Effect of interrupted leaf wetness periods on pustule development of Puccinia recondita f. sp. tritici on wheat

In growth chamber experiments, seedlings of a susceptible wheat cultivar (Rubis) were inoculated with urediospores of wheat leaf rust. Inoculated seedlings were incubated in a moist chamber. The period of exposure to leaf wetness varied in duration and progressed with or without one or more interruptions of variable duration. During the interruptions the leaves with germlings were dry. At near-optimal temperature, leaf wetness periods of six h resulted in 60 to 65% of the pustules produced with 12 or 24 h wetness periods. Interruption of a 6 h leaf wetness period by a 1 h dry period was most damaging to the rust germlings at about three to four h after inoculation. The damage became visible as a reduction in the number of resulting pustules and as a prolongation of the median latency period. Epidemiological implications of leaf wetness interruptions are discussed.     

Effect of interrupted leaf wetness periods on pustule development of Puccinia recondita f. sp. tritici on wheat

In growth chamber experiments, seedlings of a susceptible wheat cultivar (Rubis) were inoculated with urediospores of wheat leaf rust. Inoculated seedlings were incubated in a moist chamber. The period of exposure to leaf wetness varied in duration and progressed with or without one or more interruptions of variable duration. During the interruptions the leaves with germlings were dry. At near-optimal temperature, leaf wetness periods of six h resulted in 60 to 65% of the pustules produced with 12 or 24 h wetness periods. Interruption of a 6 h leaf wetness period by a 1 h dry period was most damaging to the rust germlings at about three to four h after inoculation. The damage became visible as a reduction in the number of resulting pustules and as a prolongation of the median latency period. Epidemiological implications of leaf wetness interruptions are discussed.Kiemplanten van het vatbare tarweras Rubis werden geïnoculeerd met uredosporen van de bruine roest van tarwe. De proeven vonden plaats in klimaatkamers. Geïnoculeerde planten werden geïncubeerd in incubatiehokjes met een zeer hoge luchtvochtigheid, teneinde condensatiedruppels op de bladeren en aldus bladnatperioden te krijgen. De toegediende bladnatperioden varieerden in tijdsduur en zij verliepen met of zonder één of meer onderbrekingen, ook weer van variërende duur. Tijdens de onderbrekingen stonden de planten met roestkiemlingen in het licht; het blad was dan droog. Bij ongeveer optimale temperatuur en bladnatperioden van 6 uur was het aantal verkregen puistjes 60 à 65% van het aantal verkregen puistjes na een bladnatperiode van 12 of 24 uur. Onderbreking van de 6-urige bladnatperiode door een 1-urige droge periode was voor de roestkiemlingen het schadelijkst ongeveer 3 tot 4 uur na inoculatie. De schade kwam tot uitdrukking in het kleinere aantal geproduceerde puistjes en in een verlenging van de mediane latentieperiode. De epidemiologische betekenis van onderbrekingen van de bladnatperiode wordt besproken.     

Quantitative trait loci for high-temperature adult-plant and slow-rusting resistance to Puccinia striiformis f. sp. tritici in wheat cultivars

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most damaging diseases of wheat (Triticum aestivum) globally. High-temperature adult-plant resistance (HTAPR) and slow-rusting have great potential for sustainable management of the disease. The wheat cultivars Luke and Aquileja have been previously reported to possess HTAPR and slow-rusting to stripe rust, respectively. Aquileja displayed less number of stripes per unit leaf area than Luke, while Luke showed lower infection type than Aquileja at adult-plant stages of growth under high-temperature conditions. The objectives of this study were to confirm the resistances and to map the resistance genes in Luke and Aquileja. Luke was crossed with Aquileja, and 326 of the F(2) plants were genotyped using 282 microsatellite primer pairs. These F(2) plants and their derived F(3) families were evaluated for resistance to stripe rust by inoculation in the fields and greenhouses of high- and low-temperatures. Infection type was recorded for both seedlings and adult plants, and stripe number was recorded for adult plants only. Two quantitative trait loci (QTL) were identified, on the short arm of chromosome 2B, to be significantly associated with infection type at adult-plant stages in the fields and in the high-temperature greenhouse. The locus distal to centromere, referred to as QYrlu.cau-2BS1, and the locus proximal to centromere, referred to as QYrlu.cau-2BS2, were separated by a genetic distance of about 23 cM. QYrlu.cau-2BS1 was flanked by the microsatellite markers Xwmc154 and Xgwm148, and QYrlu.cau-2BS2 was flanked by Xgwm148 and Xabrc167. QYrlu.cau-2BS1 and QYrlu.cau-2BS2 explained up to 36.6 and 41.5% of the phenotypic variation of infection type, respectively, and up to 78.1% collectively. No significant interaction between the two loci was detected. Another QTL, referred to as QYraq.cau-2BL, was detected on the long arm of chromosome 2B to be significantly associated with stripe number. QYraq.cau-2BL was flanked by the microsatellite markers Xwmc175 and Xwmc332, and it explained up to 61.5% of the phenotypic variation of stripe number. It is possible that these three QTL are previously unmapped loci for resistance to stripe rust.     

小麦叶锈菌在感病寄主上发育的组织病理学和超微结构研究

 应用荧光显微技术、微分干涉技术和生物电镜技术,系统地研究了小麦叶锈菌在感病寄主上的发育过程及其超微结构特征。小麦叶锈菌在感病品种上的发育过程可分为几个明显的阶段,即孢子的萌发、附着胞的形成、气孔下囊的分化、初生菌丝和次生菌丝的形成和生长、吸器母细胞和吸器的形成、夏孢子床和夏孢子堆的产生以及夏孢子的形成。小麦叶锈菌的胞间菌丝呈丝状,生长和分枝通常沿寄主细胞壁进行。胞间菌丝与寄主细胞的接触诱导了吸器母细胞的分化,吸器母细胞在与寄主细胞壁的接触部位发育形成入侵栓,穿透寄主细胞壁后于细胞内形成吸器。胞间菌丝和吸器母细胞均含有双核,而成熟吸器则含有单核。经常规染色后,胞间菌丝和吸器母细胞的壁与隔膜均可分辨出由多层构成。     

Uredospore production and sporulation period of Puccinia recondita f. sp. triticina on primary leaves of wheat

Uredospore production per day and per sporulation period was measured under near-optimal conditions. Pustule density influenced time and rate of pustule opening, size of pustules, time of maximum sporulation, length of the sporulation period and the time and rate of tissue necrotisation. Within limits total dry weight of spores per leaf per sporulation period was independent of pustule density; it roughly equalled the dry weight of the spore producing leaf. The longest sporulation period observed was 65 days; at low pustule densities secondary pustules replaced exhausted primary pustules. Infectivity of the spores was normal up to 46 days after inoculation. The long sporulation period was epidemiologicaly interpreted as a survival mechanism.     

Dry-dispersal and rain-splash of brown (Puccinia recondita f.sp. tritici) and yellow (P. striiformis) rust spores from infected wheat leaves exposed to simulated raindrops

The dispersal of spores from lesions of brown ( Puccinia recondita f.sp. tritici ) or yellow ( P. striiformis ) rusts of wheat by impacting drops was studied. Using a generator of uniform-size drops, drops of 2.5, 3.4, 4.2 and 4.9 mm in diameter were released from rest at heights of 5, 50 and 100 cm above horizontal and primary leaves uniformly covered with sporulating lesions. Dry-dispersal and rain-splash occurred simultaneously in response to drop impaction. A coloration technique allowed separate counting of dry-dispersed and rain-splashed spores caught on slides. More spores were rain-splashed than dry-dispersed. Neither removal mechanism affected in-vitro germination of spores, which was higher in brown than in yellow rust. For both rusts, the number of both dry-dispersed and rain-splashed spores, as well as their travel distance, increased with drop diameter and fall height. The fall speed of incident drops in relation to diameter and fall height was obtained by solving numerically the equation of vertical drop motion. The number of spores removed by a given impacting drop was found to be a power function of the calculated kinetic energy of the impacting drop. Based on this experimental relationship, a simulation study showed the relevance of rain type in the removal of spores.     

Suppression of Septoria tritici and Puccinia recondita of wheat by an antibiotic-producing fluorescent pseudomonad

A fluorescent Pseudomonas sp. (strain LEC 1) isolated from soil suppressed Septoria tritici by 88% and Puccinia recondita by 98% when applied to wheat seedlings 3 h prior to inoculation with the pathogens. Fractionation and analysis of two inhibitory compounds from cultures of strain LEC 1 on thin-layer chromatography plates yielded the phenazine antibiotics 1-hydroxyphenazine (phOH) and chlorora-phin. 1-hydroxyphenazine reduced the growth of Pythium aphanidermatum, Fusarium oxysporum f.sp. vasinfectum, Sclerotinia sclerotiorum and S. rolfsii on a denned medium, with greatest activity against P. aphanidermatum and least against S. rolfsii. Application of 160 mg/l phOH to wheat seedlings reduced S. tritici by 61% and P. recondita by 75%. Lower concentrations of the antibiotic were less effective. Growth of 5. tritici in liquid medium was reduced by phOH at 5–20 mg/l and prevented at 40 mg/l. When phOH was added to the medium 48 h after inoculation (logarithmic growth phase), growth was interrupted but later recovered with phOH concentrations up to 40 mg/l; there was no recovery at 60 mg/l. Chlororaphin inhibited the growth of S. tritici on malt agar medium.     

Selection of Populations of Puccinia recondita f. sp. tritici for Shortened Latent Period on a Partially Resistant Wheat Cultivar

ABSTRACT Wild-type fungal population 851-WT was selected for shortened latent period on cv. CI 13227 for five uredinial generations to study the adaptation of Puccinia recondita f. sp. tritici to partially resistant wheat cultivars. Differences among wild-type and selected populations for traits contributing to parasitic fitness (i.e., latent period, infection frequency, and uredinium area and growth rate) were assessed in monocyclic infection experiments on susceptible cv. Monon and partially resistant cvs. Suwon 85, Sw 72469-6, L-574-1, and CI 13227. Differences were greatest among fungal populations on cv. CI 13227. The mean latent period of selected population 851-C5 was 2 days shorter (~20%) than that of wild-type population 851-WT. In addition, uredinia of population 851-C5 expanded 40% faster and produced ~75% more urediniospores. On cv. L-574-1, the selected population was also more fit than the wild-type progenitor for initial uredinium area and growth rate and cumulative urediniospore production. In contrast to wild-type and selected populations on cvs. CI 13227 and L-574-1, selected population 851-C5 on cv. Monon produced slower expanding uredinia with fewer urediniospores than did population 851-WT on Monon. These results show that variation in the latent period of P. recondita f. sp. tritici populations is partially under genetic control and wild-type P. recondita f. sp. tritici populations contain members reproductively more fit on partially resistant wheat cultivars but not necessarily on susceptible cultivars. Such members are capable of partially overcoming quantitative host resistance.     

Effect of maleic hydrazide on parasitic fitness of Puccinia striiformis f. sp. tritici in wheat

As a growth inhibitor of the apical meristem in the plant stem, Maleic hydrazide plays an important role in modulation of plant growth. In this research, Puccinia striiformis f. sp. tritici and its host for reproduction was employed to characterize the effect of maleic hydrazide on parasitic fitness of the strain. Growth inhibition of the secondary leaves of wheat by maleic hydrazide was demonstrated. Results showed that root irrigation by maleic hydrazide at the seedling stage significantly increased the parasitic fitness of Puccinia striiformis f. sp. tritici, leading to the increase in sporulation amount, sporulation period, and germination rate of urediniospores. In addition, the ultrastructure of Puccinia striiformis f. sp. tritici urediniospores was not affected by maleic hydrazide treatment. Out data indicate that the optimal concentration and dose for the use of maleic hydrazide is 0.35 g?l^?1 and 1.5 ml/cm², respectively, facilitating the widespread application in wheat stripe rust studies.     

Nitrogen per unit leaf area affects the upper asymptote of Puccinia striiformis f.sp. tritici epidemics in winter wheat

Field trials tested which components of epidemic development of Puccinia striiformis , the cause of yellow rust, were affected by nitrogen (N) fertilizer applied to winter wheat. Both timing and amount of N were varied to affect canopy size and leaf N content, and to provide a supply of mobile N to the pathogen, by causing fresh N uptake after leaf expansion was complete. No N was applied to control plots. A logistic disease-progress function was fitted to disease-severity data, which were assessed in absolute units. Leaf area and specific leaf N (g N per m² leaf tissue) were quantified. Large and highly significant effects of N on the upper asymptotes, or 'carrying capacities' ( c ) were found. Effects on rates and points of inflection of the epidemics were not significant. Early N resulted in larger shoot numbers and leaf area, but disease was also more severe, so that by grain filling, the remaining green leaf areas were larger without N than with N. Later N treatments did not increase canopy size, but did increase symptom area compared with the control. These effects differ from the concept that N affects disease as a result of its effect on canopy growth, and therefore canopy microclimate, and suggest instead a substrate effect. Linear regression revealed that 51% of the observed differences in c were explained by variation in specific leaf N, suggesting that growth of the rust fungus may depend directly on particular components of total leaf N.     

Removal of urediniospores of brown (Puccinia recondita f.sp. tritici) and yellow (P. striiformis) rusts of wheat from infected leaves submitted to a mechanical stress

The passive spore removal from colonies due to mechanical stress was compared in the brown (Puccinia recondita f.sp. tritici) and yellow (P. striiformis) rusts of wheat. Mechanical stress was applied using either a miniaturized wind tunnel or a centrifuge. In wind-tunnel experiments, a wind of minimum velocity of 1.3 and 1.8 m s^-1 for P. recondita f.sp. tritici and P. striiformis, respectively, applied for at least 10 seconds, was necessary to remove spores. The interaction between wind velocity and cumulated duration was significant for both rusts. At low wind velocity, a longer duration was required to remove the spores than at high wind velocity, and vice versa. In centrifugation experiments, the maximum spore removal occurred for angular velocities of 10³ and 2 10³ rotations min^-1, for P. recondita f.sp. tritici and P. striiformis, respectively, applied for 5 min. Calculation of the aerodynamic and centrifugal forces showed that the forces necessary to remove spores are greater for P. striiformis than for P. recondita f.sp. tritici. This difference can be related to the size of the dispersal unit, which is larger in P. striiformis than in P. recondita f.sp. tritici due to spore clustering. These observations are consistent with the differences in the mean spore dispersal distance, which is usually smaller in P. striiformis than in P. recondita f.sp. tritici.     

不同培养载体对小麦条锈菌夏孢子人工萌发的影响

为探索适合小麦条锈菌寄主体外萌发的载体,并建立基于不同研究目的的小麦条锈菌夏孢子人工萌发技术,采用超声波水雾培养法,以小麦条锈菌生理小种CYR32为供试材料,探讨了不同培养载体对小麦条锈菌夏孢子萌发特性的影响.在最适温度和湿度条件下,以4种不同材料为培养载体,小麦条锈菌夏孢子的萌发率、芽管生长率和外观显示情况有显著差异.在尼龙纱网上的夏孢子萌发速度和芽管伸长速度最快,12 h内萌发率最高可达93.40％,芽管最长可达446.71 μm;亲水滤膜上夏孢子的萌发率和芽管长仅次于纱网;亲水塑料膜和PVDF膜上夏孢子的萌发率均高于普通亲水载玻片,而芽管长度低于普通亲水载玻片.采用侧光照明时,在亲水滤膜和PVDF膜上极易清晰观测到夏孢子及其芽管内的黄色颗粒物.在亲水塑料膜上,还可观察到夏孢子萌发12 h后,芽管尾部膨大形成类似附着胞的结构.结果显示,超声波水雾可使条锈菌夏孢子处于水分饱和的环境,而纱网纤维组成的小格具有很好的保水结露功能,能使夏孢子萌发快,萌发效率高,芽管生长快;另一方面,使用其他培养载体还可满足观测条锈菌夏孢子内黄色颗粒物向芽管内转移和芽管尾部形成类似附着胞结构的目的.     

Temperature-sensitive wheat stem rust resistance gene Sr15 is effective against Puccinia graminis f. sp. tritici race TTKSK

The wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), race TTKSK and related races pose a serious threat to world wheat production. Knowing the effectiveness of wheat stem rust resistance (Sr) genes against Pgt race TTKSK is fundamental in mitigating this threat through resistance breeding. Sr15 was previously identified as being ineffective against Pgt race TTKSK. Here, multirace disease phenotyping data, linkage analyses, allelism testing and haplotype analyses are presented to support the conclusion that Sr15 is effective against Pgt race TTKSK. Resistance to race TTKSK was mapped to Sr15 in a biparental population. Thirty-two accessions with Sr15 displayed seedling resistance phenotypes against race TTKSK. However, these accessions were susceptible as seedlings at high temperatures (22–25 °C), consistent with previous reports that the interaction between avirulent Pgt isolates and Sr15 is temperature-sensitive. Markers STS638, wri4 and KASP_IWB30995 were found to predict the presence of Sr15, suggesting the utility of these assays for marker-assisted selection in breeding programmes. The effectiveness of Sr15 to specific Pgt races and temperatures makes it a less-desirable TTKSK-effective gene. Wheat lines assayed as resistant to race TTKSK at the seedling stage may possess Sr15 and breeders should be aware of the limitations of Sr15 for conferring stem rust resistance.     

Effect of density and age of lesions on sporulation capacity and infection efficiency in wheat leaf rust (Puccinia recondita f.sp. tritici )

The effects of lesion ageing and crowding on spore production and infection efficiency of an isolate of wheat leaf rust (caused by Puccinia recondita f.sp. tritici  ) were studied under controlled conditions. Spore production per lesion per day decreased exponentially with increasing lesion density for lesions older than 13 days after inoculation. Spore production of younger lesions was not affected by crowding. A synthetic formula relating the accumulated spore production to lesion age and density was derived, allowing the evaluation of spore production per lesion on a daily basis. Infection efficiency was comparatively much less affected by lesion ageing and crowding than was spore production. The most efficient spores were produced by 'mature' lesions (14 to 21 days old). At high density, there was no compensation for reduced spore production by an increase in infection efficiency, except for 14-day-old lesions. The Daily Multiplication Factor (the product of spore production per lesion and infection efficiency) was higher at low lesion density and may contribute to a rapid increase of populations of sporulating rust lesions in wheat fields. The detrimental effect of lesion crowding, occurring later in the course of the epidemics, may have negligible effects on disease progress.     

Expression of adult plant resistance and its effect on the development of Puccinia striiformis f.sp. tritici in some Australian wheat cultivars

The onset of adult plant resistance (APR) to Puccinia striiformis was examined in seven Australian wheat cultivars under field conditions and in 14 cultivars under controlled environmental conditions. In most cultivars under field conditions the percentage leaf area affected by stripe rust at mid-tillering (GS 22–26; third leaf) was significantly less ( P < 0.05) than on the more susceptible cultivar Teal. The expression of APR was more conspicuous during tillering to node formation; at these growth stages chlorosis and/or necrosis developed in association with rust colonies on the most resistant cultivars. Under controlled conditions, the primary leaves of all cultivars except Olympic and Flinders displayed some resistance when compared with Teal (lower infection types, longer latent periods and/or less percentage leaf area affected). Studies on the spread of stripe rust from infection foci established in selected cultivars in the field indicated that the resistance detected at early growth stages in Suneca in controlled environmental studies also appeared to be effective in the field.     

Relationships and genetics of wheat effects on infection frequency and colony extension of Puccinia striiformis f. sp. tritici

Wheat cvs Aquileja and Xian Nong 4, previously reported to possess quantitative resistance to Puccinia striiformis f. sp. tritici (Pst), were crossed to assess resistance associated with infection frequency and colony extension of Pst. The parents, F ₁, F ₂, F ₃, F ₄, backcrossed to Aquileja, and backcrossed to Xian Nong 4 were sown in the field. Experimental plants were inoculated with a single-spore derived isolate of Pst. Penetration frequency, colony size and disease severity were quantified. Comparison between the parents indicated that Aquileja was better at limiting infection frequency of Pst, whereas Xian Nong 4 was better at restricting colony extension. Penetration frequency and colony size were controlled by different genes. It was estimated that three or four genes, and three genes, controlling penetration frequency and colony size respectively, segregated in the cross Aquileja × Xian Nong 4, and were transmitted with moderately high heritability in additive fashion with no detectable dominant and epistatic effects. The two traits were correlated with disease severity. Colony size and penetration frequency explained, respectively, up to 33 and 8% of the genotypic variation of disease severity. These results will be helpful in understanding quantitative resistance and breeding for enhanced resistance to Pst.     

Genetics of resistance to race TTKSK of Puccinia graminis f. sp. tritici in Triticum monococcum

Race TTKSK (or Ug99) of Puccinia graminis f. sp. tritici possesses virulence to several stem rust resistance genes commonly present in wheat cultivars grown worldwide. New variants detected in the race TTKSK lineage further broadened the virulence spectrum. The identification of sources of genetic resistance to race TTKSK and its relatives is necessary to enable the development and deployment of resistant varieties. Accessions of Triticum monococcum, an A-genome diploid wild and cultivated wheat, have previously been characterized as resistant to stem rust. Three resistance genes were identified and introgressed into hexaploid wheat: Sr21, Sr22, and Sr35. The objective of this study was to determine the genetic control and allelic relationships of resistance to race TTKSK in T. monococcum accessions identified through evaluations at the seedling stage. Generation F(2) progeny of 8 crosses between resistant and susceptible accessions and 13 crosses between resistant accessions of T. monococcum were evaluated with race TTKSK and often with North American races, including races QFCSC, TTTTF, and MCCFC. For a selected population segregating for three genes conferring resistance to race TTKSK, F(2:3) progeny were evaluated with races TTKSK, QFCSC, and TTTTF. In that population, we detected two genes conferring resistance to race TTKSK that are different from Sr21, Sr22, and Sr35. One of the new genes was effective to all races tested. The identification of these genes will facilitate the development of varieties with new resistance to race TTKSK.     

小麦条锈菌冬孢子生物学特性研究进展

由小麦条锈菌引起的小麦条锈病是我国广大麦区的严重病害,研究其冬孢子产生原因与作用对于解析该病菌的生活史及遗传变异机制至关重要.通过对国内外相关研究成果的整理,综述了小麦条锈菌冬孢子的形态特征、生物学特性、寄主范围及其作用与功能等方面的研究进展.     

Attempted somatic hybridization of Puccinia striiformis f. sp. tritici and P. striiformis f. sp. hordei

Attempts were made to produce somatic hybrids between isolates of Puccinia striiformis f. sp. tritici and f. sp. hordei. A mixed infection was produced on a common susceptible barley host, Fong Tien, using white-spored isolates of P. striiformis f. sp. tritici and yellow-spored isolates off. sp. hordei. Selection was made for non-parental spore colour on selective wheat and barley hosts, and variants thus isolated were analysed for virulence markers, and for isozyme and double-stranded RNA (dsRNA) markers, all of which clearly differentiated the parental isolates. Two white-spored (non-parental) isolates were found on the selective barley host which otherwise resembled the parental f. sp. hordei isolate in virulence, isozyme and dsRNA markers. The most likely explanation of the origin of these isolates is mutation to white spore colour in the f. sp. hordei isolate.