The Black Box of Plant Biology – The Root Zone
Strategies and protocols for studying roots are confined by the methodological challenges of studying tissues embedded in an opaque soil matrix. Techniques such as rhizotrons (glass windows), minirhizotrons (acrylic tubing), and root-exclusion tubes have dramatically improved our understanding of root growth. However, improvement in root sampling methodology must bypass the limitation of highly disruptive root excavation, viewing roots on planar surfaces, and resolution restrictions of bulk-imaging techniques. Recent non-destructive in situ methodologies for studying roots and root systems embedded within a medium currently include X-ray computed tomography (CT), ground penetrating radar, MRI, and ultrasound options. Primary complexities include root organ visualization, due to similarities between the attenuation coefficient of root tissue and organic matter, with most studies to date using more artificial large particle substrate types comprised largely of sand and subject to comprise in the relationship between root resolution and sampling volume. I will highlight recent advances in non-destructive measurements of the root environment and how these technologies can be utilized in questions surrounding resource management and provide insight into the future of root research.
Arbuscular Mycorrhizal Fungi as Natural Biofertilizers: Current Role and Potential for the Horticulture Industry
Bianciotto Valeria¹, Scariot Valentina², Berruti Andrea¹
¹Institute for Sustainable Plant Protection, SS Torino – National Research Council (CNR), Torino (Italy) c/o Department of Life Science and Systems Biology – University of Turin and
²Department of Agricultural, Forest, and Food Sciences – University of Torino, Grugliasco (Italy)
Plant roots host a wide range of microorganisms that, together with the quality of soil and climatic conditions, greatly influence plant health, growth and development. Some microorganisms can put their host in the condition to capitalize on soil fertility and optimize plant growth to a point that they are considered natural biofertilizers. The extraordinary genetic and functional diversity of fungi and their species richness in the soil make them a key component of almost all soil ecosystems with a great potential to impact several areas of agricultural biotechnology. Among these, a central role is offered by the mycorrhizal fungal symbionts. Mycorrhizae are symbiotic partnerships that are established between fungi that live in soil and the roots of most terrestrial plants. A key ecological role is played by endomycorrhizal symbioses, and with greater emphasis by the obligate mutualistic arbuscular mycorrhizal fungi (AMF). AMF can bridge the host root apparatus to distant portions of undepleted soil, providing water and soil mineral nutrients to the plant. In addition, they promote pathogen protection via spatial competition and other more complex mechanisms. In exchange, photosynthetic products are transferred to the fungus. AMF can symbiotically interact with more than 80% of vascular plant species, including important crops and ornamental plants. Therefore, AMF are primary biotic soil components that, when missing or impoverished, can lead to a less efficient ecosystem functioning. Human activities can have a detrimental impact on the microbiological features of soil. Agricultural fields, degraded lands and soilless cultures are all ecosystems in which the anthropogenic input has altered the ecological balances. Most conventional agricultural practices can exert strong selective pressure on AMF, remodel community structure and reduce species diversity. This is a drawback for agriculture, since loss of AMF diversity can result in fewer beneficial traits from which the host plant can benefit. Consequently, a process that aims at the re-establishment of the natural level of AMF richness is pivotal towards the restoration of the soil microbial balances. A sustainable strategy to achieve this goal is the direct inoculation and appropriate management of AMF diversity into the target soil. For the development of safe and successful inoculation protocols, it is important to be able to trace the survival and persistence of AMF inoculants and to quantify their effects on the native microbiota in the target soil. Next Generation Sequencing (NGS) approaches are now successfully employed to trace inoculated AMF and describe diverse AMF communities. Needless to say, AMF have attracted a great deal of interest from the agricultural world over the years. In this context, these fungi have assumed a primary role in the development of a sustainable agriculture, based fundamentally on the limitation and partial replacement of chemical fertilizers mediated by the respect of natural microbiological balances. Many studies have regarded the exploitation of the positive effects of AMF inocula on the growth of several horticultural crops, including model plants. Few studies have investigated the effects of AMF inoculation in floriculture. Usually, the technology used to propagate these plants in nurseries does not take into consideration the potential of this mutualistic symbiosis. Early inoculation of potted plants with a selected set of AMF isolates could help improve survival and performance, and potentially lead to lower agrochemical input.
Carbon Footprint and Ecosystem Services During the Life Cycle of Landscape Plants
Dewayne L. Ingram
University of Kentucky
Horticultural crop producers and marketers are seeking increasingly sustainable practices. A sustainable system is often described as being environmentally, economically, and socially sustainable. With a maturing nursery industry, economic sustainability is important and the industry has traditionally sought ways to minimize environmental impact of production. Social sustainability is revealed in purchases by the consumer. Understanding the environmental impact of production system protocols could allow managers to make informed decisions to increase efficiency, reduce potentially negative impacts, and reduce the associated variable costs. Understanding the ecosystem services of landscape plants could provide information to help market these products to increasingly environmentally-conscious consumers.
Durable Disease Resistance in Woody Ornamentals: The Breeders’ Challenge
Johan Van Huylenbroeck, Leen Leus, Gil Luypaert and Katrijn Van Laere
Institute for Agricultural and Fisheries Research (ILVO), Melle, Belgium
The consumers’ pursuit of low maintenance gardening, the environmental concern and the implementation in Europe of Integrated Pest Management (IPM) has forced growers to develop sustainable strategies for the control of pests and diseases. Preventive cultural practices, including the choice for more tolerant or resistant cultivars, are often mentioned as measures to be taken. The ball is now in the court of the breeders. Breeding programs should focus more on biotic stress resistance. However, resistance breeding in ornamentals in general and in woody ornamentals specifically is difficult due to the high diversity of plant genera and the pests and diseases. In addition, long generation cycles, complex genetics, polyploidy and the low economic value of one specific crop or cultivar makes breeding for disease resistance challenging. Traditionally breeding for disease resistance starts with screening of existing germplasm and identification of interesting sources of resistance. Knowledge of the pest or pathogen is a prerequisite to establish bio-assays and to gain information on pathotype specific resistances. Introducing natural disease resistance genes frequently involves interspecific hybridization, while the existence of robust and easy to handle inoculation protocols may facilitate subsequent selection. Fundamental insights into the plant-pathogen interaction and inducible plant defense mechanisms will open new horizons for plant breeding. We will illustrate such approaches with examples from recent studies in resistance breeding for two fungal pathogens: box blight in Buxus and powdery mildew in rose, and for one pest organism: broad mite in Rhododendron.