Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: Billy B. Rhodes x
Clear All Modify Search

Vitrification, a physiological disorder characteristic of in vitro grown plants, was observed in single-node cultures of sweet potato in mannitol-enriched medium during their second year of storage. Vitrified or vitreous sweet potato plantlets were watersoaked, translucent or glassy in appearance, with thick, swollen, leaves and stems, stunted shoot growth and poor root growth. These plantlets were not able to regenerate normal plants when transferred into fresh regeneration medium nor were they able to survive outside culture conditions.

Electron microscopy revealed changes in the ultrastructures of vitrified sweet potato plantlets. Vitrified plants had defective stomatal complex, starch grain-filled chloroplasts, disrupted cell wall, big air spaces (lacunae), high frequency of cell membrane separation from the cell wall, nuclear disintegration, and cytoplasmic disorganization. These changes in the internal structures of vitrified plants were reflected in their abnormal morphology and physiology.

Free access

Vitrification, a physiological disorder characteristic of in vitro grown plants, was observed in single-node cultures of sweet potato in mannitol-enriched medium during their second year of storage. Vitrified or vitreous sweet potato plantlets were watersoaked, translucent or glassy in appearance, with thick, swollen, leaves and stems, stunted shoot growth and poor root growth. These plantlets were not able to regenerate normal plants when transferred into fresh regeneration medium nor were they able to survive outside culture conditions.

Electron microscopy revealed changes in the ultrastructures of vitrified sweet potato plantlets. Vitrified plants had defective stomatal complex, starch grain-filled chloroplasts, disrupted cell wall, big air spaces (lacunae), high frequency of cell membrane separation from the cell wall, nuclear disintegration, and cytoplasmic disorganization. These changes in the internal structures of vitrified plants were reflected in their abnormal morphology and physiology.

Free access

Tetraploids are needed to synthesize triploid watermelons, which produce “seedless” fruit with improved quality. Traditionally, the tetraploids are induced by applying colchicine to the growing apex of seedlings or soaking the seeds with colchicine solution. This method often produces low frequency of tetraploids and high frequency of chimeras. Breeding tetraploids takes much longer time than breeding diploids because of the low female fertility. We developed a tissue culture approach that allows breeders to develop desirable tetraploids with commercially acceptable volume of seed in 2 years. This tissue culture approach includes: 1) regenerate plants via shoot organogenesis from cotyledon tissue; 2) screen tetraploids based on leaf morphology (more serrated leaf margin and wider leaf shape) before transplanting, and confirm tetraploids based on pollen morphology (larger pollen with four copi) and/or seed characteristics; 3) self-pollinate tetraploids or cross the tetraploids with diploids to accurately estimate the female fertility; 4) micropropagate the best tetraploid(s) using axillary buds during the off-season; and 5) produce tetraploid seed from the cloned tetraploids in an isolation plot and evaluate the triploids derived from the tetraploid(s) in the following season. This approach has been practiced on more than 20 genotypes over the past 4 years.

Free access

Isozyme, randomly amplified polymorphic DNA (RAPD), and simple sequence repeats (SSR) markers were used to generate a linkage map in an F2 and F3 watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai] population derived from a cross between the fusarium wilt (Fusarium oxysporum f. sp. niveum) susceptible `New Hampshire Midget' and resistant PI 296341-FR. A 112.9 cM RAPD-based map consisting of 26 markers spanning two linkage groups was generated with F2 data. With F3 data, a 139 cM RAPD-based map consisting of 13 markers covering five linkage groups was constructed. Isozyme and SSR markers were unlinked. About 40% to 48% of the RAPD markers were significantly skewed from expected Mendelian segregation ratios in both generations. Bulked segregant analysis and single-factor analysis of variance were employed to identify RAPD markers linked to fusarium wilt caused by races 1 and 2 of F. oxysporum f. sp. niveum. Current linkage estimates between the resistance trait and the marker loci were too large for effective use in a marker-assisted selection program.

Free access