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

Muhammad Zafar Iqbal,Yang Li,Qilin Tang,Xiaodong Wen,Tingzhao Rong,Weiming Jiang,Lei Zhang,Yanli Zhao,Yuegui Su,Asif Ali,Mingjun Cheng,Huaxiong Li

doi:10.1007/s00425-019-03136-z

Abstract

Main conclusionTripsacum 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 BC1 and BC2. 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.

Highlights

The narrow gene pool in maize results in retardation of its genetic improvement mainly due to invariability
An allopolyploid tri-genomic bridge plant between T. dactyloides, tetraploid maize and Z. perennis has been produced, which was backcrossed with maize to produce BC1 and B C2 with the following objectives; (1) to create maize germplasm with variable agronomic and genetic characteristics, (2) to obtain hybrids with varying genomic composition and translocation, (3) to observe distinct species chromosomal segregation behavior in one nucleus
Interspecific hybrid named as MT (2n = 4x = 56) was introduced by United States Department of Agriculture (USDA), which was produced by crossing autotetraploid maize-inbred line V182 (2n = 4x = 40) and T. dactyloides (2n = 4x = 72)

Summary

Introduction

The narrow gene pool in maize results in retardation of its genetic improvement mainly due to invariability. Eastern gamagrass (Tripsacum dactyloides), called “ice cream grass”, predominantly found at diploid (2n = 2x = 36) and tetraploid (2n = 4x = 72) levels (Farquharson 1955), belongs to the genus Tripsacum, which resides in the tertiary gene pool of maize and owns many interesting genes for maize improvement (Hardin 1994; Maazou et al 2017) It is a warm-season C4 facultative apomictic perennial forage grass having a remarkable ability to withstand various biotic and abiotic stresses (Eubanks 2006). An allopolyploid tri-genomic bridge plant between T. dactyloides, tetraploid maize and Z. perennis has been produced, which was backcrossed with maize to produce BC1 and B C2 with the following objectives; (1) to create maize germplasm with variable agronomic and genetic characteristics, (2) to obtain hybrids with varying genomic composition and translocation, (3) to observe distinct species chromosomal segregation behavior in one nucleus. The images were captured with Media Cybernetics CCD 700 (charge coupled device)

Materials and methods

Findings

Discussion