Tripsazea, a Novel Trihybrid of Zea mays, Tripsacum dactyloides, and Zeaperennis

Abstract

A trispecific hybrid, MTP (hereafter called tripsazea), was developed from intergeneric crosses involving tetraploid Zea mays (2n = 4x = 40, genome: MMMM), tetraploid Tripsacum dactyloides (2n = 4x = 72, TTTT), and tetraploid Zperennis (2n = 4x = 40, PPPP). On crossing maize-Tripsacum (2n = 4x = 56, MMTT) with Zperennis, 37 progenies with varying chromosome numbers (36-74) were obtained, and a special one (i.e., tripsazea) possessing 2n = 74 chromosomes was generated. Tripsazea is perennial and expresses phenotypic characteristics affected by its progenitor parent. Flow cytometry analysis of tripsazea and its parents showed that tripsazea underwent DNA sequence elimination during allohexaploidization. Of all the chromosomes in diakinesis I, 18.42% participated in heterogenetic pairing, including 16.43% between the M- and P-genomes, 1.59% between the M- and T-genomes, and 0.39% in T- and P-genome pairing. Tripsazea is male sterile and partly female fertile. In comparison with previously synthesized trihybrids containing maize, Tripsacum and teosinte, tripsazea has a higher chromosome number, higher seed setting rate, and vegetative propagation ability of stand and stem. However, few trihybrids possess these valuable traits at the same time. The potential of tripsazea is discussed with respect to the deployment of the genetic bridge for maize improvement and forage breeding.

Keywords: Tripsacum dactyloides; Zea mays; Zea perennis; forage breeding; maize improvement; trihybrid.

Figure 1

Seven types of chromosome numbers in trihybrids. The chromosome number in trihybrids included (A) 2n = 36, (B) 2n = 46, (C) 2n = 50, (D) 2n = 52, (E) 2n = 52, (F) 2n = 54, (G) 2n = 72, and (H) tripsazea, 2n = 74. Scale bars, 10 μm.

Figure 2

Morphology of tripsazea and comparison of its several morphological characters with three parental species. (A) One-year-old tripsazea plant by stem node propagation. (B) Tripsazea ears from axillary bud differentiation, branching of lateral inflorescence. (C) A tripsazea seedling from the axillary bud. (D) Regenerated tripsazea plants after mowing. (E) Flowering of tripsazea plants induced by short-day exposure. (F) Mature leaves from the hybrid and its parents (area 1 cm²). The ear (G), seed (H), male spikelet (I) and silk (J) from the hybrid (tripsazea: MTP) and its parental species (M, T, and P designations refer to Z. mays, T. dactyloides, and Z. perennis, respectively). Scale bars, 1 cm.

Figure 3

FCM histograms from leaves of tripsazea and its three parental species, using maize inbred line (B73) as an internal standard: (A) B73, (B) V182, (C) TZ07, (D) 9475, (E) tripsazea, and (F) comparison of the relative DNA content (data shown as mean and S.D., n = 3; different lowercase letters indicate statistically significant difference at the α = 0.05 level according to Duncan’s multiple range test).

Figure 4

The mitotic (panel A) and meiotic behavior (panel B) of tripsazea. The prophase (a), metaphase (b), anaphase (c) and telophase (d) of mitosis. Diakinesis I (e, f, and g), metaphase I (h), anaphase I (i and j) and telophase (k) of meiosis and observed allosyndetic associations and their diagram (l). Yellow (or green), pink and blue signals were from the maize, Z. perennis and T. dactyloides genomes, respectively. Scale bars, 10 µm.

Figure 5

Field-grown perennial forage maize cv. Yu5 (A and B) and its chromosomal constitution (C) (Li et al. 2015). Blue, gray blue, green, and red colors represent T. dactyloides, Z. perennis, Z. mays chromosomes and Cent-C probes, respectively. Arrows indicate translocation chromosomes between Z. mays and Z. perennis. Scale bar, 10 µm.