QTL mapping identifies novel major loci for kernel row number-associated ear fasciation, ear prolificacy and tillering in maize (Zea mays L.)

Abstract

Maize ear fasciation originates from excessive or abnormal proliferation of the ear meristem and usually manifests as flattened multiple-tipped ear and/or disordered kernel arrangement. Ear prolificacy expresses as multiple ears per plant or per node. Both ear fasciation and prolificacy can affect grain yield. The genetic control of the two traits was studied using two recombinant inbred line populations (B73 × Lo1016 and Lo964 × Lo1016) with Lo1016 and Lo964 as donors of ear fasciation and prolificacy, respectively. Ear fasciation-related traits, number of kernel rows (KRN), ear prolificacy and number of tillers were phenotyped in multi-year field experiments. Ear fasciation traits and KRN showed relatively high heritability (h ² > 0.5) except ratio of ear diameters. For all ear fasciation-related traits, fasciation level positively correlated with KRN (0.30 ≤ r ≤ 0.68). Prolificacy and tillering were not correlated and their h ² ranged from 0.41 to 0.78. QTL mapping identified four QTLs for ear fasciation, on chromosomes 1 (two QTLs), 5 and 7, the latter two overlapping with QTLs for number of kernel rows. Notably, at these QTLs, the Lo1016 alleles increased both ear fasciation and KRN across populations, thus showing potential breeding applicability. Four and five non-overlapping QTLs were mapped for ear prolificacy and tillering, respectively. Two ear fasciation QTLs, qFas1.2 and qFas7, overlapped with fasciation QTLs mapped in other studies and spanned compact plant2 and ramosa1 candidate genes. Our study identified novel ear fasciation loci and alleles positively affecting grain yield components, and ear prolificacy and tillering loci which are unexpectedly still segregating in elite maize materials, contributing useful information for genomics-assisted breeding programs.

Keywords: QTL mapping; ear fasciation; ear prolificacy; maize; tillering; yield components.

Figure 1

Distribution frequency histograms of, and correlation among all traits estimated on the two RILs (B×L and L×L) combined. The upper right part reports all correlation indexes (rho) and corresponding significant levels (p). The lower left part presents scatter plots and fitter curve (the red line inside) between two traits. The diagonal shows histogram charts of each trait. DIA (ear diameters rate), DIS (kernel row disorder), OVA (ear ovality), FAS (ear fasciation index), KRN (kernel row number), PROL (prolificacy), TIL (number of tillers), M, mean value.

Figure 2

Target ear traits analyzed in this study. (A) Representative images of the ear-fasciation phenotype observed in Lo1016 (B73 is shown as comparison). White line, 1 cm. (B) Representative images of the ear prolificacy phenotype at top ear-bearing node as observed in Lo964 (B73 is shown as comparison). Numbers (1-3) indicate different ears at the same node.

Figure 3

QTL LOD profiles obtained by the joint analysis of the two RIL populations B×L and L×L, for DIA (ear diameters rate), DIS (kernel row disorder), OVA (ear ovality), FAS (ear fasciation index), KRN (kernel row number), PROL (prolificacy), TIL (number of tillers).

Figure 4

QTL and main candidate genes consensus maps. (A) QTL consensus map for ear fasciation including QTL from literature and this study. (B) QTL consensus map for ear prolificacy, including QTL from literature and from this study. Chromosome bars and numbers represent physical distances in Mb. QTL positions are represented following physical positions reported in Supplementary Tables 7, 8. In black, QTL from this study; in green, tentative candidate genes; in blue, QTL from other studies. Full QTL information from other studies is provided in Supplementary Table 7.