Interactions of Puccinia striiformis and Mycosphaerella graminicola on Wheat

aluminum pans 20 X 20 X 5 cm. No additional fertilizer was used. The soilMadariaga B., R., and Scharen, A. L. 1986. Interactions of Puccinia striiformis and andimixnwasfsufficientlys nutritious to Mycosphaerella graminicola on wheat. Plant Disease 70: 651-654. sand mix was sufficiently nutritious to support completely healthy-appearing Puccinia striiformis and Mycosphaerella graminicola are frequently found attacking the same control plants. Supplemental light was wheat leaf. The effect of one pathogen on another and the effects of interactions between pathogens provided by 400W metal halide lamps to on host-pathogen interactions were studied. Seedlings of four spring wheat cultivars were ensure a 12-hr photoperiod. Each inoculated at different times with various combinations of P. striiformis and M. graminicola. The container was planted with 15 seeds of a two pathogens could colonize the same leaf simultaneously, and the area diseased was similar or cultivar along the border of the pan, using smaller than the area affected by each organism separately. A smaller amount of leaf tissue was an equal area for each cultivar. Plants colonized by P. striiformis when M. graminicola was present. M. graminicola acted as a hypostatic wer 6-12 days and inoculated parasite toward the rust. Wheat seedling leaves infected by P. striiformis remained green longer and were grown for 12 (2 1). had greater dry weight than leaves infected by both pathogens. This may have been due to the en they reached growth stage 12 (21). sequestering effect known to be characteristic of rusts. It is possible that M. graminicola interfered After disease symptoms appeared, 21, 26, with the redirection of translocation of assimilates that is a common effect of rusts. and 31 days after the initial inoculation, nine plants per cultivar per pan were Additional key words: Septoria tritici, stripe rust evaluated by assessing total nongreen area present on the oldest leaf. The presence of pycnidia and uredinia also Research plant pathologists tend to (4). M. graminicola as a secondary was recorded. Disease-free control plants study the effect of one disease at a time; pathogen increased when tissues were afwere maintained in all experiments. however, the occurrence of one disease in fected first by Gaeumannomyces graminis Twenty-seven plants were evaluated for a crop is the exception rather than the (Sacc.) Arx & Oliv. var. tritici Walker (2). each disease treatment. rule (23). The interaction between When Erysiphegraminis DC. f. sp. tritici A culture of M. graminicola (ORGpathogens is usually represented as a E. Marchal infected the plant first, a 82076-1) obtained from Hyslop Farm, predisposition phenomenon in which higher incidence of M. graminicola was Oregon Agricultural Experiment Station previous infection can predispose plants observed. Cultivars resistant to M. was used exclusively. The Bozeman to infection by secondary unrelated plant graminicola may show susceptible reacisolate of P. striiformis used in all pathogens (22). When two or more plant tions or pycnidial production when tissues experiments was collected in 1979 from a pathogens are present in the same host, are colonized first by E. graminis (3). field of the wheat cultivar Itana, and the interactions could be expressed as M. graminicola, teleomorph state of spores were continuously maintained at 5 antagonism, antibiosis, and/or predation the causal organism of Septoria tritici C in vacuum-sealed tubes. (5). The term parasitic epistasis could blotch, and P. striiformis West., causal M. graminicola was increased in liquid express the physiological modifications organism of stripe rust, are frequently media and adjusted to a concentration of occurring in the interacting parasites (18). found together on the same wheat plants 107 spores per milliliter of suspension. In wheat (Triticum aestivum L.), it has (8; C. C. Mork,personal communication), The liquid medium was prepared using 9 been reported that a previous attack of confounding research and causing subg of yeast extract + 9 g of sucrose and 900 Mycosphaerella graminicola (Fuckel) stantial losses in farmers' crops. Multiple ml of distilled water. After 5 days on a Schroeter induced a decrease in the infection methods have been developed wrist-action shaker at ambient laboratory incidence of Puccinia recondita Rob. ex (11,12) and used (20) where interactions temperature, abundant sporulation of the Desm. f. sp. tritici in susceptible cultivars between pathogens have not been suffifungus was obtained. Plants were cientlyconsidered. Physiological changes inoculated using a diaphragm pump in plant tissues affected by a biotrophic connected to a DeVilbiss atomizer (10). Present address of first author: Quilamapu Research organism such as P. striiformis and a P. striiformis storage tubes were Station, INIA, Casiiia 425, Chiiian, Chiie.opnd2hbereicuaoadte necrotrophic organism such as M. opnd2hbereicuaoadte Cooperative investigation of the USDA and the graminicola, acting as single colonizers, spores were placed on a slide in a humid Montana Agricultural Experiment Station. Journal have been reotd(6,7,19). Disease progchamber at 22 C to allow hydration. Series No. J-1752. pes n chne ndylefwihn Inoculation was performed by discharging Mention of a trademark or proprietary product does duced by P. stiifWormis and M. graminicola a CO2 gun loaded with 40 mg of hydrated not constitute a guarantee or warranty of the product as single and simultaneous colonizers ure diniospores twice in a settling tower to by the USDA and does not imply its approval to the were studied in these experiments, induce a slow and uniform precipitation exclusion of other products that may also be suitable. of the spores on the plants on the mobile MATERIALS AND METHODS surface below (9). After the first shot, this Ac eptedfroi publcatsiong3Fbury18)sumte Wheat cultivars with a suitable range mobile surface was moved 180 degrees forelctrni prcesin).of resistance and susceptibility to both P. from its original position to ensure a Th pblcaio cal o tisarice erderaedinpas striiformis and Ml. graminicola were more uniform dissemination of the by page charge payment. Thia article muat therefore be selected for the interaction studies (Table urediniospores. Disease incidence was hereby marked "advertisement" in accordance with 18 1). Cultivars Lemhi (CI 11415), Baart (CI assessed by visual estimation of symptoms U.S.C. § 1734 aolely to indicate this fact. 1697), Anza (CI 15284), and Lakhish and signs of the disease with the modified (Israeli) were used. Cobb scale. Areas under disease progress This article is in the public domain and not copyPlants were grown in the glasshouse curves (AU DPCs) were measured with an rightable. It may be freely reprinted with customary crediting of the source. The American maintained at 20 ± 3 C in a 1":1 mixture of area meter (Lamba Instrument CorporaPhytopathological Society, 1986. sand and sterile clay loam soil in tion Model LI-3000). Plant Disease/July 1986 651 Table 1. Interactions between Puccinia striiformis (Ps) and Mycosphaerella graminicola (Mg) on spring wheat as measured using areas under disease progress curves (AUDPC)