CSIRO PUBLISHING Australasian Plant Pathology, 2007, 36, 252–255 www.publish.csiro.au/journals/app Different types and concentrations of oat grain inoculum to quantify Septoria tritici resistance in wheat C. A. Cordo A,C , C. I. M ´ onaco A and M. R. Sim ´ on B A Facultad de Ciencias Agrarias y Forestales, Comisi´ on de Investigaciones Cient´ ıficas de la Provincia de Buenos Aires (CIC), Fitopatolog´ ıa, Universidad Nacional de La Plata, 60 y 119, Provincia de Buenos Aires, La Plata 1900, Argentina. B Facultad de Ciencias Agrarias y Forestales, Cerealicultura, Universidad Nacional de la Plata 60 y 119, Provincia de Buenos Aires, La Plata 1900, Argentina. C Corresponding author. Email: criscordo@infovia.com.ar Abstract. Two Septoria Monitoring Nursery sets were tested for resistance in the field during three consecutive years. Different concentrations of oat grains covered with mycelia of Septoria tritici were applied as inoculum. The position of the disease on the plants and the severity of the Septoria leaf blotch infection were recorded at two growth stages. A comparison between leaf pulverisation and grain application as a source of conidia was made in the last year. The percentages of necrotic lesions and pycnidial coverage were recorded on the upper three leaves of the plants at the same growth stages as for previous years. With grain inoculation, the infection reached the 7th leaf of the plants with the maximum concentration applied at tillering stage. The best concentration to obtain the highest discrimination among resistances is 120 g/m 2 . In the comparison of inoculation techniques, the results showed a higher necrosis and pycnidial coverage following leaf pulverisation than with the grain application treatment. Additional keywords: inoculation techniques, septoriosis of wheat, resistance. Introduction Leaf blotch, caused by Septoria tritici (teleomorph: Mycosphaerella graminicola), is a worldwide disease that causes appreciable economic losses to wheat crops (Eyal et al. 1985; Sim´ on et al. 2005). Its incidence depends on the inoculum concentration, crop management and the environmental conditions; cool temperatures, high humidity and frequent rain are favourable for its development (Eyal et al. 1985). Sources for resistance derived from the international collection of germplasm, the Septoria Monitoring Nursery (SMN), and from screening nurseries, confer their resistance through different genes. They can be used by breeding programs in their attempts to increase stable resistance over time. The SMN set was created to measure the virulence spectrum over a geographic area. Inoculum in the field can be applied by different methods. Oat grains colonised by mycelia of Pyricularia oryzae or Drechslera tritici repentis were described as an inoculation source by Cordo de Balonga et al. (1980) and Perell´ o et al. (2003) as an alternative to the traditional pulverisation technique. The aims of this work were to (1) determine the best concentrations of oat grain inoculated with fungal mycelium to be placed on the soil and the efficacy of this technique as compared with leaf pulverisation, and (2) to quantify the resistance of the SMN accessions using both techniques. Methods For the field experiment, the inoculum for grain application was prepared in sterilised 500-mL flasks with 100 g of oat grains and 50 mL of a liquid extract malt medium (Perell´ o et al. 1987). The grains were soaked with 10 mL of an inoculum suspension (10 7 conidia/mL) of Septoria tritici isolate FALP96088 and incubated for 15–21 days at 23 ± 2 ◦ C in darkness and shaken daily to promote good fungal growth. Each flask yielded ∼280 g of wet infected grains. After the incubation, the grains colonised by a stromatic mycelium were spread and dried on trays under laboratory conditions, then weighed and stored in nylon bags at 5 ◦ C before their use 24 h later in the field. Two concentrations of oat grain inoculum were compared in 1998 and 1999. Eleven differential spring wheat cultivars and eight lines at a similar vegetative maturation stage belonging to the 6th (1998) and 7th (1999) SMN sets (Gilchrist 1994; Gilchrist et al. 1999) were inoculated and evaluated. The best sources of resistance identified by CIMMYT were assayed at the Julio Hirschhorn Experimental Station, Los Hornos, Buenos Aires Province. The accessions (1-BOBWHITE S; 2-TIA.2/4/ CS/TH.CU//GLEN/3/ALD/PVN; 3-CHIRYA.1; 4-CHIRYA 4; 5-CS7TH.CU//GLEN/3/ALD/PVN/4/NANJING; 6-EG-A/H56 7.71//4#EG-A/3/2#CMH79.243; 7-MH86.540-A-1Y-3B-2Y-1B- 1B-1B-1Y-1M-1Y; 8-ALD/PVN//YMI#6; 9-SHA5/BOW; 10- ENCOY 1582–1B; 11-BOBWHITE S as the other derivative © Australasian Plant Pathology Society 2007 10.1071/AP07015 0815-3191/07/030252