Variability of N2 fixation in cowpea under phosphorus deficiency is related to phosphorus use efficiency
2016
Low availability of phosphorus (P) is a major constraint to legume
production, and efforts are being made to identify legume genotypes
with tolerance to low P and greater P use efficiency (PUE). Cowpea
(Vigna unguiculata L.) genotypes vary in their adaptation to low-P
soils. In order to investigate to what extent this variation may be
related to PUE for symbiotic nitrogen fixation (SNF), five genotypes,
Adrar, El Kala, Djenet, Tizi Ouzou and Bejaia, were grown in semihydroponic
culture with sufficient versus deficient P supply. At the
flowering stage, the biomass of plants and nodules and their P
contents was determined after measuring the quantity of N2 fixed.
The results showed that nodule and shoot biomass were less when P
was deficient. The genotypes that presented the maximum growth
during the experiment presented a high efficiency in use of the
rhizobial symbiosis calculated as the slope of plant biomass regression
as a function of nodulation. Under P-deficiency, efficiency in use of P
for SNF was significantly increased in the genotypes El Kala, Djenet
and Adrar and accompanied with an increase of the efficiency in use
of the rhizobial symbiosis. Hence the large differences show that
traits for more P uptake-efficient plants exist in the tested cowpea
genotypes. This opens the possibility to breed for more P uptakeefficient
varieties as a way to bring more sparingly soluble soil P into
cycling in crop production and obtain capitalisation of soil P reserves.
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