| Abstract: | Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence
P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic
differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular
mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two
semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22
genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE)
was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than
P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering
genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of
the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the
numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm
tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically
correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P
fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer.
(V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation
ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.
This revised version was published online in June 2006 with corrections to the Cover Date. |
