Attempts are underway to locate and transfer genes conferring diplosporous apomixis from Tripsacum to maize. The objective of this study was to evaluate several apomictic and sexual maize-Tripsacum hybrids for the presence or absence of Tripsacum chromosomes, PCR-RAPD generated markers, and RFLP markers that would have an association with apomictic development. Cytological and molecular analysis resulted in the identification of the Tripsacum chromosome arm carrying the gene(s) conferring diplosporous apomixis. Evaluations made on apomictic sexually derived maize + Tripsacum addition lines and an apomictic line possessing a Mz6L-Tr16L translocation were used to establish the location of the gene(s). Results of the study indicate that the successful transfer of a single Tripsacum chromosome is all that is necessary to maintain apomictic reproduction in a maize background. Additional use of this material may facilitate the development of an apomictic maize prototype and the eventual isolation of the gene(s).

The expression of gene(s) governing apomictic reproduction in Tripsacum provides the best foundation for comparing the effectiveness of apomictic reproduction in a series of maize-Tripsacum hybrids. Several 38-chromosome, apomictic maize-Tripsacum hybrids are available which possess the gene(s) conferring apomictic reproduction from Tripsacum. Without a base line for comparison, studies directed towards discerning the successful transfer or effectiveness of gene expression in a maize background are hampered. The objectives of this study are to compare the reproductive features found in apomictic Tripsacum with those in apomictic maize-Tripsacum hybrids. In addition, this study determined the feasibility of utilizing these maize-Tripsacum hybrid materials to continue an attempt to transfer the genes into a pure maize background. The frequency and occurrence of five unique reproductive features found in apomictic accessions of Tripsacum dactyloides were compared to the reproductive behaviours exhibited in the maize-Tripsacum hybrids. Results indicate the genes controlling apomixis in tetraploid Tripsacum are fully functional in maize-Tripsacum hybrids with diploid and triploid maize constitutions. The ability of the Tripsacum apomictic genes to retain full expression provides evidence to continue their transfer to a diploid or tetraploid maize background.

An apomictic form of hybrid maize (Zea mays L.) would provide an immortalized line which would be stabilized against genetic change. The development of agronomically superior, apomictic maize hybrids could provide a superior level of food security in developing nations as well as altering commercial and public maize breeding programs‐systems in developed nations. Backcross selections obtained from an apomictic, 38‐chromosome (20 maize + 18 Tripsacum L.) maize‐Tripsacum hybrid have resulted in the development of apomictic, 39‐chromosome individuals with 30 maize + nine Tripsacum chromosomes. The identification of these materials advances two major objectives: (i) the elimination of nine Tripsacum chromosomes which do not possess the gene(s) controlling apomictic reproduction; and (ii) the continued refinement of an apomictic maize line. This study was conducted to determine whether the 39 chromosome materials reproduce by apomixis. Evaluations were performed by means of cytological, isozyme, and molecular DNA methods to assay the cytological and genetic uniformity within and between the families. The lack of variation within families and among their offspring indicates that both families reproduce by apomixis. In addition, the successful transfer of apomictic genes from Tripsacum, into a maize‐Tripsacum backcross hybrid with 2n = 3x = 30 maize and 1n = 1x = 9 Tripsacum chromosomes, is demonstrated. The generation of these materials indicates that continued breeding and selection within such materials could result in the eventual development of a hybrid maize with an apomictic reproductive system.

Plant tissue culture, as a fundamental technique for genetic engineering, has great potential of epigenetic variation, of which DNA methylation is well known of importance to genome activity. We assessed DNA methylation level of explants during tissue culture of Brassica napus (cv. Yangyou 9), using high perfor mance liquid chromatography (HPLC) assisted quantification. By detecting methylation levels in hypocotyls cultured in mediums with different concentrations of hormones, we found dissected tissue cultured with 0.1 mg/L 2,4 D and 1.0 mg/L 6 BA, presented the lowest methylation level and highest induction rate of callus (91.0%). Different time point of cultured explants also showed obvious methylation variations, explants cul tured after 6 and 21 days exhibited methylation ratios of 4.33 and 8.07%, respectively. Whereas, the methyla tion ratio raised to 38.7% after 30 days cultivation, indicating that methylation level of hypocotyls ranged dur ing tissue culture. Moreover, we observed that the methylation level in callus is the highest during regeneration of rapeseed, following the regenerated plantlets and hypocotyls. This paper indicated the function of hor mones and differentiation of callus is relevant to the methylation levels during tissue culture.

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