Posted by Henry Kuska on Wed, May 29, 2002

A recent paper by Crespel, L; Gudin, S.; Meynet, J.; and Zang, D.; Theor Appl Genet, vol. 104, pages 451-456 (2002) reports on the results of crossing 2 dihaploid R. hybridia L. clones, called H61 and H3 with normal diploids R. rugosa and R. wichuraiana. The dihalpoids were created by in situ parthenogenesis induced by using irradiated pollen and embryo rescue of a rose identified as FJV6 and Sweet Promise.

The results are a little surprising (one would of expected that all of the seedlings would of been diploids like the parents). The actual results for H61 x R. wichuraiana are 8 diploids, 19 triploids and 5 pentapoids (32 total seedlings); for H61 x R. rugosa - 6 diploids, 28 triploids, 2 tetraploids, and 2 pentaploids (38 total seedlings); and for the reverse cross R. wichuraiana x H3 - 19 diploids, 9 triploids (28 total seedlings).

Thus, we see that the division does not always follow the classical expected division but "often follows abnormal (or absence of) cytokinesis". Please consult the original paper for a more technical discussion.

Theor Appl Genet, 104: 451-456 (2002)
AFLP-based estimation of 2n gametophytic heterozygosity in two parthenogenetically derived dihaploids of Rosa hybrida L.
L. Crespel, S. Gudin, J. Meynet, D. Zhang

Two dihaploid Rosa hybrida L. genotypes, derived through parthenogenesis by using irradiated pollen, were crossed with clonally propagated plants of the diploid species Rosa rugosa Thunb. and Rosa wichuraiana Crép., respectively. Three progeny groups were obtained which contained numerous polyploids, as determined by flow cytometry. Production of fertile 2n female gametes is apparently very common in one of these R. hybrida dihaploid derivatives, whereas the other one is able to produce fertile 2n pollen. Hence, an amplified fragment length polymorphism (AFLP) study was performed on the parental plants and the resulting hybrid offspring in order to estimate (1) the respective genomic parental contributions, and (2) the level of heterozygosity transmitted by the 2n unreduced gametes. Comparison of the levels of transmitted parental heterozygosity revealed that two types of 2n gametes were produced simultaneously, presumably resulting from restitution at the first and at the second meiotic division, respectively.

Plant Material
The AFLP analyses were carried out on clonally propagated plants belonging to two diploid (2n=2x=14) botanic species, Rosa wichuraiana Crép. and Rosa rugosa Thunb., two parthenogenetically derived dihaploid R. hybrida L. clones, H61 and H3, and three segregating populations: (1) a population of 32 individuals resulting from H61 x R. wichuraiana comprising eight diploids, 19 triploids and five pentaploids, (2) 38 seedlings resulting from H61 x R. rugosa comprising six diploids, 28 triploids, two tetraploids and two pentaploids, (3) 28 seedlings resulting from R. wichuraiana x H3 comprising 19 diploids and nine triploids. H61 and H3 resulted from the haploidization of the 4x cvs FJV6 and Sweet Promise, respectively. They were obtained by in situ parthenogenesis induced by using irradiated pollen (γrays at 600 Gy) and embryo rescue, as described by Meynet et al. (1994), and could be used in hybridization programs as H61 and H3 are female and male fertile, respectively (El Mokadem et al. 2000a). The ploidy level of the hybrid progenies was determined by flow cytometry, as described by Jacob et al. (1996). Previous test crosses made with a number of diploid species or tetraploid cultivars showed that R. wichuraiana and R. rugosa always produce haploid reduced gametes, as deduced from the resulting ploidy levels of the offspring, whereas dihaploid derivatives of R. hybrida currently produce unreduced gametes (El Mokadem et al. 2000b). The plants were maintained in a greenhouse at the National Agronomy Research Institute in Fréjus. The crosses were carried out, and the plants cultivated, as described by El Mokadem et al. (2000a).