Analysis on single kernel weight and oil content of different grain types in maize based on NMR

Maize haploid breeding as an important technology of modern breeding programs can shorten breeding cycles and enhance the breeding efficiency. The method of haploid produced by in vivo has become a routine process and has been adopted widely in maize breeding. The rapid and accurate recognition of haploid kernels is a prerequisite for in vivo haploid breeding technology. Therefore, how to efficiently select haploid seeds from mass hybridization kernels has been an issue during the use of parthenogenetic haploid. At present, spectral information and image recognition based on the gene R-nj expressing Navajo marker in kernels were usually used to automatically sort haploids in maize, but the expression of gene R-nj were significantly depended on the maternal genetic backgrounds, it is unavailable for some flint germplasms with the presence of a supressor. With the development of inducers with high oil and high inducing rate, the automatic sorting of maize haploid kernels become a reality based on nuclear magnetic resonance (NMR). The embryo of haploid only developed from female gamete without the fusion of the sperm cell, so the oil content of haploid kernels is usually lower than that of diploid kernels because of xenia effect. Presently, most studies only set one threshold of oil content to identify haploid and diploid kernels based on NMR. However, there are some embryo abortion kernels with very lower oil content during the process of haploid induction, it is difficult to make distinction among diploid, haploid and embryo abortion kernels based on one threshold of oil content using NMR sorting system. In this paper, the single kernel weight and oil content of diploid, haploid and embryo abortion kernels by in vivo induction were analyzed, respectively, a new concept of increasing the correct discrimination rate of haploid based on two thresholds of oil content was developed. Three different types of kernels were produced by in vivo induction using two common maize hybrids and three inbred lines as females and inducers with high oil content as the males. The measurement of single kernel weight and oil content for three types of kernels were carried out by NMR sorting system. The result showed that the rank of the single kernel weight of different grain types was haploid > diploid> embryo abortion kernels, the highly significant difference existed between diploid and embryo abortion kernels, but there was no difference between diploid and haploid kernels, haploid and embryo abortion kernels. The variation coefficient of the average performance of single kernel weight was 16.62%, lager overlaps appeared among three different types of kernels. The oil content showed that the diploid > haploid > embryo abortion kernels. The coefficient of variation of oil content for diploid kernels was the lowest with only 12.52%, followed by haploid kernels, the highest was embryo abortion kernels with 34.14%, but the oil content was not more than 2% for all the embryo abortion kernels. The step distribution with obvious boundaries for oil content among the three different grain types was found. It indicated that the oil content can be used to recognize among three different types of kernels, but the single kernel weight cannot be as a sorting standard. According to the oil content, minimum of diploid and maximum of embryo abortion kernels were set respectively as the upper and lower limit value to form double thresholds, which could improve the rate of correct discrimination for haploid and provide a reference during the process of automatically sorting haploid kernels with high efficiency.