Pyrenophora teres and Rhynchosporium secalis Establishment in a Mediterranean Malt Barley Field: Assessing Spatial, Temporal and Management Effects

Malt barley is one of the promising crops in Greece, mainly due to high yields and contract farming, which have led to an increase in malt barley acreage. Net form net blotch (NFNB), caused by Pyrenophora teres f. teres, and barley leaf scald, caused by Rhynchosporium secalis, are among the most important barley diseases worldwide and particularly in Greece. Their occurrence in malt barley can exert a significant negative effect on malt barley grain yield and quality. An experimental trial across two growing seasons was implemented in Greece in order (i) to estimate the epidemiology of NFNB and leaf scald in a barley disease-free area when the initial inoculation of the field occurs through infected seeds, (ii) to explore the spatial dynamics of disease spread under the interaction of the nitrogen rate and genotype when there are limited sources of infected host residues in the soil and (iii) to assess the relationship among the nitrogen rate, grain yield, quality variables (i.e., grain protein content and grain size) and disease severity. It was confirmed that both NFNB and leaf scald can be carried over from one season to the next on infected seed under Mediterranean conditions. However, the disease severity was more pronounced after the barley tillering phase when the soil had been successfully inoculated, which supports the hypothesis that the most important source of primary inoculum for NFNB comes from infected host residue. Increasing the rate of nitrogen application, when malt barley was cultivated in the same field for a second year in a row, caused a non-significant increase in disease severity for both pathogens from anthesis onwards. However, hotspot and commonality analyses revealed that spatial and genotypic effects were mainly responsible for hiding this effect. In addition, it was found that the effect of disease infections on yield, grain size and grain protein content varied in relation to the genotype, pathogen and stage of crop development. The importance of crop residues in the evolution of both diseases was also highlighted.

Survival and germinability of Rhynchosporium secalis conidia exposed to solar radiation

Rhynchosporium secalis, the causal agent of barley scald disease, is a fungus commonly found in the environment. Disease spread within a field and between fields occurs through the aerial dispersal of the fungal spores. However, not much is known about the survival potential of fungal conidia exposed to solar radiation. In the present study, detached conidia of R. secalis were exposed simultaneously in the field to direct sunlight or placed in an adjacent ventilated enclosure in the dark for periods ranging from 0.5 to 8h. In addition, conidia were either exposed or not exposed to UV-C light (254 nm) for periods ranging between 0.5 and 60 min in the laboratory. After exposure, conidia were placed on water agar Petri dishes and allowed to germinate for 24h. Germinability of conidia was reduced by up to 94% after 8h of exposure to solar irradiance (670-860 Wm-2) in the field in comparison to the non-exposed control. Germinability of conidia in the laboratory was reduced up to ~100% by doses of UV-C light of 3.2±0.7 Wm-2. The results of this study will contribute to a better understanding of the relationship between climatic conditions and barley scald epidemics

Efecto del deshierbe sobre la transmisión de la escaldadura de la cebada, por el hongo Rhynchosporium secalis (Oud.) Davis y en la germinación de semillas

The effect of weeding on the transmission of barley leaf blotch, as well as on the germination of seeds was studied. Ten gene tic lines and three cultivars of barley were used divided in 2 plots, each having 40 blocks of 2 x 1.5 m to provide the source of seed, as well as the data about splash transmission of scald. One plot contained weeds and the other did not. The seeds from all the 80 blocks were collected and sown in the glasshouse for germination tests and for the study of seed transmission of the fungus. The foliar area affected by leaf blotch and transmitted by splash water, in general 'was less in the weedy plot in the field, because the inoculum had more obstacles to overcome, jumping from one sick barley plant to a healthy one; thus there was less germination of the seeds from this plot. The clean plot had twice the number of leaf blotch infected plants, and a better rate of seed germination in the glasshouse.

Distribución de Rhynchosporium secalis en el mundo y en México

The present work is a review of the distribution of Rhynchosporium secalis (Oud.) Davis, causal fungus of barley leaf blotch, because this disease is of great importance to the mentioned crop. This fungus is of worldwide distribution and it is present in 34 countries at least. In Mexico, it is found in the central part of the country, in the states of Hidalgo, Puebla, Tlaxcala, Mexico, Jalisco, Zacatecas, Veracruz, Aguascalientes and Querétaro. It also attacks the bar ley of the northern part of Mexico, causing damage in Ensenada and North Baja California.

Rango de hospedantes de Rhynchosporium secalis

A worlwide list of 75 host plants of Rhynchosporium secalis (Oud.) Davis is given, as well as a list of the grasses that are not host, and of those that are secondary hosts. The aim is to help to achieve agronomic control of this barley parasite.

Diversity of Rhynchosporium secalis (Oud.) J. J. Davis strains in morphological and cultural peculiarities

Biological peculiarities of the rye scald fungus <i>Rhynchosporium secalis</i> (Oud.) J. J. Davis, in one population of North-West region were examined. Seventy-eight isolates, the causal agent of scald, were taken from infected rye plants. This isolates were analalysed on rate of growth on artificial test medium, structure and color and temperature dependence. Single-spore strains were obtained from each natural isolate. Color and structure of some single-spore isolates remained stable through repeated transfers to fresh PDA medium.

Rapid Detection and Quantification of Rhynchosporium secalis in Barley Using a Polymerase Chain Reaction

PCR primers for diagnosis of Rhynchosporium secalis in seed samples of barley were developed. For the quantification of the pathogen in seed samples a real-time PCR with SYBR Green approach was used. Amounts from 1.8 to 419.1 pg of R. secalis DNA per 100 ng of total DNA were detected in 18 samples of barley seeds contaminated by R. secalis in field conditions. The correctness of this quantitative analysis was checked using an artificial infection of seeds with 1, 2, 5 and 20% level of infection by R. secalis. The level of contamination of artificially infected samples decreased with a lowering amount of added seed powder contaminated by the pathogen, the correlation coefficient for this analysis was 0.98. While the primer pair used in these analyses shows cross-reactions with other pathogens (P. teres, Drechslera tritici-repentis, F. culmorum and F.&nbsp;poe), it is recommended to check the products of RT-PCR by agarose-gel electrophoresis, in which these pathogens are easily distinguishable from R. secalis by different lengths of the amplified fragments. &nbsp;