Plant pathogen culture collections: it takes a village to preserve these resources vital to the advancement of agricultural security and plant pathology

ABSTRACT Plant pathogen culture collections are essential resources in our fight against plant disease and for connecting discoveries of the present with established knowledge of the past. However, available infrastructure in support of culture collections is in serious need of improvement, and we continually face the risk of losing many of these collections. As novel and reemerging plant pathogens threaten agriculture, their timely identification and monitoring depends on rapid access to cultures representing the known diversity of plant pathogens along with genotypic, phenotypic, and epidemiological data associated with them. Archiving such data in a format that can be easily accessed and searched is essential for rapid assessment of potential risk and can help track the change and movement of pathogens. The underexplored pathogen diversity in nature further underscores the importance of cataloguing pathogen cultures. Realizing the potential of pathogen genomics as a foundation for developing effective disease control also hinges on how effectively we use the sequenced isolate as a reference to understand the genetic and phenotypic diversity within a pathogen species. In this letter, we propose a number of measures for improving pathogen culture collections.     

Selecting recombinants to stack high protein with high oleic acid and low linoleic acid in soybean (Glycine max)

Soybean accounts for over a quarter of the world's oilseed consumption and over 70% of the world's protein meal consumption. The separate development of high oleic, low linolenic acid (HOLL) soybean and high-protein (HP) soybean means that no soybean cultivar on the market has an optimal fatty acid profile and increased protein. The objective of this study was to develop and evaluate high protein, high oleic acid, and low linolenic acid (HP-HOLL) soybean. A five-gene stack was created using a two-phase forward breeding scheme and marker-assisted selection method. Forty-six HP-HOLL lines from three genetic backgrounds were grown in six environments in the Southeast United States. Although genotype-by-environment interaction was significant for seed composition traits, lines met the >75% and <3% cutoffs for oleic acid and linolenic acid, respectively, and met or exceeded the protein concentration of the HP parent. No negative interaction could be detected between the HP and HOLL traits. Additionally, yield testing in four environments indicated yield parity for some lines, suggesting HP and HOLL soybean cultivars with high yield could be selected.     

Rooting systems of oilseed and pulse crops I: Temporal growth patterns across the plant developmental periods

Oilseed and pulse crops have been increasingly used to diversify cereal-based cropping systems in semiarid environments, but little is known about the root characteristics of these broadleaf crops. This study was to characterize the temporal growth patterns of the roots of selected oilseed and pulse crops, and determine the response of root growth patterns to water availability in semiarid environments. Canola (Brassica napus L.), flax (Linum usitatissimum L.), mustard (Brassica juncea L.), chickpea (Cicer arietinum L.), field pea (Pisum sativum L.), lentil (Lens culinaris), and spring wheat (Triticum aestivum L.) were tested under high- (rainfall + irrigation) and low- (rainfall only) water availability conditions in southwest Saskatchewan, in 2006 and 2007. Crops were hand-planted in lysimeters of 15 cm in diameter and 100 cm in length that were installed in the field prior to seeding. Roots were sampled at the crop stages of seedling, early-flower, late-flower, late-pod, and physiological maturity. On average, root length density, surface area, diameter, and the number of tips at the seedling stage were, respectively, 41, 25, 14, and 110% greater in the drier 2007 than the corresponding values in 2006. Root growth in all crops progressed rapidly from seedling, reached a maximum at late-flower or late-pod stages, and then declined to maturity; this pattern was consistent under both high- and low-water conditions. At the late-flower stage, root growth was most sensitive to water availability, and the magnitude of the response differed between crop species. Increased water availability increased canola root length density by 70%, root surface area by 67%, and root tips by 79% compared with canola grown under low-water conditions. Water availability had a marginal influence on the root growth of flax and mustard, and had no effect on pulse crops. Wheat and two Brassica oilseeds had greater root length density, surface area and root tips throughout the entire growth period than flax and three pulses, while pulse crops had thicker roots with larger diameters than the other species. Sampling roots at the late-flower stage will allow researchers to capture best information on root morphology in oilseed and pulse crops. The different root morphological characteristics of oilseeds, pulses, and wheat may serve as a science basis upon which diversified cropping systems are developed for semiarid environments.     

RNAi as a management tool for the western corn rootworm,Diabrotica virgifera virgifera

The western corn rootworm (WCR), Diabrotica virgifera virgifera, is the most important pest of corn in the US Corn Belt. Economic estimates indicate that costs of control and yield loss associated with WCR damage exceed $US 1 billion annually. Historically, corn rootworm management has been extremely difficult because of its ability to evolve resistance to both chemical insecticides and cultural control practices. Since 2003, the only novel commercialized developments in rootworm management have been transgenic plants expressing Bt insecticidal proteins. Four transgenic insecticidal proteins are currently registered for rootworm management, and field resistance to proteins from the Cry3 family highlights the importance of developing traits with new modes of action. One of the newest approaches for controlling rootworm pests involves RNA interference (RNAi). This review describes the current understanding of the RNAi mechanisms in WCR and the use of this technology for WCR management. Further, the review addresses ecological risk assessment of RNAi and insect resistance management of RNAi for corn rootworm. © 2016 Society of Chemical Industry     

Seasonal variations in the stable carbon isotopic signature of biogenic methane in a coastal sediment

Systematic seasonal variations in the stable carbon isotopic signature of methane gas occur in the anoxic sediments of Cape Lookout Bight, a lagoonal basin on North Carolina's Outer Banks. Values for the carbon isotope ratio (delta 13C) of methane range from -57.3 per mil during summer to -68.5 per mil during winter in gas bubbles with an average methane content of 95%. The variations are hypothesized to result from changes in the pathways of microbial methane production and cycling of key substrates including acetate and hydrogen. The use of stable isotopic signatures to investigate the global methane cycle through mass balance calculations, involving various sediment and soil biogenic sources, appears to require seasonally averaged data from individual sites.     

Impact of heat stress on pod-based yield components in field pea (Pisum sativum L.)

Elevated temperatures associated with climate change result in crops being exposed to frequent spells of heat stress. Heat stress results in reduced yield in field pea (Pisum sativum L.); it is therefore important to identify cultivars with improved pod and seed retention under heat to mitigate this loss. Objectives were to investigate the effect of heat stress on phenology, yield and pod-based yield components. Sixteen pea cultivars were evaluated at normal and late (hot) seeding dates in the field in Arizona 2012 and in growth chambers with two temperature regimes (24/18°C and 35/18°C day/night temperature for 7 days) during reproductive development. We measured variation in the pattern of pod retention at four-node positions on plants, seed retention by ovule position (stylar, medial and basal) within pods and screened cultivars for pod retention, seed retention and yield. Heat stress reduced seed yield by accelerating the crop lifecycle and reducing pod number and seed size. Heat stress had the most damaging effect on younger reproductive growth (flowers and pods developed later), resulting in ovary abortion from developing flowers. Heat also accelerated seed abortion in all ovule positions within pods. Two high-yielding cultivars under control temperature, “Naparnyk” and “CDC Meadow”, maintained high yield in heat, and “MFR043” had the lowest yield. Cultivars “40-10” and “Naparnyk” retained the most ovules and seeds per pod, and “MFR043” aborted seeds when exposed to heat. In half of the cultivars, ovules at the basal peduncle end of pods were likely to abort while ovules at the medial and stylar end positions developed into seeds. For seven of the field cultivars, ovules at the medial pod position also produced mature seeds. Cultivars “40-10”, “Naparnyk” and “CDC Meadow” had greater pod and ovule retention or maintained high yield under heat stress, and were identified as heat-tolerant cultivars. Our results allow for a better understanding of pod-based yield components in field pea under heat stress and developing heat-tolerant cultivars.