Gv. Subbarao et al., GENOTYPIC VARIATION IN IRON-PHOSPHATE, AND ALUMINUM-PHOSPHATE SOLUBILIZING ACTIVITY OF PIGEONPEA ROOT EXUDATES UNDER P DEFICIENT CONDITIONS, Soil Science and Plant Nutrition, 43(2), 1997, pp. 295-305
The internal factors controlling the release of the solubilizing activ
ity (for Fe-P and Al-P) in the root exudates of pigeonpea were investi
gated. Four pigeonpea genotypes with differential abilities in taking
up P from Fe-P were grown in nutrient solution under optimum P and P-f
ree conditions. Root exudates and plant samples were collected at week
ly intervals; the solubilizing activity for Fe-P and Al-P was estimate
d. Plant samples were analyzed for total P and also for P fractions. T
he solubilizing activity in root exudates was revealed mostly under P-
deficient conditions. Under P-optimum conditions, there was a negative
activity. The solubilizing activity (for Fe-P and Al-P) was negativel
y correlated with tissue P levels. Various P fractions in leaves i.e.
inorganic-P, soluble organic-P, and insoluble organic-P showed a signi
ficant negative correlation with the Fe-P and Al-P solubilizing activi
ty. The Al-P solubilizing activity was correlated positively with the
Fe-P solubilizing activity. In ICPL 88032, there was a 12 fold increas
e in the solubilizing activity under internal P deficiency, compared t
o the P-optimum status. Though, various genotypes used in the present
study reached similar internal P levels by 9 weeks after sowing, there
were significant differences in their solubilizing activities for Fe-
P. In the genotypes ICPL 88032 and C 11 the Fe-P solubilizing activity
was significantly higher compared to ICPL 88039 and ICPL 87. The solu
bilizing activity showed a declining trend towards pod-filling (i.e. 1
2 WAS). Genotypic differences in the Fe-P solubilizing activity of the
root exudates could not account for their differential P uptake from
Fe-P. The results indicated that the Fe-P solubilizing activity of the
root exudates in pigeonpea is under genetic control and that its expr
ession is possibly regulated by the internal P status and internal P d
emand which to some extent depend on the growth stages.