In this study, a pilot scale slow sand filtration system was evaluated for biodegradation of the plant growth regulator paclobutrazol from recaptured irrigation leachate in a simulated greenhouse environment. Generated irrigation runoff containing 0.05 mg·L-1 paclobutrazol passed through 1-meter-deep slow sand filter sand beds for a period lasting 120 days. Evaluations through a broccoli hypocotyl length bioassay proved acutely sensitive to low concentrations of paclobutrazol, which is an affordable indicator of paclobutrazol presence in nursery runoff that can be utilized by nursery professionals. The SSF system proved ineffective in complete removal of PBZ as the bioassay indicated similar hypocotyl lengths grown with leachate before and after filtration.

There is a growing need in the state of California for landscape plants that require fewer inputs of water and chemicals. To address this issue, a program was initiated at UC Davis to test the landscape potential of California native plants not currently in widespread horticultural use. Ten unused or underused California native plants were screened in open-field conditions for low water tolerance during summer 2006. In all cases, there were no significant differences in the summer growth or physical appearance between four irrigation levels. Six species maintained a favorable appearance throughout the season and were advanced to demonstration gardens in seven climate zones throughout the state, where Master Gardeners are performing further assessments on their performance. These irrigation and climate zone trials are part of an ongoing program coordinated by UC Cooperative Extension, the UC Davis Arboretum and the California Center for Urban Horticulture to introduce more low water-use and low chemical-use plants through partnerships with the commercial horticultural industry.

Phosphate (Pi) the fully oxidized and assimilated form of P influences virtually all developmental and biochemical processes in plants. Paradoxically, although P is abundant in the lithosphere, the elusive soil chemistry of Pi, renders the element the most dilute and the least mobile in natural and agricultural ecosystems due to its low mobility and high fixation capacity in soil. Non-mycorrhizal Brassica does not produce specialized cluster/dauciform roots but is an effective P-user compared to other crops. In addition to P-uptake, utilization and remobilization, acquisition of orthophosphate from extra cellular sparingly P-sources can be enhanced by biochemical rescue mechanisms such as copious H+-efflux and/or carboxylates exudation into rhizosphere by roots via plasmalemma H+-ATPase and anion channels triggered by P-starvation. P-stress induced dissolution of sparingly soluble Ca-phosphate, rhizospheric pH changes due to H+-efflux, redesigning in root architectural system, and carboxylates exudations were estimated by low P-tolerant (class-I) and low P-sensitive (class-II) cultivars in different culture experiments. P-contents of cultivars were inversely related to decrease in culture media pH. Elongation rates of primary roots decreased but length of lateral roots increased under P-starvation. Class-I cultivars presented enhanced H+-efflux, carboxylates exudation and rhizosphere acidification than class-II cultivars, evidencing their adaptability to P-starved environment. These classical P-stress induced rescue strategies provided the basis of enhanced P-solublization and acquisition from sparingly soluble P-sources by Brassica cultivars to thrive in a typically stressful environment.

Phosphorus (P) is not only a constituent of key cell molecules such as ATP, nucleic acids, and phospholipids, but it is also a pivotal metabolic regulator of many processes including energy transfer, protein activation/inactivation, signal transduction cascades, biosynthesis of macromolecules, photosynthesis, respiration and carbon allocation. Plants are notoriously P-starved due to its extremely low soil bioavailability. To thrive under P-deprivation, plants elicit an elegant myriad of rescue strategies to enhance P-solublization and acquisition from bound P-forms. To evaluate relative growth responses, P-solublization, acquisition and utilization efficiency, diverse Brassica cultivars were grown with sparingly soluble P-sources [Rock-P (RP) and Ca3(PO4)2 (TCP)] or with low/high P-supply in solution and soil culture experiments, respectively. Tested cultivars showed considerable genetic diversity in biomass accumulation, concentration and contents of P and Ca, P-stress factor (PSF) and P-efficiency characteristics. Using a soil low in P (Mehlich-III-extractable-P) with (+P) or without P (0P), cultivars showed genetic diversity in P-utilization efficiency (PUE), P-efficiency (PE), P-efficiency ratio (PER) and PSF. Cultivars producing higher root biomass accumulated higher total P-contents, which in turn was related negatively to PSF and positively to shoot and total biomass. Cultivars depicting high PUE and PE, and low PSF values were better adaptable to P-stress environments.