The Symbiotic Efficiency of Some Peanut Cultivars and Their Interaction with Strains of Rhizobium Spp.

Singleton, Paul W.
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A series of greenhouse and growth room tests were conducted to investigate the interactions between strains of Rhizobium spp. and cultivars of peanut (Arachis hypogea (L.)). Two preliminary greenhouse studies. Experiments 1 and 2, involved testing five and seven strains of rhizobia respectively on two cultivars of peanut. Experiment 1 identified a strain (TAL 236) which was significantly better than other effective strains on both cultivars (Florida Giant and Starr). Data from the effective strains (those which reduced acetylene) indicated that cultivar Florida Giant fixed more nitrogen in early growth than Starr. Both cultivars had similar growth potential when provided NH4N03. Experiment 2 showed significant strain by cultivar interactions among effective strains. Burpee Spanish yielded significantly more than Florunner when inoculated with strain AH8 but significantly less than Florunner when both were inoculated with strain T-1. This interaction emphasized the danger in assuming that strains selected for high efficiency on one cultivar of peanut will perform in a similar fashion on another. Strain TAL 1000 proved to be better than the other effective strains when data from both cultivars were considered. Observations of plants during Experiments 1 and 2 indicated that plants inoculated with strains TAL 236 and TAL 1000 underwent greening of foliage earlier than those plants inoculated with less effective strains. A growth room experiment (Experiment 3) was undertaken to determine whether the earlier greening of foliage by the more effective host-strain combinations were related to the time required for nodule formation. Experiment 3 revealed a significant relation between host seed size and the time to nodule formation. However, the time to nodule formation could not be related to the degree of symbiotic effectiveness of host-strain combinations as determined in Experiments 1 and 2. Effective strains TAL 1000, TAL 236, and TAL 309 were selected to test the symbiotic effectiveness of 1 2 cultivars of peanut in Experiment 4. Differences between cultivars and significant strain by cultivar interactions were revealed. The yields of the cultivars were more uniform when provided NH4N03 than when relying on the symbiosis as a nitrogen source. Some cultivars' average symbiotic yields were over 80% of their respective yields when supplied with mineral N. Other less efficient cultivars yielded only 50% of their mineral N controls. Cultivars inoculated with TAL 1000 generally had greater yields than those inoculated with strains TAL 309 or TAL 236. These tests demonstrated the specific host by strain interactions involved in the peanut-Rhizobium symbiosis. An effective symbiosis is both host and strain determined. Strains which had been shown to be highly effective on more than one cultivar in preliminary tests did not always result in a highly effective symbiosis with other cultivars.
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