Comparison of leaf stomatal conductance models for typical desert riparian phreatophytes in northwestern China

Stomatal regulation plays a vital role related to plant functioning, especially with a limited water supply. Estimating the leaf stomatal conductance (g _s) is pivotal for further estimation of transpiration as well as energy and mass balances between air and plant in arid regions. Based on successive measurements of leaf gas exchange of two typical desert riparian phreatophytes, Tamarix ramosissima Ledeb., and Populus euphratica Oliv., we estimated g _s using the empirical, optimal, and mechanistic models. Measurements were conducted on T. ramosissima during the growing seasons in 2011 and 2012 and P. euphratica in 2013 and 2014. Estimated values were compared with those measured by the portable open-path gas exchange measurement system. Results indicated that Ye’s mechanistic model always performed best among all the g _s models tested here with R ² values of 0.878 and 0.723 for T. ramosissima in 2011 and 2012, and 0.625 and 0.867 for P. euphratica in 2013 and 2014, respectively. Meanwhile, Medlyn’s optimal model exhibited the least reliable performance with R ² at values of 0.514 and 0.398 for T. ramosissima in 2011 and 2012, and 0.385 and 0.101 for P. euphratica in 2013 and 2014, respectively. Empirical models may not be suitable for application in novel situations because they have been developed from experimental observations rather than from any mechanistic understanding or theory of stomatal behavior. Consequently, the application of Ye’s mechanistic model will be of great significance for the modeling and up-scaling of g _s in extremely arid regions in the future.     

A climatic risk analysis of the threat posed by the South American leaf blight (SALB) pathogen <Emphasis Type="Italic">Microcyclus ulei</Emphasis> to major rubber producing countries

In 2010, symptoms of cobweb disease were observed on cultivated Pleurotus eryngii crops in Spain. Based on morphological and genetic analyses, the causal agent of cobweb was identified as Cladobotryum mycophilum. Pathogenicity tests on fruit bodies were performed using conidial suspensions of three C. mycophilum isolates. The causal agent was re-isolated in 80–85 % of the fruit bodies inoculated internally and 15–40 % of those fruit bodies inoculated on the cap surface. The results pointed to a certain resistance of the P. eryngii cap surface to the mycelium of C. mycophilum. Two cropping trials inoculated with C. mycophilum were set up to evaluate the pathogenicity of the causal agent of cobweb in two casings. At the end of the growth cycle, 50–60 % of the inoculated blocks cased with mineral soil, and 20–33 % of the inoculated blocks cased with black peat showed cobweb symptoms. This difference in the appearance of the disease and its aggressiveness may be partly explained by different electrical conductivity values of the casing materials used. In vitro sensitivity of the C. mycophilum isolates and P. eryngii strains against four fungicides (chlorothalonil, prochloraz-Mn, thiabendazole and thiophanate-methyl) was assessed in radial growth experiments on fungicide-amended media. The most effective fungicides for inhibiting the in vitro growth of C. mycophilum were prochloraz-Mn and chlorothalonil, while prochloraz-Mn was also the most selective fungicide between P. eryngii and C. mycophilum, and chlorothalonil was the most toxic fungicide against the P. eryngii mycelium.     

Pathogenicity,Morpho-Species and Mating Types of <Emphasis Type="Italic">Alternaria</Emphasis> spp. causing Alternaria blight in <Emphasis Type="Italic">Pistacia</Emphasis> spp. in Turkey

Alternaria genus includes many plant pathogens on numerous hosts, causing leaf spots, rots and blights. Alternaria blight has been observed as one of the important fungal diseases of pistachio (Pistacia vera L.) as well as its wild relatives (P. terebinthus, P. lentiscus, P. khinjuk, P. atlantica, P. mutica) in Turkey. Alternaria species were sampled from Pistacia spp. hosts from different geographic regions in Turkey during field trips in late spring to early fall of 2013. Alternaria blight symptoms were observed mainly on fruits and rarely on leaves. Four hundred and twenty two of the isolates were morphologically defined as A. alternata, A. tenuissima, A. arborescens and also intermediate morpho-species between A. alternata/A. arborescens. Pathogenicity of the isolates was confirmed with host inoculations on detached fruits. Mating types of 270 isolates of Alternaria spp. from the collection were identified using a PCR-based mating type assay that amplifies either a MAT1-1 or a MAT1-2 fragment from the mating locus. Although a strongly clonal population structure was expected due to the putative asexual reproduction of these fungi, both idiomorphs were detected at equal frequencies at several different spatial scales. The distribution of mating types within each geographic region, within host species as well as in overall collection was not significantly different from 1:1. Amplified fragments of partial idiomorph sequences were obtained for representative isolates. Parsimony trees were depicted based on sequence data of mating type genes for these representative isolates as well as some other Alternaria species obtained by Genebank. Several point mutations presented a few clusters which are supported by high bootsrapped values. The Alternaria blight disease agents both from cultivated and wild hosts were pathogenic on pistachio which may cause difficulties to control the disease because of extensity of pathogen sources. Besides, equal mating type distribution of the pathogen at both geographic and host species levels suggests a potential for sexual reproduction of Alternaria spp. in Turkey.     

Loquat as a crop model for successful deficit irrigation

During three consecutive seasons, two different deficit irrigation strategies were compared with control fully irrigated trees regarding their capacity to induce early bloom and harvest in “Algerie” loquat. The first strategy, a continuous deficit irrigation strategy, consisted in a uniform reduction of 20% water needs through the entire season; the second strategy, a regulated deficit irrigation approach, while accounting for the same global reduction of 20% loquat water needs, concentrated water shortages after harvest from mid-May through the end of August. Regulated deficit irrigation resulted more successful. Postharvest regulated deficit irrigation advanced full bloom 10–20 days depending on the season. Such enhancement led to more precocious and valuable yield, with an average increase of fruit value of 0.21 € kg⁻¹. The effects of continuous deficit irrigation were less noticeable and average fruit value was increased 0.08 € kg⁻¹. Yield and fruit quality were not affected for the different deficit irrigation strategies. Water savings established around 1450 m³ ha⁻¹ year⁻¹. Deficit irrigation rose water use efficiency up to more than a 40%.     

Fasciation in <Emphasis Type="Italic">Crassula argentea</Emphasis>: molecular identification of phytoplasmas and associated antioxidative capacity

The present study reports on phytoplasma induced fasciation in Crassula argintea (Crassulaceae). DNA was extracted from symptomless and fasciated tissues and amplified by nested PCR using universal primers P1/P7 followed by R16F2n/R16R2 produced amplicons of 1.2 Kb. The nucleotide sequence analyses of the amplicons indicated that fasciated plants were infected by phytoplasma. Phylogenetic analysis placed the Crassula fasciation phytoplasmas in 16SrII-D group. Histochemical staining for reactive oxygen species indicated that phytoplasma infected (PI) tissues possess significantly higher levels of hydrogen peroxide (H₂O₂) rather than superoxide (O₂ ^·-) as compared with symptomless tissues. PI tissues were also associated with a significant increase in antioxidant enzyme activities (catalase, peroxidase, polyphenol oxidase, and glutathione reductase) and electrolyte leakage as compared with symptomless tissues.     

Pathogens of bark beetles (Coleoptera: Curculionidae) in Bulgarian forests

The occurrence and prevalence of bark beetle pathogens in forest stands in Bulgaria were investigated in 944 specimens belonging to 21 bark beetle species. Protozoa, microsporidia, fungi and nematodes occurred in 19 of all investigated species. The infections were found in the gut (nematodes, gregarines, microsporidia), gonads (microsporidia) and hemolymph (nematodes) of the infected insects. Protozoan species (Gregarina typographi, Gregarina spp.) were detected in eight bark beetle species. Morphometric data about G. typographi and Gregarina spp. are presented. The prevalence of the gregarines varied between 1.4% and 64.2%. Microsporidia of the genera Nosema and Chytridiopsis were revealed in three bark beetle species. The prevalence of microsporidia ranged between 1.5% and 11.8%. This is the first report of a microsporidium in Taphrorychus villifrons and of gregarines in T. villifrons, Pityogenes bistridentatus, P. conjunctus, and Orthotomicus erosus. The fungus Beauveria bassiana was found in 3.4% of Hylurgops palliatus specimens. Nematodes (in gut and haemolymph) were revealed in 19 bark beetle species and their prevalence varied between 10% and 98.5%.     

甘肃省小麦白粉菌群体毒性及小麦品种苗期抗白粉病性分析

由Blumeria graminis f.sp.tritici引起的小麦白粉病是危害甘肃省小麦安全生产的重要病害之一,分析病原菌毒性结构和抗病基因有效性对于指导白粉病的有效控制具有重要意义。2013年对甘肃省小麦白粉菌群体进行毒性分析结果表明,91个供试菌系中,对Pm1、Pm2、Pm3a、Pm3b、Pm3c、Pm3d、Pm3e、Pm3f、Pm4a、Pm4b、Pm5a、Pm6、Pm7、Pm8、Pm19、Pm33、Pm5+Pm6、Pm4+Pm8、Pm4b+Pm5b和PmEra的毒力频率达到70%以上,已无利用价值;对Pm13、Pm16、Pm21和Pm24的毒性频率在15%以下,尚可利用。选用甘肃省不同毒性谱的单孢堆菌系,对35个甘肃省及国内生产品种(系)进行苗期致病性测定,发现仅有‘绵麦37’具有优异抗病性。供试白粉菌系对‘定西40号’等22个品种(系)的毒性频率达到60%以上,甘肃省及中国生产品种中,苗期抗病品种(系)匮乏。     

枇杷灰斑病病原菌的鉴定

 从枇杷灰斑病病斑上分离的病原菌,经鉴定分属于2个种,即Pestalotia adusta Ell.&Ev.[Pestalotiaadusta (Ell.&Ev.) Stey]和P.eriobotrifolia Guba。它们的分生孢于形态差异很大,菌体酯酶及蛋白质电泳图谱也有明显的差别.种内不同分离物间的酯酶及蛋白质电泳图谱有很大的相似性.P.eriobotrifolia是枇杷灰斑病病原菌的优势种.