Ploidy Level Of Plantlets Research Articles

CALLUS AND PLANTLETS PRODUCED FROM IN VITRO CULTURE OF ANTHERS OF ACTINIDIA CHINENSIS

Homozygous genotypes are valuable for genomic and genetic studies in higher plants, but obtaining homozygous perennial plants using conventional breeding technologies is challenging, with the long times and large field areas required for several back-crossed generations. It is especially difficult with Actinidia because of dioecy, long generation times, high heterozygosity and variation in ploidy from diploid to octoploid. In vitro androgenesis through anther or microspore culture offers a route to develop the haploid and dihaploid plants often used in modern crop breeding, genetics and genomic studies. I report in vitro culture of anthers of six genotypes of diploid Actinidia chinensis resulting in production of callus and regeneration of plantlets. Preliminary results showed that genotype, plant growth regulators, the stage of microspore development and pre-treatments (cold, heat shock) all affected callus formation. Confirmation of their callus origin, homozygosity and determination of the ploidy levels of plantlets are underway.

EFFICIENT HAPLOID PRODUCTION ON 'WILKING' MANDARIN BY INDUCED GYNOGENESIS

Seedlessness is a major criterion for the citrus fresh fruit market. Therefore, triploid breeding appears very promising for the selection of new citrus cultivars. CIRAD has developed a method to produce triploid hybrids by somatic hybridization between diploid and haploid lines, and demonstrates the potential for haploid citrus production by induced gynogenesis in clementine. In this work we analysed the efficiency of induced gynogenesis by irradiated pollen in 'Wilking' mandarin (Citrus reticulata). Five doses of gamma irradiation of 'Meyer' lemon pollen were tested (0, 150, 200, 250, 300 Grays). Embryos were extracted from small seeds, obtained in immature fruits, and cultivated in vitro. The ploidy level of plantlets was determined by flow cytometry analysis. Irradiated pollen appeared to be efficient for gynogenesis induction in 'Wilking'. A relatively high number of haploids (7 plantlets) were obtained, essentially after hybridisation with 'Meyer' lemon pollen irradiated at 250 Grays. The ploidy level of all haploid plantlets was confirmed by chromosome counts, and molecular markers demonstrated their gynogenetic origin. These haploid lines should be useful for triploid breeding by somatic hybridisation, and also constitute interesting resources for genomic studies. (Resume d'auteur)

In vitro induction and identification of tetraploid plants of Paulownia tomentosa

Polyploidization is a major trend in plant evolution that has many advantages over diploid. In particular, the enlargement and lower fertility of polyploids are very attractive traits in forest tree breeding programs. We report here a system for the in vitro induction and identification of tetraploid plants of Paulownia tomentosa induced by colchicine treatment. Embryonic calluses derived from placentas were transferred to liquid Murashige and Skoog (MS) medium containing different concentrations of colchicine (0.01, 0.05, or 0.1%) and incubated for 24, 48, or 72 h on an orbital shaker at 110 rpm. The best result in terms of the production of tetraploid plantlets was obtained in the 48 h + 0.05% colchicine treatment, with more than 100 tetraploid plantlets being produced. The ploidy level of plantlets was verified by chromosome counts, flow cytometry, and morphology. The chromosome number of tetraploids was 2n = 4x = 80 and that of diploid plantlets was 2n = 2x = 40. The relative fluorescence intensity of tetraploids was twofold higher than that of diploids. The tetraploid and diploid plantlets differed significantly in leaf shape, with those of the former being round and those of the latter pentagonal. The mean length of the stomata was longer in tetraploid plants than diploid plants, and stomatal frequency was reduced with the increased ploidy level. The tetraploids had large floral organs that were easily distinguishable from those of diploid plants.