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The infection biology of Bipolaris oryzae and the defence responses of its host rice were studied using the rice cv. MTL 189 inoculated with two isolates of B5 (highly compatible with MTL 189) and K2 (less compatible). In the former interaction, the hyphal progress was accompanied by tissue degradation and extensive sporulation after 8 days, whereas in the latter interaction, only very limited tissue degradation and sporulation was observed. Quantitative microscopy of the infection showed that the percentages of conidia and appressoria causing penetration and fluorescent epidermal cells (FEC) were lower for isolate K2 than for isolate B5 at 12 and 24 hours after inoculation (hai). Fluorescent papillae (FP) were only seen in the less compatible interaction and the percentage of conidia causing single FEC was highest in the less compatible interaction at 12 hai, but not at 24 hai. Qualitative examination of other defence responses showed that H2O2 started to accumulate at 4 hai in the less compatible interaction, whereas it appeared in the compatible interaction only at 12 hai. The level of H2O2 was generally higher in the less compatible than in the compatible interaction. Cross sections of leaves showed that H2O2 accumulated in the outer walls of epidermal cells. Likewise, accumulation of callose and polyphenolic substances was most pronounced in the less compatible interaction and occurred at the same places as H2O2. To our knowledge, this is the first report implicating H2O2 as an early defence response against the hemibiotrophic pathogen B. oryzae during early infection stages in rice. Understanding defence reactions may aid in resistance breeding.

Kartoffel Virus Y (PVY) er årsag til et stigende antal kassationer og nedklassificeringer af læggekartoffellinier i Danmark. Kontrol af PVY er en integreret del af det danske læggekartoffelcertificeringsprogram. Tre spørgsmål om PVY-kontrol er adresseret i denne rapport: 1) Hvad er udfordringerne ved den visuelle PVY inspektion? 2) Hvad er karakteristisk ved en problematisk sort? 3) Hvad kunne et alternativt diagnostikværktøj være?14 udbredte kartoffelsorter i Danmark er rangeret baseret på indsamlet data fra Plantedirektoratets årlige marksyn og vinterafprøvninger. Ved at bruge en mixed effect model blev det fastslået at alle 14 sorter responderer individuelt i forhold til PVY infektionsniveauet, og at indvirkningen af marksynresultatet på vinterafprøvningsresultatet er signifikant forskellig for alle 14 sorter (p = 0,004179). Selv når marksynet konkluderer: ’Ingen PVY infektion’ vil det være afgørende hvilken sort der er synet, i forhold til om der vil findes PVY infektion i vinterafprøvningen (p < 2.2 x 10-16).I en mindre sammenlignende undersøgelse blev PVY fundet i to kartoffelsorter, ved brug af LFD pocket kit i opløsninger ned til 1:125. Men ved hjælp af et andet værktøj til brug ved marksyn, FTA® Plant Saver (Whatman industries Ltd.), kunne PVY detekteres med 25 fold højere følsomhed end LFD pocket kit.En spørgeskemaundersøgelse blev besvaret af Plantedirektoratets markkontrollører som understøtter litteraturstudiet og følsomhedseksperimentet med erfaringer og proffesionelle observationer., Potato Virus Y (PVY) is the cause of increasing rejection and downgrading of seed potato lots inDenmark. Control of PVY is an integrated part of the Danish Seed Potato Certification Program. Threequestions related to the PVY control are addressed in the report: 1) what are the challenges of visuallyinspecting PVY? 2) What is characteristic for a problematic cultivar? 3) What could be an alternative toolto diagnose PVY?14 commonly grown cultivars in DK are ranked based on The Plant Directorates two annual PVYinspection results. Using a statistical mixed effect model, it was found that all 14 cultivars are individualin their response to PVY. The effect on winter trial of field inspection is found to be significantly differentfor all cultivars (p = 0,004179). The cultivar has a significant influence on winter trial results even if onlyfocusing on seed lots who were, or seemed to be, free from PVY infection at the field inspection (p <2.2x 10-16)In a small comparative investigation, PVY was detected in foliage from two potato cultivars, using theLFD pocket kit technology at a dilution of up to 1:125. But, using another field adapted tool, the FTA®Plant Saver technology (Whatman industries Ltd.), PVY detection was found in both potato cultivars tobe at least 25 fold more sensitive than the LFD pocket kit.A questionnaire survey completed voluntarily by the Danish Plant Directorate field inspectors supportedthe literature survey and the clinical investigations with hands on experiences and professionalobservations.

Hemibiotrophic plant pathogens pass both biotrophic and necrotrophic phases during their infection cycle. Colletotrichum spp. exhibits two types of hemibiotrophy, i.e. intracellular and subcuticular intramural. Colletotrichum sublineolum infecting sorghum exhibits a typical intracellular type of hemibiotrophy. During the biotrophic stage of C. sublineolum infection in sorghum, several cell wall-associated defence reactions are activated and efficiently participate in stopping pathogen development. Among these defence reactions, generation and accumulation of reactive oxygen species (ROS) and cell wall barrier formation are key factors in resistance. This review focuses on the infection processes of C. sublineolum in sorghum and the defence responses activated, with special emphasis on accumulation of ROS and hydroxy-rich glyco-proteins (HRGPs).

Hydroxyproline-rich glycoproteins (HRGPs) accumulation and oxidative cross-linking is one of the earliest defense responses in plants against pathogen infection. In the present study HRGP accumulation in three sorghum genotypes i.e. SC146 (resistant), SC326 (intermediately resistant) and BTx623 (susceptible) as a response to Colletotrichum sublineolum isolate CP2126 infection is elucidated. HRGPs were monitored by hydroxyproline (Hyp) estimation. In genotypes SC146 and SC326 there was a significantly higher amounts of Hyp at 2 days after inoculation (dai) compared to genotype BTx623, indicating an infection induced accumulation of HRGPs. Western blot analysis of acid-ethanol extracted proteins with polyclonal antibody raised against pearl millet purified HRGPs identified four bands with molecular masses of ∼65, 45, 17 and 14 kDa as HRGPs. Insolubilization of the 45 kDa protein in genotypes SC146 and SC326 upon infection with C. sublineolum indicates a role of this protein in cell wall cross-linking, coinciding with heavier accumulation of hydrogen peroxide. In addition, tissue print analysis using polyclonal antibody of pearl millet HRGPs recognized these cross-linked proteins to be HRGPs. These findings indicated that HRGPs in sorghum is a component of defense reaction against C. sublineolum infection.

Sorghum, caryops.., aleurone, transfer cell, placental sac

The race specific resistance of pea to Ascochyta pisi Lib. was shown to be exhibited as a hypersensitive response associated with the production of polyphenolic substances in epidermal and mesophyll cells. The levels of transcripts representing a pathogenesis-related (PR) protein (chitinase) and an enzyme of phytoalexin biosynthesis (chalcone synthase) were shown to accumulate more rapidly during the hypersensitive response than during lesion development in the compatible interaction. A full-length (1143 bp) cDNA sequence of a pea chitinase (EC 3.2.1.14) (coding for an approx. 34 500 Da protein) was deduced by combining the overlapping sequences of three clones obtained following PCR amplification of cDNA prepared from mRNA isolated 24 h after inoculation of pea leaves with Ascochyta pisi. The combined sequences were identified as a class I chitinase corresponding to the basic A1-chitinase enzyme previously isolated from pea leaves (Vad et al., Planta, 184 (1991) 24-29). Like class III and IV chitinases, the pea sequence differs from other class I chitinases in the absence of a hydrophobic C-terminal domain. © 1993.