اثر تلقیح با سویه‌های باکتری ریزوبیوم و سطوح نیتروژن بر خصوصیات کمّی و کیفی و محتوی نیتروژن ارقام لوبیاسفید در شرایط آب‌وهوایی استان مرکزی

Introduction
Legumes, such as common beans (Phaseolus vulgaris L.) have the ability to form a symbiotic relationship with soil bacteria capable of trapping nitrogen gas (N2) from the atmosphere and converting it into ammonia, which can be used by the plant for growth, development and seed production. The capacity of legumes to fix atmospheric nitrogen gives them an advantage over non-leguminous crops when grown on soils low in nitrogen. In many region of the world where common beans are grown, nitrogen fixation is limited by unfavorable soil conditions, temperature and water stress. Despite the numerous factors that comprise nodulation and nitrogen fixation, legumes generally assimilate 50% to 70% of their nitrogen via symbiotic nitrogen fixation. However, relative to other legumes, the common beans (Phaseolus vulgaris L.) are poor nitrogen fixers. The role of biological fertilizers is important in improvement of organic farming. Rhizobium is an economically and environmentally friendly microorganism that is used as biofertilizer. Because the Markazi province is one of the most important areas for bean cultivation in the country, therefore understanding the appropriate rhizobium strains with white bean varieties recommended for cultivation in the region is important.
 
Materials & Methods
A field experiment was carried out based on a factorial randomized complete block design with three replications at Khomein Bean Research National Station (Longitude 49° 57' E, Latitude 33° 39' N and the height at the sea level 1930 m) in Markazi Province during 2010-2011. Treatments included as N1 or control (without inoculation and N fertilizer), N2 as = 100 kg N ha-1, and five different rhizobium strains (N3: R134, N4: R156, N5: R116, N6: R133 and N7: R109), and three white bean cultivars (V1: Daneshkadeh, V2: Shokoofa andV3: Dorsa). In bacterial treatments the 20 kg ha-1 N was used as starter. The plant samples were taken in two steps: 1) at the 50% flowering stage, the factors measured included: Shoot dry weight, N concentration and N uptake. 2) At the end of growing season stage the factors measured included: Shoot dry weight, N concentration, N uptake, number of pods per plant, number of seeds per pod, 100-seed weight and seed yield.
 
Results & Discussion
The results showed that cultivars had significant difference (p<0.01) on 100-seed weight, number of seeds per pod and dry matter weight, and there was significant difference (p<0.05) on number of pods per plant. Rhizobium inoculation and nitrogen levels showed significant differences (p<0.01) on grain nitrogen, dry matter weight, flowering stage nitrogen, flowering stage dry matter weight and straw nitrogen, and there was significant difference (p<0.05) on number of grains per pod. For the interaction between cultivars and rhizobium, there were significant differences (p<0.01) on 100-grain weight, dry matter weight at flowering stage, dry matter weight and straw nitrogen (p<0.05) on number of pods per plant at flowering stage nitrogen. The maximum and the minimum values of 100-grain weight obtained from V3N4 and V1N5 treatments amounts were 32.01 and 26.72 g, respectively. The maximum and the minimum values of pods per plant, obtained from V3N2 and V2N1 treatments counted were 10.7 and 6.6, respectively. The maximum dry matter weight obtained from V2N4 treatment was 209.3 g and the minimum dry matter weight belonged to V2N1 treatments was 97.3 g. The maximum nitrogen concentration gained belonged to V3N4 treatment, with 1.97 percent and the minimum nitrogen concentration belonged to V3N1 treatment, with 1.08 percent at the flowering stage. Among the rhizobium strains, the maximum grain yield and straw yield which were obtained from R156 strain amounted to 3308.3 and 3271.1 kg ha-1, respectively. The maximum amount of grain N concentration (3.09%) obtained from R116 strain. The high amount of grain nitrogen in the inoculated treatments emphasizes the use of rhizobium in the bean planted farms.
 
Conclusion
Based on this study, rhizobium inoculation for new released beans for varieties of climbing bean production are of paramount importance, especially for farmers with limited resource in areas where land is scarce and productivity is low due to nutrients depletion. R156 strains recommended for this climatic conditions, because not only attainment of high grain yield, but also grain nitrogen content is at the upper limit. Thus rhizobium inoculation and supplementation with other nutrients such as phosphorus and potassium have constructive effect in improving photosynthesis, nutrient uptake, nodulation, growth, yield and economic benefits in beans. Also, the use of rhizobium other than nitrogen supply, reduces the activity of pathogens and increases the secretion of growth hormone. Thus, the inoculation with rhizobium for the resource poor farmers to enhance biological nitrogen fixation for small and large scale production of legume is strongly recommended in Iran.