Sanja Sikora

Influence of different Sinorhizobium meliloti inocula on abundance of genes involved in nitrogen transformations in the rhizosphere of alfalfa (Medicago sativa L.)

Inoculation of leguminous seeds with selected rhizobial strains is practised in agriculture to ameliorate the plant yield by enhanced root nodulation and nitrogen uptake of the plant. However, effective symbiosis between legumes and rhizobia does not only depend on the capacity of nitrogen fixation but also on the entire nitrogen turnover in the rhizosphere. We investigated the influence of seed inoculation with two indigenous Sinorhizobium meliloti strains exhibiting different efficiency concerning plant growth promotion on nitrogen turnover processes in the rhizosphere during the growth of alfalfa. Quantification of six target genes (bacterial amoA, nirK, nirS, nosZ, nifH and archaeal amoA) within the nitrogen cycle was performed in rhizosphere samples before nodule formation, at bud development and at the late flowering stage. The results clearly demonstrated that effectiveness of rhizobial inocula is related to abundance of nifH genes in the late flowering phase of alfalfa. Moreover, other genes involved in nitrogen turnover had been affected by the inocula, e.g. higher numbers of amoA copies were observed during flowering when the more effective strain had been inoculated. However, the respective gene abundances differed overall to a greater extent between the three plant development stages than between the inoculation variants.

Genetic diversity of Bradyrhizobium japonicum field population revealed by RAPD fingerprinting

RAPD fingerprinting was used for strain identification and the assessment of genetic diversity within a field population of Bradyrhizobium japonicum. Total genomic DNAs from 13 field isolates and two inoculant strains were amplified using six different 10‐mer primers. Different and informative band patterns were obtained for all strains analysed. Cluster analysis unexpectedly revealed that none of the field isolates was identical to inoculant strains which were regularly used for soybean inoculation. Among field isolates two highly divergent groups were determined. The results indicate that RAPD is a very discriminative and efficient method for differentiating and studying genetic diversity of B. japonicum strains.

Yield and height of alfalfa (Medicago sativa L.) effected by rhizobial inoculation

Forage crops constitute the major component of dairy feeds and legumes have been viewed as excellent sources of N in agriculture.Biological nitrogen fixation by leguminous plants is a significant source of available N in both natural and managed ecosystems and that unique ability makes legumes especially valuble in forage program.Alfalfa is one of the most important protein sources for nutrition of livestock.As a legume, alfalfa forms symbiotic relation with nitrogen fixing bacteria Sinorhizobium meliloti, which symbiotic efficiency is determined by their individual genotype.The aim of this study was to determine the infuence of cultivar type of alfalfa and S.meliloti strain on forage yield and height of plants.Results of 2 years experiment revealed that DM yield was significantly higher with cultivars OS 88 and Mirna compared to other two cultivars (Posavina and OS 66). The effect of cultivars by strains was not significant, so inoculated cultivars performed significantly better DM yields in comparison to control (no inoculation).

Influence of plant growth regulator and rhizobial inoculation on nodulation and soybean nitrogen contant

Sustainable agriculture production greatly relies on the use of renewable resources of nitrogenous reserves and rational nitrogen fertilization. The inoculation of cultivated leguminous plants with selected rhizobial strains is recommended to maximize the contribution of biological nitrogen fixation to the nitrogen status of the host plant. Considering that symbiotic fixation is dependent on the photosynthetic capacity of the specific legume, special efforts have been taken to find patterns of increasing plant photosynthetic capacity. The main aim of the present study was to evaluate the influence of Bioalgeen-S90 as a growth regulator and soybean inoculation with different B. japonicum strains on nodulation and soybean nitrogen and protein content in agroecological conditions of eastern Croatia. At location Karanac application of Bioalgeen-S90 significantly increased nodule number, nodule dry weight and seed protein content compared to plots without Bioalgeen-S90 application. Statistical analysis showed superior effect of inoculation, irrespective of the strain used, compared to to control uninoculated plots for all measured properties. Significant influence of inoculation with B. japonicum strain USDA 110 on nitrogen content in stem and ureide content in xylem were determined compared to plots inoculated with strain D344. At location Mirkovac application of Bioalgeen-S90 significantly increased nodule number, ureide content in xylem and seed protein content compared to plots without Bioalgeen-S90 application. Inoculation with strain D344 significantly increased nodule number and nodule dry weight, ureide content in xylem and nitrogen content in soybean aerial parts compared to variants inoculated with strain USDA 110 and control variants.The results of this study clearly showed the positive effect of growth regulator Bioalgeen-S90 and rhizobial inoculation on nitrogen status of host plant. However, further investigations under different agroecological conditions are needed.

Contribution of breeding to increasing soybean grain yield and grain quality

The objective of this research was to determine the genetic gain in grain yield and grain quality accomplished by recently developed domestic soybean elite lines and to determine ways to improve these traits further. Realized gains were estimated by comparing recently developed most promising domestic soybean lines of maturity groups (MGs) 00, 0 and I with commercial cultivars (standards) in comparative field tests during three consecutive years (2002–2004) in Osijek, Croatia. Mean values, broad-sense heritability, genetic gain and relative genetic gain from selection were calculated for grain yield, protein and oil content in grain. The obtained results of biometrical analysis showed genetic improvement in productivity and quality of new domestic soybean elite lines within MGs 00, 0 and 1. The high agronomic performances of this breeding material will considerably contribute to the increasing and improving soybean production in our region as well as genetic improvement of domestic soybean cultivars further.

The effect of rhizobial inoculation and liming on alfalfa production in Croatia

Maize (Zea mays L.) genotypes wit It improved nitrogen utilization efficiency (NUE) are of interest to growers. Field experiments were conducted to evaluate the total N uptake in the aboveground biomass and NUE (kg grain per kg of N absorbed in the aboveground biomass). Four commercial hybrids of similar maturity ranking were grown under the high-N (200 kg N ha(-1)) and low-N (1100 kg N ha(-1)) fertilization rates over three years. Growing conditions significantly affected hybrid performance for NUE, which ranged from 42 kg grain kg N-1 in the low-yielding (dry) environment to 55 kg grain kg N-1 under higher yielding environment, When compared to the low-N rate, the average N uptake was by 32% higher at the high-N rate, whereas smaller differences occurred for the aboveground biomass (12%), grain yields (14%), stover N (28%) and grain N (13%) concentrations. Significant differences existed among tested hybrids for grain yield, aboveground biomass, grain and stover N concentration, N uptake and consequently NUE.Hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.) were evaluated as cover crops during two vegetation seasons in the Mediterranean and Continental area of Croatia. Better tolerance to low winter temperatures was observed for crimson clover. Higher plants (10 to 3 1 cm) before winter and in spring (67 to 117 cm) were measured for hairy vetch, while crimson clover had higher yields of fresh biomass (33.7 to 113.1 t ha(-1)). Concentrations of N (1.53 to 3.34%), P2O5 (0.55 to 1.04%) and K2O (2.02 to 5.32%) in plant tissue were higher for hairy vetch. However, due to higher yields of dry matter, crimson clover accumulated more N (105 to 239 kg ha(-1)), P2O5 (28 to 83 kg ha(-1)), and K2O (105 to 440 kg ha(-1)) than hairy vetch. According to our results crimson clover could be recommended as a cover crop in Mediterranean and Continental area of Croatia.

Genetic Diversity and Symbiotic Efficiency of Indigenous Common Bean Rhizobia in Croatia

Nodule bacteria (rhizobia) in symbiotic associations with legumes enable considerable entries of biologically fixed nitrogen into soil. Efforts are therefore made to intensify the natural process of symbiotic nitrogen fixation by legume inoculation. Studies of field populations of rhizobia open up the possibility to preserve and probably exploit some indigenous strains with hidden symbiotic or ecological potentials. The main aim of the present study is to determine genetic diversity of common bean rhizobia isolated from different field sites in central Croatia and to evaluate their symbiotic efficiency and compatibility with host plants. The isolation procedure revealed that most soil samples contained no indigenous common bean rhizobia. The results indicate that the cropping history had a significant impact on the presence of indigenous strains. Although all isolates were found to belong to species Rhizobium leguminosarum, significant genetic diversity at the strain level was determined. Application of both random amplification of polymorphic DNA (RAPD) and enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC- -PCR) methods resulted in similar grouping of strains. Symbiotic efficiency of indigenous rhizobia as well as their compatibility with two commonly grown bean varieties were tested in field experiments. Application of indigenous rhizobial strains as inoculants resulted in significantly different values of nodulation, seed yield as well as plant nitrogen and seed protein contents. The most abundant nodulation and the highest plant nitrogen and protein contents were determined in plants inoculated with R. leguminosarum strains S17/2 and S21/6. Although, in general, the inoculation had a positive impact on seed yield, differences depending on the applied strain were not determined. The overall results show the high degree of symbiotic efficiency of the specific indigenous strain S21/6. These results indicate different symbiotic potential of indigenous strains and confirmed the importance of rhizobial strain selection. These are the first studies of indigenous common bean rhizobia in Croatia that provide the basis for further characterization and selection of highly efficient indigenous strains and their potential use in agricultural practice and future research.

Symbiotic nitrogen fixation and sustainable soybean production

One of the biggest challenges for the safe maize production is the yield stability in a wide range of environments with different soil fertility, weather conditions, prevailing pests and diseases as well as cultural practices. In order to achieve it, new hybrids with higher tolerance to biotic and abiotic stress are continuously being created. In order to compare performance of maize hybrids in environments with different levels and types of stress, and relate it to the stalk lodging incidence, we compared performance of 64 maize hybrids obtained by crossing 16 inbred lines with four inbred testers in three different environments. Two environments at same location (Rugvica) differed in crop rotation, and the third environment at location Botinec was considered as dry because of low water capacity of the soil. Mixed models that included all design elements and genetic background of hybrids were used to analyze the effect of lodging on yield in different environments. The results show that stalk lodging had a significant effect on yield, but significant lodging x environment interaction indicates that this effect was rather environment specific.Sweet pepper Istra F1 hybrid was grown in a greenhouse on K rich soil. For evaluation of K antagonism, two K rates (55 and 85 kg ha-1) were applied in a randomized complete block design with four replications. Total number of fruits, total number of BER affected fruits as well as average fruit mass were recorded for each harvest. Fruit and leaf K and Ca content were determined at three plant growth stages (at the stage of the first, third and fifth fruit cluster). Higher K rate gave higher : average fruit mass (169.45 g), total number of fruits per plant (7.95), number of BER affected fruits per plant (3.82), K in leaves (5.44% DM), K in fruits (6.35% DM), but negatively correlated with Ca concentration in fruits (0.57% DM) and leaves (3.24% DM). This resulted in decreased marketable yield of sweet pepper fruits.