Micronutrient needs of tropical food crops

The trace element requirements of tropical crops are reviewed with special reference to their role, the differences between crop species, the differences between cultivars, paths of trace element uptake, effects of climate, the importance of crop management and yield levels

Response to bradyrhizobium strain of peanut cultivars grown under iron stress

An Fe efficient (Arachis hypogaea L. cv. 71–234) and an Fe inefficient (cv. Tainan 9) peanut cultivar were subjected to four inoculation treatments (NH4NO3 without inoculation, NC 92, TAL 1000 and a mixture of these two Bradyrhizobium sp. (Arachis) strains with THA 205) and grown under Fe stress conditions in complete nutrient solution including 0.2 mM NH4NO3 and 0.012 mM FeEDDHA at pH 8.6 maintained by addition of 5 mM NaHCO3 and solid CaCO3. During the first four weeks, cv. 71–234 grew better than cv. Tainan 9 in all inoculation treatments but by eight weeks these differences had largely disappeared. By contrast, inoculation treatments had no effects on shoot and root dry matter at four weeks but large effects at eight weeks when plants inoculated with NC 92 alone or in a mixture had similar or more dry matter than those given NH4NO3 and double that of those with TAL 1000 alone. At four weeks, both cultivars had 250, 150, and 3 nodules per plant and acetylene reduction rates of 27, 17, <1 nmol/min/plant with NC 92, mixed inoculum, and TAL 1000 respectively: they also had 40, 150, and 1000 nodule initials per plant. At eight weeks both cultivars with TAL 1000 alone had N concentrations in their shoots well below those of all other treatments. Catechol type siderophore activity was present in solutions inoculated with NC 92 alone or in mixed inoculum but absent from those with TAL 1000 alone. It is suggested that strains of Bradyrhizobium sp. differ profoundly in their ability to obtain iron from their environment for development of their symbiotic systems in peanut

Differences between Bradyrhizobium strains NC92 and TAL1000 in their nodulation and nitrogen fixation with peanut in iron deficient soil

The effects of Bradyrhizobium (strains NC92 and TAL1000) and Fe supply on nodulation and nitrogen fixation of two peanut (Arachis hypogaea L.) cultivars (cv. Tainan 9 (Fe inefficient) and cv. 71-234 (Fe efficient)) grown under Fe deficient conditions (imposed by adding 40% CaCO3 to a ferruginous soil) were examined in a glasshouse experiment. When inoculated with TAL1000 without Fe, both cultivars had low shoot N concentration, very low nodule numbers and weight and no measurable acetylene reduction activity per plant. Inoculation with NC92 without Fe increased all these parameters substantially; addition of Fe with NC92 had no further effect on N concentration but doubled nodule number, weight and acetylene reduction activity per plant. Addition of Fe with TAL1000 increased all parameters to the same level as Fe+NC92, indicating that the poorer nodulation and N2 fixation of TAL1000 in the absence of Fe, resulted from a poorer ability in getting its Fe supply from the alkaline soil. The nodules from all treatments with measurable activity had the same specific acetylene reduction activity suggesting that Fe deficiency limited nodule development. The results support previous suggestions that Bradyrhizobium strains differ greatly in their ability to obtain Fe from soils and that selection of Fe efficient strains could complement plant breeding in the selection of legume crops for Fe deficient soils