Maize breeding techniques

Seeds are the most important means of production, and new varieties are the core foundation of agricultural scientific and technological progress. Maize breeding and production practice show that 43% to 60% of the increase in maize yield is achieved through excellent varieties and their popularization. therefore, the cultivation and promotion of new maize varieties play a decisive role in improving the level of maize per unit yield and the comprehensive production capacity of grain.

Characteristics of Maize breeding

The main characteristic of maize is natural cross-pollination, the field composition of natural pollination population is in a highly heterogeneous state, and the individual genotype is in a high heterozygous state, which determines that in the population of natural pollination of maize, the comparison of phenotypes among plants is of little significance, and the choice can be correctly decided through a certain process of genotype selection. At the same time, because of the high heterozygosity of individual genotypes, the phenotypic selection is unreliable, so a large number of individuals must be tested or identified in order to confirm whether the phenotype is really inherited. For these reasons, in the process of maize breeding, it is generally necessary to go through multi-generation selection and comparison in order to develop new inbred lines or varieties.

Heterosis breeding is the mainstream of modern maize breeding, the basic way is to select homozygous parent inbred lines, and then cross parent inbred lines to select hybrids with strong heterosis. The heterosis of F1 generation is used in production. The breeding of inbred lines requires not only good characters, but also high coordination ability. It is of equal importance to the selection of agronomic characters and combining ability of inbred lines and should not be neglected. This greatly increases the difficulty of breeding and prolongs the breeding cycle. Moreover, although the characters of inbred lines are related to those of hybrids, there is still a distance between them. At the level of hybrids, agronomic characters should be selected and identified, and the heterosis levels of main target characters should be compared. finally, a good hybrid variety was bred.

Breeding of Maize inbred Lines

1. Good agronomic characters

① plant characters: mainly include plant type and lodging resistance. The plant characters are generally divided into compact type, semi-compact type and peaceful spreading type according to the extended posture of the upper leaves of the ear. According to plant height, it can be divided into tall stem, middle stem, dwarf, semi-dwarf and so on.

② panicle traits: panicle traits are generally composed of panicle type, grain type, number of rows per ear and so on. There are many kinds of panicle types, the most obvious are long spike type, thick spike type, cylinder type, cone type, spindle type and so on. The grain type can be divided into horse tooth type and hard grain type and their various transition types. It is best to give consideration to the selection of long panicle type and thick panicle type in the breeding of inbred lines. The number of grains per row of long panicle type was more, but the number of grain rows was less. The number of grains per row of thick panicle type is more, but the number of grains per row can not be many. The grain number of inbred lines is generally 10-20 rows. Lines 12-14 are more moderate. The selection of grain type should be determined according to the breeding objectives. generally, the hybrids of inbred lines with hard grain type have good commercial quality, and the hybrids with partial horse teeth are easy to produce higher yield and starch content. In addition, the consistency of grain size, grain weight and grain color also need to be considered.

③ stress resistance: it should have a certain resistance or tolerance to the main maize diseases and natural disaster conditions to ensure the stability of seed production and the stable play of heterosis. Neatness and consistency: agronomic characters are required to be neat and consistent in appearance and basically homozygous in genotype.

2. High combining ability

Combining ability refers to the potential ability of hybrid parents to play a role in the heterosis of their hybrid progenies. the combining ability of inbred lines determines the yield-increasing ability and utilization value of hybrids in the future, so it is the most important character of inbred lines. combining ability can be divided into general combining ability and special combining ability. The genetic basis of the former comes from the gene additive effect of parents, while the latter is determined by the non-additive effect of parent genes. They are relatively independent in heredity. Therefore, the two should not be neglected in the breeding of inbred lines.

3. Strong seed production performance.

Whether the hybrids with high yield, high quality and good resistance can be popularized or become the main varieties, a very important condition is to have excellent seed production performance, including strong germination ability and germination potential of parent seeds, good seedling growth, easy to protect seedlings, and coordination between male and female. The male parent has good pollen distribution, large amount of pollen and long flowering period. The female parent has long tassel stalk, easy heading, fast and neat silking, good fruiting, uniform grain and high yield. The response of parents to light and temperature is small, the coordination of florescence is easy, and seed production is easy to be successful.

4. Basic materials for breeding inbred lines.

Fundamentally speaking, the strong heterosis of maize hybrids comes from sufficient genetic differences among parents. Therefore, the basic materials for breeding inbred lines must come from various sources and have a wide genetic basis. There are four sources of selection materials: the first is local germplasm, including the old local variety population, or inbred lines from local varieties, etc. There may be good resistance sources or good quality materials under some special ecological conditions, so special attention should be paid to collection. The second kind is hybrids, which mainly refers to the hybrids applied or introduced in production, and also includes the hybrids used for line selection with inbred lines, of which the single cross is the most widely used.

It is generally believed that the selection of hybrids widely used in local or remote production is a shortcut to develop excellent inbred lines, which have good agronomic characters and high combining ability. The third is the comprehensive species or recurrent improved population, the frequency of good genes and the recombination rate of good genotypes in these populations are relatively high, but the degree of aggregation of favorable genes may not be as good as that of single cross, so it is usually necessary to increase the amount of selection in the process of line selection. The fourth is the offspring of distant hybrids. There are many wild related species of maize, which are rich in excellent characters, but because of the difficulty of interspecific hybridization, serious sterility or segregation of offspring and slow stability, it is difficult to select inbred lines directly, so it is rarely used now.