Efficiency of Nodule Initiation in Cowpea and Soybean

Abstract

When serial dilutions of a suspension of Bradyrhizobium japonicum strain 138 were inoculated onto both soybean and cowpea roots, the formation of nodules in the initially susceptible region of the roots of both hosts was found to be linearly dependent on the log of the inoculum dosage until an optimum dosage was reached. Approximately 30-to 100-fold higher dosages were required to elicit half-maximal nodulation on cowpea than on soybean in the initially susceptible zone of the root. However, at optimal dosages, about six times as many nodules formed in this region on cowpea roots than on soybean roots. There was no appreciable difference in the apparent rate of nodule initiation on these two hosts nor in the number of inoculum bacteria in contact with the root. These results are consistent with the possibility that cowpea roots have a substantially higher threshold of response to symbiotic signals from the bacteria than do soybean roots. Storage ofB.japonicum cells in distilled water for several weeks did not affect their viability or efficiency of nodule initiation on soybean. However, the nodulation efficiency of these same cells on cowpea diminished markedly over a 2 week period. These differential effects of water storage indicate that at least some aspects of signal production by the bacteria during nodule initiation are different on the two hosts. Mutants of B. japonicum 138 defective in synthesis of soybean lectin binding polysaccharide were defective in their efficiency of nodule initiation on soybean but not on cowpea. These results also suggest that B. japonicum may produce different substances to initiate nodules on these two hosts.Rhizobium and Bradyrhizobium are soil bacteria able to symbiotically infect and nodulate a wide diversity of legumes, reducing atmospheric nitrogen in these nodules to ammonia for the plant in exchange for fixed carbon (1,12

Enhanced nodulation and symbiotic effectiveness of Medicago truncatula when co-inoculated with Pseudomonas fluorescens WSM3457 and Ensifer (Sinorhizobium) medicae WSM419

“…The relative location of nodules on the root system is a useful index of the time taken for infection, i.e. nodules located on the upper part of the root system are those that were initiated earlier than those on the lower parts of the root system (Bhuvaneswari et al 1988;. Thus, the increased crown nodulation observed on co-inoculated M. truncatula in this study further supports the data demonstrating that root infection occurred earlier with co-inoculation.…”

Fodder production, yield and nodulation of some elite cowpea (Vigna unguiculata [L.] Walp.) lines in central Malawi

“…The highest nodule number came from Sudan 1 (21.7 nodules/plant), followed by IT8282E-16 (18.9), IT95-1090-12 (14.42) and 1T99K-1060 (14.0) Only two entries (Sudan 1 and IT99K-1060) appear to give grain and forage yields of about 2 tha -1 or more and high nodule numbers. These results concur with the ranges of 3-21 nodules per plant reported by Bhuvaneswari et al (1998). Ndor et al (2012) showed that nodules per plant in cowpeas increased from 20 to 32 when P application was raised from 0 to 40 kg ha -1 P. The authors reported cowpeas yield increase from about 1.0 to 1.5 t ha -1 with associated with the same P application rates.…”

Reduced availability of rhizobia limits the performance but not invasiveness of introduced Acacia

“…Highly promiscuous plant hosts are able to nodulate with a wide range of rhizobia strains and at low bacterial densities, while less promiscuous hosts show greater strain specificity and require higher bacterial densities before they nodulate (Roughley 1987;Bhuvaneswari, Lesniak & Bauer 1988;Thrall, Burdon & Woods 2000;Thrall et al 2005Thrall et al , 2007. In addition, plant hosts themselves influence the availability of rhizobia in the soil (Thrall, Burdon & Woods 2000), with rhizobia population numbers increasing rapidly in response to compatible plant hosts (Purchase & Nutman 1957;Parker 2001) and declining when they are absent (Thrall et al 2001).…”