Relationship between meiotic behaviour and fertility in backcross-1 derivatives of the [(Gossypium hirsutum × G. thurberi)2 × G. longicalyx] trispecies hybrid

Abstract

Wild cotton species are an important source of desirable genes for genetic improvement of cultivated cotton Gossypium hirsutum Linnaeus, 1763. For the success of such an improvement, chromosome pairings and recombinations in hybrids are fundamental. The wild African species G. longicalyx Hutchinson & Lee, 1958 could be used as donor of the desirable trait of fiber fineness. Twelve BC1 plants obtained from the backcrossing of [(G. hirsutum × G. thurberi Todaro, 1877)² × G. longicalyx] (A_hD_hD₁F₁, 2n = 4x = 52) trispecies hybrid (HTL) by G. hirsutum (cv. C2) (A_hA_hD_hD_h, 2n = 4x = 52) were investigated for meiotic behaviour and plant fertility. Their chromosome associations varied as follows: (2.5 to 11.5) I + (17 to 22) II + (0.31 to 1.93) III + (0.09 to 1.93) IV + (0 to 0.07) V + (0 to 0.14) VI. Their pollen fertility ranged from 4.67 to 32.10 %. Only four BC1 plants produced a few seeds through self-pollination. The remaining BC1 were totally self-sterile and usually presented the highest number of univalents. All BC1 materials produced BC2 seeds (0.44 to 6.50 seeds per backcross) with the number of seeds negatively correlated with the number of univalents (R² = 0.45, P < 0.05). Most BC1 plants gave significantly finer fiber compared to the cultivated G. hirsutum. SSR markers showed a segregation of wild alleles among the backcross derivatives and Genomic in situ hybridization (GISH) revealed presence of entire chromosomes of G. longicalyx as well as recombinant chromosomes in the backcross derivatives. The significance and details of these results are presented and the prospects of successfully exploiting these plant materials are discussed.

Keywords: Gossypium spp; chromosome; cytogenetics; fiber fineness; hybrid; in situ hybridization; meiosis; plant breeding.

Figure 1.

Polyacrylamide gel with BNL3279 SSR marker presenting allele segregations in the parental species, the hexaploid, the HTL tri-species hybrids and the BC1 plants. 1G. hirsutum2G. thurberi3G. longicalyx4 the hexaploid (G. hirsutum × G. thurberi)²5–13 HTL tri-species hybrid plants (G. hirsutum x G. thurberi)² × G. longicalyx14–24 BC1 plants (HTL x G.hirsutum). Black arrow: allele of G. hirsutum, Blue arrow: allele of G. thurberi, Red arrow: allele of G. longicalyx.

Figure 2.

Cotton pollen grain viability revealed by acetic-carmine staining. AG. hirsutum viable pollen grains with good colour and uniform size B mixture of viable and non viable pollen grains of a [(G. hirsutum × G. thurberi)² × G. longicalyx] backcross-1 plant. Scale bars: 100 μm.

Figure 3.

Meiotic metaphase I plates in G. hirsutum and in the HTL BC1/4 plant. A Meiotic metaphase I cell showing 26 bivalents in control G. hirsutumB meiotic metaphase I cell showing 8 univalents (long arrows), 20 bivalents and 1 quadrivalent (short arrow) in HTL BC1/4. Scale bars: 5 μm.

Figure 4.

Meiotic aspect with abnormalities in HTL BC1 plants. A Leptotene B diakinesis C metaphase I with univalent chromosomes in early ascension (arrow) D anaphase I E telophase I with the presence of laggard chromosomes (arrows) F metaphase II with laggard chromosomes (arrows) G anaphase II with presence of laggard chromosome (arrow) H microsporocytes with a mixture of tetrad and polyads with micronuclei. Scale bars: 20 μm.

Figure 5.

Genomic in situ hybridization on mitotic metaphase chromosomes of the HTL trispecies hybrid [(G. hirsutum × G. thurberi)² × G. longicalyx)] and a BC2 progeny. A Mitotic metaphase showing 52 chromosomes of the HTL hybrid revealed by counterstaining with DAPI B mitotic metaphase showing in the HTL hybrid 13 green chromosomes from G. longicalyx, 13 yellow-orange chromosomes from the A-subgenome of G. hirsutum and 26 red chromosomes from G. thurberi and the D-subgenome of G. hirsutum revealed after the superimposition of FITC detection and Texas Red detection C mitotic metaphase showing 52 chromosomes in a HTL BC2 revealed by counterstaining with DAPI D mitotic metaphase in a HTL BC2 showing an entire chromosome of G. longicalyx (white arrow) and an intergenomic recombination (red arrow) showing movement of G. longicalyx chromatin into a chromosome of the A-subgenome of G. hirsutum. Scale bars: 5 μm.