Hybridisation between the annual diploid sunflower ( Helianthus annuus)and the perennial diploid species Helianthus mollis and Helianthus orgyalis was obtained by means of a normal crossing procedure or embryo rescue. Hybridisation success was low. All plants examined cytologically appeared to be diploid. However, the phenotypes of these diploids were not intermediate between the parents and, despite great variation, they resembled the female parent-type predominantly. Thirty five percent of plants issued from sunflower pollinated with perennial Helianthus had a phenotype resembling the female sunflower parent. On average, only 5% of the minimum number of expected RAPD and RFLP bands from male parents were recovered in plants produced from mature seeds after pollination of sunflower by H. mollis. More hybrids were found among plants obtained from embryo rescue, with an average of 25% of the male parent bands recovered per plant. Analysis of individual plants indicated the occurrence of various levels of hybridisation. There was a significant positive correlation between the number of phenotype traits related to hybrid status and the number of bands derived from the male parent. A single hybrid plant might possibly represent the product of a 'normal' hybridisation event. The mechanisms behind these unusual events and the consequences for the breeder are discussed.
To obtain introgressed sunflower lines with improved disease resistance, interspecific crosses were performed with foreign perennial species. We report on several unusual features displayed by these hybrid plants. The methods used to produce the kernels affected yield and genotypes of progeny. Phenotypic traits and DNA markers were investigated in 97 plants derived from cross-pollination between annual diploid cultivated sunflower (Helianthus annuus) and the perennial diploid species H. mollis or H. orgyalis, and the reverse reciprocal crosses. The level of hybridization in progeny was determined using RAPD and RFLP markers. Hybridization was performed by leaving embryos to develop normally on the head (classical crossing) or using embryo rescue. All observed plants derived from H. mollis were diploid (2n = 34). Phenotypes were predominantly similar to the female when cultivated sunflower was the female parent. Progeny from crosses using a wild species as the female parent resembled that parent. Thus, reciprocal crosses led to different progeny. F1 sister progeny shared different sets of molecular markers representing a few of those of the wild species used as the pollen donor. Our results indicate mechanisms leading to the unusual event of partial hybridization. Possible mechanisms behind these unusual events and their possible impact on evolution are discussed.
Summary Young leaves of different rubber‐tree clones were inoculated with Microcyclus ulei under controlled conditions. Under ultraviolet light, intense blue fluorescent light was emitted from the penetration site 6 h after inoculation. The speed of the appearance of this fluorescence was related to the degree of resistance of the clones: 12–36 h in totally resistant clones, 36–120 h in marked partially resistant clones, and 120 h in weak partially resistant clones. The source of this fluorescence may have been scopoletin. Strong accumulation of this coumarin may inhibit pathogen invasion in a very early phase. Four days after inoculation, intense accumulation of lignins in only a few cells at the penetration sites was observed in totally resistant clones. Intense lignin accumulation around lesions may also stop pathogen development in some partially resistant clones
Application of in vitro culture techniques to Hevea brasiliensis has encountered serious difficulties. In particular, protoplasts have been found to be recalcitrant to division. The aim of the present work was to compare biochemically non-mitotic protoplasts isolated from young Hevea stems with mitotic protoplasts from Citrus, tobacco and rice cells. Hevea tissue maceration did not promote ethylene production contrary to the mitotic systems, rather aminocyclopropanecarboxylic acid (ACC) synthesis occurred. Large increases in superoxide dismutase (SOD) and peroxidase (PER) activities during maceration indicated the occurrence of a peroxidative phenomenon. During Hevea protoplast culture, a rapid decrease in viability was associated with an increase in ethylene production, reactions common to stress conditions. Activities of enzymes involved in the production and elimination of toxic oxygen forms were not related to protoplast reactivity. Differences in polyamine content and especially the high putresceine/spermididine + spermine ratio could be used, together with ethylene rise during culture, as markers of Hevea protoplast recalcitrance in culture. Thus, a number of physiological phenomena are associated with lack of mitotic division of stem protoplasts of rubber.
Conditions for successful culture of rubber tree (Hevea brasiliensis) protoplasts were investigated. Protoplasts, derived from embryogenic callus, regenerated cell walls then underwent division when embedded in alginate and cultivated on a modified Murashige and Sook medium (9 μM 2,4-dichlorophenoxyacetic acid, 0.6 M glucose, 0.93 μM kinetin, NH 4 (+) reduced by half) in the presence of nurse cells (tobacco feeder cell layer). The presence of nurse cells was essential to maintain viability and sustain protoplast division. Several parameters which influenced the plating efficiency were analysed, such as the density of feeder cells and the duration of contact of the feeder layer.
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