GAMA, E. E. G.

GUIMARAES, P. E. O.

MARRIEL, I. E.

MEIRELLES, W. F.

OLIVEIRA, A. C.

PACHECO, C. A. P.

PARENTONI, S. N.

SANTOS, M. X. dos

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Combining Ability for Nitrogen Use in a Selected Set of ImbredLines from a Tropical Maize Population._____________________________________________________________________________XXIV Congresso Nacional de Milho e Sorgo - 01 a 05 de setembro de 2002 - Florianópolis - SC_____________________________________________________________________________GAMA,E.E.G.1, MARRIEL, I.E.1, GUIMARÃES, P.E.O.1, PARENTONI, S.N.1, SANTOS, M.X.1, PACHECO, C.A.P.1, MEIRELLES, W.F.1 e OLIVEIRA, A.C.11Pesquisadores, Embrapa Milho e Sorgo. Cx. Postal 151, CEP, 35701-970 Sete Lagoas, MG. E-mail: gamaelto@cnpms.embrapa.br Key words: Zea mays L., nitrogen stress, general and specific combining ability, yield.IntroductionNitrogen deficiency is one of the most important stresses affecting maize production in tropical areas (Lafitte and Bänziger, 1995). The great majority of tropical soils present low levels of fertility, consequently higher levels of yields require higher inputs of chemical fertilizers, mainly of Nitrogen. Thus, a maize cultivar with genetic potential to utilize N efficiently could produce economically in poor soils with low levels of fertilizer applications or high yields with better inputs of fertilizers due its capacity to utilize N efficiently. Moll et al. (1987) and Pollmer et al. (1979) pointed out that variation in the capacity of maize genotypes to take up N from the soil and to utilize plant nitrogen for grain production has been widely reported. Genetic variation in response to N supply of inbred line ( Balko and Russel, 1980), has been observed and it appears to be possible to develop hybrids with tolerance to low N in soils. In most breeding programs one of the main objectives is to identify inbred lines with productive potential "per se" and high combining ability for hybrid production that express high heterotic levels for grain yield. Maize cultivars present different behavior when grown in low levels of N and show different N partition and biomes inside the plant, especially in terms of N removed from the vegetative tissues (Ta and Wieland, 1992). With respect to genetics parameters related to N use efficiency, dominance effects had the great contribution to the observed genetic variance (Clark and Duncan, 1991). The genetic variation due to the general combining ability was greater related to N plant structure (productivity and dry matter), indicating that differences among crosses could be attributed to additive gene effects( Rizzi et al., 1993). The objectives of this work were to evaluate the N use efficiency of inbred lines and determine de relative importance of general and specific combining ability for N efficiency by using a diallel crosses.Material and MethodsA selected group of ten tropical inbred lines of maize derived from a tropical yellow dent tuxpeño synthetic population (CMS 61) was crossed in a diallel system through controlled hand pollinations. The resulting 45 single crosses, the 10 parental lines and a control - N use efficient line, were grown in the experimental area of Embrapa Milho e Sorgo/Embrapa, in Sete Lagoas, MG, in 2000. For both trials was used a lattice design 7 x 8 with two replications, and plot size was a single 5 m row spacing 0,90x 0,20m between and within rows, respectively. Each of the two nitrogen levels was considered a separate field trial plant adjacent to each other in a Latosoil dark-red, dystrophic and of clay texture, typical of the savannas Brazil Center areas, with low levels of N. The first area, with N stress (N0 =10 kg ha-1 of N), was planted using 250 kg ha-1 of the formula 4:14:8 plus Zn and 20 kg of FTE BR 12 (micronutrient source). The second area, with no N stress (N1=120 kg ha-1 of N) was used 250 kg ha-1 of the formula 4:14:8 plus Zn, 20 kg ha-1 of FTE BR 12 (micronutrient source) and 30 kg ha-1 of N. At the latter, five weeks after sowing, 90 kg ha-1 of N (Urea) was side dressed applied. Data were collected for ear yield (EY), plant height (PH), ear height (EH), number of root and stalk lodge (NRSL),  and prolificacy (Prol). Each experiment was analysed separately as a lattice design. Analysis of genotypes distribution was performed based on N stress index (NSI) on EY under N stress condition to classify the most tolerant materials to the N stress imposed in the trials. Also date for YE were analyzed using Griffing(1956) Model I, Method 2 to calculate general and specific combining ability.Results and DiscussionNitrogen treatment had a significant effect on ear yield (EY), plant height (PH), ear height (EH), and prolificacy (Prol) traits. Yield reduction under low nitrogen level (N0) in comparison to higher level (N1) treatments, in terms of average EY, ranged from 1206 kg ha-1 to 2080 kg ha-1 for lines and from 4346 kg ha-1  to 6730 kg ha-1  for the crosses. Yield under N0 level was lowest for line L 3 and highest for line L 2, and yield under N1 level line L 4 was lowest and highest for line L 8. Differences among inbred lines and single crosses were observed for PH, EH and Prol traits. Inbred L3 presented the lowest values under low N level, and there were consisting differences for the results under high level of N, for these three traits. For the trait Prol, means of single crosses were greater under N0 level than for N1 level, but happened the opposite for the inbred lines maybe due to the reduction in PH and EH. Nitrogen treatments had an important effect on the means of inbred lines under N1 in comparison with N0 resulting in a reduction of 18,9% (PH), 27,5% (EH) and 27,6% (Prol). Similarly, the reduction for single crosses means were 12,9%, 22,9% and 22,5% for PH, EH and Prol, respectively. Thus, as was expected reductions in terms of average performance were lower for single crosses than for the lines. Similar results were found by Laffite et al., 1995, Kling et al., 1997; and Arellano et al. 1997. The analysis of variance for ear yield showed significant (P<0,01) for genotypes under N1 and N0 levels (Table 1). Table 1. Summaries of the analysis of variance for ear yield (kg ha-1) for maize inbred lines and a diallel set of 45 crosses among these lines in experiments with two levels of N. EMS/Embrapa, SL(MG), 2002.** significant at the 1% level of probability F test;ns= Non significantSignificant (P<0,01) was detected for SCA under both N treatments, but GCA was only significant (P<0,001) under N1. Arellano, et al. 1997, found significant differences for GCA and SCA effects in a study involving a diallel of 14 inbred lines, and because SCA effects for yield were larger under low N level, they consider that these effects were more important under low than under high N availability. On the other hand, Below et al. (1997) working with six temperate lines found that additive effects were more important than dominance effects. Estimates of the SCA and GCA effects for both N levels, for EY of the 10 inbred lines are presented in Table 2.Table 2. Estimates of specific (above diagonal - N1 and below diagonal - N0) combining abilities (SCA) and general combining abilities (GCA N1 and GCA N0) for ear yield, for a diallel set of crosses among ten inbred lines, in experiments with two levels of Nitrogen. EMS/Embrapa,SL,(MG),2000.DP (Gi) =199,991 e DP (Gi - Gj) = 297,997-- N1= 120kg/N 1ha ; N0= 10 kg/N 1haDP (Gi) =206,160 e DP (Gi - Gj) = 307,322 (N0)DP (Sij) =672,363 e DP (Sij - Six) =988,332 (N1)DP (Sij) = 693,415 e DP (Sij - Six) =1019,24 (N0)GCA and SCA effects differed according to the level of available nitrogen. Although the additive effects have been detected, the SCA effects predominated over the GCA. The GCA estimated effects were positive for the lines L1, L2, L3, L6, L7 and L10, under N0 level. Under N1 level, lines L1, L2, L6, L7, L8 and L10 also presented favorable GCA effects. Therefore, five out of the ten lines present high GCA effects in both N0 and N1 levels. Lines L4, L5 and L9 had negative GCA effects at both levels of N. This led to a conclusion that the involvement of additive gene action should facilitate selection efforts for better line identification under non-stress environments. Normally, breeders is interested in hybrid combinations, with SCA more favorable and where there is at least one of the lines with GCA effect more favorable. Therefore, crosses like L1 x L2 should be highly desirable.Trials conducted at low yielding environments have a higher frequency of producing statistically non-significant differences, or having a larger coefficient of error variation than trials conducted under high yielding environments. This is because the error variance usually does not decrease as much as the genetic variance when going from high to low yielding environments (Bänziger et al., 1997). Even though the environmental and economical limitations related to N fertilizer utilization, traditionally the greater majority of the maize breeding programs in the tropics are under optimum fertilization conditions where heritability and potential selection genetic gains are usually much greater.Therefore, our results agree with earlier results found (Laffite and Edmeades, 1995) that show yield of inbred lines related to N use are under genetic control. As shown by the results of the others traits, the identification of traits related to EY at high and low N levels could allow the development or identification of hybrids with high performance to stress environments. A further part of this study was the examination of the most promising lines to N efficiency. As seen in Fig 1, quadrant 1 characterized by low NSI (N Stress Index) and yield was composed of all the lines and the inbred tester, and was classified as low yieldings and non-responsive to N stress. In quadrant 3, characterized by high NSI and yield, was composed of 17 single crosses, and were classified as high yieldings and responsive to N stress. NSI= (YN1 – YN0) / (Y 1N  – Y 0N )YN1 =production under N1; Y 0N = mean production under N0ReferencesARELLANO, V.J.L., CASTILLO, F.G., ALCANTAR, G.G. AND MARTÍNEZ, A.G.  Parámetros Genéticos de la Eficiencia en el Uso de Nitrógeno en Líneas de Maíz de Valles Altos. In: SYMPOSIUM OF DEVELOPING DROUGHT AND LOW N - TOLERANT MAIZE, 1996, El Batan. Proceedings... El Batan: CIMMYT, 1997. p. 320-325. Editado por G.O. Edmeades; M.Banzige H.R. Mickelson; C.B. Pena-Valdivia.  BALKO, L.G.; RUSSELL, W.A. Effects of rates of nitrogen fertilizer on maize inbred lines and hybrid progeny. I. Prediction of yield responses. Maydica, Bergamo, v.25, p. 65-79,1980.BÄNZIGER, M. ; LAFITTE, H.R. Efficiency of secondary traits for improving maize for low-nitrogen target environments. Crop Science, Madison,  v.37, p.1110-1117, 1997.CLARK, R.B.; DUNCAN, R.R. Improvement of plant mineral nutrition through breeding. Field Crops Research, Amsterdam, v. 27,p.219-240, 1991.GRIFFING, B.. Concept of general and specific combining ability in relation to diallel crossing systems. Australian  Journal of Biological Sciences, Melbourne, v.9, p.463-493, 1956.KLING, J.G., OIKEN, S.O.; AKINTOYE, H.A.; HEUBERGER H.T.; HORST, W.J.  Potential for Developing Nitrogen Use Efficient Maize for Low Input Agricultural Systems in the Moist Savannas of  Africa. In: SYMPOSIUM OF DEVELOPING DROUGHT AND LOW N - TOLERANT MAIZE, 1996, El Batan: Proceedings... El Batan: CIMMYT, 1997, p.490-501.LAFITTE, H.R.; EDMEADES, G.O. Association between traits in tropical maize inbred lines and their hybrids under high and low soil nitrogen. Maydica, Bergamo, v.40,p. 259-267, 1995.LAFITTE, H.R. AND BÄNZIGER, M. 1996. Maize population improvement for low soil Nitrogen: Selection gains and the identification of secondary traits. In G.O. Edmeades, M. Bänziger, H.R.Mickelson, and C.B. Pena-Valdivia (Eds.) Developing Drought and Low N-Tolerant Maize. Proceedings of a Symposium, March 25-29,1996, CIMMYT, El Batán, México. México, D.F.,CIMMYT.MOLL, R.H., KAMPRATH,  E.J.; JACKSON, W.A. Analysis and interpretation of factors which contribute to efficiency of nitrogen utilization. Agronomy Journal, Madison, 1982, v.74, p.562-564, 1982.MURULI, B.L.; PAUSEN, G.M. Improvement of nitrogen use efficiency and its relationship to others traits in maize. Maydica Bergammo,  v.26, p.63-73, 1981.POLLMER, W.G.; EBERHARD, D.; KLEIN, D.; DHILLON, B.S. Genetic control of nitrogen uptake and translocation in maize. Crop Science, Madison, v.19, p. 83-86, 1979.TA, C.T.; WIELAND, R.T. Nitrogen partitioning in maize during ear development. Crop Science, Madison,  v.32, p.443-451, 1992._____________________________________________________________________________XXIV Congresso Nacional de Milho e Sorgo - 01 a 05 de setembro de 2002 - Florianópolis - SC_____________________________________________________________________________

Combining ability for nitrogen use in a selected set of imbred lines from a tropical maize population.

Combining ability for nitrogen use in a selected set of imbred lines from a tropical maize population.

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