<p>Willows (<em>Salix</em> spp.) are a very diverse group of catkin-bearing trees and shrubs that are widely distributed across temperate regions of the globe. Some species respond well to being grown in short rotation coppice (SRC) cycles, which are much shorter than conventional forestry. Coppicing reinvigorates growth and the biomass rapidly accumulated can be used as a source of renewable carbon for bioenergy and biofuels. As SRC willows re-distribute nutrients during the perennial cycle they require only minimal nitrogen fertilizer for growth. This results in fuel chains with potentially high greenhouse gas reductions. To exploit their potential for renewable energy, willows need to be kept free of pests and diseases and yields need to be improved without significantly increasing the requirements for fertilizers and water. The biomass composition needs to be optimized for different end-uses. Yields also need to be sustainable on land less productive for food crops to reduce conflicts over land use. Advances in understanding the physiology and growth of willow, and in the identification of genes underlying key traits, are now at the stage where they can start to be used in breeding programs to help achieve these goals.</p><p><strong>Karp A, Hanley SJ, Trybush SO, Macalpine W, Pei M, Shield I </strong>(2011) Genetic improvement of willow for bioenergy and biofuels. <em>J. Integr. Plant Biol</em>. <strong>53</strong>(2), 151&ndash;165.</p>

Macronutrients concentrations were measured during the establishment year of short rotation coppice of Salix viminalis, Populus trichocarpa, Eucalyptus gunnii irrigated with secondary treated effluent. Twenty four plots of 12.25 m2 located in Cranfield, Bedfordshire, UK on heavy fine clay were drip-irrigated in order to maintain their soil moisture at field capacity. Soil water was sampled at 30 cm and 60 cm with soil water suction cup samplers fortnightly. Willow and eucalyptus received more than 900 mm of effluent corresponding to more than 290 kg-N/ha, 30 kg-P/ha and 220 kg-K/ha. Poplar and unplanted plots received less than 190 kg-N/ha, 17 kg-P/ha and 120 kg-K/ha. For soil water nitrogen concentrations as for potassium concentrations, there was an irrigation effect only on eucalyptus planted plots. On all plots, there was no significant effect of tree presence or species. There was no phosphorus measurable in soil water samples. Groundwater chemistry was unaffected by irrigation. Thus, intensive irrigation of short rotation coppice during the establishment year should not be considered as a major threat to groundwater quality. Willows and eucalyptus can absorb almost a third more effluent than poplar and unplanted plots without having any significant effect on soil water chemistry.

Callus induction, callus growth, and plantlet regeneration were examined using leaf explants of three Salixexigua clones. Calli were initiated on three basal media supplemented with 0.1 mg/L (0.44 μM) or 0.5 mg/L (2.2 μM) of benzylaminopurine and 0.1 mg/L (0.45 μM) or 0.5 mg/L (2.3 μM) of 2,4-dichlorophenoxyacetic acid in a factorial fashion. After 7 weeks of growth, callus production was highest on woody plant medium. Developed calli were subsequently cultured on woody plant medium supplemented with either 0.1 or 0.5 mg/L of benzylaminopurine for shoot induction. Shoot primordia developed only at 0.1 mg/L (0.44 μM) benzylaminopurine in two clones, suggesting clonal variation in organogenic response. Shoots larger than 1.0 cm in length were successfully rooted in half-strength Murashige and Skoog medium without hormones.

Black willow (Salix nigra Marsh.) is the largest and only commercially important willow species in North America. It is a candidate for phytoremediation of polluted soils because it is fast-growing and thrives on floodplains throughout eastern USA. Our objective was to develop a protocol for the in vitro regeneration of black willow plants that could serve as target material for gene transformation. Unexpanded inflorescence explants were excised from dormant buds collected from three source trees and cultured on woody plant medium (WPM) supplemented with one of: (1) 0.1 mg l(-1) thidiazuron (TDZ); (2) 0.5 mg l(-1) 6-benzoaminopurine (BAP); or (3) 1 mg l(-1) BAP. All plant growth regulator (PGR) treatments induced direct adventitious bud formation from the genotypes. The percentage of explants producing buds ranged from 20 to 92%, depending on genotype and treatment. Although most of the TDZ-treated inflorescences produced buds, these buds failed to elongate into shoots. Buds on explants treated with BAP elongated into shoots that were easily rooted in vitro and further established in potting mix in high humidity. The PGR treatments significantly affected shoot regeneration frequency (P < 0.01). The highest shoot regeneration frequency (36%) was achieved with Genotype 3 cultured on 0.5 mg l(-1) BAP. Mean number of shoots per explant varied from one to five. The ability of black willow inflorescences to produce adventitious shoots makes them potential targets for Agrobacterium-mediated transformation with heavy-metal-resistant genes for phytoremediation.

The factors influencing transfer of an intron - containing β-glucuronidase gene to apple leaf explants were studied during early steps of an Agrobacterium tumefaciens-mediated transformation procedure. The gene transfer process was evaluated by counting the number of β-glucuronidase expressing leaf zones immediately after cocultivation, as well as by counting the number of β-glucuronidase expressing calli developing on the explants after 6 weeks of postcultivation in the presence of 50 mg/l kanamycin. Of three different tested disarmed A. tumefaciens strains, EHA101(pEHA101) was the most effective for apple transformation. Cocultivation of leaf explants with A. tumefaciens on a medium with a high cytokinin level was more conducive to gene transfer than cocultivation on media with high auxin concentrations. Precultivation of leaf explants, prior to cocultivation, slightly increased the number of β-glucuronidase expressing zones measured immediately after cocultivation, but it drastically decreased the number of transformed calli appearing on the explants 6 weeks after infection. Other factors examined were: Agrobacterium cell density during infection, bacterial growth phase, nature of the carbon source, explant age, and explant genotype.