用SSR标记研究柑橘属及其近缘属植物的亲缘关系

用SSR标记分析了29份柑橘属及近缘属植物的亲缘关系。7对SSR引物在29个样品中扩增得到114个等位基因,平均每个位点有16.3个等位基因。计算匹配系数后用邻接法进行聚类,结果表明,澳洲指橘与柑橘属的亲缘关系很近;SSR位点的高纯合频率支持富民枳种的地位;枳与柑橘属的关系较远,枳不大可能是从柑橘属衍生而来;Swingle的亚属的划分以及田中的原生柑橘类和后生柑橘类的划分界线不清晰;现代栽培柑橘的起源与大翼橙关系密切;柑橘属的枸橼、柚和宽皮橘都很好地分离,支持其为现代栽培柑橘的3个基本种的观点。     

Studies on Taxonomy and Evolution of Citrus and Its Related Genera by Isozyme Analysis

The leaf or bark tissue extracts of 108 biotypes of Citrus and its five related genera were analyzed by polyacrylamide gel electrophoresis for isozymes of peroxidase, glutamate oxaloacetate transaminase, phosphoglucose isomerase, phosphoglucose mutase, superoxide dismutase, tetrazolium oxidase, NADP+- dependent malate dehydrogenase and esterase. The inter-or intra-generic differences of isozymograms were compared. Dissimilarities of the isozyme patterns among the samples were calculated by computer based on the UPGMA method to demonstrate the phylogenetic relationship of the biotypes. There are remarkable isozymogramatic differences among the six genera. Generally speaking, each genus possesses its own unique bands. Based on the cluster analysis, the total Citrus biotypes are classified into seven groups, i.e. Honghe papeda, Mauritius papeda, Pummelo, Ichang papeda, Citron, Lemon-lime and Mandarin-orange. Ichang papeda is suggested to be the third subgenus of the genus Citrus. The Fuming trifoliata orange is accepted as a new species of Poncirus-P. polyandra S. Q. Ding. It might be the evolutionary bridge between Poncirus and Citrus, and one of the “missing links” as suggested by W. T. Swingle. Microacrumen (small- fruited mandarin) is the primitive form of the mandarins. It seems better to consid er“ Horse-nose mandarin ”or “Xipigoushigan mandarin” as the typic mandarin originated in China. Euacrumen (large-fruited mandarin) might have arised through two ways. One is hybridization of Microacrumen and C. sinensis, and the other is just the variation of Microacrumen. Ancestors of some biotypes are inferred based on isozyme data. Fortunella obovata Tan. may be a hybrid of Fortunella and Citrus. C. unshiu Marc. arose from the nucellar mutation of“Huangyanbendiguangju mandarin”( C. nobilis Lour.) in Huangyan of Zhejiang Province. C. junos Sieb. came from hybridization of Ichang papeda and mandarin. C. grandis Osbeck and mandarin may have been involved in the origin of C. aurantium L.. C. limonia Osbeck may be a hybrid between C. medica L. and mandarin. The evolutionary trend of citrus fruit trees is proposed, anda tentative phylogenetic diagram is drawn.     

A Study on Glutamate Oxaloacetate Transaminase Isozymes of Citrus Germplasm Resources

The glutamate oxaloacetate transaminase isozymes (GOT) extracted from 125 biotypes of Citrus and its relatives, Fortunella, Poncirus and Microcitrus were analyzed using polyacrylamide gel electrophoresis to investigate the taxonomic relationships among citrus plants. Besides all the isozymes reported before, two new bands were detected and designated their putative alleles B and C in GOT-l. Among pummelo cultivars wide variations were found. Most of the mandarins were identical, having SS for GOI-1 and MM for GOT-2 except for Zou-Pi-Gan and Yao-Gan, which both had FS at GOT-1 and might be hybrids. This finding suggests that all of the mandarins may have originated from a common ancestor. Sour orange biotypes showed a considerable variation in GOT isozymes. Most of the sour oranges in China were assumed to be hybrids between pummelo and mandarin based on GOT isozyme patterns, but two biotypes, Xiao-Hong-Cheng and Zhu-lan, had FS at GOT-1 and MB at GOT-2, which strongly suggests that they be hybrids of pummelo and Ichang papeda because B allele of GOT-2 occurs only in Ichang papeda and its close relatives Yuzu and Ichang lemon. From this study Yuzu is assumed to be derived from hybridizationof Ichan, papeda and mandarin.     

A Numerical Taxonomic Study of Citrus and Its Close Relatives

Fifty nine taxa of Citrus, Fortunella and Poncirus were studied by hierarchical agglomerative clustering analysis and quantas type 3 analysis using 86 morphological characters. Five affinity groups were obtained in Citrus. The first group includes C. medica, C. limon, C. limonia, C. aurantifolia and C. iambhiri; the second includes C. grandis, C. aurantium, C. sinensis and C. paradisi; the third is mandarin (C. reticulata); the forth is C. ichangensis; The last is C. hongheensis. Mandarin oranges show two subgroups: one comprise satsuma, King, Shagan, Tankan and Bendiguangju, and the other consists of the remaining typical mandrins. The two papeda oranges, honghe papeda and ichang papeda, could not be clustered into the same group, indicating that they might have evolved from two compeletly different ancestors. Pumelos(C. grandis) show some relationships to honghe papeda orange. C. limonia is assumed to be a hybrid between rough lemon and mandarin. The sweet orange(C. sinensis) is considered to be the offspring of pomelo and mandarin. Zhekiang jinju a small mandarin generally considered similar to calamondin in China, should be a true mandarin orange based on our results. Poncirus was well distinguished from the other two genera, Citrus and Fortunella, by the numerical methods used in this study. Our results show that citron (C. medica), mandarin (C. reticulata) and pumelo (C. grandis) are the original species of the subgenus Citrus, which was congruent with the re-sults obtained by Barrett and Soost (1976), Potvin (1983) and Handa (1985).     

Systematic Evolutional Relation of Chemical Components of the Essential Oils from 11 Taxa of Citrus Leaves

With fused silica capillary column for GC, according to Kovats retention index ITP of GC and GC-MS-DS double identification, chemical components of the essential oils from 11 taxa in Citrus leaves were studied. It has been found that the characteristic component of Papeda seedon is citronellal; that of ilurantiurn section is “myrcene and linalool” or “sabinene and liaalool”; that of Microacrumen subsection is linalool; that of Macroacrumen subsection is Z-, E-liaalooloxide and that the characteristic components of Citrophorum section are neral and geranial and those of Cephalocitrus section are neral, geranial and carvone. Our study indicates that there are different GC configurations for various taxonomic units. The differences narrow from sections to species and from species to cultivars. The differences are greatest among sections and remarkable among different species of the same section. Different culativars of the same species of the same section have similar Gig patterns. All these differences or similarities reflect their close or distant relationships, which are the important bases for setting up natural classification. The systematic evolution of the sections of genus Citrus may correlate well with the characteristic components, the biosynthesis pathways and the morphological characters.     

3',5'-Di-C-beta-glucopyranosylphloretin, a flavonoid characteristic of the genus Fortunella

Dihydrochalcone derivative, 3',5'-di-C-beta-glucopyranosylphloretin (1), is present in the genus Fortunella, (F. crassifolia, F. japonica, F. margarita, F. polyandra and F. hindsii). These species accumulate a large quantity of 1 in their fruits (peel, 6.5-15.2 mg/g in dry wt; juice sac, 1.5-10.5 mg/g) and in their leaves (21.3-60.2 mg/g). Twenty-seven Tanaka's Citrus species examined lack 1, but C. madurensis and C. halimii contain 1 in large quantities in their peels (25.1 and 33.6 mg/g) and juice sacs (4.1 and 4.2 mg/g). Poncirus species do not contain 1. Fortunella-citrus hybrids, the Orangequat [C. unshiuxF. crassifolia], the Thomasville citrangequat [Fortunella sp.x(C. sinensisxPoncirus trifoliata)], and seven hybrid progenies [F. margaritaxC. junos], contain large amounts of 1 in their peels (17.0-7.9 mg/g) and juice sacs (2.0-9.9 mg/g). These facts suggest that accumulation of 1 is a generic trait of the genus Fortunella and that the inheritance of the trait among the intergeneric hybrids is controlled by a dominant allele. Thus C. madurensis and C. halimii are thought to originate from natural hybrids between the genera Citrus and Fortunella. Phloridzin, which has the same aglycon as 1, was not detected in the citrus plants examined.     

Flavonoid composition of fruit tissues of citrus species

An HPLC analysis was performed on the concentrations of flavonoids in 42 species and cultivars of the Citrus genus and those of two Fortunella and one Poncirus species according to the classification system established by Tanaka. The composition of 8 flavanones and 9 flavone/ols for these species was determined in the albedo, flavedo, segment epidermis and juice vesicle tissues, and those in the fruit and peel tissues were calculated from the composition data of the tissues. A principal component analysis showed that such neohesperidosyl flavonoids as neoeriocitrin, naringin, neohesperidin, and rhoifolin had large factor loading values in the first principal component for each tissue. The flavonoid composition of citrus fruits was approximately the same within each section of Tanaka's system, except for the species in the Aurantium section and those with a peculiar flavonoid composition such as Bergamot (C. bergamia), Marsh grapefruit (C. paradisi), Sour orange (C. aurantium), and Shunkokan (C. shunkokan). The Aurantium section included both naringin-rich and hesperidin-rich species.     

Taxonomic and phylogenetic relationships among the genera of the True Citrus Fruit Trees Group (Aurantioideae,Rutaceae) based on AFLP markers

Fifty-nine genotypes representing six genera of the True Citrus Fruit Trees Group (Aurantioideae, Rutaceae) were analyzed using AFLP technique to study their taxonomic and phylogenetic relationships. Fifteen primer combinations (out of 64 screened) were selected based on the polymorphism and quality of the bands produced by the primer and used in the present study. A total of 312 bands were obtained, of which 305 (97.8%) were polymorphic. The UPGMA tree of all genotypes was constructed based on the AFLP data using PAUP* beta version 4.0b8 software. Our AFLP molecular tree clearly confirms that the True Citrus Fruit Trees Group is monophyletic and supports the division of the group into genera mainly based on morphological characters, except that the genus Fortunella was nested within the genus Citrus cluster (as a monophyletic sub-branch). The subdivision of the genus Citrus into subgen. Papeda and subgen. Eucitrus as suggested by W. T. Swingle based on morphological characters and the point of view that C. medica, C. grandis and C. reticulata are the three basic species of the subgen. Eucitrus were also supported by our molecular data. In addition, contrary to the expectation based on morphological data, however, our molecular data demonstrated that C. ichangensis is more closely related to C. junos of the subgen. Eucitrus than to the C. hystrix of the subgen. Papeda. Furthermore, our study provided the first evidence that C. mangshanensis is basal to all the loose-skin citrus types. Finally, the taxonomic and phylogenetic relationships among the six genera and the important genotypes of the genus Citrus were dis-cussed in detail.     

部分柑桔属及其近缘属Giemsa C-带带型研究

本文应用Giemsa显带技术研究了枳属(Poncirus)、金柑属(Fortunella)和柑桔属(Citrus)16个分类群的染色体。枳属以末端带和着丝点带为主,金柑属与柑桔属主要以末端带为主;统计分析了各分类群每对染色体及全组染色体的异染色质含量,并列出其带型公式;探讨了金柑属的分类学地位;赞同把柚(C.grandis)作为柑桔属的基本种之一;根据异染色质含量的变化对柑桔属的带型演化进行了讨论。     

Citrus phylogeny and genetic origin of important species as investigated by molecular markers

Citrus phylogeny was investigated using RAPD, SCAR and cpDNA markers. The genotypes analyzed included 36 accessions belonging to Citrus together with 1 accession from each of the related genera Poncirus, Fortunella, Microcitrus and Eremocitrus. Phylogenetic analysis with 262 RAPDs and 14 SCARs indicated that Fortunella is phylogenetically close to Citrus while the other three related genera are distant from Citrus and from each other. Within Citrus, the separation into two subgenera, Citrus and Papeda, designated by Swingle, was clearly observed except for C. celebica and C. indica. Almost all the accessions belonging to subgenus Citrus fell into three clusters, each including 1 genotype that was considered to be a true species. Different phylogenetic relationships were revealed with cpDNA data. Citrus genotypes were separated into subgenera Archicitrus and Metacitrus, as proposed by Tanaka, while the division of subgenera Citrus and Papeda disappeared. C. medica and C. indica were quite distant from other citrus as well from related genera. C. ichangensis appeared to be the ancestor of the mandarin cluster, including C. tachibana. Lemon and Palestine sweet lime were clustered into the Pummelo cluster led by C. latipes. C. aurantifolia was located in the Micrantha cluster. Furthermore, genetic origin was studied on 17 cultivated citrus genotypes by the same molecular markers, and a hybrid origin was hypothesized for all the tested genotypes. The assumptions are discussed with respect to previous studies; similar results were obtained for the origin of orange and grapefruit. Hybrids of citron and sour orange were assumed for lemon, Palestine sweet lime, bergamot and Volkamer lemon, while a citron × mandarin hybrid was assumed for Rangpur lime and Rough lemon. For Mexican lime our molecular data indicated C. micrantha to be the female parent and C. medica as the male one. Received: 5 October 1999 / Accepted: 3 November 1999     

Identification of QTLs associated with citrus resistance toPhytophthora gummosis

Citrus gummosis, caused by Phytophthora spp., is an important citrus disease in Brazil. Almost all citrus rootstock varieties are susceptible to it to some degree, whereas resistance is present in Poncirus trifoliata, a closely related species. The objective of this study was to detect QTLs linked to citrus Phytophthora gummosis resistance. Eighty individuals of the F1 progeny, obtained by controlled crosses between Sunki mandarin Citrus sunki (susceptible) and Poncirus trifoliata cv. Rubidoux (resistant), were evaluated. Resistance to Phytophthora parasitica was evaluated by inoculating stems of young plants with a disc of fungal mycelia and measuring lesion lengths a month later. Two QTLs linked to gummosis resistance were detected in linkage groups 1 and 5 of the P. trifoliata map, and one QTL in linkage group 2 of the C. sunki map. The phenotypic variation explained by individual QTLs was 14% for C. sunki and ranged from 16 to 24% for P. trifoliata. The low character heritability (h2 = 18.7%) and the detection of more than one QTL associated with citrus Phytophthora gummosis resistance showed that inheritance of the resistance is quantitative.     

真正柑桔果树群植物的分支学研究

本文用相容性分析方法(Compatability snalysis)分析了真正柑桔果树群(芸香科Rutaceae-柑桔亚科Aurantioideae-柑桔族(Citreae)-柑桔亚族(Citrinae)植物内各属间的分支学关系。给出了建立在7个相容性性状组成的最大族所决定的分支图。性状极性的确定使用了外群法。结果表明,柑桔属(Citrus L.)和多蕊桔属(Clymenia Swing)构成一个单系类群,他们的姐妹群是金柑属(Fortunella Swing.)。被认为起源于中国的3个属,柑桔属(Citrus)、金柑属(Fortunella)和积属(Poncirus Raf.)并未构成一个单系类群。本文还利用分支关系分析和讨论了真正柑桔果树群的种系发生关系。     

A Classification of Tylenchulus semipenetrans Biotypes

The presence of two biotypes of the citrus nematode (Tylenchulus semipenetrans) in Italian citrus and olive orchards has been confirmed by comparing host specificity. Host reaction to California biotypes C1 and C3 and to three populations from Arizona, Texas, and Florida indicates that of these five United States biotypes, all except C3 consistently fit biotype C1. These findings, and the results of host-range studies in other countries, show that four biotypes of T. semipenetrans are distributed worldwide: the "Poncirus biotype," the "Citrus biotype," the "Mediterranean biotype," and the "Grass biotype."     

Growth and root hydraulic conductivity of several citrus rootstocks under salt and polyethylene glycol stresses

The water relations responses to salt of several important citrus rootstocks such as Swingle citrumelo, sour orange, and Milam lemon have not been studied in detail before. Studies were set up to compare growth and root hydraulic properties of these rootstocks to other citrus rootstocks by exposing them to NaCl and polyethylene glycol (PEG) stresses. Seedlings of 7 citrus rootstocks were irrigated for 5 months with nutrient solutions containing NaCl or PEG that had been adjusted to osmotic potentials of -0.10, -0.20 or -0.35 MPa. The 7 rootstocks studied were sour orange (Citrus aurantium), Cleopatra mandarin (Citrus reticulata Blanco), Swingle citrumelo (C. paradisi x P. trifoliata), Carrizo citrange (C. sinensis x P. trifoliata), rough lemon (Citrus jambhiri Lush), Milam lemon (C. jambhiri hybrid), and trifoliate orange (Poncirus trifoliata [L.] Raf.). In both shoot and root growth, Cleopatra mandarin and sour orange were the least sensitive to salt, Milam and trifoliate orange were the most sensitive, and rough lemon, Swingle, and Carrizo were intermediate in sensitivity. Even though the roots were exposed to solutions of equal osmotic potentials, plant growth and root conductivity were reduced more by the PEG treatments than the corresponding NaCl treatments. At -0.10 and -0.20 MPa, shoot and root dry weights were reduced 16 to 55% by NaCl and 24 to 68% by PEG. Shoot root ratio was lowered at the higher concentrations, particularly by PEG. There was a major decrease in root conductivity caused by NaCl at -0.10 MPa (19 to 30% in sour orange and Cleopatra mandarin and 78 to 85% in trifoliate orange and Milam). Conductivity decreased more at -0.20 and -0.35 MPa, but not proportionally as much as at -0.10 MPa. Root weight per unit length increased at the higher salt levels, particularly in trifoliate orange. Water flow rate through root systems followed the same trend as root conductivity; salt affected sour orange and Cleopatra mandarin the least and trifoliate orange and Milam the most. However, reductions in fibrous root length by salt treatment differed. Root lengths of Swingle and Carrizo were least affected by salt while sour orange. Milam, and rough lemon were the most affected. Hence, even though sour orange and Cleopatra mandarin were more tolerant than the other rootstocks in terms of water flow rate or root conductivity, these 2 rootstocks showed a proportionally greater decrease in root length than Carrizo, Swingle, or trifoliate orange.     

Tetraploid citrus rootstocks are more tolerant to salt stress than diploid

Citrus trees are subject to several abiotic constraints such as salinity. Providing new rootstocks more tolerant is thus a requirement. In this article, we investigated salt stress tolerance of three tetraploid rootstock genotypes when compared to their respective diploid rootstocks (Poncirus trifoliata, Carrizo citrange, Cleopatra mandarin). Plant growth, leaf fall and ion contents were investigated. At the end of the experiment, leaf fall was observed only for diploid Poncirus trifoliata plants as well as chlorosis symptoms for Poncirus trifoliata and Carrizo citrange diploid plants. The diploid Cleopatra mandarin plants growth rate was not affected by salt stress and has even been increased for tetraploid Cleopatra mandarin. Ion contents investigation has shown lower accumulations of chloride ions in leaves of the tetraploid plants when compared to diploid plants. Our results suggest that citrus tetraploid rootstocks are more tolerant to salt stress than their corresponding diploid. To cite this article: B. Saleh et al., C. R. Biologies 331 (2008).     

Improved Transformation Efficiency in Citrus by Plasmolysis Treatment

Procedures for high efficiency production of transgenic citrus plants using an Agrobacterium tumefaciens system with plasmolysis treatment were developed. Longitudinally cut epicotyl segments of eight different citrus species [’Milam’ Rough lemon (Citrus jambhiri Lush), ‘Volkamer’ lemon (Citrus volkameriana L), Rangpur lime (Citrus limonia L), ‘Hamlin’ sweet orange (Citrus sinensis L Osbeck), ‘Duncan’ grapefruit (’Citrus paradisi’ Macf), Sour orange (Citrus aurantium L), ‘Cleopatra’ mandarin (Citrus reticulata Blanco) and Carrizo citrange (Citrus sinensis L Osbeck x Poncirus trifoliata L Raf) ] were plasmolyzed in different concentrations of sucrose and maltose [0, 3, 6, 8, 9, 10, 12 % (w/v) ] prior to Agrobacterium inoculation. Plasmolyzed epicotyl explants were cocultivated with either the hypervirulent Agrobacterium tumefaciens strain, the EHA-101 (harboring a binary vector pGA482GG) or Agl-1 (carrying pCAMBIA1303 vector). Both binary vectors contained neomycin phosphotransferase II (NPT II) and β-glucuronidase (GUS) genes. The binary vector, pCAMBIA1303 also contained a fused mGFP5 gene at the 3’ end of GUS gene as a reporter. Epicotyl explants of Rangpur lime, Rough and ‘Volkamer’ lemons plasmolyzed in 9–12 % maltose showed transient GUS gene expression comprising up to 95 % of the cut surface of explants, while Carrizo citrange showed 80 % expression when they were plasmolyzed in 6–10 % sucrose. On the other hand, epicotyl explants of ‘Hamlin’ sweet orange, Grapefruit, Sour orange and ‘Cleopatra’ mandarin showed transient GUS expession in 80–90 % of explants with 6–10 % sucrose. Basal portions of the regenerated putative transgenic shoots harvested from the cut surface of epicotyl explants within 2–3 months, were assayed for GUS, and apical portions were shoot-tip grafted in vivo for the production of whole plants. The transformation efficiencies in different species obtained are the highest so far reported for citrus.     

Genetic diversity in the orange subfamily Aurantioideae. II. Genetic relationships among genera and species

Genetic relationships were studied by means of ten isoenzymatic systems, at the genus and species level, using two distances and four methods of aggregation in a germplasm collection of 198 cultivars and accessions of 54 species belonging to Citrus and 13 related genera. The most consistent results were obtained by the chord distance and the neighbor-joining clustering method. Citrus species were distributed in two main groups: the orange-mandarin group and the lime lemon-citron-pummelo group. The species C. halimii and C. tachibana are not included in these groups. Mandarin species fall into three main subgroups: one includes C. sinensis; the second, C. aurantium, the third, small-fruit species. The citron, the pummelo and the ancient lemon subgroups form a cluster to which the species belonging to subgenus Papeda and the cultivated limes, lemons and bergamots are related. Microcitrus spp, to which Severinia buxifolia and Atalantia ceylanica seem to be related, cluster with the lime lemon-citron-pummelo group while Fortunella is close to the orange-mandarin group. Poncirus trifoliata, the most important species for citrus rootstock improvement is located far from Citrus but connected to it through Fortunella spp. A broad distribution of species has been found that should be taken into account to sample new genotypes in the search of desired characters in order to fully and efficiently use genetic resources for citrus improvement.     

The relationships among lemons, limes and citron: a chromosomal comparison

Lemons, limes and citron constitute a group of closely related Citrus species, whose species delimitations and taxonomic relationships are unclear. In order to identify karyotypic similarities and species relationships within this group, the CMA+/DAPI- banding pattern and the distribution of the 5S and 45S rDNA sites of 10 accessions of lime, lemon, and citron were investigated. The four cultivars of C. limon analyzed showed the same pattern of CMA+ bands and rDNA sites, suggesting that they originated from a single germplasm, later differentiated by distinct somatic mutations. The lemons C. jambhiri, C. limonia and C. volkameriana displayed karyotypes very similar to each other, but they differed from C. limon by the absence of a single chromosome with one band in each telomere. The limes, C. aurantifolia and C. limettioides, seemed less related to each other and exhibited different heteromorphic chromosome pairs. In C. aurantifolia, the presence of a chromosome type unknown in all other Citrus species cytologically known so far supports the assumption that this accession may be derived from a hybrid with a species from the subgenus Papeda or from another genus. Citrus medica was the only homozygous accession of this group and all of its chromosome types were clearly represented in limes and lemons, some of them forming heteromorphic pairs. The analysis of the distribution of rDNA sites allowed a further refinement of the comparison among accessions. The lemons and limes were heterozygous for all rDNA sites, whereas C. medica was entirely homozygous. These data support the hypothesis that C. medica is a true species while the other nine accessions are hybrids.     

Host-Specific Effects of Toxin from the Rough Lemon Pathotype of Alternaria alternata on Mitochondria

Host-specific toxin from the rough lemon (Citrus jambhiri Lush) pathotype of Alternaria alternata (ACR toxin) was tested for effects on mitochondria isolated from several citrus species. The toxin caused uncoupling of oxidative phosphorylation and changes in membrane potential in mitochondria from leaves of the susceptible host (rough lemon); the effects differed from those of carbonylcyanide-m-chlorophenylhydrazone, a typical protonophore. ACR toxin also inhibited malate oxidation, apparently because of lack of NAD⁺ in the matrix. In contrast, the toxin had no effect on mitochondria from citrus species (Dancy tangerine and Emperor mandarin [Citrus reticulata Blanco], and grapefruit [Citrus paradisi Macf.]) that are not hosts of the fungus. The effects of the toxin on mitochondria from rough lemon are similar to the effects of a host-specific toxin from Helminthosporium maydis (HMT) on mitochondria from T-cytoplasm maize. Both ACR and HMT toxins are highly selective for the respective host plants. HMT toxin and methomyl had no effect (toxic or protective) on the activity of ACR toxin against mitochondria from rough lemon.