Sourcing Rhizobium leguminosarum biovar viciae strains from Mediterranean centres of origin to optimize nitrogen fixation in forage legumes grown on acid soils

Over the last three decades, farming systems in Europe and Australia have seen a decline in legume plantings, leading to reduced soil carbon and fertility, and an increase in plant disease, reliance on industrial nitrogen fertilizer and herbicides. In Australia, one reason for this decline has been the movement towards sowing crops and forages into dry soil, before the opening rains, as a consequence of climate variability. This practice predicates against the survival of rhizobial inoculants, and hence generates uncertainty about legume performance. The research reported here was initiated to improve the robustness of a specific forage legume/rhizobia symbiosis to increase nitrogen fixation in low pH, infertile soils. Rhizobial strains (Rhizobium leguminosarum biovar viciae) from Pisum sativum L. were sourced from acid soils in southern Italy and southern Australia. Strains were evaluated for N fixation on the forage legumes P. sativum, Vicia sativa and Vicia villosa, then for survival and persistence in acid soils (pH_Ca 4.6). Fourteen of the strains produced a higher percentage of nitrogen derived from the atmosphere (%Ndfa) compared to commercial comparator strain SU303 (<78%). Twenty‐two strains survived sufficiently into the second season to form more nodules than SU303, which only achieved 3% of plants nodulated. Elite strains WSM4643 and WSM4645 produced six times more nodulated plants than SU303 and had significantly higher saprophytic competence in acid soil. These strains have the ability to optimize symbiotic associations with field peas and vetch in soils with low fertility, carbon and pH that are restrictive to the current commercial strain SU303.     

Optimizing the growth of forage and grain legumes on low pH soils through the application of superior Rhizobium leguminosarum biovar viciae strains

Climate variability and current farming practices have led to declining soil fertility and pH, with a heavy reliance on fertilizers and herbicides. The addition of forage and grain legumes to farming systems not only improves soil health but also increases farm profitability through nitrogen (N) fertilizer cost offsets. However, the formation of effective symbioses between legumes and rhizobia can be unreliable and is considered at risk when combined with dry sowing practices such as those that have been designed to obviate effects of climate change. This research was initiated to improve the robustness of the legume/rhizobia symbiosis in low pH, infertile and dry soils. Production from two cultivars of field pea (Pisum sativum) and two species of vetch (Vicia spp.), and symbiotic outcomes when inoculated with a range of experimental rhizobial strains (Rhizobium leguminosarum biovar viciae), was assessed in broad acre field trials which simulated farmer practice. New rhizobia strains increased nodulation, N fixation, produced more biomass and higher seed yield than comparator commercial strains. Strain WSM4643 also demonstrated superior survival when desiccated compared to current commercial strains in the laboratory and on seed when delivered as inoculant in peat carriers. WSM4643 is a suitable prospect for a commercial inoculant in Australia and other agricultural areas of the world where growing peas and vetch on soils generally considered problematic for this legume/rhizobia symbiosis. A particular advantage of WSM4643 may be that it potentiates sowing inoculated legumes into dry soil, which is a contemporary response by farmers to climate variation.     

Dynamics of DNA double-strand breaks revealed by clustering of damaged chromosome domains

Interactions between ends from different DNA double-strand breaks (DSBs) can produce tumorigenic chromosome translocations. Two theories for the juxta-position of DSBs in translocations, the static "contact-first" and the dynamic "breakage-first" theory, differ fundamentally in their requirement for DSB mobility. To determine whether or not DSB-containing chromosome domains are mobile and can interact, we introduced linear tracks of DSBs in nuclei. We observed changes in track morphology within minutes after DSB induction, indicating movement of the domains. In a subpopulation of cells, the domains clustered. Juxtaposition of different DSB-containing chromosome domains through clustering, which was most extensive in G1 phase cells, suggests an adhesion process in which we implicate the Mre11 complex. Our results support the breakage-first theory to explain the origin of chromosomal translocations.     

Origin and history of old cucurbit cultivars in Israel and the sources of several internationally important market types

Over the past century, Israel was a focal point for the improvement of local cucurbit landraces and introduction of cucurbit germplasm. Some improved open-pollinated cucurbit cultivars developed in Israel became established as market types of considerable economic importance far beyond its borders. The origin and history of these cultivars is not widely known and therefore the purpose of the present work was to collect and compare the records relevant to the development of these cultivars, and to describe them more fully. The four economically most important cultivars originated through mass-selection by amateur breeders and were named after their respective farming communities. The ‘Bet Alfa’ cucumber (Cucumis sativus) was selected from a local landrace and introduced in 1936. The ‘Malali’ watermelon (Citrullus lanatus) originated as a rogue in a local landrace and was commercialized around 1940. The ‘Ananas Yoqne‘am’ melon (Cucumis melo) was selected from a local landrace and commercialized around 1950. The ‘Ha‘Ogen’ melon was selected from a cultivar introduced from Hungary and commercialized in the 1950s. The outstanding fruit quality of these four cultivars resulted in their widespread planting in Israel and neighboring countries. Moreover, the quality of the cucumber and melon cultivars inspired successive improvements, notably introgression of disease resistance and development of hybrids, by Israeli breeder-geneticists. The ever-increasing demand for their high-quality fruits established as international market types the Bet Alfa cucumber, the Ananas Yoqne‘am melon, and the Ha‘Ogen melon and its derivative, the Galia melon, and each is intensively bred today by local and multinational seed companies.     

Lethal temperature for pinewood nematode, Bursaphelenchus xylophilus, in infested wood using radio frequency (RF) energy

We evaluated radio frequency (RF) dielectric heating for eradication of pinewood nematodes (PWN) in infested wood. Thirteen temperatures were tested (from ambient to 70 °C) on small wood samples (2.5 × 3.8 × 0.64 cm) to determine the minimum lethal temperature (100 % mortality), which was 56 °C [based on infra-red (IR) thermal images data 55.5–57.4 °C] with a 1 min hold time. We also used thermal probes inside the wood to confirm that temperatures were ≥56 °C. Thirty additional samples were tested bracketing the minimum lethal temperature using 54, 56 and 58 °C with additional replications to produce the minimum sample size equivalent of 100 % mortality of at least 93,616 nematodes to satisfy the Probit 9 efficacy requirement. This minimum lethal temperature was further verified by treating infested large wood blocks (10.2 × 10.2 × 25.4 cm). All samples that met or exceeded the 56 °C lethal temperature for the required 1 min hold time (as measured by probes inserted in the wood and on the wood surface by IR) produced 100 % mortality. The sample size required to show Probit 9 efficacy was also satisfied. This study supports the consideration of RF in addition to microwave (MW) dielectric heating as alternative treatments of wood packaging material for inclusion in ISPM No. 15, provided the treatment delivers the target lethal temperature throughout the profile of the material in industrial scale operations.     

Insecticide resistance profiles can be misleading in predicting the survival of Myzus persicae genotypes on potato crops following the application of different insecticide classes

BACKGROUND: The accuracy of predicting the survival of insecticide‐resistant aphids following the application of commonly used insecticides from the carbamate, the pyrethroid, a mix of the two or the neonicotinoid chemical classes was evaluated in a potato field in Scotland. Equal proportions of five genotypes of the peach‐potato aphid, Myzus persicae (Sulzer), with none, resistance to dimethyl‐carbamates, resistance to pyrethroids or combinations conferring resistance to both chemical classes were released into potato field plots. The insecticides were sprayed separately onto these plots, the aphid populations were analysed after 6–8 days and the process repeated. RESULTS: For each assessment after the three separate spray events, plots treated with the carbamate had 48, 147 and 28%, those treated with pyrethroid 53, 210 and 89%, those treated with carbamate/pyrethroid 28, 108 and 64% and those treated with neonicotinoid 43, 55 and 11% of the numbers of M. persicae by comparison with untreated controls. Only the proportions of surviving aphids from the genotype containing no insecticide resistance traits and the genotype containing elevated carboxylesterases matched ratios predicted from the selective advantage afforded by the resistance traits alone. Survival of aphids from the other three genotypes that carried 1–3 of the insecticide resistance traits differed from expectations in all cases, possibly owing to physiological differences, including their vulnerability to predators and hymenopterous parasitoids present at the site and/or their carrying unknown insecticide resistance mechanisms. CONCLUSION: Control strategies based on knowledge of the genetically determined insecticide resistance profile of an M. persicae population alone are insufficient. Hence, other important factors contributing to aphid survival under insecticide pressure need to be considered. Copyright © 2012 Society of Chemical Industry     

Exploration of Sugar Functionality in Sugar‐Snap and Wire‐Cut Cookie Baking: Implications for Potential Sucrose Replacement or Reduction

The sugar series—xylose, glucose, fructose, and sucrose—can be used diagnostically to explore the effects of sugar type on differential scanning calorimetry (DSC), Rapid Visco‐Analyser (RVA), and cookie baking performance because of the differences in glass‐forming abilities (related to plasticization) and solubility parameters (related to solvent preference) of different sugars. Sugar concentration (% S), total solvent (TS), and dough formulation defined a core experimental design for cookie baking with the four sugar types and two baking methods. Although wire‐cut cookie baking (66% S and 64 TS) showed the same trends as sugar‐snap cookie baking (73% S and 79 TS) for diameter, height, and moisture content, the wire‐cut formulation enabled greater discrimination among the effects of different sugar types on dough and cookie responses. Use of two different crystal sizes of sucrose confirmed the dominant impact of both gluten development during dough mixing and starch pasting during cookie baking on collapse: the greater rate of dissolution of smaller sucrose crystals resulted in greater surface crack for sugar‐snap cookies, and lower height for wire‐cut cookies. Because the historical definition of an “excellent quality cookie flour” is based on the performance of a flour in a cookie formulated with sucrose, the effect of sugar type on cookie making is to transform the apparent baking performance of a flour. Whereas formulation with sucrose optimizes the flour performance for cookie baking, formulation with xylose exaggerates the worst aspects of cookie flour functionality and makes even the best cookie flour look like a “poor quality cookie flour”. Use of solvent retention capacity (SRC), DSC, RVA, and wire‐cut cookie baking as predictive research tools demonstrated that identification of a flour with an optimized SRC pattern is the key to successful mitigation of the detrimental effects of sucrose replacement on cookie processing and product attributes.     

Temporal and spatial dimension of dissolved oxygen saturation with fluidic oscillator and Mazzei air injector in soil-less irrigation systems

The wider scale use of aerated water for irrigation has been limited by dis-uniformity of aeration in the field, limited longevity of oxygen in irrigation water and lack of knowledge of what oxygen concentration brings optimal growth. Two options are presented for increasing dissolved oxygen (DO) in irrigation water: Venturi (VT) and fluidic oscillator (FO) aeration systems. Sweet corn was grown in pots to evaluate the effect of aerated water. Compared to the control treatment (CK), VT and FO showed an increase in irrigated water DO in the irrigation tank and feeding pots after aeration. Incorporation of surfactant in the irrigation water significantly improved DO level for the VT and FO treatment. Typically the DO levels reached a peak when the pump is turned off and then decline to a minimum after 24 h. The VT and FO systems had a higher magnitude and duration of the DO level in the water in all treatments compared to the CK system. The FO aeration maintained the longest duration of elevated DO in the water by a factor of two compared to the VT aeration. Compared to the CK, the best result on longevity and DO concentration was achieved using 4 ppm of a non-ionic surfactant. The corn biomass was significantly greater for the VT compared to both the FO and CK treatments.