Response of cowpea lines to low Phosphorus tolerance and response to external application of P

Abstract

Low availability of phosphorus (P) is a major constraint to crop production in Sahel and Sudan Savanna of West Africa, and efforts are being made to identify cowpea genotypes with tolerance to low P and greater P use efficiency. Arbuscular mycorrhizal fungi (AMF) enhance P uptake in low P soil. Cowpea breeding lines (200) were examined at 3 P levels (0P, 90 kg P ha-1 as Rock Phosphate and 30 kg P ha-1 as Simple Super Phosphate (SSP) in 2002 at Minjibir, Nigeria and Toumnia, Niger. Wide apparent variation in grain and fodder yields was found among the 200 genotypes. Grain yield response to RP and SSP ranged from 1 to 160%. Based on the genotypes performance at low and high (SSP), genotypes were classified. Fifteen genotypes were selected from the different P use and response groups and further examined in the greenhouse and field studies for growth characteristics related to tolerance to low applied P. Phosphorus application significantly (P ≤ 0.05) increased the grain and fodder yield at both locations., shoot-root ratio but decreased AMF colonization of cowpea roots. There were large differences in the relative P used in efficiency and the values ranged from –11 to 38 kg grain (kg P)-1 applied. AMF infection was reduced by at least 50%, while shoot-to-root ratio was significantly increased with P application. Variation between genotypes was significant for certain paired means but not consistent for all parameters measured, and the locations. The cowpea genotypes differ in AMF colonization, shoot growth relative root development, and relative P use efficiency for tolerance to low P soils and response to external application. Key words: Arbuscular mycorrhizal fungi (AMF), cowpea genotypes, P-tolerance/response, relative P-use efficiency, shoot, root ratio.