Effects of temperature and photoperiod on germination and germ tube development of dikaryotic stages of Pileolaria terebinthi

The germination and germ tube development of urediospores, aeciospores and teliospores of Pileolaria terebinthi, the causal agent of Pistacia spp. rust, were investigated under different temperature and light conditions. The urediospores and aeciospores germinated in a range of 10–30°C, the optimum being 25–30°C. Both spore types died after 24 h exposure at 35°C. Incubation at -5°C for 24 h caused a significant decrease in spore germinability and germ tube growth. A significant increase in germination and germ tube growth was observed in the dark. Teliospores germinated well in a range of 15–30°C. Differentiation of basidia occurred at 20–25°C. Optimum temperature for teliospore germination and basidium differentiation was found to be 20°C. The maximum differentiation of basidia was observed in short day exposures (0.5 h light/23.5 h dark). No basidia differentiated under continuous fluorescent illumination

Biology and Feeding Behaviour of Ladybird, Clitostethus arcuatus, the Predator of the Ash Whitefly, Siphoninus phillyreae, in Fars Province, Iran

Clitostethus arcuatus (Rossi) (Coleoptera: Coccinellidae) is considered as one of the most important natural biological control agents of the ash whitefly, Siphoninus phillyreae (Haliday) (Hemiptera: Aleyrodidae) in Iran. In the current survey, the development, survival, longevity, fecundity, feeding behaviour, and population dynamics of the predator under laboratory and field conditions were studied. The longevity of female insects was significantly longer than that of males. Total feeding of 4th larval instars and females was significantly higher than males and other larval instars. The overall mortality rate from egg to adult under laboratory conditions was 22.7% while under field conditions it was 38.2%. Copulation lasted approximately 67 minutes while the average pre-mating and pre-oviposition times recorded were 3.8 and 1.8 days, respectively. The mean number of eggs laid by each female was 181. The adults could survive starvation for 4 days with a normal longevity of 62–73 days. The maximum population density of the predator was recorded in late August that coincided with the decline of the S. phillyreae population. C. arcuatus had four generations per year, and the adults were observed until mid December. Possible application of C. arcuatus for biological control of S. phillyreae in integrated pest management programs is discussed

Metabolic profiling and factor analysis to discriminate quantitative resistance in wheat cultivars against fusarium head blight

Metabolic profiles of spikelets of wheat cultivars, Roblin and Sumai3, respectively, susceptible and resistant to fusarium head blight (FHB) were analyzed using GC/MS to develop a technology to discriminate resistance. More than 700 peaks were detected and a total of 55 compounds were tentatively identified, of which 49 were induced/up-regulated following pathogen inoculation, including 23 in Roblin and 26 in Sumai3. However, only five metabolites were significantly different both between cultivars and inoculations. Metahydroxycinnamic acid, though was detected in all four treatments, exhibited a six-fold increase in abundance in Sumai3 following pathogen inoculation, with no corresponding change in Roblin. The abundance of myo-inositol in Sumai3 was higher than that in Roblin, and in both the abundance increased following pathogen inoculation. The compounds common to all treatments were subjected to factor analysis to identify groups of compounds, based on significant factor-loadings, associated with susceptibility or resistance against FHB. The treatment involving pathogen-inoculation of the resistant cv. Sumai3 was associated with the highest scores for the first and second factors that can be used for the discrimination of resistance against FHB. The first factor was associated with higher abundances of several fatty acids and aromatic compounds, while the second factor was associated with metabolites such as p- and m-coumaric acids, myo-inositol and other sugars, and malonic acid. The treatments involving pathogen-inoculation had higher factor scores for the third factor than the water inoculated, the highest being for the susceptible cultivar Roblin, and may be useful in explaining susceptibility/pathogenesis. The third factor had positive correlation with metabolites from different groups, mostly amino acids, fatty acids, and aromatics. The various compounds detected in this study are discussed, in terms of their possible roles in plant defense against pathogen-stress, their metabolic pathways of synthesis, and their potential application for screening cultivars of wheat for resistance to FHB.H. Hamzehzarghani, A.C. Kushalappa, Y. Dionb, S. Rioux, A. Comeau, V. Yaylayan, W.D. Marshall and D.E. Matherhttp://www.elsevier.com/wps/find/journaldescription.cws_home/622932/description#descriptio

Molecular typing reveals high genetic diversity of Xanthomonas translucens strains infecting small-grain cereals in Iran

This study provides a phylogeographic insight into the population diversity of Xanthomonas translucens strains causing bacterial leaf streak disease of small-grain cereals in Iran. Among the 65 bacterial strains isolated from wheat, barley, and gramineous weeds in eight Iranian provinces, multilocus sequence analysis and typing (MLSA and MLST) of four housekeeping genes (dnaK, fyuA, gyrB, and rpoD), identified 57 strains as X. translucens pv. undulosa, while eight strains were identified as X. translucens pv. translucens. Although the pathogenicity patterns on oat and ryegrass weed species varied among the strains, all X. translucens pv. undulosa strains were pathogenic on barley, Harding's grass, rye (except for XtKm35) and wheat, and all X. translucens pv. translucens strains were pathogenic on barley and Harding's grass, while none of the latter group was pathogenic on rye or wheat (except for XtKm18). MLST using the 65 strains isolated in Iran, as well as the sequences of the four genes from 112 strains of worldwide origin retrieved from the GenBank database, revealed higher genetic diversity (i.e., haplotype frequency, haplotype diversity, and percentage of polymorphic sites) among the Iranian population of X. translucens than among the North American strains of the pathogen. High genetic diversity of the BLS pathogen in Iran was in congruence with the fact that the Iranian Plateau is considered the center of origin of cultivated wheat. However, further studies using larger collections of strains are warranted to precisely elucidate the global population diversity and center of origin of the pathogen. IMPORTANCE Bacterial leaf streak (BLS) of small-grain cereals (i.e., wheat and barley) is one of the economically important diseases of gramineous crops worldwide. The disease occurs in many countries across the globe, with particular importance in regions characterized by high levels of precipitation. Two genetically distinct xanthomonads-namely, Xanthomonas translucens pv. undulosa and X. translucens pv. translucens-have been reported to cause BLS disease on small-grain cereals. As seed-borne pathogens, the causal agents are included in the A2 list of quarantine pathogens by the European and Mediterranean Plant Protection Organization (EPPO). Despite its global distribution and high economic importance, the population structure, genetic diversity, and phylogeography of X. translucens remain undetermined. This study, using MLSA and MLST, provides a global-scale phylogeography of X. translucens strains infecting small-grain cereals. Based on the diversity parameters, neutrality indices, and population structure, we observe higher genetic diversity of the BLS pathogen in Iran, which is geographically close to the center of origin of common wheat, than has so far been observed in other areas of the world, including North America. The results obtained in this study provide a novel insight into the genetic diversity and population structure of the BLS pathogen of small-grain cereals on a global scale

Induced root-secreted phenolic compounds as a belowground plant defense

Rhizosphere is the complex place of numerous interactions between plant roots, microbes and soil fauna. Whereas plant interactions with aboveground organisms are largely described, unravelling plant belowground interactions remains challenging. Plant root chemical communication can lead to positive interactions with nodulating bacteria, mycorriza or biocontrol agents or to negative interactions with pathogens or root herbivores. A recent study1 suggested that root exudates contribute to plant pathogen resistance via secretion of antimicrobial compounds. These findings point to the importance of plant root exudates as belowground signalling molecules, particularly in defense responses. In our report,2 we showed that under Fusarium attack the barley root system launched secretion of phenolic compounds with antimicrobial activity. The secretion of de novo biosynthesized t-cinnamic acid induced within 2 days illustrates the dynamic of plant defense mechanisms at the root level. We discuss the costs and benefits of induced defense responses in the rhizosphere. We suggest that plant defense through root exudation may be cultivar dependent and higher in wild or less domesticated varieties