Allopolyploidization facilitates gene flow and speciation among corn, Zea perennis and Tripsacum dactyloides

Abstract

Main conclusion Tripsacum dactyloides is closely related to Zea mays since Zea perennis and the MTP tri-species hybrid have four possible reproductive modes. Eastern gamagrass (Tripsacum dactyloides L.) and tetraploid perennial teosinte (Zea perennis) are well known to possess genes conferring resistance against biotic and abiotic stresses as well as adaptation to flood and aluminum toxic soils. However, plant breeders have been hampered to utilize these and other beneficial traits for maize improvement due to sterility in their hybrids. By crossing a tetraploid maize-inbred line × T. dactyloides, a female fertile hybrid was produced that was crossed with Z. perennis to yield a tri-genomic female fertile hybrid, which was backcrossed with diploid maize to produce BC 1 and BC 2. The tri-genomic hybrid provided a new way to transfer genetic material from both species into maize by utilizing conventional plant breeding methods. On the basis of cytogenetic observations using multi-color genomic in situ hybridization, the progenies were classified into four groups, in which chromosomes could be scaled both up and down with ease to produce material for varying breeding and genetic purposes via apomixis or sexual reproduction. In the present study, pathways were found to recover maize and to obtain specific translocations as well as a speedy recovery of the T. dactyloides-maize addition line in a second backcross generation. However, phenotypes of the recovered maize were in most cases far from maize as a result of genetic load from T. dactyloides and Z. perennis, and could not be directly used as a maize-inbred line but could serve as an intermediate material for maize improvement. A series of hybrids was produced (having varying chromosome number, constitution, and translocations) with agronomic traits from all three parental species. The present study provides an application of overcoming the initial interspecific barriers among these species. Moreover, T. dactyloides is closely related to Z. mays L. ssp. mays since Z. perennis and the MTP tri-species hybrid have four possible reproductive modes. Keywords Apomixes • Chromosome translocation • Eastern gamagrass • Germplasm expansion • Perennial tetraploid teosinte • Tri-genomic bridge plant Abbreviations mcGISH Multi-color Genomic in Situ-Hybridization MTP Maize, T. dactyloides, and Z. perennis hybrid Mz Maize, Zea mays L. ssp. mays Zp Zea perennis

Analysis of the genitor origin of an intergeneric hybrid clone between <i>Zea</i> and <i>Tripsacum</i> for forage production by McGISH

“…Second, an allotetraploid (maize-Tripsacum) was generated from crossing tetraploid maize with tetraploid Tripsacum dactyloides via an n + n mating and embryo rescuing. Next, MTP, which has 74 chromosomes with two missing Tripsacum chromosomes, was created from crossing a maize-Tripsacum plant with the perennial tetraploid teosinte (Z. perennis) by a 2n + n mating (Iqbal et al 2019). Thereafter, among the progeny from MTP under open-pollination conditions (Z. mays or Z. perennis), one clone (Yu6) was outstanding and was approved as a forage crop.…”

“…9475) were isolated from young leaves using a modified 2× CTAB method (Fu et al 2015), and then labeled with probes with a DIG-High Prime Kit and a Biotin Nick Translation Kit (Roche, Basel, Switzerland), respectively, according to the manufacturer's instructions. The McGISH technique was performed according to the methods of Iqbal et al (2019). The McGISH images were visualized via a phase video microscope (Olympus BX61, Tokyo, Japan) equipped with a charge-coupled-device camera (700 mm CCD) and via Image Pro Plus 6.0 (Media Cybernetics, Silver Spring, USA).…”

“…Yu6 can be vegetatively propagated via its aerial stems or mother stands. Its seed parent is a near-allohexaploid hybrid (called MTP, see Iqbal et al 2019) involving maize (Zea mays ssp. mays L.), eastern gamagrass (Tripsacum dactyloides L.) and perennial tetraploid teosinte [Z. perennis (Hitchc.)…”

“…perennis hybrids (Cheng et al 2016, Iqbal et al 2018 and the maize-T. dactyloides-Z. perennis hybrids (Iqbal et al 2019, Li et al 2015. When MTP was backcrossed with maize, MTP showed its reproductive versatility by McGISH analysis, namely, 2n, 2n + n, n + n, and an irregular type (Iqbal et al 2019).…”

“…perennis hybrids (Iqbal et al 2019, Li et al 2015. When MTP was backcrossed with maize, MTP showed its reproductive versatility by McGISH analysis, namely, 2n, 2n + n, n + n, and an irregular type (Iqbal et al 2019). In the 2n type, one unreduced 2n female gamete (having the somatic chromosome number) forms seed asexually.…”