Correlation analysis between different panicle positions, seed setting rates and panicle structure. SUER: upper panicle setting rate, SMER: middle panicle setting rate, SPER: lower panicle setting rate, SUF: upper panicle full grain rate, SMF: middle panicle full grain rate, SPF: lower panicle full grain rate, SUEP: upper panicle withered grain rate, SMEP: middle panicle withered grain rate, SPEP: lower panicle withered grain rate, AU: angle of the primary branch for upper panicle, AM: angle of the primary branch for middle panicle, AL: angle of the primary branch for lower panicle, BP: rachis diameter, LSS: number of large vascular bundles in rachis, LNLPP: number of small vascular bundles in rachis, SsLB: area of large vascular bundles in rachis, SsSB: area of small vascular bundles in rachis, LPB: primary branch diameter, LNLPP: number of large vascular bundles in primary branch, LSLPP: number of small vascular bundles in primary branch, LPPLB: large vascular bundle area of primary branch; LPPSB: small vascular bundle area of primary branch. * and ** represent significant levels of 0.05 and 0.01, respectively.