engleski

Variation in P use efficiency in maize genotypes differing in genetic structure

There are two major mechanisms in plants maintaining improved growth and development under P-deficient conditions. In maize, most recent studies deal with the first mechanism of P acquisition. However, for maize breeding, the second mechanism of P use seems to be of more relevance, since it is directly associated with grain yield. Consequently, detection and development of P use efficient genotypes receive recently more attention in maize breeding even in temperate areas. By the earlier study it was found that some inbred lines belonging to the BSSS maize family (Iowa Stiff Stalk Synthetic) from U.S. Corn Belt represent an interesting material for studying the physiological basis of P use efficiency. Additionally, both inbred lines as parents, as well as their subsequent generations should be taken into consideration since maize hybrids of divergent parents could express heterosis for several P efficiency parameters, making the situation more complex. In this study, results from experiments grown in Croatia in 2003 and 2004 were presented in order to examine P use efficiency in two Croatian OS hybrids including their respective parents and four crossing generations. Six generations of two widely spread commercial hybrids in Croatia (single crosses) of OSSK 596 and OSSK 602 were included: two parents R1, R2, and crossing generations F1, F2, as well as first backcrosses to R1 (BC1) and to R2 (BC2) making total of twelve genotypes. As a part of greater investigation, cross generations (F1, F2, BC1, BC2) were planted together in a randomized complete block design (RCBD), while parents were planted in separate experiment, also in RCBD. Both adjacent experiments were set in three replications. In both hybrids, the respective parent R1 is of SSS origin, whilst R2 parents have Lancaster background (MBS, 1994). The two-year trial was planted at two locations in Croatia (Zelcin and Gundinci) in 2003 and 2004. Location in Zelcin had soil with P-deficient conditions (35 mg P per kg of soil), whereas location Gundinci had soil with optimal P concentration (166 mg/kg), according to the LE extraction method. Usual crop management practice for maize was applied. Grain yields were calculated on the 14% moisture basis. P use efficiency was calculated as percentage (yield at P deficient soil/yield at P optimal soil) x 100. There was significant difference for grain yield between two locations, as well as between two years of investigation (data not shown). As expected, generation means differed significantly from each other for grain yield at all four environments. Means for P efficiency were also significantly different across generations in both hybrids, but difference between two years was even greater, particularly in OSSK 602. The mean P efficiency across generations in OSSK 596 were 79.6% and 96.2% in 2003 and 2004 respectively, while in OSSK 602 these were 65.2% and 85.7% in respective two years, indicating that OSSK 596 had in average higher P use efficiency. Patterns in differences of P efficiency over the years varied across generations: all four parents (respective R1 and R2) in both hybrids had the smallest differences compared to other generations. Two parents varied markedly for mean P efficiency in OSSK596. The parent R1 had P efficiency greater than 100% in both years, showing that this BSSS inbred line had consistently higher grain yield on P-deficient soil. Generally, no heterosis was expressed in this hybrid. On contrary, two inbred parents in OSSK 602 had similar P efficiencies. Four crossing generations had notably higher efficiency in 2004, exceeding both parent. It suggests that heterosis for P efficiency was present that year in this cross. BSSS maize family represent an interesting material for studying the physiological basis of P use efficiency. Inbred lines from the family had different mechanisms of P efficiency. In some instances there is heterosis for P use efficiency, but further work is required to clarify this occurrence.

maize ; phosphorus ; genotype ; efficiency

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