A test of taxonomic predictivity: resistance to early blight in wild relatives of cultivated potato

Host plant resistance offers an attractive method of control for early blight (caused by the foliar fungus Alternaria solani), a widespread disease that appears annually in potato crops worldwide. We tested the assumed ability of taxonomy to predict the presence of early blight resistance genes in wild Solanum species for which resistance was observed in related species. We also tested associations to ploidy, crossing group, breeding system, and geography. As in a prior study of Sclerotinia sclerotiorum (white mold) resistance, tremendous variation for resistance to early blight was found to occur within and among species. There was no discernable relationship between the distribution of resistant phenotypes and taxonomic series (based on an intuitive interpretation of morphological data), clade (based on a cladistic analysis of plastid DNA data), ploidy, breeding system, geographic distance, or climate parameters. Species and individual accessions with high proportions of early blight resistant plants were identified, but high levels of inter- and intra-accession variability were observed. Consequently, the designation of species or accessions as resistant or susceptible must take this variation into account. This study calls into question the assumption that taxonomic or geographic data can be used to predict sources of early blight resistance in wild Solanum species.     

Inheritance of resistance in <Emphasis Type="Italic">Solanum nigrum</Emphasis> to <Emphasis Type="Italic">Phytophthora infestans</Emphasis>

Solanum nigrum, black nightshade, is a wild non-tuber bearing hexaploid species with a high level of resistance to Phytophthora infestans (Colon et al. 1993), the causal agent of potato late blight, the most devastating disease in potato production. However, the genetic mode of resistance in S. nigrum is still poorly understood. In the present study, two S. nigrum accessions, 984750019 (N19) and #13, resistant (R) and susceptible (S), respectively, to three different isolates of P. infestans, were sexually crossed. The various kinds of progeny including F1, F2, F3, and backcross populations (BC₁; F1 × S), as well as two populations produced by self-pollinating the R parent and S parent, were each screened for susceptibility to P. infestans isolate MP 324 using detached leaf assays. Fifty seedling plant individuals of the F1 progeny were each resistant to this specific isolate, similarly to the seedling plants resulting from self-pollination of the resistant R parent. Thirty seedling plants obtained from self-pollination of the S parent were susceptible. Among a total of 180 F2 plants, the segregation ratio between resistant and susceptible plants was approximately 3: 1. Among the 66 seedling plants of the BC₁ progeny originating from crossing an F1 plant with the susceptible S parent, there were 26 susceptible and 40 resistant plants to P. infestans. The segregation patterns obtained indicated monogenic dominant inheritance of resistance to P. infestans isolate MP 324 in S. nigrum acc. 984750019. This gene, conferring resistance to P. infestans, may be useful for the transformation of potato cultivars susceptible to late blight.     

Tomato early blight (Alternaria solani): the pathogen, genetics, and breeding for resistance

Alternaria solani causes diseases on foliage (early blight), basal stems of seedlings (collar rot), stems of adult plants (stem lesions), and fruits (fruit rot) of tomato. Early blight is the most destructive of these diseases and hence receives considerable attention in breeding. For over 60 years, breeding for early blight resistance has been practiced, but the development of cultivars with high levels of resistance has been hampered by the lack of sources of strong resistance in the cultivated tomato and by the quantitative expression and polygenic inheritance of the resistance. In some accessions of wild species, high levels of early blight resistance have been found, but breeding lines still have unfavorable horticultural traits from the donor parent. Recently, the first linkage maps with loci controlling early blight resistance have been developed based on interspecific crosses. These maps may facilitate marker-assisted selection. This overview presents the current knowledge about the A. solani–tomato complex with respect to its biology, genetics, and breeding.     

Host Specialization not Detected Among Isolates of the EC-1 Lineage of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> Attacking Wild and Cultivated Potatoes in Peru

To determine whether populations of Phytophthora infestans attacking wild and cultivated potatoes in the highlands of Peru are specialized on their hosts of origin, we characterized isolates using several neutral markers, metalaxyl resistance and for aggressiveness in a detached leaf assay. One hundred and fifty-three isolates were collected from the northern and central highlands of Peru from different potato cultivars (both modern and native cultivars) and from different species of wild, tuber-bearing potatoes. All the isolates analyzed belonged to one of four clonal lineages that had been described previously in Peru: EC-1, US-1, PE-3 and PE-7. The EC-1 lineage (n = 133) was dominant and present in similar frequencies on wild and cultivated potatoes. PE-3 (n = 14) was found primarily on cultivated potatoes, with only one isolate coming from a wild host. US-1 (n = 2) and PE-7 (n = 4) were rare; all but one (PE-7) occurred on wild potatoes. Isolates from the EC-1 lineage from modern cultivars were compared in three separate detached leaf inoculation assays with EC-1 isolates from the wild potato species S. sogarandinum, S. bill-hookerii or S. huancabambense, respectively. No significant interactions between isolate type (from wild or cultivated potato) and host type (wild or cultivated) were measured for any assay. It appears that the pathogen genotypes in the EC-1 lineage indiscriminately attack both wild and cultivated tuber-bearing solanaceous hosts in Peru, and breeders should be able to select for resistance using the common EC-1 lineage.     

AsSod基因调控茄链格孢致病性及对胁迫的响应

由茄链格孢Alternaria solani引起的马铃薯早疫病是马铃薯生产上的重要病害之一,可导致马铃薯大面积减产,进而造成巨大的经济损失.本研究在获得缺失AsSod基因的茄链格孢突变株(ΔsSod)的基础上,对△sSod进行了不同的胁迫处理.结果 表明,相比于野生型菌株和回复株,突变株ΔAsSod对细胞壁胁迫因子SD...     

马铃薯早疫病病原菌鉴定及其对不同药剂的敏感性

 为了明确马铃薯早疫病病原菌及其对不同药剂的敏感性,2009~2011年从河北省5个县采集180个早疫病样,以常规方法进行分离与纯化。根据病原菌的形态特征和致病性,结合其rDNA-ITS区域的序列分析对病原菌进行鉴定,并采用菌丝生长速率法测定病原菌对不同药剂的敏感性。结果分离到两种菌（A、B）,分离比例为4:6。致病性测定证实分离菌A和B均为马铃薯早疫病病原菌。经形态学鉴定,初步认定A为茄链格孢（Alternaria solani）,B为链格孢（Alternaria alternata）。采用通用引物ITS1/ITS4对病原菌A和B的rDNA-ITS序列区扩增并测序,通过与GenBank数据库比对,A与A.solani同源性为98%,B与A.alternata 的同源性达100%。两种病原菌对咯菌腈、吡唑醚菌酯、啶酰菌胺、苯醚甲环唑等药剂的敏感性差异极显著,而对异菌脲的敏感性差异不显著。因此,将河北省马铃薯早疫病菌鉴定为茄链格孢（A.solani)和链格孢（A.alternata）,二者对同一药剂的敏感性不同。     

Phytophthora infestans: a review of past and current studies on potato late blight

Phytophthora infestans is the causal agent of potato late blight. Genotypes of Japanese populations of P. infestans have been classified as US-1, JP-1, JP-2, JP-3, and JP-4 based on analyses of DNA polymorphisms. These populations may have been introduced to Japan by the migration of P. infestans from other countries and by domestic changes produced through sexual and asexual propagation. Resistance to late blight has been an ongoing desire of potato farmers in Japan and elsewhere. Recurrent backcrossing of Solanum demissum to varieties of S. tuberosum has been used to transfer late blight resistance. Many varieties carry the R1 gene, whereas others carry R2, R3, and/or R4. However, R genes provided only transient resistance to late blight. New races rapidly overcome R-gene-mediated resistance. The R genes of potato generally encode receptors that recognize secretory effector (Avr) proteins produced by P. infestans. These effector proteins induce robust resistance in potato varieties containing R genes, while they suppress resistance in potato varieties lacking R genes. Conserved molecules from Phytophthora species such as fatty acids, glucans, and elicitins also act as elicitors in Solanaceae species. These P. infestans-derived elicitors induce defensive reactions, including the accumulation of phytoalexins and hypersensitive cell death. A future challenge will be to combine our accumulated knowledge with that from other scientific fields to develop a disease management approach for late blight.     

Differentiation of the closely related species,Alternaria solani and A. tomatophila,by molecular and morphological features and aggressiveness

The main causal agent of early blight, the noxious disease of solanaceous crops, is generally considered to be Alternaria solani Sorauer (in a broad sense). However, heterogeneity in many morphological features of this pathogen has been noted suggesting that the disease may not be caused by a single species. Recent research has revealed that several large-spored Alternaria species may cause disease of potato and tomato including A. solani sensu stricto and A. tomatophila. The goal of our research was to compare Russian large-spored Alternaria isolates from tomato and potato to test the hypothesis that early blight of tomato and potato are caused by different species. Cluster analysis of genetic distances estimated from 12 polymorphic molecular markers (universally primed-polymerase chain reaction and randomly amplified polymorphic DNA) revealed two groups of isolates accepted here as A. solani and A. tomatophila that were supported by morphology and host plant association. Differentiation of species was supported by phylogeny derived from the DNA sequences of a portion of the Alt a1, gpd and calmodulin genes. Species-specific primers based on the Alt a1 and calmodulin gene sequences for both species were designed. Under laboratory conditions, A. solani isolates were equally aggressive on both tomato and potato, whereas A. tomatophila was highly aggressive to tomato but only weakly aggressive to potato. In the field, A. solani was isolated from potato, tomato and from several wild potato species including S. schickii, S. papita and S. kurtzianum. The majority (90 %) of A. solani isolates carried the mating type locus 1 (MAT1) idiomorph MAT1-1 while the majority (88 %) of A. tomatophila isolates carried the MAT1-2 idiomorph.     

Genetic diversity and host differentiation among isolates of Phytophthora infestans from cultivated potato and wild solanaceous hosts in Peru

To test the hypothesis that isolates of Phytophthora infestans attacking wild Solanaceae exhibit specialization for particular host species, 115 isolates of P. infestans were collected from cultivated potatoes, nontuber-bearing Solanum spp. of the Basarthrum section and wild tomatoes from five departments in the northern and central highlands of Peru, and characterized using several neutral markers. All isolates belonged to one of four clonal lineages described previously in Peru: EC-1, US-1, PE-3 and PE-7. There was a strong association of three lineages with host species: PE-3 was only isolated from cultivated potato, while PE-7 and US-1 were only isolated from nontuber-bearing Solanum spp. ( Basarthrum section and wild tomatoes). EC-1 was isolated from all host groups sampled. A subset ( n  = 74) of the isolates was evaluated for metalaxyl resistance. High levels of resistance were found almost exclusively in EC-1 and PE-3, while US-1 and PE-7 isolates were generally sensitive. In a detached-leaf assay for lesion diameter using five EC-1 isolates from S. caripense and seven EC-1 isolates from cultivated potato, there was a significant interaction between isolate origin and inoculated host, caused by higher aggressiveness of EC-1 from cultivated potato on its host of origin. In a comparison of EC-1 (seven isolates from cultivated potato) and US-1 (three isolates from S. caripense ), each pathogen lineage was more aggressive on its original host species, causing a highly significant interaction between isolate origin and inoculated host. Wild tomatoes and nontuber-bearing Solanum spp. harbour several pathogen lineages in Peru and could serve as reservoirs of inoculum that might contribute to epidemics on potato or tomato. Potential risks associated with the use of wild Solanum hosts as sources of resistance to P. infestans are discussed .     

Identification and characterization of RB-orthologous genes from the late blight resistant wild potato species Solanum verrucosum

Late blight, caused by the oomycete pathogen, Phytophthora infestans, is a devastating disease of potatoes and tomatoes. A key long-term management strategy for combating this disease is to develop potato cultivars with high levels of durable resistance through identification and integration of major resistance genes. The RBgene, cloned from the Mexican diploid potato species Solanum bulbocastanum, confers broad-spectrum resistance to potato late blight. Here, we have determined the late blight resistance phenotypes of eight accessions of Solanum verrucosum, another wild diploid potato species, using greenhouse inoculations and discovered variability among the accessions. While most accessions were resistant, one accession was notably more susceptible. Transcribed orthologs of the RB gene from the eight S. verrucosum accessions were cloned using a homology-based PCR approach. Sequence analysis revealed that the RB^ver orthologs share up to 83.5% nucleotide identity with RB^blb. Stable introduction of the RB ortholog from late blight resistant S. verrucosum PI275260 into susceptible S. tuberosum confers resistance to P. infestans. Interestingly, this functional RB^ver ortholog contains an insertion of a complete leucine rich repeat when compared to RB^blb, and differs from the RB^ver ortholog from a susceptible accession at only four amino acid residues.     

部分马铃薯主栽品种对晚疫病的田间抗性研究

为摸清贵州省低海拔地区主栽马铃薯品种对晚疫病的抗性情况,2012年对贵州省13个主栽马铃薯品种进行晚疫病抗性鉴定试验。结果表明：Z-30、BP05-003（产量在25500kg／hm2以上）对晚疫病表现为中感,为早、中熟品种,适宜在低海拔发病不重的区域推广;滇黔芋2号、米拉（产量在13500kg／hm2以上）对晚疫病表现为感病,如在晚疫病常发区、重发区种植,生产上应加大防治力度;BPHFl01、20-4．5、威薯002为中感及感病品种,产量一般,为晚熟品种,适宜在高海拔地区种植,需要加强晚疫病防治并配套高产栽培技术。     

吡唑醚菌酯与苯醚甲环唑混合物对茄链格孢的联合毒力及其对马铃薯产量的影响

为明确吡唑醚菌酯与苯醚甲环唑混合物对茄链格孢Alternaria solani毒力的增效作用,采用菌丝生长速率法和孢子萌发法测定了吡唑醚菌酯、苯醚甲环唑及其不同比例混合物对茄链格孢的毒力,以Wadley公式评价其联合毒力,并通过田间试验评价了混合物对马铃薯早疫病的防治效果及其对马铃薯产量的影响。结果表明:吡唑醚菌酯与苯醚甲环唑质量比为1∶1、2∶1、3∶1、4∶1、5∶1、1∶2和1∶5的混合物对抑制菌丝生长表现为增效,其中配比1∶2的增效最明显,增效系数(SR)为2.05,但该配比混合物对抑制分生孢子萌发仅表现为相加作用(SR 1.29)。在田间药效试验中,配比为1∶2的混合物对马铃薯早疫病的防效显著高于相同剂量的单剂及其他常用药剂的防效,增产率达46.8%,亦显著高于对照药剂。     

Resistance to Root-knot Nematodes (Meloidogyne spp.) in Vegetable Crops

Abstract

The development of root-knot nematode resistant vegetable varieties has provided an alternative control method to chemical and crop rotation. The term resistance is discussed. Work on 18 vegetables is reviewed.

Thirty tomato strains resistant to one or more Meloidogyne sp. are listed, there was a marked absence of reports on varieties resistant to M. hapla. Several workers have observed resistance in some cultivated and wild Solanum spp. The resistance could be increased by further sib and backcrossing experiments. Eggplant varieties tested for resistance to Meloidogyne spp. showed varying degrees of resistance in about 14 varieties. Further backcrossing studies between Solanum melongena and S. sysimbrifolium could provide useful results. Tests on resistance to nematodes in pepper have revealed many resistant varieties. All the pepper varieties tested were susceptible to M. hapla. The nature of resistance in sweet potato has been studied. Some varieties of Cucumis spp. have been found to be resistant to Meloidogyne spp. Since no resistance was found in C. melo, these wild species could be used in the development of a commercial muskmelon variety. Tests with 83 watermelon varieties indicated that all varieties were resistant to M. hapla. It was difficult to find resistance to Meloidogyne spp. in Cucurbita, but tests on wild species have yet to be carried out. Work on lima bean, snap bean, pea, soyabean, cowpea and broadbean has produced a limited number of resistant vegetable varieties, which are described. Since resistance patterns in plants may change under different environmental or biological conditions, it is essential to test varieties under these conditions for a long period before they are released for commercial cultivation. The advantages of using resistant vegetable varieties, as compared with other methods of pest control, are outlined.     

Adaptation of Phytophthora infestans to Partial Resistance in Potato: Evidence from French and Moroccan Populations

ABSTRACT The use of partially resistant cultivars should become an essential component of a sustainable management strategy of potato late blight, caused by Phytophthora infestans. It is therefore important to determine to what extent P. infestans populations can be selected for increased aggressiveness by potato cultivars with different levels of partial resistance. To this end, we sampled P. infestans populations from France and Morocco, chosen as locations where late blight occurs regularly but which differ in the distribution of potato cultivars. Cross-inoculation experiments were used to determine the aggressiveness of all populations to potato cvs. Bintje (prevalent in France but not grown in Morocco) and Désirée (popular in Morocco but cultivated to a very small extent in France). French populations were more aggressive on cv. Bintje than on cv. Désirée, irrespective of the site they were sampled from. Their aggressiveness increased between early and late samplings, suggesting that both cultivars selected for increased aggressiveness during epidemics. By contrast, Moroccan populations were more aggressive on Désirée, regarded as partially resistant in Europe, than on Bintje, highly susceptible under European conditions. These data indicate that P. infestans populations adapt to locally dominant cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, partial resistance. This adaptive pattern may render partial resistance nondurable if not properly managed.     

乙烯信号参与调控水稻纹枯病抗性的研究

 乙烯(ET)信号在植物抵抗各种逆境反应中具有重要作用,但目前关于乙烯信号在调控水稻纹枯病抗性中的作用仍缺乏系统研究。本研究以感纹枯病水稻品种Lemont和抗纹枯病水稻品种YSBR1为材料,分析了纹枯病菌接种后乙烯合成关键基因及信号传导途径中标志基因的表达水平,结果显示,纹枯病菌侵染可显著诱导相关基因的表达、激活乙烯信号。进一步采用乙烯合成抑制剂和信号激活剂处理水稻并进行接种鉴定,结果显示,两种化学剂分别可抑制或激活乙烯信号;无论是Lemont还是YSBR1,激活其乙烯信号均可显著增强抗病性,而抑制该信号均显著降低抗病性。对3个乙烯受体突变体(ethylene response2, etr2; ethylene response3, etr3; ethylene response sensor2, ers2)进行温室接种鉴定,发现突变体的病斑长度均极显著高于野生型对照。以上研究表明乙烯信号在水稻对纹枯病菌的防卫反应或基础抗性中具有十分重要的作用,结果将为进一步解析“水稻-纹枯病菌”间的互作机制、制定合适的病害综合防控策略提供理论基础。     

Insights on gene expression response of a characterized resistant genotype of Solanum commersonii Dun. against Ralstonia solanacearum

Solanum commersonii is a wild species related to the cultivated potato. Some S. commersonii genotypes have been proven to be resistant to the pathogenic bacteria Ralstonia solanacearum, which causes damage in potato and other economically important crops. Here an expression analysis of the response of a resistant S. commersonii genotype against R. solanacearum was performed using microarrays. The aims of this work were to elucidate the molecular processes involved in the interaction, establish the timing of the response, and contribute to identify genes related to the resistance. The response to the treatment was already initiated at 6 h post-inoculation (hpi) and was established at 24 hpi; during this period, a high number of genes was differentially expressed and several candidate genes for the resistance of S. commersonii to R. solanacearum were identified. At an early stage, the photosynthetic process was highly repressed and several genes encoding proteins related to reactive oxygen species (ROS) production were differentially expressed. The induction of ERF and ACC-oxidase genes related to the ethylene pathway and PR1 related to the salicylic acid pathway suggested the induction of both pathways, and back up the previously reported hemibiotrophic nature of the pathogen. Five genes related to plant defence and observed to be differentially expressed at the first two time points were validated by real time PCR. This work gives a glimpse to the molecular processes involved in S. commersonii resistance and identifies the species as a valuable genetic source for potato breeding against bacterial wilt.     

Sensitivity to a Phytotoxin from Rhizoctonia solani Correlates with Sheath Blight Susceptibility in Rice

ABSTRACT Sheath blight is one of the most important and intractable diseases of rice (Oryza sativa) where limited control has been achieved using traditional approaches. Quantitative inheritance, extraneous traits, and environmental factors confound genetic analysis of host resistance. A method was developed to isolate and utilize a phytotoxin from Rhizoctonia solani to investigate the genetics of sheath blight susceptibility. Infiltration of the toxin preparation into plant leaves induced necrosis in rice, maize, and tomato. Using 17 rice cultivars known to vary in sheath blight resistance, genotypes were identified that were sensitive (tox-S) and insensitive (tox-I) to the toxin, and a correlation (r = 0.66) between toxin sensitivity and disease susceptibility was observed. Given the broad host range of R. solani, genotypes of host species may be both tox-S and tox-I. A total of 154 F(2) progeny from a cross between Cypress (tox-S) and Jasmine 85 (tox-I) segregated in a 9:7 ratio for tox-S/tox-I, indicating an epistatic interaction between two genes controls sensitivity to the toxin in rice. This work provides the means to genetically map toxin sensitivity genes and eliminate susceptible genotypes when developing sheath blight-resistant rice cultivars.     

山东省玉米纹枯病菌对噻呋酰胺的敏感性及其抗性突变体的生物学性状

为明确山东省玉米纹枯病菌对噻呋酰胺的敏感性及其抗药性风险,采用菌丝生长速率法分别测定了采自山东泰安、临沂、潍坊、莱芜、日照及青岛6个地区的102株玉米纹枯病菌对噻呋酰胺的敏感性。结果表明:其EC₅₀值分布范围为0.010～0.194 μg/mL,平均EC₅₀ 值为 (0.086 ± 0.004) μg/mL,且敏感性呈连续单峰曲线分布。通过紫外诱导与药剂驯化的方法各获得5株耐药性菌株 (TA3-X2、TA17-X6、LY8-3、QD14-Y7和WF6-A2) 和1株抗性突变体 (QD2-Y4),其抗性水平在6.46～20.08倍之间,突变频率分别为0.87%和0.52%。对抗性突变体生物学性状的研究表明,紫外诱导获得的5株耐药性菌株其耐药性不能稳定遗传,而经药剂驯化获得的1株抗性突变体QD2-Y4的抗药性可稳定遗传;耐药性菌株TA3-X2的菌丝生长速率高于亲本菌株,其余菌株与亲本菌株差异不明显;5株耐药性菌株和1株抗性突变体的菌丝干重和菌核干重均低于亲本菌株;TA3-X2、WF6-A2及QD2-Y4的致病力低于亲本菌株,TA17-X6、LY8-3及QD14-Y7的致病力与亲本菌株无明显差异。交互抗性测定表明,噻呋酰胺抗性突变体与戊唑醇、丙环唑、咯菌腈、井冈霉素、苯醚甲环唑和多菌灵之间均无交互抗性,与啶酰菌胺和氟唑菌苯胺之间则存在交互抗性。研究表明,山东省6个地区的玉米纹枯病菌对噻呋酰胺比较敏感,推测噻呋酰胺可作为防治玉米纹枯病的理想候选药剂。     

Population structure and host range of the potato late blight pathogen Phytophthora infestans in Peru spanning two decades

The genetic diversity of the late blight pathogen Phytophthora infestans infecting cultivated potato and alternative hosts growing in the vicinity of fields in the main potato-growing areas of the Peruvian Andes was characterized using collections from 1997–2013 as reference. The Peruvian P. infestans population, including previously collected and current isolates, consists of four clonal lineages (EC-1, US-1, PE-3 and PE-7) that belong to the A1 mating type and have been present in the country for decades. The first report of US-1 was in isolates collected between 1982 and 1986; meanwhile, EC-1 and PE-3 appeared for the first time in isolates from 1992 and PE-7 was found in 1997. The pathogen has a very broad host range among the solanaceous plants infecting cultivated potato, tomato, pear melon and several wild species. The solanaceous species growing in the vicinity of the potato fields sampled were identified and surveyed for late blight-like symptoms. Phytophthora infestans was isolated from nine wild species, including three new host species: Solanum zahlbruckneri, Solanum grandidentatum and Iochroma grandiflorum. There was no clear host specialization, but geographical substructuring was found as well as changes in the pathogen populations at the regional level. The clonal lineage EC-1, which is mostly resistant to metalaxyl, has complex virulence and contains a high level of subclonal variation, continues to dominate the population. Some multilocus genotypes of the EC-1 lineage were sampled in high frequencies and were found among the previously collected and new samples.