Benzoxazinones are naturally occurring secondary metabolites of some Gramineae plants, responsible for their resistance to some pathogenic fungi and for their allelopathic action. Six varieties of winter wheat grown in fields under organic or conventional systems and 11 old accessions were tested for two consecutive seasons and three plant development stages for the concentration in their roots of cyclic hydroxamic acids and their degradation products. This is the first report of six benzoxazinones analyzed in plants grown in the field. An analytical technique employing LC-DAD was used for determination. It was shown that 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one, its degradation product 6-methoxybenzoxazolin-2-one, and the lactam 2-hydroxy-7-methoxy-1,4-benzoxazin-2-one were predominant compounds in all tested samples. Their concentrations significantly differed with plant development stage and season, but no significant differences were found between varieties and between plant cultivation systems. The concentrations of 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and its degradation product benzoxazolin-2-one (BOA) were much lower, ranging from 60 to 430 mg/kg of dry matter, depending on accession, stage of development, and season. There was no significant difference found between plants grown in different cultivation systems, but there were significant differences between old and new varieties; concentrations of DIBOA and its derivatives were significantly lower in old accessions. It was concluded that the concentrations of DIBOA and BOA, which are precursors of highly fungicidal 2-aminophenol, 2-amino-3H-phenoxazin-3-one, and 2-acetylamino-3H-phenoxazin-3-one, are theoretically high enough to protect plants against some soilborne pathogens.

The benzoxazolinones benzoxazolin-2(3H)-one (BOA) and 6-methoxybenzoxazolin-2(3H)-one (MBOA) and selected degradation products of these compounds were examined for their in vitro antifungal activity against Cephalosporium gramineum, Gaeumannomyces graminis var. graminis, and Fusarium culmorum. BOA was also applied to the soil-incorporated inoculum of C. gramineum to test its capability of reducing Cephalosporium stripe disease in winter wheat. MBOA reduced the mycelial growth of G. graminis var. tritici, C. gramineum, and F. culmorum by 50% (EC50) at the concentrations of 77, 134, and 271 microg/mL of corn meal agar, respectively, and the corresponding BOA EC50 values for the fungi were 11, 189, and 456 microg/mL. BOA degradation products 2-amino-3H-phenoxazin-3-one (APO), 2-acetylamino-3H-phenoxazin-3-one (AAPO), and o-aminophenol (o-AP) were much more inhibitory to the growth of C. gramineum and G. graminis var. tritici than the parent compounds. APO, AAPO, and o-AP EC50 values were found to be as low as 0.58, 4.57, and 1.4 microg/mL, respectively, for C. gramineum and 0.78, 2.18, and 0.80 microg/mL for G. graminis var. tritici. These compounds applied at the corresponding concentrations did not significantly affect the mycelial growth of F. culmorum. The treatment of C. gramineum inoculum with a 1% water solution of BOA resulted in a significant reduction infection of winter wheat with C. gramineum as compared to the control with the untreated inoculum,but this treatment was not as effective as the application of a commercial fungicide.

No abstract

The increase in legume production in sustainable agriculture depends not only on the effectiveness of the selected nitrogen-fixing inoculants but also on their competitiveness in a soil environment containing an indigenous rhizobial population. In this study, we investigated the effect of pretreatment of red clover seeds with specific Nod factor (LCOs) on germination, growth, and nodulation of clover growing under sterile conditions and in the soil. We demonstrated that, although the symbiotic ability and competitiveness of the inoculant strain RtKO17 was not improved under competitive soil conditions, LCOs treatment of clover seeds significantly enhanced clover nodulation and growth of plants.

Using a sand pouch-plant infection method, populations of several species of root-nodule bacteria (rhizobia) were enumerated in eighty soils collected throughout Poland. Rhizobium leguminosarum bv. viciae (symbionts of pea, faba bean, vetch) and R. leguminosarum bv. trifolii (symbionts of clover) were detected in 77 and 76 soils, respectively. Most of these soils contained moderate and high numbers of these species of the rhizobia. Symbionts of beans, R. leguminosarum bv. phaseoli, were assessed in 76 soils; of this number 15 soils had no detectable populations of bean rhizobia and in 40 soils high or moderate numbers of these bacteria were found. Bradyrhizobium sp. (Lupinus), root-nodule bacteria of lupine and serradella, were absent in 19 soils, out of 80 tested, and 34 soils were colonised by high or moderate populations of bradyrhizobia. Sinorhizobium meliloti, rhizobia nodulating alfalfa, were sparse in the examined soils; with 56 soil containing no detectable numbers of S. meliloti and only 6 soils harbouring high or moderate populations of this species. The estimated numbers of the rhizobia in the studied soils were also related to some physical and chemical properties of these soils

This study was based on a three-factor experiment carried out since 1980 on a loamy sand (Albic Luvisol) in which arable crops were grown in two 4-years rotations: RotA (grain maize, winter wheat, spring barley and silage maize) and RotB [grain maize, winter wheat plus mustard green manure (GM), spring barley and grass–clover ley (GCL)]. The soil in RotB with an increased input of OM (GM and 1-year GCL) accumulated significantly larger amounts of soil organic carbon and soil microbial biomass C, had higher activities of dehydrogenase and acid phosphatase enzymes and gave significantly higher winter wheat grain yields compared to the soil in RotA. However, in the absence of liming, the soil in RotB, contrary to that in RotA, became more acidic, had reduced activity of alkaline phosphatase and lower contents of Ca and Mg, and contained a diminished proportion of the >0.5 mm macroaggregates fraction. These soil deteriorative effects of crop rotations delivering larger amounts of OM have not been reported so far. In both rotations FYM applied once per 4-year rotation at 40 Mg ha−1 improved all the tested soil properties and had mitigating effects on the negative changes found in the soil of RotB.

No abstract

Effects of pre-sowing soybean seed inoculation with Bradyrhizobium japonicum alone or with mixed inoculants containing soybean rhizobia and Azotobacter chroococcum were compared. In the pot experiment all the tested strains of soybean rhizobia in pure cultures or in mixtures with A. chroococcum significantly improved nodulation of soybean plants and seed yields of this crop. In micro-plot experiments pre-sowing soybean seeds treatment with the inoculant containing the most effective strain 94P of B. japonicum alone or with the mixed inoculant of strain 94P and A. chroococcum were equally effective in improving nodulation intensity and seed yields of soybean in comparison to the uninoculated soybean.