新疆地区小麦白粉病菌寄主范围的研究

用小麦白粉病菌11个生理小种的混合菌种,对新疆地区的小麦近缘植物的7个属22个种的47份材料进行接种,除6份免疫外,其余均接种成功.用其中6个属19个种的29份小麦近缘植物产生的白粉病菌,对小麦回接,参试的29份材料全部回接成功.小麦白粉病菌对小麦近缘植物的寄生像在小麦上一样,有明显的寄生专化性.感病的小麦近缘植物的78.0%对小麦白粉病菌的感病性,随生育期增长而急剧下降.文中并对小麦白粉病中间寄主的作用进行了讨论.     

Molecular cloning,characterization and expression analysis of two catalase isozyme genes in barley

Clones representing two distinct barley catalase genes, Cat1 and Cat2, were found in a cDNA library prepared from seedling polysomal mRNA. Both clones were sequenced, and their deduced amino acid sequences were found to have high homology with maize and rice catalase genes. Cat1 had a 91% deduced amino acid sequence identity to CAT-1 of maize and 92% to CAT B of rice. Cat2 had 72 and 79% amino acid sequence identities to maize CAT-2 and-3 and 89% to CAT A of rice. Barley, maize or rice isozymes could be divided into two distinct groups by amino acid homologies, with one group homologous to the mitochondria-associated CAT-3 of maize and the other homologous to the maize peroxisomal/glyoxysomal CAT-1. Both barley CATs contained possible peroxisomal targeting signals, but neither had favorable mitochondrial targeting sequences. Cat1 mRNA occurred in whole endosperms (aleurones plus starchy endosperm), in isolated aleurones and in developing seeds, but Cat2 mRNA was virtually absent. Both mRNAs displayed different developmental expression patterns in scutella of germinating seeds. Cat2 mRNA predominated in etiolated seedling shoots and leaf blades. Barley genomic DNA contained two genes for Cat1 and one gene for Cat2. The Cat2 gene was mapped to the long arm of chromosome 4, 2.9 cM in telomeric orientation from the mlo locus conferring resistance to the powdery mildew fungus (Erysiphe graminis f.sp. hordei).     

Surface lipids of Sphaerotheca fuliginea spores

The major components (50%) of the surface lipid extract of fungal spores (5.6% of dry spore wt) of Sphaerotheca fuliginea are esters of primary alcohols and fatty acids. Esters (15%) of primary alcohols and a Δ^2t acid are present. The major acid moieties of the alkyl esters are C₂₂ and C₂₄ and of the Δ^2t alkyl ester is Δ^2t C₂₂; for both classes eicosanol is the major primary alcohol. The major ester of each class was concluded to be eicosanyl docosanoate and eicosanyl trans-2-docosenoate. Minor components are saturated and Δ^2t methyl and diol diesters and free fatty acids. The major acid moieties of the diol diesters are C₂₂ and C₂₄ and the major diol is 1,12-dodecanediol.     

Mutual interplay between phytopathogenic powdery mildew fungi and other microorganisms

Powdery mildew is a common and widespread plant disease of considerable agronomic relevance. It is caused by obligate biotrophic fungal pathogens which, in most cases, epiphytically colonize aboveground plant tissues. The disease has been typically studied as a binary interaction of the fungal pathogen with its plant hosts, neglecting, for the most part, the mutual interplay with the wealth of other microorganisms residing in the phyllo- and/or rhizosphere and roots. However, the establishment of powdery mildew disease can be impacted by the presence/absence of host-associated microbiota (epi- and endophytes) and, conversely, plant colonization by powdery mildew fungi might disturb indigenous microbial community structures. In addition, other (foliar) phytopathogens could interact with powdery mildews, and mycoparasites may affect the outcome of plant–powdery mildew interactions. In this review, we discuss the current knowledge regarding the intricate and multifaceted interplay of powdery mildew fungi, host plants and other microorganisms, and outline current gaps in our knowledge, thereby setting the basis for potential future research directions.     

TaRPP13-3, a CC-NBS-LRR-like gene located on chr 7D,promotes disease resistance to wheat powdery mildew in Brock

Disease resistance (R) gene, RPP13, plays an important role in the resistance of plants to pathogen infections; its function in resistance of wheat to powdery mildew remains unknown. In this study, a RNA-Seq technique was used to monitor expression of genes in susceptible wheat ‘Jing411’ and resistant near-isogenic line ‘BJ-1’ in response to powdery mildew infection. Overall, 413 differential expression genes were observed and identified as involved in disease resistance. RPP13 homologous gene on wheat chromosome 7D was preliminarily identified using the wheat 660K SNP chip. RPP13 was highly expressed in ‘BJ-1’ and encodes 1,027 amino acids, including CC, NB and LRR domain, termed TaRPP13-3. After inoculation with powdery mildew, expression of TaRPP13-3 in resistant wheat changed with time, but average expression was higher when compared to susceptible variety, thus indicating that TaRPP13-3 is involved in resistance to powdery mildew. Virus-induced gene silencing (VIGS) was used to inhibit expression of TaRPP13-3 in resistant parent ‘Brock’. Results indicated that silencing of TaRPP13-3 led to decreased disease resistance in ‘Brock’. Overall results of this study indicate that TaRPP13-3 gene is involved in the defence response of wheat to powdery mildew and plays a positive role in wheat powdery mildew interactions.     

A single gene in Fusarium oxysporum limits host range

Fusarium oxysoporum f. sp. radicis-cucumerinum (Forc) is able to cause disease in cucumber, melon, and watermelon, while F. oxysporum f. sp. melonis (Fom) can only infect melon plants. Earlier research showed that mobile chromosomes in Forc and Fom determine the difference in host range between Forc and Fom. By closely comparing these pathogenicity chromosomes combined with RNA-sequencing data, we selected 11 candidate genes that we tested for involvement in the difference in host range between Forc and Fom. One of these candidates is a putative effector gene on the Fom pathogenicity chromosome that has nonidentical homologs on the Forc pathogenicity chromosome. Four independent Forc transformants with this gene from Fom showed strongly reduced or no pathogenicity towards cucumber, while retaining pathogenicity towards melon and watermelon. This suggests that the protein encoded by this gene is recognized by an immune receptor in cucumber plants. This is the first time that a single gene has been demonstrated to determine a difference in host specificity between formae speciales of F. oxysporum.