Spectral response of winter wheat to crop development and various agronomic limitations

For maximizing the effective applications of remote sensing in crop recognition, crop performance assessment and canopy variables estimation at large areas, it is essential to fully understand the spectral response of canopy to crop development and varying growing conditions. In this paper, the spectral properties of winter wheat canopy under different growth stages and different agronomic conditions were investigated at the field level based on reflectance measurements. It was proved that crop growth and development, nitrogen fertilization rates, nutrient deficit (e.g. lacking any kind of nitrogen, phosphorus and kalium fertilizer or lacking all of them), irrigation frequency and plant density had direct influence on canopy reflectance in 400-900 nm which including the visible/near infrared bands, and resulted in great changes of spectral curves. It was suggested that spectral reflectance of crop canopy can well reflect the growth and development of crop and the impacts from various factors, and was feasible to provide vital information for crop monitoring and assessment. ©2010 IEEE.

Biological wastes as plant growth substrate amendments

Globally, agriculture is being intensified with mechanization and increased use of synthetic fertilizers and pesticides. There has been a scaling up of production to satisfy the demands of supermarket distribution. Problems associated with intensification of production, trade globalisation and a larger market demand for greater volumes of fresh produce, include consumers' concern about pesticide residues and leaching of nutrients and pesticides into the environment, as well as increases in the transmission of human food-poisoning pathogens on raw vegetables and in fruit juices. The first part of this research was concerned with the evaluation of a biological control strategy for soil-borne pathogens, these are difficult to eliminate and the chemicals of which the most effective fumigants e.g. methyl bromide, are being withdrawn form use. Chitin-containing crustaceans shellfish waste was investigated as a selective growth substrate amendment in the field, in glasshouse and in storage trials against Sclerotinia disease of Helianthus tuberosus, Phytophthora fragariae disease of Fragaria vesca and Fusarium disease of Dianthus. Results showed that addition to shellfish waste stimulated substrate microbial populations and lytic activity and induced plant defense proteins, namely chitinases and cellulases. Protective effects were seen in all crop models but the results indicate that further trials are required to confirm long-term efficacy. The second part of the research investigated the persistence of enteric bacteria in raw salad vegetables using model food poisoning isolates. In clinical investigations plants are sampled for bacterial contamination but no attempt is made to differentiate between epiphytes and endophytes. Results here indicate that the mode isolates persist endophytically thereby escaping conventional chlorine washes and they may also induce host defenses, which results in their suppression and in negative results in conventional plate count screening. Finally a discussion of criteria that should be considered for a HACCP plan for safe raw salad vegetable production is presented.

Novel bioassays to examine the host-finding ability of plant-parasitic nematodes

We present two novel bioassays to be used in the examination of plant-parasitic nematode host-finding ability. The host-finding 'pipette-bulb assay' was constructed from modelled Pasteur pipette bulbs and connecting barrels using parafilm fastenings. This assay examines the direction of second-stage juvenile (J2) migration in response to a host seedling, through a moistened sand substrate, which underlies terminal upward-facing 'seedling bulbs', one containing a host seedling in potting compost, the other with only potting compost. An equal watering regime through both upward-facing seedling bulbs creates a directional concentration gradient of host diffusate chemotactic factors. Positive chemotactic stimuli cause the J2 to orientate and migrate towards the host plant. We present validation data collected from assays of the root-knot nematode, Meloidogyne incognita, and the potato cyst nematode, Globodera pallida, which indicate a highly significant positive attraction of J2 of both species to respective host plants. This represents a simple, quick and inexpensive method of assessing host-finding behaviour in the laboratory. We consider that the pipette-bulb assay improves on previous host-finding/chemo-attraction assays through creating a more biologically relevant environment for experimental J2; analysis is quick and easy, allowing the straightforward interpretation of results. In addition, we have developed an 'agar trough' sensory assay variant which we believe can be used rapidly to ratify nematode responses to chemical gustatory or olfactory cues. This was constructed from a water agar substrate such that two counting wells were connected by a raised central trough, all flooded with water. Two small water agar plugs were dehydrated briefly in an oven and then hydrated in either an attractant, repellent or water control; these plugs were then placed in the terminal counting wells and subsequently leached the attractant or repellent to form a concentration gradient along the central trough, which contained the initial J2 innoculum. Our data show that both M. incognita and G. pallida J2 are positively attracted to host diffusates. In addition, they displayed a strong repulsion in response to 1 M NaCl2. J2 of M. incognita displayed a mild aversion to a non-host oak root diffusate, whereas G. pallida J2 displayed a strong aversion to the same non-host diffusate; neither species responded to a compost leachate. We believe that the agar trough assay improves on previous methods by facilitating rapid diffusion of attractant or repellents. Both of the aforementioned assays were designed as tools to assess the impact of RNAi-based reverse genetics screens for gene targets involved in chemosensory orientation.

Alternate wetting and drying irrigation for rice in Bangladesh: Is it sustainable and has plant breeding something to offer?

The crop management practice of alternate wetting and drying (AWD) is being promoted by IRRI and the national research and extension program in Bangladesh and other parts of the world as a water-saving irrigation practice that reduces the environmental impact of dry season rice production through decreased water usage, and potentially increases yield. Evidence is growing that AWD will dramatically reduce the concentration of arsenic in harvested rice grains conferring a third major advantage over permanently flooded dry season rice production. AWD may also increase the concentration of essential dietary micronutrients in the grain. However, three crucial aspects of AWD irrigation require further investigation. First, why is yield generally altered in AWD? Second, is AWD sustainable economically (viability of farmers' livelihoods) and environmentally (aquifer water table heights) over long-term use? Third, are current cultivars optimized for this irrigation system? This paper describes a multidisciplinary research project that could be conceived which would answer these questions by combining advanced soil biogeochemistry with crop physiology, genomics, and systems biology. The description attempts to show how the breakthroughs in next generation sequencing could be exploited to better utilize local collections of germplasm and identify the molecular mechanisms underlying biological adaptation to the environment within the context of soil chemistry and plant physiology.

Mechanisms of plant resistance to metal and metalloid ions and potential biotechnological applications

Metal and metalloid resistances in plant species and genotypes/accessions are becoming increasingly better understood at the molecular and physiological level. Much of the recent focus into metal resistances has been on hyperaccumulators as these are excellent systems to study resistances due to their very abnormal metal(loid) physiology and because of their biotechnological potential. Advances into the mechanistic basis of metal(loid) resistances have been made through the investigation of metal(loid) transporters, the construction of mutants with altered metal(loid) transport and metabolism, a better understanding of the genetic basis of resistance and hyperaccumulation and investigations into the role of metal(loid) ion chelators. This review highlights these recent advances. © Springer 2005.

Relationship between plant phosphorus status and the kinetics of arsenate influx in clones of deschampsia cespitosa (L.) beauv. that differ in their tolerance to arsenate

Uptake kinetics of arsenate were determined in arsenate tolerant and non-tolerant clones of the grass Deschampsia cespitosa under differing root phosphorus status to investigate the mechanism controlling the suppression of arsenate influx observed in tolerant clones. Influx was always lower in tolerants compared to non-tolerants. Short term influx of arsenate by the high affinity uptake system in both tolerant clones was relatively insensitive to root phosphorus status. This was in contrast to the literature where the regulation of the phosphate (arsenate) uptake system is normally much more responsive to plant phosphorus status. The low affinity uptake system in both tolerant and non-tolerant clones, unlike the high affinity uptake system, was more closely regulated by root phosphate status and was repressed to a much greater degree under increasing root phosphorus levels than the high affinity system. © 1994 Kluwer Academic Publishers.