Genetic loci mapping for ear axis weight using recombinant inbred line (RIL) population under different nitrogen regimes in maize

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1 Africn Journl of Biotechnology Vol. 10(42), pp , 8 August, 2011 Avilble online t DOI: /AJB ISSN Acdemic Journls Full Length Reserch Pper Genetic loci mpping for er xis weight using recombinnt inbred line (RIL) popultion under different nitrogen regimes in mize Zu-Ping Zheng 1, Xio-Hong Liu 2 *, Xun Wu 1, Yong-Si Zhng 2 nd Chun He 1 1 Nnchong Institute of Agriculturl Sciences, Nnchong City , P. R. Chin. 2 Key Lbortory of Southwest Chin Wildlife Resources Conservtion (Ministry of Eduction), College of Life Sciences, Chin West Norml University, Nnchong City , P. R. Chin. Accepted 17 June, 2011 Er xis weight (EAW) is one of the importnt gronomic trits in mize (Ze mys L.), relted to yield. To understnd its genetic bsis, recombinnt inbred line (RIL) popultion, derived from the cross Mo17 Hungzo4, ws used for quntittive trit locus mpping (QTL) for EAW under high nd low nitrogen (N) regimes. The results showed tht totl of three QTLs were mpped on chromosomes 2 (two) nd 4 (one) under the two N regimes, which could explin phenotypic vrinces from 4.76 to 7.12%. They were ner to their linked mrkers, with mpping intervl of 0.2 to 1.0 cm. The two loci on chromosome 2 (bin 2.09) mde EAW increse due to positive dditive effects, while the other locus on chromosome 4 (bin 4.08) mde EAW decrese to some extent, owing to negtive dditive effects. These results re beneficil for understnding the genetic bsis of KNE nd developing mrker-ssisted selection in mize breeding project. Key words: Mize (Ze mys L.), er xis weight, quntittive trit locus, recombinnt inbred line, nitrogen. INTRODUCTION The previous studies on QTL mpping for mize (Ze mys L.) er-relted trits were concentrted on yield per plnt (Hung et l., 2010), 100-kernel weight (Guo et l., 2008), er weight (Sbdin et l., 2008), row number per er (Lu et l., 2006) nd kernel number per row (Li et l., 2010). For er xis weight (EAW), lthough it is lso n importnt gronomic trit relted to yield in mize breeding progrm, the study on its genetic bsis ws hrdly reported, except for Wng et l. (2007). As well known, different prentl lines my led to different results in QTL number, chromosoml loction or genetic effect. For exmple, using X178 nd B73 s prentl inbred lines, Xio et l. (2005) identified six QTLs for kernel number per er on chromosomes 1 (three), 3 (one) nd 9 (two), but the report by Agrm et l. (1999), using B73 nd G79 s mpping prents, showed tht there were four QTLs for the sme trit on chromosomes 1 (one), 6 (one), 7 (one) nd 9 (one). * Corresponding uthor. E-mil: lxhxhsfdx@yhoo.com.cn. Consequently, it is necessry to choose different prentl lines to mp the QTLs for EAW in mize. In ddition, different environmentl conditions cn lso led to different results in QTL number, position or genetic effect. Among the ecologicl conditions influencing mize growth nd development, N content in soil is very importnt. Currently, most mize in the world re grown under N-deficient conditions (Ribut et l., 2007). From literture, different N conditions hve been frequently used to detect QTLs in plnt such s rice (Oryz stiv L.) (Lin et l., 2005), mize (Liu et l., 2008) nd whet (Triticum estivum L.) (An et l., 2006), but the studies on using different N environments to mp QTL for mize EAW were not reported. Accordingly, it is meningful tht different N regimes re used for QTL mpping ffecting EAW in mize. Therefore, the two prentl lines Mo17 nd Hungzo4 were used s mpping prents, bsed on their RIL popultion; the QTL(s) controlling EAW were identified under two N regimes. The objectives here were to (1) relize the genetic bsis of EAW more clerly in mize; (2) find some moleculr mrkers co-segregted with the

2 8256 Afr. J. Biotechnol. Tble 1. The phenotypic vlues of prentl lines nd F 1 for EAW. N regime M017 HZ4 F 1 hybrid Men (g) SD Men (g) SD Men (g) SD HNR LNR Tble 2. Descriptive sttistics of RIL popultion for EAW under two N regimes. N regime Rnge (g) Minimum (g) Mximum (g) Men (g) SD b CV (%) Skewness Kurtosis HNR LNR SD, Stndrd devition; b CV, coefficient of vrition. genetic loci controlling EAW which cn be used for MAS in mize. MATERIALS AND METHODS Plnt mterils The experimentl mterils involved in this study included mize inbred lines Mo17 (high EAW) nd Hungzo4 (low EAW) s prents, their F 1 hybrid nd RIL popultion consisting of 239 RILs. Mo17 nd Hungzo4 re the representtive lines of Lncster nd Tngsipingtou heterotic groups, respectively, the F 1 hybrid nd RIL popultion were derived from the cross between the two prentl lines. Experiment mesurements nd phenotypic observtion Prentl lines, F 1 nd the RIL popultion were sown in rndomized complete block design with six replictes t the experiment frm of Nnchong Institute of Agriculturl Sciences, Nnchong City, P. R. Chin, with single-plnt plnting nd 15 plnts per replicte, of which three replictes were under high N regime (HNR) by ppending ure 300 kg/h nd the other three replictes were under low N regime (LNR) with no ppended N fertilizer. The verge contents of totl N nd lkline hydrolysis N in 30-cmdepth soil were nd %, respectively. At the time of hrvest, eight plnts in the middle of every replicte were individully investigted for the trit EAW. Bsed on the investigted dt of the RIL popultion, SPSS11.5 softwre ( ws used to perform descriptive sttistics, nlysis of vrince (ANOVA) nd correltion nlysis for the trit EAW. QTL detection Bsed on the dt of EAW in the RIL popultion nd the estblished genetic mp consisting of 100 SSR mrkers nd covering centimorgn (cm) of mpping distnce (Liu et l., 2009), the QTL(s) controlling EAW under two N regimes were severlly nlyzed by composite intervl mpping (CIM) method of Windows QTL Crtogrpher 2.5 softwre (Wng et l., 2010), scnning intervl of 2 cm between mrkers nd puttive QTLs with window size of 10 cm. The LOD (log10 of odds rtio) threshold vlue for the QTL significnce ws determined by 1000-time permuttion test (α = 0.05) (Doerge nd Churchill 1996); cofctors used for clcultion of CIM were selected by the progrm using forwrd stepwise regression, LOD curves were creted by scnning ll linkge groups, the QTLs with LOD vlue greter thn the threshold vlue ws presented nd their position, genetic effects nd percentge of phenotypic vrition were estimted t the significnt LOD pek in the region. The QTLs identified under the two N regimes were mpped with Mpchrt 2.1 softwre (Voorrips, 2002). RESULTS AND DISCUSSION Sttistics nlyses Sttistic results indicted tht the tested lines presented vrition in EAW (Tble 1) for the three lines including prents nd F 1 hybrid; F 1 hybrid hd the highest vlues under both N regimes becuse of heterosis, followed by Hungzo4. Moreover, ll the three lines possessed higher vlues under HNR thn those under LNR. For the RIL popultion, the results of the descriptive sttistics re listed in Tble 2. Among the eight sttistic prmeters, ll of them showed higher vlues under HNR thn those under LNR except for minimum nd skewness. The results of ANOVA of the RIL popultion on EAW under two N regimes re demonstrted in Tble 3. Different lines of the RIL popultion provided differences t 0.01 probbility level under ny one of the two N regimes. Nevertheless, the two-group dt of the popultion obtined under two N environments presented positive reltion t 0.01 probbility level (r = 0.846). In ddition, from the frequency distribution grphs (Figures 1, b), the dt of the RIL popultion under both N regimes could well gree with norml distribution, which ment tht the trit EAW is quntittive trit nd is controlled by multiple genes in mize. QTL identifiction Permuttion test indicted tht the LOD threshold vlues

3 Zheng et l Tble 3. ANOVA of the RIL popultion on EAW under two N regimes. N regime Vrition source Sum of squres df Men squre F Significnce Between groups ** <0.01 HNR Within groups Totl LNR Between groups ** <0.01 Within groups Totl There were four missing vlues mong the RIL popultion consisting of 239 RILs; ** significnt difference t 0.01 probbility level. Figure 1. Frequency distribution grphs of the RIL popultion for EAW under two N regimes. A, EAW under HNR; B, EAW under LNR. The mens of prentl lines re indicted by rrows, P1 for Mo17 nd P2 for Hungzo4. Tble 4. Positions nd effects of the QTLs ssocited with EAW identified under two N regimes. N regime QTL Chromosome The proximl mrkers Mpping intervl (cm) b LOD c R 2 (%) Additive effect HNR Qew1 2 Bnlg1520 (bin2.09) LNR Qew2 2 Umc1736 (bin2.09) Qew3 4 Umc2188 (bin4.08) The mpping intervl between QTL nd linker mrker; B the log 10 of odds rtio; C percentge of phenotypic vrition explined by QTL. of QTL significnce ssocited with EAW should be set t 2.61 nd 2.51 under HNR nd LNR, respectively. Bsed on the LOD vlues, totl of three QTLs were detected under both N regimes (Tble 4 nd Figure 2). The QTL identified under HNR (nmed Qew1) ws locted on chromosome 2, linked with Bnlg1520, with mpping intervl of 1.0 cm nd this locus could explin 6.81% of the phenotypic vrince nd mde EAW increse (0.67 g) due to dditive effect. For the two QTLs mpped under LNR, one ws on chromosome 2 (nmed Qew2), while the other ws on chromosome 4 (nmed Qew3). With 0.9 nd 0.2 cm ner to their linked mrkers Umc1736 nd Umc2188, respectively, they could ccount for 7.12 nd 4.76% of the phenotypic vrince, respectively. The two genetic loci identified under LNR presented contrry genetic effects due to different dditive effects; Qew2 nd Qew3 could mke EAW increse nd decrese, respectively.

4 8258 Afr. J. Biotechnol. Figure 2. Chromosoml positions of the QTLs for EAW identified using the RIL popultion derived from Mo17 Hungzo4 under two N regimes. Qew1 nd Qew2 were detected under HNR, while Qew3 ws identified under LNR. Tble 5. The QTLs for EAW were reported in different studies in mize. Reference Prentl line Popultion Environment QTL number (chromosoml position) Wng et l. (2007) Lo1067 nd Yi72 F 2 Two wter regimes 3 (one on chromosome 1 nd two on chromosome 2) This study Mo17 nd Hungzo4 RIL Two N regimes 3 (two on chromosome 2 nd one on chromosome 4) The QTLs for EAW were lso reported by Wng et l. (2007), but our study ws different from theirs in mny spects nd the min differences re listed in Tble 5. From QTL position, the QTLs identified in this study were obviously different from the previous, so they belonged to new loci ssocited with EAW in mize. It cn be mentioned tht the segregting popultion in our experiment ws immortl due to the presence of homologous lines nd cn be used in different regions nd time. However, this kind of popultion in Wng et l. (2007) ws temporry nd cnnot be utilized gin, becuse of no continued plnts use for further phenotypic nd genetic nlysis (Pilet et l., 2001). Additionlly, the environmentl conditions used for QTL mpping in the report by Wng et l. (2007) were different wter-content in the soil, wheres in our experiment, two N regimes were employed in QTL mpping. It is importnt to note tht different N conditions were first designed to mp QTL for EAW. Conclusions A RIL popultion, derived from the two prentl lines Mo17 nd Hungzo4, ws used to mp the QTLs ssocited with EAW under two N regimes. The results showed tht totl of three QTLs were mpped on chromosomes 2 (Qew1 nd Qew2) nd 4 (Qew3) which could explin the phenotypic vrinces from 4.76 to 7.12%. They were ner to their linked mrkers Bnlg1520, Umc1736 nd Umc2188, respectively, with mpping intervl 0.2 to 1.0 cm. The two loci on chromo-

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