Doubled haploids in tropical maize: II. Quantitative genetic parameters for testcross performance

Abstract

Single crosses (SC) of elite inbreds and open-pollinated populations (OP) are suitable source germplasm for doubled haploid (DH) line development in hybrid maize breeding, given that they combine a high population mean (x) for testcross performance with adequate response to selection (DG). This is the first study reporting testcross grain yield (TCGY) and dry matter content (TCDMC) evaluations of 131 DH lines developed from ten tropical source germplasm comprising five OP (OP1-OP5) and five SC (SC1-SC5). Gene diversity (D) and the average number of alleles (A r ) per locus was estimated for DH lines based on 24 simple sequence repeat markers. Analysis across three environments revealed no significant differences between x of OP-and SC-derived DH lines for TCGY and TCDMC. Significant genetic variance for both traits was only detected among OP-derived DH lines which may be explained by a larger number of segregating quantitative trait loci (QTL) as suggested by higher D and A r values than in SC-derived DH lines. The usefulness criterion (U ¼ x þ DG) was higher for OP-derived DH lines for TCDMC, but higher for SCderived DH lines for TCGY. DH lines from OP1, OP2, and OP3 showed high TCGY, suggesting that they may be useful in tropical hybrid breeding. We conclude that tropical OP represent a valuable source of untapped genetic variation that can efficiently be exploited with DH technology for hybrid maize breeding.

Unlocking the Genetic Diversity of Maize Landraces with Doubled Haploids Opens New Avenues for Breeding

“…Although improved seed set, reduced number of barren stalks, reduced anthesis-silking interval and lower incidence of common smut might suggest some positive purging of detrimental alleles [34], [35], the absence of grain yield improvement in the synthetic populations was disappointing and contrary to expectations [25], [27]. It must be noted, however, that seeds of the synthetic populations were produced on less vigorous homozygous lines while the seeds of the landraces were produced on vigorous heterozygous plants.…”

“…Unlocking the genetic diversity present in the huge collections of maize landraces accessions by developing homozygous lines from these highly heterogeneous populations [18], [27] is of great interest for breeding. Both the single seed descent (SSD) and the in vivo double haploid (DH) techniques would be appropriate methods to produce fixed lines and purge the genetic load present in landraces.…”

“…The parameter U ( α ) combines the estimate of the population mean and Δ G ( α ) and allows a comparison between populations, with regard to the prospects to identify individuals or lines with superior performance. The parameters Δ G ( α ) and U ( α ) were computed following Prigge et al [27] for a selected proportion of α  = 10% ( U 10% ) and 40% ( U 40% ), corresponding to a selection intensity of i  = 1.76 and 0.97, respectively. Response from selection was computed as Δ G ( α ) =  i ( α ) hσ g , where i ( α ) is the selection intensity, h the square root of the heritability, and σ g the genotypic standard deviation [59].…”

“…First studies using the in-vivo DH technique to produce fixed lines from European and tropical landraces showed a generally lower testcross performances but also a high improvement potential of such materials [18], [27]. Yet, information about the per se performance of a broad set of DH lines derived from landraces would be of equal interest with regard to their introgression into modern breeding material.…”

Breeding Potential of European Flint Maize Landraces Evaluated by their Testcross Performance

“…This is in agreement with the results of Wilde et al (2010), who reported that testcrosses of flint landraces and double haploid (DH) lines extracted from them without selection yielded 22 to 26% less than the commercial check hybrids. For tropical germplasms, Prigge et al (2012) found only a 17% lower GY for testcrosses of DH lines extracted from open‐pollinated varieties compared with the check hybrids. In our study, testcrosses of the best landrace, Viey, yielded only 17% less than the commercial checks.…”