The programmed degradation of macromolecules during petal senescence allows the plant to remobilize nutrients from dying to developing tissues. Ethylene is involved in regulating the timing of nucleic acid degradation in petunia, but it is not clear if ethylene has a role in the remobilization of phosphorus during petal senescence. To investigate ethylene's role in nutrient remobilization, the P content of petals (collectively called the corolla) during early development and senescence was compared in ethylene-sensitive wild type Petunia×hybrida ‘Mitchell Diploid’ (MD) and transgenic petunias with reduced sensitivity to ethylene (35S::etr1-1). When compared to the total P content of corollas on the day of flower opening (the early non-senescing stage), P in MD corollas had decreased 74% by the late stage of senescence (advanced wilting). By contrast, P levels were only reduced by an average of 32% during etr1-1 corolla (lines 44568 and Z00-35-10) senescence. A high-affinity phosphate transporter, PhPT1 (PhPht1;1), was cloned from senescing petunia corollas by RT-PCR. PhPT1 expression was up-regulated during MD corolla senescence and a much smaller increase was detected during the senescence of etr1-1 petunia corollas. PhPT1 mRNA levels showed a rapid increase in detached corollas (treated at 1 d after flower opening) following treatment with low levels of ethylene (0.1 μl l^-1). Transcripts accumulated in the presence of the protein synthesis inhibitor, cycloheximide, indicating that PhPT1 is a primary ethylene response gene. PhPT1 is a putative phosphate transporter that may function in Pi translocation during senescence.

Pollination reduces flower longevity in many angiosperms by accelerating corolla senescence. This response requires hormone signaling between the floral organs and results in the degradation of macromolecules and organelles within the petals to allow for nutrient remobilization to developing seeds. To investigate early pollination-induced changes in petal gene expression, we utilized high-throughput sequencing to identify transcripts that were differentially expressed between corollas of pollinated Petunia × hybrida flowers and their unpollinated controls at 12, 18, and 24 hours after opening. In total, close to 0.5 billion Illumina 101 bp reads were generated, de novo assembled, and annotated, resulting in an EST library of approximately 33 K genes. Over 4,700 unique, differentially expressed genes were identified using comparisons between the pollinated and unpollinated libraries followed by pairwise comparisons of pollinated libraries to unpollinated libraries from the same time point (i.e. 12-P/U, 18-P/U, and 24-P/U) in the Bioconductor R package DESeq2. Over 500 gene ontology terms were enriched. The response to auxin stimulus and response to 1-aminocyclopropane-1-carboxylic acid terms were enriched by 12 hours after pollination (hap). Using weighted gene correlation network analysis (WGCNA), three pollination-specific modules were identified. Module I had increased expression across pollinated corollas at 12, 18, and 24 h, and modules II and III had a peak of expression in pollinated corollas at 18 h. A total of 15 enriched KEGG pathways were identified. Many of the genes from these pathways were involved in metabolic processes or signaling. More than 300 differentially expressed transcription factors were identified. Gene expression changes in corollas were detected within 12 hap, well before fertilization and corolla wilting or ethylene evolution. Significant changes in gene expression occurred at 18 hap, including the up-regulation of autophagy and down-regulation of ribosomal genes and genes involved in carbon fixation. This transcriptomic database will greatly expand the genetic resources available in petunia. Additionally, it will guide future research aimed at identifying the best targets for increasing flower longevity by delaying corolla senescence.

Senescence represents the last phase of petal development during which macromolecules and organelles are degraded and nutrients are recycled to developing tissues. To understand better the post-transcriptional changes regulating petal senescence, a proteomic approach was used to profile protein changes during the senescence of Petunia×hybrida ‘Mitchell Diploid’ corollas. Total soluble proteins were extracted from unpollinated petunia corollas at 0, 24, 48, and 72 h after flower opening and at 24, 48, and 72 h after pollination. Two-dimensional gel electrophoresis (2-DE) was used to identify proteins that were differentially expressed in non-senescing (unpollinated) and senescing (pollinated) corollas, and image analysis was used to determine which proteins were up- or down-regulated by the experimentally determined cut-off of 2.1-fold for P <0.05. One hundred and thirty-three differentially expressed protein spots were selected for sequencing. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to determine the identity of these proteins. Searching translated EST databases and the NCBI non-redundant protein database, it was possible to assign a putative identification to greater than 90% of these proteins. Many of the senescence up-regulated proteins were putatively involved in defence and stress responses or macromolecule catabolism. Some proteins, not previously characterized during flower senescence, were identified, including an orthologue of the tomato abscisic acid stress ripening protein 4 (ASR4). Gene expression patterns did not always correlate with protein expression, confirming that both proteomic and genomic approaches will be required to obtain a detailed understanding of the regulation of petal senescence.

Analyses of multiple field experiments indicated that the incidence and relative abundance of root-colonizing phlD+ Pseudomonas spp. were influenced by crop rotation, tillage, organic amendments, and chemical seed treatments in subtle but reproducible ways. In no-till corn plots, 2-year rotations with soybean resulted in plants with approximately twofold fewer phlD+ pseudomonads per gram of root, but 3-year rotations with oat and hay led to population increases of the same magnitude. Interestingly, tillage inverted these observed effects of cropping sequence in two consecutive growing seasons, indicating a complex but reproducible interaction between rotation and tillage on the rhizosphere abundance of 2,4-diacetlyphloroglucinol (DAPG) producers. Amending conventionally managed sweet corn plots with dairy manure compost improved plant health and also increased the incidence of root colonization when compared with nonamended plots. Soil pH was negatively correlated to rhizosphere abundance of phlD+ pseudomonads in no-till and nonamended soils, with the exception of the continuous corn treatments. Chemical seed treatments intended to control fungal pathogens and insect pests on corn also led to more abundant populations of phlD in different tilled soils. However, increased root disease severity generally was associated with elevated levels of root colonization by phlD+ pseudomonads in no-till plots. Interestingly, within a cropping sequence treatment, correlations between the relative abundance of phlD and crop stand or yield were generally positive on corn, and the strength of those correlations was greater in plots experiencing more root disease pressure. In contrast, such correlations were generally negative in soybean, a difference that may be partially explained by difference in application of N fertilizers and soil pH. Our findings indicate that farming practices can alter the relative abundance and incidence of phlD+ pseudomonads in the rhizosphere and that practices that reduce root disease severity (i.e., rotation, tillage, and chemical seed treatment) are not universally linked to increased root colonization by DAPG-producers.

The primary causal agents of anthracnose-like fruit rots in Ohio and their potential resistance to fungicides commonly used to control these fungal pathogens were determined. Nineteen tomato production fields throughout the state were sampled in 2002 and 2003 for fruit with anthracnose-like lesions. Fungi were isolated from these samples, classified using restriction fragment length polymorphism analysis, and identified by internal transcribed spacer sequence analysis. Some of the fungi isolated may represent secondary invaders of preexisting wounds or lesions. Colletotrichum spp. were most abundant in our collection, representing 136 of the 187 isolates. In addition, there were 23 Alternaria, 12 Fusarium, 12 Phomopsis, and 4 Mucor isolates. Colletotrichum, Alternaria, and Fusarium spp. were found throughout the major tomato production areas in the state. In a laboratory investigation, a subset of the Colletotrichum, Alternaria, and Fusarium isolates caused symptoms similar to early development of anthracnose on wounded tomato fruit. In vitro inhibition assays indicated that most Colletotrichum isolates were sensitive to labeled rates of azoxystrobin, chlorothalonil, and mancozeb. However, some Alternaria isolates were less sensitive to azoxystrobin and chlorothalonil than the Colletotrichum isolates. In addition, most Fusarium isolates were also more insensitive to azoxystrobin and mancozeb, and most Phomopsis isolates were not inhibited by azoxystrobin at the levels tested. The patterns of insensitivity to azoxystrobin and chlorothalonil were also observed in situ with excised fruit. Because the fungicides tested are not currently labeled for control of tomato diseases caused by Fusarium or Phomopsis, these results indicate that some pathogen species that can cause anthracnose-like symptoms may not be entirely sensitive to fungicides commonly used in tomato production.

ISHS International Conference on Quality Management in Supply Chains of Ornamentals NUTRIENT REMOBILIZATION DURING POLLINATION-INDUCED COROLLA SENESCENCE IN PETUNIA