Genetic analysis of an interspecific cross in ornamental Viburnum (Viburnum).

A genetic analysis was performed on a population derived from crosses between Viburnum lantana and Viburnum carlesii. Linkage maps were developed for each species using AFLP, random amplified polymorphic DNA (RAPD), and sequence-tagged site markers and a half-sib approach that took advantage of both the polymorphism between the species and the heterozygosity within each parent. The map for V. lantana consisted of 153 DNA markers and spanned approximately 750 cM, whereas that for V. carlesii contained 133 markers and covered 700 cM. These maps were used to determine the location of several major genes influencing leaf spot resistance, Verticillium wilt resistance, bud color, and flower scent. Both species contained moderate levels of heterozygosity. Flow cytometric analysis revealed that the genome of V. lantana was 40% larger than that of V. carlesii, and this difference was paralleled by a proportionally greater number of intercross markers (markers segregating 3:1) from V. lantana than from V. carlesii. In addition, V. lantana (n = 9) displayed a 10th linkage group for which no homolog in V. carlesii (n = 9) could be found and which contained only markers present in the former species and absent in the latter. These results suggest that Viburnum could be an interesting genetic model for Caprifoliaceae sensu lato.

Leaf ontogeny influences leaf phenolics and the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin in hybrid poplar against gypsy moth.

We tested the hypothesis that ontogenetic variation in leaf chemistry could affect the efficacy of genetically expressed Bacillus thuringiensis cry1A(a) d-endotoxin, and thus provide spatial variation in (1) foliage protection and (2) selective pressures that could delay the resistance of folivores. Our model consisted of clonal hybrid Populus plants (NC5339). Consumption of foliage and relative growth rates of gypsy moth, Lymantria dispar (L.) increased, and phenolic glycoside concentrations decreased, as leaves from transformed plants containing the cry1A(a) d-endotoxin and nontransformed plants matured from leaf plastochron index (LPI) 1-6. Feeding and growth rates were negatively correlated with phenolic glycosides in both transformed and nontransformed foliage. The presence of the B. thuringiensis d-endotoxin was at most, additive to the effect of the phenolic glycosides. Feeding and growth rates were positively correlated with condensed tannins in transformed foliage, but there was no relationship with condensed tannins in nontransformed foliage. The results indicate that the presence of foliar allelochemicals of poplar can enhance the effectiveness of genetically expressed B. thuringiensis d-endotoxin against gypsy moth larvae. However, the spatial variation in gypsy moth performance in response to the combination of foliar allelochemicals and d-endotoxin was not greater than the effect of ontogenetic variation in foliar allelochemicals alone. These results suggest that for this important pest, foliage protection may be obtained without genetically engineered defenses, and instead, by relying on ontogenetic and clonal variation in allelochemicals. The benefits of combining novel resistance mechanisms with natural ones will depend upon the specific folivore's adaptation to natural resistance mechanisms, such as allelochemicals. Moreover, some of the greatest benefits from transgenic resistance may arise from the need to protect trees from multiple pests, some of which may not be deterred by, or may even prefer, allelochemicals that confer protection from a few species.

Resorption protection. Anthocyanins facilitate nutrient recovery in autumn by shielding leaves from potentially damaging light levels.

The resorption protection hypothesis, which states that anthocyanins protect foliar nutrient resorption during senescence by shielding photosynthetic tissues from excess light, was tested using wild-type (WT) and anthocyanin-deficient mutants of three deciduous woody species, Cornus sericea, Vaccinium elliottii (Chapmn.), and Viburnum sargentii (Koehne). WT Betula papyrifera (Marsh) was included to compare the senescence performance of a species that does not produce anthocyanins in autumn. Plants were subjected to three environmental regimes during senescence: an outdoor treatment; a 5-d high-stress (high light and low temperature) treatment followed by transfer to a low-stress environment and a low-stress treatment that served as control. In the outdoor treatment, the appearance of anthocyanins in senescing leaves of WT plants was concomitant with the development of photo-inhibition in mutant plants of all three anthocyanin-producing species. In the high-stress environment, WT plants maintained higher photochemical efficiencies than mutants and were able to recover when transferred to the low-stress environment, whereas mutant leaves dropped while still green and displayed signs of irreversible photooxidative damage. Nitrogen resorption efficiencies and proficiencies of all mutants in both stressful treatments were significantly lower than the WT counterparts. B. papyrifera displayed photochemical efficiencies and nitrogen resorption performance comparable with the highest of the anthocyanin-producing species in all three senescing environments, indicating a photoprotective strategy divergent from the other species studied. These results strongly support the resorption protection hypothesis of anthocyanins in senescing leaves.

Thermally induced changes in shoot morphology of Hancornia speciosa microcultures: evidence of mediation by ethylene.

A shoot microculture protocol for the tropical fruit tree Hancornia speciosa Gom. was developed based on high temperature stimulation of axillary branching. An increase in the culture temperature from 25 to 31 degrees C (continuous over a 4-week period) stimulated the elongation of newly subcultured micro-shoots. Increases in culture temperature from 31 to 35 degrees C suppressed elongation but induced branching of all shoots. Increasing temperature to 37 degrees C reduced both shoot elongation and branching severely. Thermoperiodic regimes involving daily exposure for 8 or 16 h at 35 degrees C followed by 31 degrees C for the remainder of the day were only moderately effective in stimulating branching. However, maintaining cultures at 35 degrees C for 2 weeks followed by growth at a constant temperature of 31 degrees C led to vigorous branching. We hypothesize that thermally induced branching is mediated by a reduction in ethylene biosynthesis. In cultures of nodal segments grown at 31 degrees C, ethylene evolution peaked 12 to 16 days after subculture, and then gradually decreased until the end of the culture cycle. Compared with cultures held at 31 degrees C, those grown at 35 degrees C showed an earlier peak and a reduced rate of ethylene evolution throughout most of the culture cycle, and less 1-aminocyclopropane-1-carboxylate (ACC) synthase mRNA transcript and ACC oxidase activity. An inhibitor of ethylene biosynthesis (L-(2-aminoethoxyvinyl)-glycine) at 4.5 &mgr;M mimicked the effect of elevated temperature (35 degrees C) in stimulating lateral branching. The branching pattern of shoots grown at 35 degrees C in the presence of 1 &mgr;l l(-1) ethylene gas resembled that of shoots grown at 31 degrees C. We conclude that a reduction in ethylene evolution has a role in thermal induction of branching in H. speciosa. Heat induced release of axillary buds may be useful in the microculture of trees with strong apical dominance that cannot be overcome by cytokinin treatment.