Advances in genetic mapping of Septoria nodorum blotch resistance in wheat and applications in resistance breeding

Septoria nodorum blotch (SNB) caused by the necrotrophic fungus Parastagonospora nodorum is an important wheat disease in many high rainfall areas across the world. It reduces both yield and grain quality by causing symptoms on wheat leaves and glumes, and can cause yield losses up to 30% under warm and humid conditions. This book chapter gives an update on the recent progress in genetic mapping of SNB resistance in wheat, with focus on adult plant leaf blotch and glume blotch resistance with relevance to resistance breeding. This is followed by a case study on the investigation of the naturally occurring P. nodorum population in Norway and mapping of resistance loci in relevant wheat germplasm using MAGIC populations and GWAS panels as well as how this information can be used to improve resistance breeding and disease management. In the end, some future perspectives of SNB resistance breeding is provided.

The Effect of Foliar Fertilization with Micronutrients on Disease Severity and Mycotoxin Concentrations in the Grain of Winter Spelt (Triticum Aestivum spp. Spelta L.): A Case Study

The effect of mineral fertilization (NPK), foliar fertilization with micronutrients (Cu, Zn and Mn) and the NanoGro biostimulant on the severity of leaf, spike, stem base and root diseases in winter spelt cv. Schwabenkorn was evaluated in a field-plot experiment. A mycological analysis was performed and the content of Fusarium mycotoxins in grain was determined. Mineral fertilization (NPK), foliar fertilization with micronutrients and the NanoGro biostimulant exerted varied effects on the severity of Septoria leaf blotch and Septoria glume blotch, they promoted the spread of brown rust (excluding the NPK + NanoGro treatment) and inhibited the spread of black head mold (excluding the NPK treatment), eyespot and Fusarium foot and root rot (excluding the NPK + Mn treatment). Fertilization had no influence on grain yield or the content of Fusarium mycotoxins in grain. The concentrations of deoxynivalenol (DON), nivalenol (NIV), zearalenone (ZEA) and fumonisins FB1 + FB2 did not exceed the maximum permissible levels (except for DON in NPK + Cu + Zn + Mn and NPK + NanoGro treatments). Throughout the experiment, ergosterol (ERG) concentrations were highest in the grain of unfertilized spelt plants.

Contribution of Parastagonospora nodorum to the leaf and glume blotch of durum wheat in Bulgaria

Parastagonospora nodorum is an important necrotrophic fungal pathogen causing leaf and glume blotch of wheat worldwide. The disease can result in significant losses in grain yield and quality. The purpose of the current investigation was to estimate the occurrence of P. nodorum as a foliar and ear pathogen of durum wheat and disease severity on a set of cultivars under natural infection. Field experiments were performed at two locations (Sofia and Chirpan) in the period 2010-2017. Twelve winter cultivars of durum wheat were involved in the study. P. nodorum was not found at both locations in 2010 and 2011. Thereafter the pathogen was recorded on the leaves of durum wheat in Sofia every year except 2013. Symptoms included chlorosis and necrosis of the leaf tissue. The strongest manifestation of the disease was observed in 2016 and especially in 2017. In Chirpan leaf blotch was noticed only in 2 out of 8 growing seasons. The ear infection led to development of dark brown patches on the glumes, which later became purple-brown. These symptoms were noted in Sofia in 2014, 2016 and 2017. In Chirpan, glume blotch of studied cultivars was recorded in 2017 but in the previous year the symptoms were widely observed on some genotypes among the initial breeding material of durum wheat. In the present investigation P. nodorum caused leaf and glume blotch only. Symptoms on stems, nodes and leaf sheaths were not noted at both locations. The 12 cultivars under study differed in their susceptibility to leaf and glume blotch. The leaf symptoms caused by P. nodorum were recorded on all cultivars, but were more pronounced on Zvezditsa, Deyana and GK Bétadur. The glume blotch was more noticeable on Vazhod. The results of this multiyear research showed that although P. nodorum did not appear every year, the pathogen could contribute to the leaf and glume blotch of durum wheat under conditions favourable for disease development. The evaluation of cultivars demonstrated encouraging preliminary results. Several cultivars showed lower disease severity on flag leaf and no or little infection on the ear. They deserve further studies on resistance to P. nodorum.

Diagrammatic scale for the assessment of blast on wheat spikes

The correct quantification of blast caused by the fungus Magnaporthe oryzae on wheat (Triticum aestivum) spikes is an important component to understand the development of this disease aimed at its control. Visual quantification based on a diagrammatic scale can be a practical and efficient strategy that has already proven to be useful against several plant pathosystems, including diseases affecting wheat spikes like glume blotch and fusarium head blight. Spikes showing different disease severity values were collected from a wheat field with the aim of elaborating a diagrammatic scale to quantify blast severity on wheat spikes. The spikes were photographed and blast severity was determined by using resources of the software ImageJ. A diagrammatic scale was developed with the following disease severity values: 3.7, 7.5, 21.4, 30.5, 43.8, 57.3, 68.1, 86.0, and 100.0%. An asymptomatic spike was added to the scale. Scale validation was performed by eight people who estimated blast severity by using digitalized images of 40 wheat spikes. The precision and the accuracy of the evaluations varied according to the rater (0.82<R²<0.90, -6.12<a<2.94, 0.85<b<1.16), and systematic errors in overestimating or underestimating the disease were not found among the raters, demonstrating that the developed scale is suitable to evaluate blast on wheat spikes.

Health of leaves and ears of spring wheat (Triticum aestivum L.) cultivated after different forecrops

The research was conduced in the years 2000-2002. The aim of the research was to determinate the health of leaves and ears of spring wheat cultivated after spring cruciferae plants such as: spring oilseed rape (<i>Brassica napus</i> ssp. <i>oleiferus</i> Metz.), chiiiese mustard (<i>Brassica juncea</i> L.), white mustard (<i>Sinapis alba</i> L.), ole iferous radish (<i>Raphanus sativus</i> var. <i>oleiferus</i> L.), false flax (<i>Camelina sativa</i> L.), crambe (<i>Crambe abbysinica</i> Hoechst.), as well as after oat (<i>Avena sativa</i> L.) as con trol. Spring wheat cv. Torka was sown after: pIoughed stubble cultivated on this field, ploughed stubble and straw, ploughed stubble with straw and 30 kg nitrogen per hectare. During all the years of studies on leaves and ears of spring wheat septo ria of leaf blotch and glume blotch (<i>Mycosphaerella graminicola, Phaeosphaeria nodorum</i>) were found. Brown rust (<i>Puccinia recondita</i> f. sp. <i>tritici</i>) was seen on leaves of wheat only during years 2001-2002. Besides on ears fusarium ear blight (Fusarimn sp.) was present in 2002 and sooty mould (<i>Cladosporium sp., Alternaria</i> sp.) in 2001. According to health of overground parts of plants the good forecrops to spring wheat were oat, chinese mustard, oleiferous radish. The biggest impact on presence of diseases of leaves and ears had the weather during years of studies. The use of after harvest rests didn't have significant influence on health of leaves and ears of spring wheat.