Podosphaera pannosa (syn. Sphaerotheca pannosa) on Rosa and Prunus spp.: Characterization of Pathotypes by Differential Plant Reactions and ITS Sequences

The powdery mildew fungus Podosphaera pannosa (Wallr.: Fr.) de Bary (syn. Sphaerotheca pannosa) is a major problem on roses worldwide. Twenty‐six monoconidial isolates of Podosphaera collected on roses and Prunus spp. in Belgium, Germany, France, Denmark, Israel and The Netherlands were characterized on the basis of differential reactions on in vitro rose genotypes and Prunus avium L. and by DNA sequence analysis of the rDNA ITS (internal transcribed spacer) region. Twenty‐four isolates were determined as P. pannosa. Amongst these, different groups could be distinguished. A first group of 18 isolates was highly virulent on rose and avirulent or very weakly virulent on P. avium. A second group of four isolates was highly virulent on both rose and P. avium. Analysis of the ITS sequence could discriminate these two groups of P. pannosa strains by a one base pair difference. Finally, two isolates of powdery mildew collected on Prunus sp. could be classified as P. pannosa based on their ITS sequence, which was identical to the ITS sequence of the isolates only highly virulent on roses. However, these two isolates were not able to infect roses. These results indicate that different strains of P. pannosa exist with varying host specificity. We demonstrated by ITS sequencing and plant reactions that the host range of P. pannosa comprises roses and Prunus spp.     

Effect of different environmental conditions in vitro on sucrose metabolism and antioxidant enzymatic activities in cultured shoots of Nicotiana tabacum L.

Nicotinan tabacum L. shoot cultures were used as a model to evaluate the effect of bottom cooling and double layer system on plant quality and metabolism. The percentage of hyperhydric shoots produced, decreased 35% when bottom cooling was applied, while non hyperhydric, high quality plants were obtained with a combination of bottom cooling and the double layer system. However, in the latter case, the multiplication rate was completely inhibited due to the presence of charcoal in the liquid medium. Sucrose metabolism (mainly invertase activity) was significantly enhanced by the sucrose supplement present in the liquid medium. Activities of superoxide dismutase and catalase were highest in hyperhydric cultures.     

Impact of sugar concentration in vitro on photosynthesis and carbon metabolism during ex vitro acclimatization of Spathiphyllum plantlets

Photosynthesis and carbon metabolism were followed during the acclimatization of micropropagated Spathiphyllum cv. Petite shootlets cultured with two different sucrose concentrations (3 and 6%). Increased sugar supply resulted in inhibition of photosynthesis, nonfunctional photosynthetic reaction centers, a more mixotrophic metabolism and higher starch and sucrose reserves at the end of the in vitro period. During the first days of acclimatization, net photosynthesis and adenosine diphosphoglucose (ADPG) pyrophosphorylase (EC 2.7.7.27) activity decreased for both treatments. In this period, sucrose was mainly used as nutrient reserve by plants cultured on 6% sucrose, as evidenced by a strong increase in sucrose synthase (EC 2.4.1.13) activity together with a severe decline in sucrose content. In the same period, sucrose breakdown and synthesis were in balance for plants cultured on 3% sucrose and the starch content increased slightly. After one week plants started to recover and full photosynthetic capacity developed. Two weeks after ex vitro transplantation, no differences between plants micropropagated with 3 or 6% sucrose could be found for photosynthesis, carbohydrate pools or enzyme activities. At the end of acclimatization the starch content increased again.     

Exploitation of flow cytometry for plant breeding

In this review, the different applications of flow cytometry in plant breeding are highlighted. Four main breeding related purposes can be distinguished for flow cytometry: (i) Characterisation of available plant material, including screening of possible parent plants for breeding programs as well as evaluation of population biodiversity; (ii) Offspring screening after interspecific, interploidy or aberrant crosses; (iii) Ploidy level determination after haploidization and polyploidization treatments and (iv) Particle sorting, that allows separation of plant cells based on morphological or fluorescent characteristics. An overview and discussion of these various applications indicates that flow cytometry is a relatively quick, cheap and reliable tool for many breeding related objectives.     

Regeneration of cell suspension derived <Emphasis Type="Italic">Apium graveolens</Emphasis> L. protoplasts

Cytoplasmatic male sterility (CMS), which can be achieved by protoplast fusion and regeneration, has potential to greatly facilitate hybrid breeding of celery (Apium graveolens L.). Therefore as a first step we developed a simple and efficient protoplast isolation and regeneration protocol for three commercial A. graveolens varieties (green and white celery and celeriac). To this end, cell suspensions from independent cell lines of open pollinated cultivars and inbred lines were initiated as a source for protoplast isolation. Comparative analyses showed that culturing was most successful in modified Kao and Michayluk liquid medium supplemented with 0.3 mg l^?1 2,4-D. The cytokinin type (TDZ or zeatin) and concentration had no significant effect on regeneration efficiency. Microcalli were obtained within 15 days to 5 weeks after protoplast isolation. Supplementing the culture medium with 25% conditioned medium increased microcolony formation for some of the cultured lines. Plants were obtained within 2 months of microcallus culturing and these were all diploid, suggesting genetic inheritance consistency. The efficiency of regeneration mainly depended on the specific genotype, with outcrossing genotypes displaying high heterogeneity in regeneration responses whereas inbred lines did not regenerate. The protocol presented here enables to implement protoplast fusion in celery breeding.     

Genetic diversity,population structure,and traditional culture of Camellia reticulata

Camellia reticulata is an arbor tree that has been cultivated in southwestern China by various sociolinguistic groups for esthetic purposes as well as to derive an edible seed oil. This study examined the influence of management, socio‐economic factors, and religion on the genetic diversity patterns of Camellia reticulata utilizing a combination of ethnobotanical and molecular genetic approaches. Semi‐structured interviews and key informant interviews were carried out with local communities in China's Yunnan Province. We collected plant material (n = 190 individuals) from five populations at study sites using single‐dose AFLP markers in order to access the genetic diversity within and between populations. A total of 387 DNA fragments were produced by four AFLP primer sets. All DNA fragments were found to be polymorphic (100%). A relatively high level of genetic diversity was revealed in C. reticulata samples at both the species (H_sp = 0.3397, I_sp = 0.5236) and population (percentage of polymorphic loci = 85.63%, H_pop = 0.2937, I_pop = 0.4421) levels. Findings further revealed a relatively high degree of genetic diversity within C. reticulata populations (Analysis of Molecular Variance = 96.31%). The higher genetic diversity within populations than among populations of C. reticulata from different geographies is likely due to the cultural and social influences associated with its long cultivation history for esthetic and culinary purposes by diverse sociolinguistic groups. This study highlights the influence of human management, socio‐economic factors, and other cultural variables on the genetic and morphological diversity of C. reticulata at a regional level. Findings emphasize the important role of traditional culture on the conservation and utilization of plant genetic diversity.     

Time course of catalase and superoxide dismutase during acclimatization and growth of micropropagated Calathea and Spathiphyllum plants

Catalase and superoxide dismutase (SOD) activities were followed in leaves during ex vitro acclimatization and growth of micropropagated Spathiphyllum floribundum Schott Petite and Calathea louisae Gagnep Maui Queen. During acclimatization of both plants catalase activity increased, reaching a maximum 4 weeks after transplantation, while total superoxide dismutase activity increased with plant growth reaching a maximum in the 24th week. Variations in the pattern of catalase and SOD isoforms were observed; a second Mn-SOD band appeared in Spathiphyllum 12 weeks after transfer from in vitro, while in Calathea plants an additional Mn-SOD form was present from the second until the fourth week after transplantation. The observed changes reflect the plants' capacity to develop antioxidant mechanisms during acclimatization. These findings indicate that the adaptation of micropropagated plants to ex vitro conditions is more extended in time than generally accepted.     

Branching gene expression during chrysanthemum axillary bud outgrowth regulated by strigolactone and auxin transport

Shoot branching is essential in ornamental chrysanthemum production and determines final plant shape and quality. Auxin is associated with apical dominance to indirectly inhibit bud outgrowth. Two non-mutually exclusive models exist for indirect auxin inhibition. Basipetal auxin transport inhibits axillary bud outgrowth by limiting auxin export from buds to stem (canalization model) or by increasing strigolactone levels (second messenger model). Here we analyzed bud outgrowth in treatments with auxin (IAA), strigolactone (GR24) and auxin transport inhibitor (NPA) using a split-plate bioassay with isolated chrysanthemum stem segments. Besides measuring bud length, dividing cell percentage was measured with flow cytometry and RT-qPCR was used to monitor expression levels of genes involved in auxin transport (CmPIN1) and signaling (CmAXR2), bud dormancy (CmBRC1, CmDRM1) and strigolactone biosynthesis (CmMAX1, CmMAX3). Treatments over a 5-day period showed bud outgrowth in the control and inhibition with IAA and IAA?+?GR24. Bud outgrowth in the control coincided with high dividing cell percentage, decreased expression of CmBRC1 and CmDRM1 and increased CmPIN1 expression. Inhibition by IAA and IAA?+?GR24 coincided with low dividing cell percentage and unchanged or increased expressions of CmBRC1, CmDRM1 and CmPIN1. Treatment with GR24 showed restricted bud outgrowth that was counteracted by NPA. This restricted bud outgrowth was still concomitant with a high dividing cell percentage and coincided with decreased expression of dormancy genes. These results indicate incomplete inhibition of bud outgrowth by GR24 treatment and suggest involvement of auxin transport in the mechanism of bud inhibition by strigolactones, supporting the canalization model.     

Introgression of rol genes from rhizogenic Agrobacterium strains into Escallonia spp.

Plant Cell, Tissue and Organ Culture (PCTOC) - The introgression of rol-genes of rhizogenic Agrobacterium into the plant genome induces changes in plant phenotype and physiology. However, only...