Flowering annuals : petunias

"Petunias have become one of the most popular flowering annual garden plants. They are relatively free from insect and disease problems, have a long flowering period, are easy to grow, and are available in a wide range of form and color."--First page.R.R. Rothenberger and B. Fick (Department of Horticulture, College of Agriculture)Types of petunias -- Cultural practices -- Varieties -- Starting petunias indoors -- Diseases and insects.Revised 6/90/8M--Page 4

Oidium longipes, a new powdery mildew fungus on petunia in the USA: A potential threat to ornamental and vegetable solanaceous crops

This is the first North American report of Oidium longipes, an anamorphic powdery mildew species described recently in Europe. It was found on vegetatively propagated petunia grown in a commercial greenhouse in New Jersey, USA, where it caused a rapidly spreading disease. The pathogen might have originated offshore and may have already been distributed in the United States through horticultural trade. During field surveys in Europe, it was found on petunia in Hungary and Austria as well; this is the first report of O. longipes from these two countries. A detailed light microscopy study of American and European specimens of O. longipes, including freshly collected samples and authentic herbarium specimens, revealed that its conidiophore morphology is more variable than illustrated in the original species description or in subsequent works. Microcycle conidiation, a process not yet known to occur in powdery mildews, was repeatedly observed in O. longipes. The rDNA internal transcribed spacer (ITS) sequences were identical in colonies containing different conidiophore types as well as in a total of five specimens collected from petunia in the United States, Austria, Hungary, Germany, and Switzerland. A phylogenetic analysis of the ITS sequences revealed that the closest known relative of O. longipes is O. lycopersici, known to infect tomato only in Australia. Cross-inoculation tests showed that O. longipes from petunia heavily infected tobacco cv. Xanthi, while the tomato and eggplant cultivars tested were moderately susceptible to this pathogen. These results indicate that its spread represents a potential danger to a number of solanaceous crops. Our ad hoc field surveys conducted in 2006 and 2007 did not detect it outside New Jersey in the United States; all the other powdery mildew–infected petunias, collected in New York and Indiana, were infected by Podosphaera xanthii. In Europe, most of the powdery mildew–infected petunias examined in this study were infected by P. xanthii or Golovinomyces orontii. Our multiple inoculation tests revealed that the same petunia plants and even the same leaves can be infected concomitantly by O. longipes, O. neolycopersici, G. orontii, and P. xanthii. Thus, it is at present unclear to what extent O. longipes contributes to the powdery mildew epidemics that develop year after year on solanaceous plants in many parts of the world

Transcriptional profiling of Petunia seedlings reveals candidate regulators of the cold stress response

Petunias are important ornamentals with the capacity for cold acclimation. So far, there is limited information concerning gene regulation and signaling pathways related to the cold stress response in petunias. A custom-designed petunia microarray representing 24816 genes was used to perform transcriptome profiling in petunia seedlings subjected to cold at 2°C for 0.5 h, 2 h, 24 h and 5 d. A total of 2071 transcripts displayed differential expression patterns under cold stress, of which 1149 were up-regulated and 922 were down-regulated. Gene ontology enrichment analysis demarcated related biological processes, suggesting a possible link between flavonoid metabolism and plant adaptation to low temperatures. Many novel stress-responsive regulators were revealed, suggesting that diverse regulatory pathways may exist in petunias in addition to the well-characterized CBF pathway. The expression changes of selected genes under cold and other abiotic stress conditions were confirmed by real-time RT-PCR. Furthermore, weighted gene co-expression network analysis divided the petunia genes on the array into 65 modules that showed high co-expression and identified stress-specific hub genes with high connectivity. Our identification of these transcriptional responses and groups of differentially expressed regulators will facilitate the functional dissection of the molecular mechanism in petunias responding to environment stresses and extend our ability to improve cold tolerance in plants

Flowering annuals : petunias (1996)

Petunias have become one of the most popular flowering annual garden plants. They are relatively free from insect and disease problems, have a long flowering period, are easy to grow, and are available in a wide range of form and color. The petunia has come a long way from its native Argentina. From the original white and magenta species, hybridizers have developed petunias in every color except a pure, bright yellow, and they are coming closer to that every year. From the simple single flower, they have developed large, ruffled, fringed and double forms.Reprinted 1/96/7M

The influence of R2R3-MYB transcription factors in Campanula medium and Petunia hybrida

Flower color is one of the most important traits for ornamental plants. Anthocyanin is the main pigment in flowers and the vegetative tissue in most higher plants. Both wild campanulas and petunias have blue/purple flowers because of the delphinidin-based anthocyanins. However, most of the flower color in the genus Campanula is mostly blue, rarely white, and a very few species are pink, while modern commercial petunias are known for their wide range of flower color in different patterns. Many kinds of research have proven that the R2R3-MYB transcription factors are responsible for regulating anthocyanin biosynthesis in different tissues. In Petunia spec., ANTHOCYANIN-2 (AN2) is considered to be the major contributor to coloration in the petal limb, while several other paralogs are involved in other tissues or stress responses. Unlike petunias, which have a convenient system for regeneration and a stable genetic plant transformation, there are no related reports for C. medium. Therefore, an efficient protocol for regeneration and Agrobacterium‑mediated transformation based on leaf disk by using GFP as the reporter gene for C. medium was established in the first part. In the second chapter, two strategies were designed to change the anthocyanin pattern in C. medium. The first is the redirection of delphinidin-based anthocyanins to pelargonidin-based anthocyanins in a blue cultivar. The second strategy was to improve the pigmentation in a pink-flowering variety of C. medium by overexpression of an R2R3-MYB transcription factor (PhAN2). In the third chapter, the same AN2 overexpression vectors used for Campanula and another flowerspecific guided AN2 constructs were also transferred into an an2- genetic petunia cultivar. The results indicated that overexpression of AN2 leads to various physiological changes in addition to increased pigmentation. The mechanism of the flower limb coloration of phenotypically "darkly-veined"petunias, and the roles of different R2R3-MYB genes were characterized in the last part. Overall, several conclusions obtained in this dissertation: (i) genetic transformation of C. medium is available; (ii) PhAN2 and PhAN4 can activate anthocyanin biosynthesis in several tissues of Campanula and Petunia and the role of PhAN2 in plant growth physiology may be diverse; (iii) the restoration of anthocyanins in the petals of commercial "dark-veined" petunias from a whiteflowered ancestor is achieved by up-regulation of AN4 as part of a long-term breeding process by humans rather than by natural selection