Induced Resistance: Potential for Control of Postharvest Diseases of Horticultural Crops

Fortunately, plants have developed highly effective mechanisms with which to defend themselves when attacked by potentially disease-causing microorganisms. If not, then they would succumb to the many pathogenic fungi, bacteria, viruses, nematodes and insect pests, and disease would prevail. These natural defence systems of plants can be deliberately activated to provide some protection against the major pathogens responsible for causing severe yield losses in agricultural and horticultural crops. This is the basis of what is known as ‘induced’ or ‘acquired’ disease resistance in plants. Although the phenomenon of induced resistance has been known amongst plant pathologists for over 100 years, its inclusion into pest and disease management programmes has been a relatively recent development, ie. within the last 5 years. This review will discuss very briefly some of the characteristics of the induced resistance phenomenon, outline some of the advantages and limitations to its implementation and provide some examples within a postharvest pathology context. Finally some approaches being investigated by the fruit pathology team at DPI Indooroopilly and collaborators will be outlined.

Microbial ecology of the equine hindgut during oligofructose-induced laminitis

Alimentary carbohydrate overload is a significant cause of laminitis in horses and is correlated with drastic shifts in the composition of hindgut microbiota. Equine hindgut streptococcal species (EHSS), predominantly Streptococcus lutetiensis, have been shown to be the most common microorganisms culturable from the equine caecum prior to the onset of laminitis. However, the inherent biases of culture-based methods are estimated to preclude up to 70% of the normal caecal microbiota. The objective of this study was to evaluate bacterial population shifts occurring in the equine caecum throughout the course of oligofructose-induced laminitis using several culture-independent techniques and to correlate these with caecal lactate, volatile fatty acid and degrees of polymerization 3-7 fructo-oligosaccharide concentrations. Our data conclusively show that of the total microbiota present in the equine hindgut, the EHSS S. lutetiensis is the predominant microorganism that proliferates prior to the onset of laminitis, utilizing oligofructose to produce large quantities of lactate. Population shifts in lactobacilli and Escherichia coli subpopulations occur secondarily to the EHSS population shifts, thus confirming that lactobacilli and coliforms have no role in laminitis. A large, curved, Gram-negative rod previously observed during the early phases of laminitis induction was most closely related to the Anaerovibrio genus and most likely represents a new, yet to be cultured, genus and species. Correlation of fluorescence in situ hybridization and quantitative real-time PCR results provide evidence supporting the hypothesis that laminitis is associated with the death en masse and rapid cell lysis of EHSS. If EHSS are lysed, liberated cellular components may initiate laminitis.

Sorghum stay-green QTL individually reduce post-flowering drought-induced leaf senescence

Sorghum is an important source of food, feed, and biofuel, especially in the semi-arid tropics because this cereal is well adapted to harsh, drought-prone environments. Post-flowering drought adaptation in sorghum is associated with the stay-green phenotype. Alleles that contribute to this complex trait have been mapped to four major QTL, Stg1-Stg4, using a population derived from BTx642 and RTx7000. Near-isogenic RTx7000 lines containing BTx642 DNA spanning one or more of the four stay-green QTL were constructed. The size and location of BTx642 DNA regions in each RTx7000 NIL were analysed using 62 DNA markers spanning the four stay-green QTL. RTx7000 NILs were identified that contained BTx642 DNA completely or partially spanning Stg1, Stg2, Stg3, or Stg4. NILs were also identified that contained sub-portions of each QTL and various combinations of the four major stay-green QTL. Physiological analysis of four RTx7000 NILs containing only Stg1, Stg2, Stg3, or Stg4 showed that BTx642 alleles in each of these loci could contribute to the stay-green phenotype. RTx7000 NILs containing BTx642 DNA corresponding to Stg2 retained more green leaf area at maturity under terminal drought conditions than RTx7000 or the other RTx7000 NILs. Under post-anthesis water deficit, a trend for delayed onset of leaf senescence compared with RTx7000 was also exhibited by the Stg2, Stg3, and Stg4 NILs, while significantly lower rates of leaf senescence in relation to RTx7000 were displayed by all of the Stg NILs to varying degrees, but particularly by the Stg2 NIL. Greener leaves at anthesis relative to RTx7000, indicated by higher SPAD values, were exhibited by the Stg1 and Stg4 NILs. The RTx7000 NILs created in this study provide the starting point for in-depth analysis of stay-green physiology, interaction among stay-green QTL and map-based cloning of the genes that underlie this trait.

Quality of handling and holding yard environment, and beef cattle temperament: 1. Relationships with flight speed and fear of humans.

Numerous tests have been used to measure beef cattle temperament, but limited research has addressed the relationship between such tests and whether temperament can be modified. One-hundred-and-forty-four steers were given one of three human handling and yarding experiences on six occasions during a 12-month grazing period post-weaning (backgrounding): Good handling/yarding, Poor handling/yarding and Minimal handling/yarding. At the end of this phase the cattle were lot-fed for 78 days, with no handling/yarding treatments imposed, before being transported for commercial slaughter. Temperament was assessed at the start of the experiment, during backgrounding and lot-feeding by flight speed (FS) and a fear of humans test, which measured the proximity to a stimulus person (zone average; ZA), the closest approach to the person (CA) and the amount the cattle moved around the test arena (total transitions; TT). During backgrounding, FS decreased for all treatments and at the end of backgrounding there was no difference between them. The rate of decline, however, was greatest in the Good group, smallest in the Minimal group with the Poor intermediate. In contrast, ZA was affected by treatment, with a greater reduction for the Good group than the others (P = 0.012). During lot-feeding, treatment did not affect FS, but all groups showed a decrease in ZA, with the greatest change in the Poor group, the least in the Good and the Minimal intermediate (P = 0.052). CA was positively correlated with ZA (r = 0.18 to 0.66) and negatively with TT (r = -0.180 to -0.659). FS was consistently correlated with TT only (r = 0.17 to 0.49). These findings suggest that FS and TT measure a similar characteristic, as do ZA and CA, but that these characteristics are different from one another, indicating that temperament is not a unitary trait, but has different facets. FS and TT measure one facet that we suggest is general agitation, whilst ZA and CA measure fear of people. Thus, the cattle became less agitated during backgrounding, but the effect was not permanently influenced by the quantity and quality of handling/yarding. However, Good handling/yarding reduced fearfulness of people. Fear of people was also reduced during lot-feeding, probably as a consequence of frequent exposure to humans in a situation that was neutral or positive for the cattle.

Metabolite mobilization in the stem galls of Parthenium hysterophorus induced by Epiblema strenuana inferred from the signatures of isotopic carbon and nitrogen and concentrations of total non-structural carbohydrates

Parthenium hysterophorus L. (Asteraceae) is a weed of national significance in Australia. Among the several arthropod agents introduced into Australia to control populations of P. hysterophorus biologically, Epiblema strenuana Walker (Lepidoptera: Tortricidae) is the most widespread and abundant agent. By intercepting the normal transport mechanisms of P. hysterophorus, the larvae of E. strenuana drain nutrients, other metabolic products, and energy, and place the host plant under intense metabolic stress. In this study, determinations of total non-structural carbohydrates (TNC) levels and carbon and nitrogen isotope ratios of fixed products in different parts of the plant tissue, including the gall, have been made to establish the function of gall as a sink for the nutrients. Values of δ13C and δ15N in galls were significantly different than those in proximal and distal stems, whereas the TNC levels were insignificant, when measured in the total population of P. hysterophorus, regardless of plant age. However, carbon, nitrogen, and TNC signatures presented significant results, when assayed in different developmental stages of P. hysterophorus. Carbon isotope ratios in galls were consistently more negative than those from the compared plant organs. Nitrogen isotope ratios in galls, on the contrary, were either similar to or less negative than the compared plant organs, especially within a single host-plant stage population (i.e., either rosette, preflowering, or flowering stage). TNC levels varied within compared plant populations. The stem distal to the gall functioned more efficiently as a nodal channel than the stem proximal to the gall, especially in the translocation of nitrogenous nutrients. Our findings indicate that the gall induced by E. strenuana functions as a sink for the assayed nutrients, although some variations have been observed in the patterns of nutrient mobilization. By creating a sink for the nutrients in the gall, E. strenuana is able to place the overall plant metabolism under stress, and this ability indicates E. strenuana has the necessary potential for use as a biological-control agent.

Insect induced bud fall in cultivated hibiscus and aspects of the biology of Macroura concolor (Macleay) (Coleoptera: Nitidulidae)

The influence of insect attack on bud fall and subsequent poor flowering in cultivated hibiscus (Hibiscus rosa-sinensis) was studied in cages and in the field in southern Queensland. Three species of Hemiptera (most importantly Aulacosternum nigrorubrum but also Nezara viridula and Tectocoris diophthalmus) caused some bud fall in 2 plantations studied. Adults of Macroura concolor suppressed flowering for long periods in spring and summer. Data from white funnel traps and counts in flowers showed that M. concolor was most active in these seasons. Methiocarb (0.75 g a.i./litre) reduced beetle numbers and increased flowering. When 15 or more adults of M. concolor occurred per bud (or flower) most buds fell and few flowers were produced, but when beetles declined to 10 or fewer many buds survived and widespread flowering occurred. Larvae fed in fallen buds and flowers and the mean duration of development of the combined immature stages was 14 days at 26 deg C. The preference of adults of M. concolor for pale coloured flowers was examined. Hibiscus plants produced most buds from December to June with lower numbers in winter and spring (July to November). Bud production in spring and early summer (September-December) varied greatly and probably contributed to poor flowering, however, even when large numbers of buds occurred very few flowers were produced because of the activities of M. concolor.

Impact Induced Bruising in Ripening ‘Hass’ Avocado Fruit

This article describes the relationship between avocado fruit firmness, level of impact energy absorbed by the fruit, and post impact fruit holding duration with the incidence of bruising.

Induced Variations in Brassinosteroid Genes Define Barley Height and Sturdiness, and Expand the Green Revolution Genetic Toolkit

Reduced plant height and culm robustness are quantitative characteristics important for assuring cereal crop yield and quality under adverse weather conditions. A very limited number of short-culm mutant alleles were introduced into commercial crop cultivars during the Green Revolution. We identified phenotypic traits, including sturdy culm, specific for deficiencies in brassinosteroid biosynthesis and signaling in semidwarf mutants of barley (Hordeum vulgare). This set of characteristic traits was explored to perform a phenotypic screen of near-isogenic short-culm mutant lines from the brachytic, breviaristatum, dense spike, erectoides, semibrachytic, semidwarf, and slender dwarf mutant groups. In silico mapping of brassinosteroid-related genes in the barley genome in combination with sequencing of barley mutant lines assigned more than 20 historic mutants to three brassinosteroid-biosynthesis genes (BRASSINOSTEROID-6-OXIDASE, CONSTITUTIVE PHOTOMORPHOGENIC DWARF, and DIMINUTO) and one brassinosteroid-signaling gene (BRASSINOSTEROID-INSENSITIVE1 [HvBRI1]). Analyses of F2 and M2 populations, allelic crosses, and modeling of nonsynonymous amino acid exchanges in protein crystal structures gave a further understanding of the control of barley plant architecture and sturdiness by brassinosteroid-related genes. Alternatives to the widely used but highly temperature-sensitive uzu1.a allele of HvBRI1 represent potential genetic building blocks for breeding strategies with sturdy and climate-tolerant barley cultivars.

Top-predator control-induced trophic cascades: an alternative hypothesis to the conclusion of Colman et al.

Recently argued that observed positive relationships between dingoes and small mammals were a result of top-down processes whereby lethal dingo control reduced dingoes and increased mesopredators and herbivores, which then suppressed small mammals. Here, I show that the prerequisite negative effects of dingo control on dingoes were not shown, and that the same positive relationships observed may simply represent well-known bottom-up processes whereby more generalist predators are found in places with more of their preferred prey. Identification of top-predator controlinduced trophic cascades first requires demonstration of some actual effect of control on predators, typically possible only through manipulative experiments with the ability to identify cause and effect.

Induced carotenoid accumulation in Dunaliella salina and Tetraselmis suecica by plant hormones and UV-C radiation

Carotenoids prevent different degenerative diseases and improve human health. Microalgae are commercially exploited for carotenoids, including astaxanthin and β-carotene. Two commercially important microalgae, Dunaliella salina and Tetraselmis suecica, were treated with plant hormones salicylic acid (SA) and methyl jasmonate (MJ), or by UV-C radiation (T. suecica only) and a combination thereof. Significant increases in total carotenoids were found for D. salina and T. suecica after treatment with MJ (10 μmol/L) and SA (70–250 μmol/L), respectively. T. suecica also had significant increases in total carotenoids following UV-C radiation compared to control cultures. Among the carotenoids, lutein was the highest induced carotenoid. A combination of these two treatments also showed a significant increase in total carotenoids and lutein for T. suecica, when compared to controls. Plant hormones and UV-C radiation may be useful tools for increasing carotenoid accumulation in green microalgae although the responses are species- and dose-specific and should be trialed in medium to large scale to explore commercial production.

Cyanidin 3-glucoside improves diet-induced metabolic syndrome in rats

Increased consumption of dark-coloured fruits and vegetables may mitigate metabolic syndrome. This study has determined the changes in metabolic parameters, and in cardiovascular and liver structure and function, following chronic administration of either cyanidin 3-glucoside (CG) or Queen Garnet plum juice (QG) containing cyanidin glycosides to rats fed either a corn starch (C) or a high-carbohydrate, high-fat (H) diet. Eight to nine-week-old male Wistar rats were randomly divided into six groups for 16-week feeding with C, C with CG or QG, H or H with CG or QG. C or H were supplemented with CG or QG at a dose of ∼8 mg/kg/day cyanidin glycosides from week 8 to 16. H rats developed signs of metabolic syndrome including visceral adiposity, impaired glucose tolerance, hypertension, cardiovascular remodelling, increased collagen depots in left ventricle, non-alcoholic fatty liver disease, increased plasma liver enzymes and increased inflammatory cell infiltration in the heart and liver. Both CG and QG reversed these cardiovascular, liver and metabolic signs. However, no intact anthocyanins or common methylated/conjugated metabolites could be detected in the plasma samples and plasma hippuric acid concentrations were unchanged. Our results suggest CG is the most likely mediator of the responses to QG but that further investigation of the pharmacokinetics of oral CG in rats is required.