Abstract
The grain filling rate (GFR) is an important dynamic trait that determines the final grain yield and is controlled by a network of genes and environment factors. To determine the genetic basis of the GFR, a conditional quantitative trait locus (QTL) analysis method was conducted using time-related phenotypic values of the GFR collected from a set of 243 immortalized F2 (IF2) population, which were evaluated at two locations over 2 years. The GFR gradually rose in the 0–15 days after pollination (DAP) and 16–22 DAP, reaching a maximum at 23–29 DAP, and then gradually decreasing. The variation of kernel weight (KW) was mainly decided by the GFR, and not by the grain filling duration (GFD). Thirty-three different unconditional QTLs were identified for the GFR at the six sampling stages over 2 years. Among them, QTLs qGFR7b, qGFR9 and qGFR6d were identified at the same stages at two locations over 2 years. In addition, 14 conditional QTLs for GFR were detected at five stages. The conditional QTL qGFR7c was identified at stage V|IV (37–43 DAP) at two locations over 2 years, and qGFR7b was detected at the sixth stage (44–50 DAP) in all four environments, except at Anyang location in 2009. QTLs qQTL7b and qQTL6f were identified by unconditional and conditional QTL mapping at the same stages, and might represent major QTLs for regulating the GFR in maize in the IF2 population. Moreover, most of the QTLs identified were co-located with QTLs from previous studies that were associated with GFR, enzyme activities of starch synthesis, soluble carbohydrates, and grain filling related genes. These results indicated that the GFR is regulated by many genes, which are specifically expressed at different grain filling stages, and the specific expression of the genes between 16–35 DAP might be very important for deciding the final kernel weight.
Highlights
Grain yield has been a main target in cereal breeding, especially for maize (Zea mays L.), a critical source of food, fuel, feed, and fiber worldwide. [1] In maize, grain yield can be defined as the product of kernel sink capacity and grain filling efficiency, [2] and the grain filling rate (GFR) is regulated by multi-genes or by quantitative trait locus (QTL), as well as cultivation conditions, showing complex dynamic changes
[1] In maize, grain yield can be defined as the product of kernel sink capacity and grain filling efficiency, [2] and the GFR is regulated by multi-genes or by QTLs, as well as cultivation conditions, showing complex dynamic changes
Climate Conditions in the Two Locations Temperature and sunlight conditions during the maize grain filling duration of the immortalized F2 (IF2) population across 2 years are shown in Fig. 1a and b
Summary
Grain yield has been a main target in cereal breeding, especially for maize (Zea mays L.), a critical source of food, fuel, feed, and fiber worldwide. [1] In maize, grain yield can be defined as the product of kernel sink capacity and grain filling efficiency, [2] and the GFR is regulated by multi-genes or by QTLs, as well as cultivation conditions, showing complex dynamic changes. Grain filling is a critical and dynamic process that determines final grain yield. It depends on carbohydrates derived from two different sources: from photosynthesis in the leaf during the grain filling procedure and from accumulated nonstructural carbohydrates in culms and leaf sheaths. [15] The lag phase is a period of active cell division, followed by differentiation and DNA endoreduplication, with almost no dry matter accumulation. During this phase, the GFR is low. [20] After reaching the maximum, the GFR gradually decreases, and the final kernel weight is achieved during the maturation drying phase. The GFR is low. [19] At the end of the lag phase, the GFR starts to rise and reaching its maximum value in the middle of the effective grain filling period. [15] In the effective grain filling period, the GFR and the duration of the effective grain filling period determine the final weight. [20] After reaching the maximum, the GFR gradually decreases, and the final kernel weight is achieved during the maturation drying phase. [15,21] there are many factors that could affect the GFR during the three phases, the genotype has the most important role in affecting the GFR in cereal crops. [22,23] Under these circumstances, the GFR shows a logistic curve during the grain filling procedure
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