ࡱ> DFC7 <0bjbjUU .B7|7|Pl$2RRRRRRRR  $C cP RRRRR RRG RRR R  RF m$ ]0   Phosphorus use efficiency in maize breeding `imi D.1, Kova evi V.2, Rastija Mirta2, Lon ari Z2. i Jambrovi A.1 1 Agricultural Institute Osijek, Juzno predgradje 17 HR-31000 Osijek, Croatia; e-mail: domagoj@poljinos.hr 2 Faculty of Agriculture, University of Osijek, Trg sv. Trojstva 3, HR-31000 Osijek, Croatia Abstract Due to large area of phosphorus (P) deficient soils worldwide, breeding for P use efficiency becomes of commercial interest in maize. In this study, results from experiments grown in Croatia in 2003 and 2004 were presented in order to examine P efficiency in two well-known Os hybrids as well as in their respective parents and four crossing generations. The two-year trial was planted at two locations (Zel in and Gundinci) differing markedly in P concentrations in soil. The results showed that 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. There was heterosis for P efficiency in this hybrid in 2004, but further work is required to clarify this occurrence. Key words: maize, grain yield, P deficient soil, P use efficiency Introduction Detection and development of phosphorus (P)-efficient genotypes with greater ability to grow and yield under P-deficient condition receive recently more attention in maize breeding, even in temperate areas. `imi et al, (2006) found that Os inbred lines belonging to the BSSS maize family (Iowa Stiff Stalk Synthetic) represent an interesting material for studying the physiological basis of P efficiency. However, since maize crosses of divergent parents could express heterosis for several P efficiency parameters (Hageman and Lambert, 1988), both inbred lines as parents, as well as their subsequent generations should be taken into consideration. In this study, results from experiments grown in Croatia in 2003 and 2004 were presented in order to examine P efficiency in two well-known Os hybrids as well as in their respective parents and four crossing generations. Materials and methods This study included six generations of two widely spread commercial hybrids (single crosses) of OSSK 596 and OSSK 602: 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. The two-year trial was planted at two locations (Zel in and Gundinci) in 2003 and 2004. Location in Zel in had soil with P-deficient conditions (35 mg P2O5 per kg of soil), whereas location Gundinci had soil with optimal P level (166 mg/kg), according to the LE extraction (Lakanen and Ervio, 1971). Usual crop management practice for maize was applied. P-concentration was determined by inductively coupled plasma (ICP) technique after milling and microwave digestion in the laboratory of the Research Institute for Soil Science and Agricultural Chemistry of Hungarian Academy of Sciences in Budapest, Hungary. The analyses were made by Jobin-Yvon Ultrace 238 ICP-AES spectrometer. Grain yields were calculated on the 14% moisture basis. P efficiency was calculated as percentage (yield at P deficient soil / yield at P optimal soil) 100. Results and discussion 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 (Figure 1). 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. However, 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.  Figure 1. Mean phosphorus (P) use efficiency (%) across six generations of two maize hybris in two years calculated as ratio of grain yields at two environments differing in P concentration in soil Conclusion BSSS maize family represent an interesting material for studying the physiological basis of P efficiency. Inbred lines from the family had different mechanisms of P efficiency. In some instances there is heterosis for P efficiency, but further work is required to clarify this occurrence. References Hageman, R. H., Lambert, R.J. (1988): The use of physiological traits for corn improvement. In: Sprague G.F., Dudley J.W., eds. Corn and Corn Improvement. Agron. Monogr. 18. 3rd ed. Madison, WI: ASA, CSSA, and SSSA: 431-461. Lakanen E., Ervi R. (1971): A comparison of eight extractants for the determination of plant available micronutrients in soil. Acta Agr. Fenn. 123: 223-232. `imi, D., Kova evi, V., `imi, B., Rengel, Z. (2006): Genotypic differences among maize inbred lines in phosphorus efficiency on soils differing in acidity. J Plant Nutr Soil Sci (in press) SA}ETAK U inkovitost koriatenja fosfora u oplemenjivanju kukuruza U svijetu je sve vei udio obradivih povraina koje u tlu nemaju dovoljno iskoristivog fosfora (P), pa je oplemenjivanje kukuruza na poveanu u inkovitost koriatenja P u posljednje vrijeme postalo i komercijalno zanimljivo. U ovom radu prikazani su rezultati pokusa s dva poznata Os hibrida (OSSK 596 i OSSK 602) i njihovih odnosnih generacijskih materijala (roditelji, (R1, R2), F1 i F2 generacije kri~anaca, kao i prva povratna kri~anja na oba roditelja (BC1, BC2)), kako bi se ustanovilo ima li razlike u u inkovitosti koriatenja P meu aest generacija pojedinog kri~anca. Pokus je bio posijan 2003. i 2004. g. na dvije lokacije (Zel in i Gundinci) koje se zna ajno razlikuju u sadr~aju P u tlu. Rezultati pokazuju da postoje razlike izmeu aest generacija u mehanizmima u inkovitosti koriatenja P kroz dvije godine ispitivanja: sva etiri roditelja u oba hibrida imali su najmanje razlike u usporedbi s generacijama kri~anaca. Roditelji hibrida OSSK 596 su se znatno meusobno razlikovali u prosje noj u inkovitosti. Roditelj R1 imao je prosje nu u inkovitost veu od 100%, ukazujui da je taj roditelj bio u inkovitiji u koriatenju P na tlu s manjkom P. Openito, u hibridu OSSK 596 nije uo ena pojava heterozisa za svojstvo P u inkovitosti. Meutim, roditelji hibrida OSSK 602 su imali sli an postotak u inkovitosti koriatenja P i uo en je heterozis u ovom hibridu u 2004. g. Daljnja istra~ivanja su nu~na da se objasni neredovita pojava heterozisa za ovo svojstvo. 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