic associa-tion wi th all the pearl mil let lines tested, wi th incidenceas high as 23% in ICMSR 260, the genotype that had alsosupported the highest incidence when inoculated wi thC. fusiformis. However, severities were always low, at 1-5%. Consistent findings were obtained in the pearl milletlines that were common to the 2 consecutive years' ex-periments. Arc-sine transformed data for experiments in1992 showed the mean comparative incidence ofClaviceps africana in a sorghum A- l ine (100 %) versusthree pearl mi l let lines (2.5,11.5, and 18%) were signif i-cantly different at P = 0.01. A l l infections on pearl mil letlines were veri f ied as the sphacelial stage (Sphaceliasorghi) of C. africana microscopically by virtue of theirconidial characteristics; the sphacelial fructification ofC. fusiformis is quite different f rom that of S. sorghi. After one passage through a pearl mil let host,C. africana, did not apparently become more infectiouson this host. Rather, the results suggest that infectivitymay have declined. Indeed, although C. africana inoc-ulum passaged through pearl mil let stil l infected male-sterile sorghum, it did so wi th reduced (49%) severity.84 ISMN 37,1996DiscussionThe experimental observations confirm pearl mil let as anadditional host of endemic C. africana under high diseasepressure in Zimbabwe, even in the more diff icult condi-tions for infection during years of severe drought insouthern Afr ica. Whi le this may not be of local practicalimportance, the recent global extension of ergot diseasein sorghum for the first time in South America east of theAndes in 1995 (Reis et al. 1996) and in Queensland,Australia in 1996, has greatly heightened interest in andconcern for the economic consequences of the disease.Relatively little firm evidence on reservoirs of inoculumexists in the literature and the present short report,coupled wi th similar recent findings in Brazi l (E M Reis,personal communication) and Queensland (M Ryley, per-sonal communication) formalizes a role for pearl mil letthat may at least be helpful in phytosanitary considera-tions to reduce further adverse impact of C. africana disease in sorghum. Whereas ergot disease principallyinfluences F1 hybr id seed production, the effects on grainsorghum production could become significant if wide-spread reservoirs of infection become established.ReferencesBoon-Long, T. 1992. Sorghum diseases of Thailand.Pages 41-43 in Sorghum and millets diseases: a secondTable 1. Comparative experimental ergot disease incidence in pearl millet genotypes by the natural pathogen,Claviceps fusiformis, and the unnatural pathogen, Claviceps africana, in Zimbabwe, 1991 and 1992.Disease inc idence (%)C. a f r i c a n a af terN a t u r a l pa thogen passage t h r o u g hC. f u s i f o r m i s Unna tu ra l pa thogen C. a f r i c a n a pear l m i l l e tPear l m i l l e t l i ne 1991 1991 1992 1991I C M P E S 2 5 -1 3 -I C M P E S 3 5 - 1 1 . 5 ( 7 0 ) -I C M P E S 3 9 0 ( 1 2 )2 1 5 ( 1 3 8 ) 1 0 2 ( 4 7 )I C M P E S 4 5 2 3 ( 1 3 ) 1 6 ( 1 2 4 ) 4 3 ( 5 4 )I C M S R 221 1 4 ( 1 4 ) 1 7 ( 2 1 8 ) 2 ( 7 4 )I C M S R 2 6 0 43 ( 1 5 ) 23 ( 1 6 7 ) 7 ( 7 7 )I C M H 4 5 1 0 ( 1 0 ) 7 ( 6 2 ) 4 ( 2 3 )P M V 1 3 6 ( 1 1 ) 2 0 ( 1 8 3 ) 1 8 ( 1 1 4 ) 11 ( 6 5 )8 5 2 B 7 ( 6 7 ) 2 . 5 ( 7 8 ) 7 ( 14 ) -1. - = not tested.2. Number of inoculated inflorescences shown in parentheses.-----world review (de Mi l l iano, W.A.J., Frederiksen, R.A.,and Bengston, G.D., eds.). Patancheru 502 324, AndhraPradesh, India: International Crops Research Institute forthe Semi-Ar id Tropics.Chinnadurai, G., and Govindaswamy, C.V. 1971. Hostrange of the sugary disease pathogen. Madras Agr i -cultural Journal 58:600-603.de Mil l iano, W.A.J. 1991. Sorghum diseases in SouthernAfr ica. Pages 9-19 in Sorghum and millets diseases: a second world review (de Mi l l iano, W.A.J., Frederiksen,R.A., and Bengston, G.D., eds.). Patancheru 502 324,Andhra Pradesh, India: International Crops Research In-stitute for the Semi-Arid Tropics.Frederickson, D.E., Mantle, P.G., and de Mill iano,W.A.J . 1991. Claviceps africana sp. nov.; the distinctiveergot pathogen of sorghum in Afr ica. Mycological Re-search 95:1101-1107.Frederickson, D.E., and Leuschner, K.L. (In press.)Potential use of benomyl for the control of ergot(Claviceps africana) in sorghum A-lines in Zimbabwe.Plant Disease.Futrell, M.C. , and Webster, O.J. 1966. Host range andepidemiology of the sorghum ergot organism. Plant Dis-ease Reporter 50:828-831.McLaren, N.W. 1994. Efficacy of systemic fungicidesand t iming of preventative sprays in the control of sugarydisease of grain sorghum (Sorghum bicolor). South A f r i -can Journal of Plants and Soil 11:30-33.Mughogho, L.K. 1986. Ergot. Pages 38-49 in Compen-dium of sorghum diseases (Frederiksen, R.A., ed.).American Phytopathological Society.Reis, E .M. , Mantle, P.G., and Hassan, H.A.-G. 1996.First report in the Americas of sorghum ergot disease,caused by a pathogen diagnosed as Claviceps africana. Plant Disease 80:463.Sundaram, N.V. 1974. Natural occurrence of Sphacelia sorghi on Pennisetum typhoides. Indian Phytopathology27:124-125.Effect of Different Levels of Nitrogenand T ime of Sowing on Incidence ofGra in M o l d in Pearl Mi l le tPadma Sri M, and A V Ramana Reddy(Sri Venkateswara Agricultural College, AndhraPradesh Agricultural University, Tirupati, AndhraPradesh, India)Pearl mil let, Pennisetum glaucum (L.) R. Br., the fourthmost important food crop in India, it is a drought-tolerantcrop widely distributed in the semi-arid tropics. Amongseveral factors that restrict the production potential ofpearl mil let, head molds play a dominent role in reducingproduction, and the market value of grain in Chittoor andCuddapah districts of Andhra Pradesh.In preliminary studies conducted in the laboratory,several fungi, e.g., Curvularia spp, Alternaria spp, Fu-sarium spp, Drechslera spp, and Penicillium spp werefound associated with head mold of pearl mil let. Similarresults were also reported by Luttrell (1954) in USA, andGirisham and Reddy (1985). Therefore, this study wasmade to determine the effect of different levels of nitro-gen, and different sowings dates on the incidence of moldin pearl millet.The seeds were sown at 10-day intervals, starting 27Jul 1989 at a seed rate of 4 kg ha-1, in a nursery that wasmaintained weed-free for 21 days. After fertil izers hadbeen applied to the main field, 21-day-old healthy seed-ings were transplanted into it at the rate of one seedlingh i l l- 1, wi th 45 cm between rows and 15 cm within therows.The experiment was conducted using a split-plot de-sign with sowing dates as the main plots (18 x 13.5 m),and N levels as subplots (3.6 x 2.7 m). A l l the treatmentswere replicated thrice. The five sowing dates and fivenitrogen levels used in 1989 as treatments were D1 (27Jul), D 2 (7 Aug), D 3 (17 Aug), D 4 (27 Aug), D 5 (7 Sep),N0 (0 kg N ha-1), N, (25 kg N ha-1), N2 (50 kg N ha-1), N3(75 kg N ha-1), N4 (100 kg N ha-1).There were 25 treatments for various combinations ofsowing dates and nitrogen levels:T 1 - D 1 N o T 6 - D 2 N 0 T 1 1 -D 3 N 0 T16 - D4 N0 T21 - D5 N0T 2 - D 1 N 1 T 7 - D 2 N 1 T 1 2 - D 3 N 1 T 1 7 -D 4 N 1 T22 - D5 N1T 3 - D 1 N 2 T 8 - D 2 N 2 T 1 3 -D 3 N 2 T 1 8 -D 4 N 2 T23 - D5 N2T 4 - D 1 N 3 T 9 - D 2 N 3 T 1 4 -D 3 N 3 T 1 9 -D 4 N 3 T24 - D5 N3T 5 - D 1 N 4 T1 0 -D2N4 T 1 5 -D 3 N 4 T20 - D4 N4 T25 - D5 N4The results indicated that there was minimum (12.9%)mold incidence in the crop sown on 17 Aug with 0 kg N ha-1. Such low incidence may be due to the prevailinghigh temperature (36.4°C) coupled with low (68.4%) rel-ISMN 37,1996 85

Pearl Millet as an Alternate Host of the Sorghum Ergot Pathogen, Claviceps africana

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Pearl Millet as an Alternate Host of the Sorghum Ergot Pathogen, Claviceps africana

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