A Japanese powdery mildew isolate with exceptionally large infection efficiency on Mlo-resistant barley

A Japanese field isolate (Race I) of Erysiphe graminis f.sp, hordei was tested on 17 barley lines carrying the mlo powdery mildew resistance gene. Race I produced many successful infections with infection type larger than or equal to 2 on six lines (M66, MC20, SRI, SR7, A tem and Totem), On the remaining 11 lines it reacted with infection type 0. Colony numbers on the Mlo-lines were between 26% and 12 9% of the numbers on a susceptible cultivar Manchuria, These numbers were larger than, or similar to those produced by isolate HL3/5, which has the highest recorded infection efficiency on Mlo-resistant cultivars. The interaction between isolates and lines was highly significant. The isolate GE3, from which HL3/5 was derived by selection, gave rise to occasional colonies corresponding to less than 03° o of the number produced on cv. Manchuria.     

Antioxidant,ethylene and membrane leakage responses to powdery mildew infection of near-isogenic barley lines with various types of resistance

Leaves of powdery mildew-susceptible barley (Hordeum vulgare cv. Ingrid) and related near-isogenic lines bearing various resistance genes (Mla12, Mlg or mlo5) were inoculated with Blumeria graminis f. sp. hordei race A6. Fungal attack induced several-fold increases in ethylene emission and electrolyte leakage in leaves of susceptible Ingrid beginning 3 days after inoculation. Activities of peroxidase, superoxide dismutase, glutathione S-transferase, ascorbate peroxidase and glutathione reductase enzymes were induced markedly in susceptible leaves 5–7 days after inoculation. Similar, but less pronounced pathogen-induced changes were detected in inoculated leaves of Mla-type resistant plants that show hypersensitive cell death upon inoculation, and, to an even lesser extent, in the Mlg and mlo lines, where no visible symptoms accompanied the incompatible interaction. Glutathione content increased only in susceptible barley 7 days after inoculation. Catalase activity, total ascorbate content and redox state were not influenced by inoculation in any of the genotypes. The activity of dehydroascorbate reductase was significantly reduced 3–5 days after inoculation in the susceptible parental plants and after 5 days in Mla and Mlg lines, while it was stable in the mlo barley. Slightly elevated levels of H₂O₂ were observed in the inoculated resistant plants. In contrast, H₂O₂ content decreased in the susceptible line 7 days after pathogen attack. These data indicate that high levels of antioxidants are involved in the compatible interaction of susceptible barley and powdery mildew by protecting the pathogen from oxidative damage.     

Ontogenic resistance and plant disease management: a case study of grape powdery mildew

ABSTRACT A fundamental principle of integrated pest management is that actions taken to manage disease should be commensurate with the risk of infection and loss. One of the less-studied factors that determines this risk is ontogenic, or age-related resistance of the host. Ontogenic resistance may operate at the whole plant level or in specific organs or tissues. Until recently, grape berries were thought to remain susceptible to powdery mildew (Uncinula necator) until late in their development. However, the development of ontogenic resistance is actually quite rapid in berries, and fruit become nearly immune to infection within 4 weeks after fruit set. Our objective was to determine how and at what stage the pathogen was halted in the infection process on ontogenically resistant berries. Adhesion of conidia, germination, and appressorium formation were not impeded on older berries. However, once berries were approximately 3 weeks old and older, few germlings were able to form secondary hyphae. Ontogenically resistant berries responded rapidly to infection by synthesis of a germin-like protein that had been previously shown to play a role in host defense against barley powdery mildew. On susceptible berries, cell discoloration around penetration sites indicated the oxidation of phenolic compounds; a process that was followed by localized cell death. However, the pathogen was still able to infect such cells prior to their death, continue secondary growth, and thereby colonize young berries. Formation of papillae was not involved in the differential resistance mechanism of older berries. In susceptible berries, papillae formed frequently at infection sites but did not always contain the pathogen, whereas in resistant berries, the pathogen was always halted prior to the formation of papillae. The host defense, which conditions ontogenic resistance, operates in the earliest stages of the infection process, in the absence of gross anatomical barriers, prior to the formation of a functional haustorium and prior to the development of a conspicuous penetration pore. We also found that diffuse powdery mildew colonies that were not visible in the field predisposed berries to bunch rot by Botrytis cinerea, increased the levels of infestation by spoilage microorganisms, and substantially degraded wine quality. Our improved understanding of the nature, causes, and stability of ontogenic resistance in the grapevine/ powdery mildew system has supported substantial changes in how fungicides are used to control the disease. Present applications are more focused on the period of maximum fruit susceptibility instead of following a calendar-based schedule. This has improved control, reduced losses, and in many cases reduced the number of fungicide applications required to suppress the disease. Particularly where fungicides are deployed in a programmatic fashion and ontogenic resistance is dynamic, there may be equivalent improvements to be made in other hostpathogen systems through studies of how host susceptibility changes through time.     

细胞乳突的形成和小麦白粉菌成功侵染的关系

 用一套己知抗白粉病单基因的小麦材料,研究了小麦白粉菌诱发寄主表皮细胞产生的乳突与成功侵染的关系。抗病小麦叶片上,诱发产生乳突的分生孢子占测定分生孢子数的58.8%,感病品种为63.8%。这表明抗性不同的小麦材料接种白粉菌之后,叶表皮细胞内形成乳突的百分率相近,然从在抗病材料和感病材料中形成的乳突阻止病原物发育和成功侵染的作用不相同,在抗病叶片上,诱发产生乳突的分生孢于中有88%停留在压力孢阶段,不继续发育,仅有12%能突破乳突形成吸器,使得侵染成功。与此对照,在感病叶片上只有32%诱发乳突的分生孢子不能穿透乳突,而68%则能突破乳突。成功地与寄主建立寄生关系。我们的研究表明,乳突能否成功地阻止白粉菌侵入可能与乳突形成的迟早有关。     

Cytological events in tomato leaves inoculated with conidia of <Emphasis Type="Italic">Blumeria graminis</Emphasis> f. sp. <Emphasis Type="Italic">hordei</Emphasis> and <Emphasis Type="Italic">Oidium neolycopersici</Emphasis> KTP-01

Leaves of tomato and barley were inoculated with conidia of Blumeria graminis f. sp. hordei race 1 (R1) or Oidium neolycopersici (KTP-01) to observe cytological responses in search of resistance to powdery mildew. Both conidia formed appressoria at similar rates on tomato or barley leaves, indicating that no resistance was expressed during the prepenetration stage of these fungi. On R1-inoculated tomato leaves, appressoria penetrated the papillae, but subsequent haustorium formation was inhibited by hypersensitive necrosis in the invaded epidermal cells. On the other hand, KTP-01 (pathogenic to tomato leaves) successfully developed functional haustoria in epidermal cells to elongate secondary hyphae, although the hyphal elongation from some conidia was later suppressed by delayed hypersensitive necrosis in some haustorium-harboring epidermal cells. Thus, the present study indicated that the resistance of tomato to powdery mildew fungi was associated with a hypersensitive response in invaded epidermal cells but not the prevention of fungal penetration through host papilla.     

大麦白粉菌种群毒性监测及抗性材料鉴定

2005和2006年从我国冬大麦区采集和分离大麦白粉菌单胞菌株729个,利用Pallas近等基因系进行致病型鉴定和群体毒性频率分析.同时,利用分离得到的不同致病型菌株,通过抗谱分析的方法鉴定了328份大麦品种(系)的白粉病抗性和抗病基因.结果显示:大麦白粉菌群体对抗病基因Mlal Mla(A12)、Mla3、Mla6 Mla14、Mla7 Mla(No3)、Mla7 Ml(Lg2)、Mla9 Mlk、Mla9、Mlal3 MlaRu3、Mlpl、Mlg(Cp)和mlo5的毒性频率为0;对Mla12 MlaEm2、Mla7 Mlk、Mlat Mla8、Mla10MlaDu2和Mlk1的毒性频率很低,分别为0.1%、0.4%、0.9%、2.8%和4.2%.两年共鉴定出不同的致病型21个,致病型000、001和003在两个年度皆为优势致病型.所鉴定的328份材料绝大多数感病,仅37份抗病材料,能明确推导出抗白粉病基因的品种(品系)很少,这些品种(品系)含有的抗白粉病基因为Mr(Bw)Mla8、Mlg、Mira Mla8、Mla9 Mla1、Mla Mla(A12)和mlo5.     

The importance of non‐penetrated papillae formation in the resistance response of triticale to powdery mildew (Blumeria graminis)

Triticale is the intergeneric hybrid between wheat and rye. With the expansion of the triticale growing area, powdery mildew has emerged and become a significant disease on this new host. Recent research demonstrated that this ‘new’ powdery mildew on triticale has emerged through a host range expansion of powdery mildew of wheat. Moreover, isolates sampled from triticale still infect their previous host, wheat, but isolates sampled from wheat hardly infect triticale. Race‐specific and adult‐plant resistance have been identified in triticale cultivars. The main objective of this study was to characterize the cellular basis of powdery mildew resistance in triticale. Commonalities with resistance responses in other cereals such as wheat, barley and oat are discussed. A detailed comparative histological study of various resistance responses during cross‐inoculation of either virulent or avirulent wheat and triticale isolates on both hosts was carried out. The present data provide evidence that for incompatible interactions, the formation of non‐penetrated papillae is the predominant resistance response, while the hypersensitive response (HR) acts as a second line of defence, to cut the fungus off from nutrients, if penetration resistance fails. It is not clear yet what causes the slower growth and reduced colony size of triticale isolates when inoculated on wheat. Possibly, post‐penetration resistance mechanisms, other than HR, are switched on during these (semi‐) compatible interactions. Molecular studies on gene expression and gene function of defence‐related genes might reveal further insights into the genetic basis of these resistance responses.     

A microscopic study of the wheat-powdery mildew relationship after application of the systemic compounds procaine,griseofulvin and 6-azauracil

On wheat seedlings systemically protected by root application of procaine-hydrochloride, griseofulvin or 6-azauracil, germination of oidia ofErysiphe graminis f. sp.tritici and penetration of this fungus into the epidermal cell wall was as high as on control plants. Inhibition of powdery mildew development became apparent only after the penetration process had started. About 85% of the infections were halted within 24 hours after the inoculation, and did not result in the formation of a haustorium. In the other cases usually not more than one haustorium per infection court was formed, which often showed anomalies, characteristic for each compound used. Development of mycelium was scanty or absent and no sporulation occurred. Similarly, on plants of a resistant wheat variety, powdery mildew inhibition became apparent only after penetration of the host had started. There was no development of mycelium or sporulation. A severe reaction of certain epidermal cells to penetration by powdery mildew was observed on resistant as well as on treated and untreated susceptible plants. However, in relation to the total number of infections, the percentage of this type of reaction was low.     

Characterization of Resistance Mechanisms to Erysiphe pisi in Medicago truncatula

ABSTRACT In this work, we studied the resistance of 277 Medicago truncatula accessions against powdery mildew and further characterized the defense mechanisms of resistant plants. Ten resistant accessions were selected according to macroscopic assessment. Histological studies showed a range of defense mechanisms, acting alone or combined, that impeded fungal development at different stages. Some accessions allowed a reduced spore germination frequency compared with that of the susceptible control. In others, the fungus was arrested at penetration stage due to papilla formation. Epidermal cells of several accessions were penetrated by the fungus but then hypersensitive response (HR) leading to cell death hampered fungal development. In some cases, cell death was very fast and no haustorium could be observed in epidermal cells, whereas in others, haustoria and secondary hyphae indicated a slow HR. Finally, in some accessions in which no HR was observed, colony growth was restricted through posthaustorial defense mechanisms. Characterization of defense mechanisms will be useful for further cellular and molecular studies to unravel the bases of resistance in this species in particular and in legume-powdery mildew interaction in general.     

Temporary partial breakdown of mlo-resistance in spring barley by sudden relief of soil water-stress under field conditions: the effects of genetic background and mlo allele

This study, carried out under field conditions, assessed the extent to which temporary breakdown of mlo- resistance, following relief of water-stress, was determined by genetic background and mlo allele. Commercial barley cultivars expressing the mlo gene for resistance to powdery mildew ( Erysiphe graminis ( Blumeria graminis ) f.sp. hordei ) were tested as well as doubled haploid progeny from spring barley genotypes, a proportion of which were sown in the field in two successive years. Plants were protected from natural rain by a mobile rain shelter and either watered by trickle-irrigation or allowed to dry. Percentage mildew infection resulting from natural inoculum was recorded and the doubled haploid genotypes were classified as resistant, intermediate or susceptible on the basis of their control (watered) treatment scores. In each of the three designated classes, particular genotypes developed infection levels, following relief of water-stress, that were higher than those observed on the well-watered controls. This was found not to be related to the mlo allele as there was no significant difference between the increases observed on resistant plants carrying mlo9 and resistant plants carrying mlo11 . Differences in the degree of breakdown of resistance were attributed to genetic background rather than to the specific mlo allele.     

Nonhost versus host resistance to the grapevine downy mildew, Plasmopara viticola, studied at the tissue level

Following inoculation of host and nonhost plants with Plasmopara viticola, the grapevine downy mildew, a histological survey was undertaken to identify the stage where its development is contained in nonhosts and in resistant host plants. Three herbaceous nonhost species, Beta vulgaris, Lactuca sativa, and Capsicum annuum, and three grapevine species displaying different level of resistance (Vitis vinifera [susceptible], Vitis riparia [partially resistant] and Muscadinia rotundifolia [totally resistant]) where inoculated by P. viticola using a controlled leaf disk inoculation bioassay. During the early steps of infection, defined as encystment of zoospores on stomata, penetration of the germ tube, and production of the vesicle with the primary hypha, there was no evidence of a clear-cut preference to grapevine tissues that could attest to host specificity. The main difference between host grapevine species and nonhosts was observed during the haustorium formation stage. In nonhost tissues, the infection was stopped by cell wall-associated defense responses before any mature haustorium could appear. Defense responses in resistant grapevines were triggered when haustoria were fully visible and corresponded to hypersensitive responses. These observations illustrate that, for P. viticola, haustorium formation is not only a key stage for the establishment of biotrophy but also for the host specificity and the recognition by grapevine resistance factors.     

Comparative analysis of early H2O2 accumulation in compatible and incompatible wheat–powdery mildew interactions

Comparative analysis was carried out for hydrogen peroxide (H₂O₂) accumulation in response to powdery mildew (Blumeria graminis[Erysiphe graminis] f.sp. tritici) primary germ tube (PGT) and appressorial germ tube (AGT) contact, and in papilla (cell wall apposition) and hypersensitive responses (HR) in wheat (Triticum aestivum). Using primary leaves of three susceptible wheat lines (Bainong 3217; Beijing 837; Jingshuang 16) and five resistant lines [Mardler (Pm2 + Pm6); Ulka/8 × Cc (Pm2); Mardler/7 × Bainong 3217 (Pm2); Pm16; Pm16/7 × Beijing 837 (Pm16)], early H₂O₂ accumulation between 10 and 48 h after inoculation was studied. Strong H₂O₂ accumulation was found in effective papillae and associated cytosolic vesicles in both susceptible and resistant wheat lines, suggesting the important role of H₂O₂ in effective papillae formed as a general plant defence against powdery mildew. High frequency of effective papilla formation was observed in all five resistant lines. Among resistant lines, hypersensitive cell death was detected earlier in Mardler and Ulka/8 × Cc than in Pm16 and Pm16/7 × Beijing 837. In all cases this was associated with H₂O₂ accumulation in attacked epidermal cells. Interestingly, penetration resistance but not HR appeared to be mediated by the Pm2 gene in the Mardler/7 × Bainong 3217 line, suggesting that Pm2 may govern an HR-independent defence pathway in this genetic background. As effective papillae and HR did not occur in the same cells, papilla deposition may be independent of the HR response, despite the fact that both defence mechanisms were associated with high H₂O₂ accumulation. In wheat powdery mildew-incompatible interactions, HR acts as a second line of defence to contain infection when the papilla defence fails.     

The resistance to powdery mildew (Oidium lycopersicum) in Lycopersicon species is mainly associated with hypersensitive response

The cultivated tomato ( Lycopersicon esculentum) is susceptible to powdery mildew ( Oidium lycopersicum). Six accessions of three related Lycopersicon species show high levels of resistance (Lindhout et al., 1994b). The present research aimed at describing the development of O. lycopersicum on susceptible cv Moneymaker and characterizing the defence response to O. lycopersicum in Lycopersicon accessions by histological analysis. Spore germination and (primary) haustorium formation in resistant accessions were as frequent as in the susceptible L. esculentum cv Moneymaker. A high frequency of necrosis of epidermal cells in which a haustorium was formed appeared to be the major defence response, indicating that resistance to O. lycopersicum in the Lycopersicon genus was predominantly based on the hypersensitive reaction. However, the resistance in L. parviflorum was less associated with hypersensitivity than in other resistant accessions, suggesting the existence of a different but still unknown resistance mechanism. In addition, evidence is provided that the level of resistance could depend on the genetic background and the plant age.     

Mining wild barley for powdery mildew resistance

Powdery mildew, caused by Blumeria graminis f. sp. hordei (Bgh), is a worldwide disease problem on barley (Hordeum vulgare) with potentially severe impact on yield. Historically, resistance genes have been identified chiefly from cultivated lines and landraces; however, wild barley (H. vulgare subsp. spontaneum) accessions have proven to be extraordinarily rich sources of powdery mildew resistance. This study describes the characterization of a collection of 316 wild barley accessions, known as the Wild Barley Diversity Collection (WBDC), for resistance to powdery mildew and the genetic location of powdery mildew resistance loci. The WBDC was phenotyped for reaction to 40 different Bgh isolates at the seedling stage and genotyped with 10 508 molecular markers. Accessions resistant to all 40 isolates of Bgh were not found; however, three accessions (WBDC 053, 085 and 089) exhibited resistance to 38 of the isolates. Gene postulation analyses revealed that many accessions, while resistant, contained none of the 12 genes present in the Pallas near‐isogenic lines Mla1, Mla3, Mla6, Mla7, Mla9, Mla12, Mla13, Mlk1, MlLa, Mlg, Mlat and Ml(Ru2), suggesting that the accessions carry novel genes or gene combinations. A genome‐wide association study of powdery mildew resistance in the WBDC identified 21 significant marker‐trait associations that resolved into 15 quantitative trait loci. Seven of these loci have not been previously associated with powdery mildew resistance. Taken together, these results demonstrate that the WBDC is a rich source of powdery mildew resistance, and provide genetic tools for incorporating the resistance into barley breeding programmes.     

Microscopical studies of resistance to powdery mildew disease in the hop cultivar Wye Target

Microscopical studies of fungal development and host responses during infection of the hop cultivars Northern Brewer (susceptible) and Wye Target (resistant) with a Zenith isolate of Sphaerotheca humuli are described. Resistance to powdery mildew disease in cv. Wye Target is principally determined by the R₂ major gene. Fungal growth was typically restricted in cv. Wye Target following formation of a single haustorial initial or haustorium which failed to develop the characteristic lobes found in susceptible cells. The hypersensitive reaction of penetrated epidermal cells was associated with death of haustorial initials but the associated appressorium remained alive during the first 2 days after inoculation. In leaves expressing resistance, histochemical staining revealed deposition of lignin-like material and callose in penetrated cells and to a lesser extent in underlying palisade mesophyll cells. Transmission electron microscopy and enzymic digestion clearly demonstrated extensive paramural deposition of β-1.3 glucans (callose) in reacting mesophyll cells. Plant cell death, lignification and widespread callose deposition were rarely observed at infection sites in cv. Northern Brewer but collars of callose were deposited around the necks of all haustoria formed.     

A Compromised Mlo Pathway Affects the Response of Barley to the Necrotrophic Fungus Bipolaris sorokiniana (Teleomorph: Cochliobolus sativus) and Its Toxins

ABSTRACT In search of new durable disease resistance traits in barley to control leaf spot blotch disease caused by the necrotrophic fungus Bipolaris sorokiniana (teleomorph: Cochliobolus sativus), we developed macroscopic and microscopic scales to judge spot blotch disease development on barley. Infection of barley was associated with cell wall penetration and accumulation of hydrogen peroxide. The latter appeared to take place in cell wall swellings under fungal penetration attempts as well as during cell death provoked by the necrotrophic pathogen. Additionally, we tested the influence of a compromised Mlo pathway that confers broad resistance against powdery mildew fungus (Blumeria graminis f. sp. hordei). Powdery mildew-resistant genotypes with mutations at the Mlo locus (mlo genotypes) showed a higher sensitivity to infiltration of toxic culture filtrate of Bipolaris sorokiniana as compared with wild-type barley. Mutants defective in Ror, a gene required for mlo-specified powdery mildew resistance, were also more sensitive to Bipolaris sorokiniana toxins than wild-type barley but showed less symptoms than mlo5 parents. Fungal culture filtrates induced an H2O2 burst in all mutants, whereas wild-type (Mlo) barley was less sensitive. The results support the hypothesis that the barley Mlo gene product functions as a suppresser of cell death. Therefore, a compromised Mlo pathway is effective for control of biotrophic powdery mildew fungus but not for necrotrophic Bipolaris sorokiniana. We discuss the problem of finding resistance traits that are effective against both biotrophic and necrotrophic pathogens with emphasis on the role of the anti-oxidative system of plant cells.     

A major gene for powdery mildew resistance transferred to common wheat from wild einkorn wheat

ABSTRACT A major gene for resistance to wheat powdery mildew (Blumeria graminis f. sp. tritici = Erysiphe graminis f. sp. tritici) has been successfully transferred into hexaploid common wheat (Triticum aestivum, 2n = 6x = 42, AABBDD) from wild einkorn wheat (Triticum monococcum subsp. aegilopoides, 2n = 2x = 14, AA). NC96BGTA5 is a germ plasm line with the pedigree Saluda x 3/PI427662. The response patterns for powdery mildew resistance in NC96BGTA5 were tested with 30 differential isolates of B. graminis f. sp. tritici, and the line was resistant to all tested isolates. The analyses of P(1), P(2), F(1), F(2), and BC(1)F(1) populations derived from NC96BGTA5 revealed two genes for wheat powdery mildew resistance in the NC96BGTA5 line. One gene, Pm3a, was from its recurrent parent Saluda, and the second was a new gene introgressed from wild einkorn wheat. The gene was determined to be different from Pm1 to Pm21 by gene-for-gene and pedigree analyses. The new gene was identified as linked to the Pm3a gene based on the F(2) and BC(1)F(1) populations derived from a cross between NC96BGTA5 and a susceptible cultivar NK-Coker 68-15, and the data indicated that the gene was located on chromosome 1A. It is proposed that this new gene be designated Pm25 for wheat powdery mildew resistance in NC96BGTA5. Three random amplified polymorphic DNA markers, OPX06(1050), OPAG04(950), and OPAI14(600), were found to be linked to this new gene.     

Host Barriers and Responses to Uncinula necator in Developing Grape Berries

ABSTRACT Grape berries are highly susceptible to powdery mildew 1 week after bloom but acquire ontogenic resistance 2 to 3 weeks later. We recently demonstrated that germinating conidia of the grape powdery mildew pathogen (Uncinula necator) cease development before penetration of the cuticle on older resistant berries. The mechanism that halts U. necator at that particular stage was not known. Several previous studies investigated potential host barriers or cell responses to powdery mildew in berries and leaves, but none included observation of the direct effect of these factors on pathogen development. We found that cuticle thickness increased with berry age, but that ingress by the pathogen halted before formation of a visible penetration pore. Cell wall thickness remained unchanged over the first 4 weeks after bloom, the time during which berries progressed from highly susceptible to nearly immune. Autofluorescent polyphenolic compounds accumulated at a higher frequency beneath appressoria on highly susceptible berries than on highly resistant berries; and oxidation of the above phenolics, indicated by cell discoloration, developed at a significantly higher frequency on susceptible berries. Beneath the first-formed appressoria of all germinated conidia, papillae occurred at a significantly higher frequency on 2- to 5-day-old berries than on 30- to 31-day-old fruit. The relatively few papillae observed on older berries were, in most cases (82.8 to 97.3%), found beneath appressoria of conidia that had failed to produce secondary hyphae. This contrasted with the more abundantly produced papillae on younger berries, where only 35.4 to 41.0% were located beneath appressoria of conidia that had failed to produce secondary hyphae. A pathogenesis-related gene (VvPR-1) was much more highly induced in susceptible berries than in resistant berries after inoculation with U. necator. In contrast, a germin-like protein (VvGLP3) was expressed within 16 h of inoculation in resistant, but not in susceptible berries. Our results suggest that several putative barriers to infection, i.e., cuticle and cell wall thickness, antimicrobial phenolics, and two previously described pathogenesis-related proteins, are not principal causes in halting pathogen ingress on ontogenically resistant berries, but rather that infection is halted by one or more of the following: (i) a preformed physical or biochemical barrier near the cuticle surface, or (ii) the rapid synthesis of an antifungal compound in older berries during the first few hours of the infection process.     

Powdery mildew resistance in selections from moroccan barley landraces

Thirty barley landraces collected from Morocco in 1985 and 1989, and held in the Polish Gene Bank, IHAR, Radzików, Poland, were screened for resistance to powdery mildew. Fifteen tested landraces (50%) showed powdery mildew resistance reactions and 24 single plant lines were selected. Eighteen lines originating from 13 landraces were tested with 17 isolates of powdery mildew and another six lines originating from six landraces were tested with 23; the isolates were chosen according to their virulence spectra observed on the ‘Pallas’ isolines differential set. Three lines (E 1090-2-2, E 1110-3-2 and E 1077-1-1) showed resistance to all powdery mildew virulence genes prevalent in Europe. In 21 lines, unknown genes alone or in combination with specific ones were detected. Five different resistance alleles(Mlat, Mlal, Mla3, Mlg andMl(CP)) were postulated to be present in the tested lines, alone or in combination:Mlat was postulated to be present in nine (~38%) lines;Mlg andMl(CP) in two lines, andMla1 andMla3 in one tested line each. The use of newly identified sources of resistance in barley breeding as a means of controlling powdery mildew is discussed.     

小麦的种和品种对白粉病抗性的初步研究

 在对白粉病具不同抗性的11个小麦的种和品种上进行的按种试验表明,在接种后8小时内,分生孢子达到最高萌发率(约为60%),并形成附着孢。在抗病的和感病的小麦叶片上,分生孢子的萌发率和萌发速度没有差异。接种后12小时,在感病的材料上,发现真菌侵入寄主,但在抗病的材料上,发现最早侵入时间,至少要比在感病材料上约晚4小时。接种后36小时,在高感的材料上,萌发的分生孢子有83%已侵入寄主,其中约有70~80%已形成吸胞。在感病、抗病和高抗材料上的侵入率,分别为70,45,27%。形成或开始形成吸胞的分别为55~61,14~27,4~8%。在抗病材料的表皮细胞内,真菌形成的吸胞较小,并有点畸形。在抗病材料的叶面上,真菌的菌丛稀薄,产孢也很少。