Genetic variation in acquisition, and utilization of phosphorus from iron-bound phosphorus in pigeonpea

In earlier experiments it was observed that pigeonpea is one of the few crop species that can utilize fixed forms of soil-P, particularly iron-bound P (Fe-P). The present investigation was aimed at assessing the genotypic variation in P uptake from Fe-P in pigeonpea. Fifteen pigeonpea germplasm lines that comprised genotypes of different maturity groups and three wild relatives were grown in vermiculite supplied with 15 mg P either as Fe-P or Ca-P for 60 d. Significant genetic variation in P uptake from Fe-P was observed; also P-use efficiency varied substantially among the genotypes. Dry matter production was positively correlated with P uptake both under Fe-P and Ca-P treatments (r=0.78**; r=0.63*; n=15). There was no significant relation between P-use efficiency and dry matter production, Wild related species did not show higher P uptake from Fe-P than the cultivated pigeonpea. From Fe-P, the P uptake was only 36% of that from Ca-P. The best genotypes in the present study took up an amount of P equivalent to 55% of that from Ca-P. Significant differences were detected in P-uptake efficiency (mu g P mg(-1) root d.wt.) among the genotypes, but P uptake efficiency did not correlate with total P uptake. A positive correlation was found between P uptake and root dry matter production under Ca-P and Fe-P treatments (r=0.70**; r=0.58*; n=15). The differential P uptake by ICPL 88039, C 11, ICPL 88032, and ICPL 87 from Fe-P in the vermiculite study was confirmed in soil culture where the soil contained a small amount of available P, but substantial amounts of Al-and Fe-P. The results demonstrated the presence of a significant genotypic variation in P uptake from Fe-P in pigeonpea.