A report by CIMMYT maize scientists highlights the benefits, both current and potential, of doubled haploid (DH) technology in a recent article published in Theoretical and Applied Genetics.
The word haploid
indicates that the cells in a plant has half the number of chromosomes as its
parent. Haploids occur very rarely in maize but their frequency can be
increased significantly by using haploid inducers, which are specific
genotypes of maize with defects in their pollen. Haploids can be separated from
diploids using several phenotypic markers at the seed or seedling stage.
Haploids are sterile, so they must undergo chromosome doubling in order to
begin meiosis and reproduce. Doubled haploids are formed through the
spontaneous or artificial duplication of chromosomes in identified
haploids.
In this photo John Okoth Ochieng, CIMMYT field assistant, compares a diploid (left) and haploid maize seed (right). The haploid seed is recognizable from the purple anthocyanin color marker. Photo: Jennifer Johnson.
CIMMYT scientists have
laid out several objectives for the future of doubled haploid breeding in this
report. Focus areas involve improving the haploid induction rate (HIR),
improving the speed and accuracy of haploid identification, increasing the
chromosomal doubling rates and improving the seed yield from doubled haploid
plants. Various methods to achieve these improvements are outlined in the
manuscript.
The DH process is
invaluable in maize breeding because it cuts the time required to breed
targeted varieties significantly. Because of this, seeds of improved varieties
can be developed and sent out to consumers quickly and efficiently. The global
need for maize as food and feed is increasing. CIMMYT works to keep up with
this demand and provide food for all who need it.
Representatives from CIMMYT and UAS-Bangalore signed the collaboration agreement on February 18, 2019.
The International Maize and Wheat Improvement Center (CIMMYT) and the University of Agricultural Sciences-Bangalore (UAS-Bangalore) have signed a collaboration agreement for establishing a maize doubled haploid (DH) facility at the Agricultural Research Station in Kunigal (ARS-Kunigal), Tumkur district, Karnataka state, India.
Haploid inducers are a specially developed maize genetic stock that are used to develop doubled haploid (DH) maize lines. DH maize lines are highly uniform, genetically pure and stable, making the maize breeding process more intuitive and efficient by simplifying logistics.
Purple maize varieties with high anthocyanin accumulation can have significant nutritional and economic value, but cannot be identified using the R1-nj marker.
Doubled haploid (DH) technology provides important benefits to maize breeding programs, as DH lines enhance genetic gains and improve breeding efficiency in addition to offering significant economic advantages. DH lines can be generated in less than half as many seasons as lines generated through traditional breeding, thus saving valuable time, resources and energy. The large scale production of DH lines is dependent on the identification of haploids at an early seedling stage. Haploids have traditionally been identified by the R1-nj (Navajo) anthocyanin color marker which, when crossed with haploid inducer lines through induction crosses, will produce haploid progeny seed with purple markings on its outer layer, or pericarp. This is to differentiate haploid from diploid seedlings, which are not useful for DH breeding.
The 