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Germination characteristics and nutritional qualities of oat seed are the most important factors influencing plant growth, crop yield and food quality. Pantoea agglomerans has been reported as a pathogen causing leaf blight diseases, but little is known about the influence of this bacterium on seed germination, seedling growth and seed quality of oat. The aim of our work is to evaluate the effects of this seed-borne pathogenic bacterium on seed germination, seedling growth and nutritional quality of Avena sativa (B7) and A. nuda (B2). Interestingly, the germination rate (GR), germination potential (GP), germination index (GI) and vigor index (VI), shoot length, root length, dry weight, ash, protein, total starch, β-glucan, phytic acid, total phosphorus and Ca of A. nuda and A. sativa were significantly (P<0.05) decreased by P. agglomerans, and the AGT was significantly (P<0.05) prolonged. Furthermore, A. nuda had a higher seed germination, seedling growth and nutritional quality than A. sativa under CK and P. agglomerans treatments. This study demonstrated that P. agglomerans has strong pathogenicity to oat seeds, meanwhile, it also inhibits seed germination and seedling growth and causes losses in nutritional quality of oat seeds in storage. This is the first comprehensive study of pathogenicity of P. agglomerans to oat seeds, and its influence on seed germination, seedling growth and seed nutritional quality of covered and naked oat seeds.

Addition of live mycelium ofRhizoctonia solani to three slightly, acid sands collected in winter from a field after a previous potato crop resulted in accumulation of hyperparasites and less infestation of sprouts of infected seed potatoes. A similar effect was observed in alkaline marine sandy loam soils, but only after a second addition of live mycelium. The predominant hyperparasite in these experiments wasVerticillium biguttatum. Toevoeging van levend mycelium vanRhizoctonia solani aan licht zure zandgronden, in de winter verzameld van velden na een aardappelteelt, leidde tot een ophoping van hyperparasieten en een afneme vanR. solani en resulteerde uiteindelijk in bescherming van aardappelspruiten tegenR. solani. Dit effect werd ook in mariene zavels waargenomen, echter pas na een tweede toevoeging van mycelium. Verticillium biguttatum bleek de meest voorkomende hyperparasiet te zijn.

A monogenic recessive resistance to Rice yellow mottle virus (RYMV) found in the Oryza sativa indica cultivar Gigante and in a few Oryza glaberrima cultivars provided a higher level of resistance than either a polygenic partial resistance found in some japonica cultivars which delayed symptom expression or transgenic resistances which were partial and temporary. This high resistance was overcome by several isolates, but the percentage of such virulent isolates in the fields was low. There was no relationship between the virulence of an isolate towards the high resistance and its aggressiveness in other cultivars. Isolates with either of the two components of pathogenicity – virulence and aggressiveness – were found in each strain and in all regions of Africa, in both wild and cultivated grass species. There was no loss of fitness of resistance-breaking (RB) isolates as they were not counter-selected, impaired or outperformed after serial passages in susceptible cultivars, even in mixture with avirulent quasi-isogenic wild type isolates. Resistance breaking was highly dependent on the amount of virus inoculated and on the mode of transmission. Implications of these results for the durability of the resistances to RYMV and for the development of integrated disease management strategies are discussed.

Uit papiervlekken van prei, afkomstig uit verschillende plaatsen van ons land, werd een schimmel geïsoleerd, die gedetermineerd kon worden alsPhytophthora porri Foister. Er bestaan echter enkele verschillen tussen de beschreven soort en de Nederlandse isolaties. In Nederland worden nooit conidiën op het aangetaste blad waargenomen, terwijl wij hiervoor op havermoutagar afmetingen vinden, die kleiner zijn danFoister aangeeft. Ook voor optimum-, minimum- en maximumtemperaturen vindtFoister andere waarden. In een bespuitingsproef gaven koperoxychloride, captan en zineb alle zeer goede resultaten. A species ofPhytophthora, identical in general characteristics withPhytophthora porri (Foister, 1932), was isolated from diseased leaves of leeks in the Netherlands. However, the fungus differed fromFoister's description in that no conidia were formed on the leaves, and those formed on oatmeal agar measured 38.2×28.5μ, in contrast to 51×35μ measured byFoister. The minimum temperature for growth was just above 0°C, the optimum ranged from 12°–22°C and the maximum was about 26°C (table 2). This again is not in agreement withFoister's findings. Spraying five times at three-weekly intervals with CuOCl, captan and zineb gave fairly good control (table 3).

Certain phosphate salts are known inducers of systemic acquired resistance (SAR). In the present study, a local spray application of dipotassium hydrogenphosphate (K2HPO4) was effective in inducing a high level of systemic protection in cucumber plants against anthracnose caused by Colletotrichum lagenarium. Resistance induction by K2HPO4 was associated with localized cell death in cucumber leaves treated with the phosphate salt. The cell death observed, subsequently resulted in the appearance of macroscopically visible, necrotic spots. Appearing lesions resembled those provoked by tobacco necrosis virus (TNV) during a hypersensitive response (HR) that leads to pathogen-induced activation of SAR. Phosphate-mediated cell death was preceeded by a rapid generation of superoxide and hydrogen peroxide. As a further consequence of phosphate application, a local and systemic increase in free and conjugated salicylic acid (SA) levels was detected. The phosphate-induced responses were also identified with a similar time range in cucumber leaves that had been pre-inoculated with TNV. In contrast, none of these responses was triggered by application of the commercial plant activator benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester (BTH), which nevertheless was highly effective in inducing SAR in cucumber against anthracnose. In conclusion, the chemical SAR inducer K2HPO4 and the biological inducer TNV share some common early steps in signal transduction leading to SAR in cucumber, which differ from those involved in BTH-mediated SAR.

Endophytic bacteria have attracted a great attention because they produce chemicals that increase the resistance of host plants against diseases. In the current study, 40 strains of endophytic bacteria from Kobreasia capillifolia of an alpine grassland were screened for the inhibitory effect against the tomato leaf pathogen Pseudomonas syringae. The endophytic bacterium strain 262XY2’ developed a clear inhibition zone of growth with a bacteriostatic band width of 0.67 cm against P. syringae on the cultural plates. The strain 262XY2’ also showed an inhibitory activity to Bipolaris sorokiniana, Stysanus stemonitis, Alternaria soloni, Botrytis cinerea, Fusarium solani and F. oxysporum. It was able to fix nitrogen, dissolve phosphorus and produce indole 3-acetic acid (IAA). Based on morphological characteristics and the molecular sequence analyses of 16S rRNA and gyrB genes, the 262XY2’ strain was identified as Bacillus subtilis. B. subtilis 262XY2’ strain tagged with the green fluorescence protein (GFP) was found to colonize stably in the roots, stems and leaves of tomato plants, and could be re-isolated from the rhizosphere soil after 0 to 60 days of inoculation. Moreover, it also exhibited a control effect of 48.55% against tomato leaf spot caused by P. syringae. Our results indicate that the antagonistic bacteria B. subtilis 262XY2’ has the potential to be used as a biocontrol agent for tomato leaf spot.

Isolates of Phytophthora infestans were obtained from late blighted plants from several potato-growing regions of Uruguay in 1998 and 1999. Of these, 25 representative isolates (4 from 1998, 21 from 1999) from the main potato-growing areas of the country, were characterised in terms of mating type, metalaxyl resistance, allozyme genotype, mitochondrial haplotype, RG57 fingerprint (1999 isolates only) and pathotype. All isolates proved to be A2 mating type, monomorphic and homozygous at the loci coding for glucose-6-phosphate isomerase and peptidase (Gpi 100/100, Pep 100/100) and to possess mitochondrial haplotype IIa. Metalaxyl-resistant isolates constituted 92% of the total. All the 1999 isolates possessed the same RG57 fingerprint, which was that previously reported as associated with the clonal lineage BR-1 from Brazil and Bolivia, which is also A2, Gpi 100/100, Pep 100/100. Most of the isolates displayed broad-spectrum virulence and five carried virulence to 10 of the 11 R genes tested despite the absence of R genes in commercially grown potato cultivars. It was concluded that the Uruguayan P. infestans isolates resembled isolates from neighbouring South American countries, notably Brazil, and belong to the new populations of the pathogen now predominant in many countries.