Breeding early maturing maize by conventional methods and biotechnology

• Research unit: EU RFP
• Project number: 97.0483

Key words (English)

Zea mays L.; early maturity; early flowering; gametic embryogenesis; QTL-mapping

Alternative project number (English)

EU project number: IC18-CT98-0304

Research programs (English)

EU-programme: 4. Frame Research Programme - 8.1 Cooperation with 3rd countries & intern. organisations

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: Universität Hamburg (D)

Abstract (English)

EEarly maturity and early flowering are major breeding goals for maize worldwide and particularly in Asia because earliness can contribute to yield stability in marginal regions. This project aims at the analysis and the development of earliness in maize by molecular and by conventional approaches.Cloning and expression analysis of FPF genes from maizeThe cloning of maize genes homologue to the flowering promoting factors (FPF) known from Brassicacees revealed the existance of a FPF gene family in maize consisting of at least 10 members. Their tissue specific expression pattern was studied by Northern blotting. The results indicate that not all maize FPF genes play a role in the genetic control of flowering time. As soon as the functional analysis is completed a homologues FPF1 gene specifically expressed in floral tissue will be overexpressed in maize to generate early flowering genotypes.Overexpression of the Sinapis alba FPF1 geneMore than 20 independent transgenic plants were obtained by particle bombardment of immature zygotic embryos but analysis in the greenhouse did not reveal any significant alterations in the phenotype in comparison to the wildtype. In particular no significant modification of flowering time was observed.In an alternative approach DNA delivery was performed by microinjection of DNA into ovaries. Although herbicide tolerant progenies of these plants have been selected and positively tested by PCR, the ultimate proof of concept by southern blotting is still missing. In case the transgenic nature of the progenies can be confirmed, this transformation protocol will be of very high interest, because it does not require the regeneration of shoots from tissue culture and, thus, potentially could be applied to a wide range of genotypes, including those which are recalcitrant to other methods. Mapping of earliness genesQTLs for early flowering and early maturity have been identified in different mapping populations consisting of recombinant inbred lines or F3 progenies of near isogenic lines. During the last year both groups involved in the mapping project refined the genetic maps of their populations in order to increase the significance of the QTL analysis. The mapping of FPF genes and earliness genes known from other species is still in progress.Conventional breedingFive early flowering and early maturing inbred lines with good agronomic properties (Agron lines) have been selected and single cross hybrids were generated. These hybrids, the parental inbred and three commercially available early flowering single cross hybrids were grown at Farm Suwan (Thailand) and analysed for their flowering time, maturity at harvesting, kernel yield and other agronomic traits. At least one combination (Agron37 x Agron43) was found, which was flowering up to one week earlier than commercial lines and nevertheless gave a very competitive kernel yield. This encouraging results will be confirmed in further field trials.Gametic embryogenesisThe development of routine protocols for the establishment of doubled haploid (DH) lines by gametic embryogenesis is a highly desired enabling tool for the breeding approach as well as for the transgenic approach because it can dramatically shorten the time required to obtain homozygous material.Haploid gametic embryos can be obtained from male (androgenesis) and female (gynogenesis) gamets by in vitro culture of anthes and ovaries. Most of the project partners have established procedures for in vitro androgenesis in their labs. The main objective of this work was the improvement of the efficiency of in vitro androgenesis with respect to chromosome doubling, plant regeneration and plant survival. Special attention was drawn to the adaptation of the respective procedures to local germplasm and local conditions. The bottleneck of DH production by androgenesis turned out to be the chromosome doubling and the self fertility of the regenerated plants.Thanks to improved protocols sufficient numbers of DH lines derived from crosses between early flowering and highly responding genotypes became available for field trials and the development of experimental single cross hybrids with DH parental lines is in progress.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0483