A Quantitative Method for the Inoculation of Wheat Seedlings with Pycnidiospores of Septoria nodorum

Abstract

EYAL, Z., and A. L. SCHAREN. 1977. A quantitative method for the inoculation of wheat seedlings with pycnidiospores of Septoria nodorum. Phytopathology 67: 712-714. A quantitative inoculation method was developed that The relationships between numbers of spores reaching permits the evaluation of symptoms produced by seedling leaves and symptoms produced (number of lesions pycnidiospores of Septoria nodorum on wheat cultivars in and percent necrosis) were evaluated for four spring wheat the seedling stage. The following parameters were quantified: cultivars. The wheat cultivar, Fortuna, was very susceptible number of spores per suspension volume; volume sprayed to the disease, whereas Manitou was relatively resistant. The onto wheat seedlings; and the speed at which plants were use of our method to detect, measure, and screen for revolved during inoculation. The number of spores deposited resistance to S. nodorum, and its possible use in genetic on glass slides placed among the wheat seedlings gave an studies on the inheritance of resistance is discussed. estimate of the number of spores deposited on leaf surfaces. Additional key words: Triticum aestivum, glume blotch. Septoria glume blotch of wheat, which is caused by MATERIALS AND METHODS Septoria nodorum (Berk.) Berk. (perfect state = Leptosphaeria nodorum Mfiller), reduces yields in many The isolates of S. nodorum used in this study originally parts of the world (1, 2, 3, 4, 5, 11). Br6nnimann (3) were collected from wheat fields in Montana. Only the reported losses in experimental blots of 46.4% in winter most virulent isolates were kept for the study. Cultures wheat and 40.4% in spring wheat. The disease is were grown on yeast-malt agar in petri dishes for 7 days at associated mainly with humid conditions, but the 20 C under constant light from 20W cool-white proliferation of susceptible wheat cultivars also has fluorescent lamps (6.6 X 103 ergs/ cm 2 / sec) (8, 9, 10). The exacerbated its importance in dryland wheat-growing plates were flooded with 3-5 ml of sterile water and the areas (4, 5, 11). cirrhi that contained pycnidiospores were removed by Germplasm with resistance to Septoria glume bloth is gently rubbing the agar surface with a glass rod. A spore scarce, and the mode of inheritance of the known suspension from several agar plates was used to inoculate resistance is not well understood (1,4, 5, 11). Tolerance to the seedlings. the disease limits yield losses and is manageable in Four spring wheat cultivars that varied in their breeding programs (3). A major obstacle in breeding for resistance to S. nodorum were used: DeKalb's SB-8, resistance to the disease has been the lack of reliable Fortuna (C.I. 13596), Manitou (C.I. 13775), and World screening and selection methods at an early stage of plant Seeds' WO 1812 (C.I. 14585). Seeds of all cultivars were development. Several investigators have suggested means sown in straight lines and at equal spacing on the to inoculate and screen cereal cultivars based on foliar periphery of 20 X 20 X 6.5 cm-square plastic containers symptoms on seedlings or adult plants, or on yield (30-40 seeds/cultivar) 10 days before the inoculation. The comparisons (1, 2, 5, 6, 7, 11). The lack of a quantitative plants were kept in growth chambers at 15 C night/ 23 C inoculation method also has been an impediment to day temperatures, and a 12-hr day length with a light studies of the disease under controlled conditions. intensity of 1.7 X 104 ergs/cm / sec. Each plastic container The objective of this study was to devise a method for was placed on a phonograph turntable equipped with a quantitative inoculation of wheat seedlings to measure variable speed mechanism [33, 45, and 78 revolutions per the response of cultivars to the parasite. minute]. Two glass slides (7.5 X 1.25 cm) were placed back to back and held in a clothes pin standing upright among the wheat seedlings. Two of these spore catchers were Copyright © 1977 The American Phytopathological Society, 3340 placed on opposite sides of the container. Pilot Knob Road, St. Paul, MN 55121. All rights reserved. Fifteen ml of spore suspension was sprayed onto plants