Phyllochron and tillering of wheat in response to soil aluminum toxicity and phosphorus deficiency

Soil constraints affect potential grain yield of wheat. Among these constraints acidic soils are especially important due to their combined effect on aluminum (Al) toxicity and phosphorus (P) fixation. The objective of the present study was to evaluate the response of final leaf number (FLN), phyllochron and tillering dynamic of wheat in response to different Al and P concentrations in the soil under field conditions. Two field experiments were conducted in an Andisol in Valdivia (39°47'S, 73°14'W), Chile, during the 2006-07 (Expt 1) and 2007-08 (Expt 2) growing seasons. Treatments in Expt 1 consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivities to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable soil Al levels (from 0 to 2.7cmolckg⁻¹). In Expt 2 treatments consisted of a control, two levels of Al toxicity and two P treatments with three replicates in both experiments. Leaf appearance was measured from seedling emergence to anthesis; their dynamics were recorded according to the scale developed by Haun. FLN and tiller appearance were recorded in the same plants at the same time. Exchangeable Al affected FLN in Expt 1 showing a linear association in both cultivars (r=0.99). In Expt 2 FLN was unaffected by both Al and P levels because there was a lower soil Al concentration in this experiment. Leaf appearance rate (LAR) was adjusted to bilinear equations, differentiating among early and later leaves. In Expt 1 soil Al concentration affected phyllochron of early leaves, increasing this trait by 14 and 33 degree-days in the Al-sensitive and Al-tolerant cultivars, respectively. Similarly, phyllocron of later leaves was also increased but at a higher extent in the same cultivars (62 and 38 degree-days). Both Al toxicity and P shortage decreased the maximum (MNT) and final number of tillers (FNT). Leaf area index at anthesis was positively associated with FLN (r=0.77) and MNT (r=0.95 and 0.99 in the Al-sensitive and Al-tolerant cultivars, respectively), with no regard to Al or P constraints.