In order to study the species composition of endophytes from wheat healthy plants in Buenos Aires Province (Argentina) and to determine their infection frequencies from leaves, stems, glumes and grains, wheat plants were collected from five cultivars at five growth stages from crop emergence to harvest. A total of 1,750 plant segments (leaves, stems, glumes and grains) were processed from the five wheat cultivars at five growth stages, and 722 isolates of endophytic fungi recovered were identified as 30 fungal genera. Alternaria alternata, Cladosporium herbarum, Epicoccum nigrum, Cryptococcus sp., Rhodotorula rubra, Penicillium sp. and Fusarium graminearum were the fungi that showed the highest colonization frequency (CF%) in all the tissues and organs analysed. The number of taxa isolated was greater in the leaves than those in the other organs analysed.

tion of the influence of N supply on the disease severity have been studied with contrasting results (Johnston et Nitrogen fertilization is required for achieving high yields in wheat al., 1979;Howard et al., 1994; Leitch and Jenkins, 1995; (Triticum aestivum L.), but N may enhance the development of leaf Lovell and Royle, 1999). Simó n et al. (1998) found that blotch (Septoria tritici Roberge in Desmaz., teleomorph Mycosphaerella graminicola (Fuckel) J. Schrö t. in Cohn). The present study in conducive conditions, N fertilization increases the was undertaken to investigate how Septoria leaf blotch affects yield, severity of Septoria leaf blotch and discussed the effect yield components, and test weight (TW) of different cultivars under of different factors affecting the influence of N supply. different N supplies. Field experiments with six cultivars were carried Most of previous papers studying the influence of N out in a split-split plot design during 1996 and 1997. Inoculation treaton the expression of disease concerned the expansion ments were the main plots, N fertilization levels were the subplots, of the necrotic area or pycnidial coverage on foliage. and cultivars were the sub-subplots. Thousand-kernel weight (TKW) Few studies include the incidence of this agronomic was higher and TW lower in 1996 than in 1997. Interaction year ϫ practice on yield and yield component losses. Leitch inoculation was not significant for any trait; year ϫ fertilization was and Jenkins (1995) observed that control of Septoria significant for yield and EPM 2 , and year ϫ cultivar was significant leaf blotch increased yield, with the magnitude of this for all traits except TKW. The separated analysis for each year indicated that additional N increased yield, EPM 2 , and KPE, but not effect greater at the higher rate of N applied. Johnston TKW or TW. Inoculation with S. tritici reduced yield and KPE, in et al. (1979) found a greater increase in yield in fertilized both years and TKW, TW, and EPM 2 in 1996. Differences between conditions compared with nonfertilized conditions when cultivars occurred for all traits except EPM 2 in 1996. The percentage fungicides were applied in only one of two years. reduction in yield, yield components, and TW due to the inoculation If the increase in the severity of the disease under N was similar in fertilized and nonfertilized conditions, despite the infertilization causes a reduction in yield and yield compocrease in the area under disease progress curve (AUDPC) values by nents, higher amounts of fungicides would be necessary N fertilization in 1996. Cultivar differences in tolerance is suggested.under high-N input systems. The aim of this work was to evaluate the influence of an early artificial infection of S. tritici on the yield, yield components, and TW 1974

No abstract

The relationship between resistance to Septoria tritici blotch with plant height and heading date has been in most cases attributed to genetic associations. More efficient selection for higher levels of quantitative resistance may result if the nature of the association between susceptibility with earliness and shortness can be determined. Genetic resistance to Septoria tritici blotch and its relationships with plant height and heading date were recorded in 50 Argentinean wheat (Triticum aestivum L.) cultivars in three environments (two in the field and one in the greenhouse) with one virulent isolate of Mycosphaerella graminicola (Fuckel) Schroeter, in Cohn (anamorph Septoria tritici Rob. ex Desm.). Furthermore, a set of 16 cultivars was tested with seven isolates of M. graminicola in the greenhouse at the adult stage. Cultivars varied greatly in resistance to the disease and plant material was identified with moderate to high levels of resistance to several isolates. The field and greenhouse experiments demonstrated no evidence of genetic associations between plant height, heading date, and resistance, indicating that selection of early and short lines with high levels of quantitative resistance is possible. The relationships between those traits were mainly caused by environmental and epidemiological factors, which indicates that management of cultivars should be optimized to minimize these associations.

No abstract

Leaf blotch of wheat is a widespread and highly active disease that affects wheat production. In addition to the use of chemicals and proper cultivation methods, microbial antagonists are used to control plant pathogens. Trichoderma spp. stimulate a systemic induced response in plants. Therefore, the efficacy of Trichoderma spp. against wheat leaf blotch was evaluated under greenhouse conditions. The susceptible plants were sprayed with Septoria tritici conidiospores. In order to select an efficient method of pretreatment with Trichoderma spp., leaf spraying and seed coating with 14 isolates were tested in 2003 and 2004. The extent of leaf necrosis area and pycnidial coverage was estimated. Antagonism was assessed by the capacity of each Trichoderma spp. isolate to restrict the progress of leaf blotch, 21 days after inoculation. Of the two methods, seed coating was more efficacious against leaf blotch than leaf spraying. Amongst the 14 isolates tested, the isolate prepared from T. harzianum (Th5) produced the highest level of protection. None of the treatments caused changes in plant stem diameter or dry weight. Trichoderma spp. did not get into leaves while S. tritici was present, even in asymptomatic leaf extracts. In addition, the leaf apoplast antifungal proteolytic activity was measured in plants 7, 15, and 22 days after sowing. This antifungal action decreased in plants only inoculated with S. tritici , but increased in those grown from seeds coated with the T. harzianum (Th5) isolate. This increase conferred resistance to the susceptible wheat cultivar. The endogenous germin-like protease inhibitor coordinated the proteolytic action. These results suggest that T. harzianum stimulates a biochemical systemic induced response against leaf blotch.

Nitrogen (N) fertilization is required for achieving high yields in wheat (Triticum aestivum L.) but may enhance the development of Septoria tritici Rob. ex Desm. A study was undertaken to investigate how N supply influences the area under disease progress curve (AUDPC). Two field experiments were carried out in a typical argiudol in 1996 and 1997. Six cultivars were grown at two N treatments (0 and 100–150 kg N/ha) in a split plot design. Percentage of necrosis (severity) of the two upper leaves of each treatment was evaluated three times during the growing season. Height and heading date were also scored and related to the resistance level. In 1996, with weather conditions conducive to the disease, AUDPC values were higher in the fertilized treatment. In 1997, with insufficient rain immediately after inoculation, the disease only progressed faster under N fertilization in the flag leaf, which was exposed to conducive environmental conditions from its appearance. The effect of N fertilization was influenced by the cultivar characteristics, climatic and agronomic conditions. Knowledge that N fertilization promotes the development of S. tritici in conducive conditions will be useful for deciding management strategies of the cultivars and for optimizing conditions for the selection in breeding programmes.

Camacho Casas et al., 1995) or short stature (Rosielle and Brown, 1979;Baltazar et al., 1990;Camacho Casas The effects of plant height and heading date on the expression of et al., 1995); however, Arama et al. (1999) and Simó n the resistance to Septoria tritici blotch, which is caused by the fungus Mycosphaerella graminicola (Fuckel) Schroeter, in Cohn (Septoria et al. (2001) did not detect genetic associations between tritici Rob. ex Desm.), were investigated in wheat (Triticum aestivum resistance and plant height or heading date. Van Beu-L.) near isogenic lines in the Mercia and Cappelle-Desprez backningen and Kohli (1990) indicated that the associations ground and differing in dwarfing genes (Rht) or in genes for insensitivbetween plant height and heading date are due to epideity to photoperiod (Ppd ). The experimental design was a randomized miological factors. block design with four replications conducted over 2 yr. Necrosis Assuming no genetic associations, it is important to (i) percentage at boot (growth stage GS 49), milk (GS 73), and dough determine whether plant height or heading date affects stage (GS 85); area under disease progress curve (AUDPC); plant expression of resistance to Septoria tritici blotch and height; and heading date were recorded. The shortest lines, Mercia (ii) detect the influence of epidemiological or environ-Rht 12, Mercia Rht 3, and Cappelle-Desprez Rht 3, showed higher mental factors. Genotypes that are genetically similar necrosis percentage and AUDPC values than their respective controls. Mercia lines with Ppd 1 and Cappelle-Desprez Ppd1 and Ppd 2, the perimental J. Hirschhorn, Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Argentina, dur-Published in Crop Sci. 44:2078-2085 (2004). ing 2000 and 2001. Plots were 1 m long by 0.60 m (three rows)