Response of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt-dependent oxidative stress: increased activities of antioxidant enzymes in root plastids

Root plastids of the cultivated tomato Lycopersicon esculentum (Lem) exhibited salt-induced oxidative stress as indicated by the increased H 2 O 2 and lipid peroxidation levels which were accompanied with increased contents of the oxidized forms of ascorbate and glutathione. In contrast, H 2 O 2 level decreased, lipid peroxidation level slightly decreased and the levels of the reduced forms of ascorbate and glutathione increased in plastids of L. pennellii (Lpa) species in response to salinity. This better protection of Lpa root plastids from salt-induced oxidative stress was correlated with increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (POD), monodehydroascorbate reductase (MDHAR), glutathione peroxidase (GPX), glutathione- S -transferase (GST) and phospholipid hydroperoxide glutathione peroxidase (PHGPX). In the plastids of both species, activities of SOD, APX, and POD could be resolved into several isozymes. In Lem plastids two Cu/ZnSOD isozymes were found whereas in Lpa an additional FeSOD type could also be detected. In response to salinity, activities of selected SOD, APX, and POD isozymes were increased in Lpa, while in Lem plastids the activities of most of SOD and POD isozymes decreased. Taken together, it is suggested that plastids play an important role in the adaptation of Lpa roots to salinity.     

Response of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt-dependent oxidative stress: The root antioxidative system

The response of the antioxidant system to salt stress was studied in the roots of the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (Lem) and its wild salt-tolerant relative L. pennellii (Corr.) D'Arcy accession Atico (Lpa). Roots of control and salt (100 m M NaCl)-stressed plants were sampled at various times after commencement of salinization. A gradual increase in the membrane lipid peroxidation in salt-stressed root of Lem was accompanied with decreased activities of the antioxidant enzymes: superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and decreased contents of the antioxidants ascorbate and glutathione and their redox states. In contrast, increased activities of the SOD, CAT, APX, monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and increased contents of the reduced forms of ascorbate and glutathione and their redox states were found in salt-stressed roots of Lpa, in which the level of membrane lipid peroxidation remained unchanged. It seems that the better protection of Lpa roots from salt-induced oxidative damage results, at least partially, from the increased activity of their antioxidative system.     

Salinity effects on water relations in Lycopersicon esculentum and its wild salt-tolerant relative species L. pennellii

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt tolerant relative L. pennellii (Correll) D'Arcy accession PE-47, were grown during spring-summer 1989 under unheated plastic greenhouse conditions. Plants were submitted to two different salt treatments using 0 and 140 mM NaCI irrigation water. In both tomato species, salinity caused a proportionally larger reduction in leaf area than in leaf weight and, in L. esculentum , a proportionally larger decrease in stem weight than in leaf weight. Daily variations in leaf water potential (Ψ₁) were fundamentally due to changes in the evaporative demand of the atmosphere. Reductions in Ψ₁ due to salinity were consistent only in L. esculentum . In all the conditions studied, leaf turgor was maintained. Leaf conductance (g₁)was higher in L. esculentum than in L. pennellii .Salinity induced a clear reduction in g₁ levels in L. esculentum whereas, in L. pennellii , this reduction was noted only in May. In both species the Ψ^o_s (leaf osmotic potential at full turgor) levels were reduced by salinity. The bulk modulus of elasticity (E) and relative water content at turgor loss point (RWC_tlp) were not affected by salinity. The RWC_tlp values in L. pennellii seem to be controlled by E values.     

Salinity up-regulates the antioxidative system in root mitochondria and peroxisomes of the wild salt-tolerant tomato species Lycopersicon pennellii

The effect of salinity on the antioxidative system of root mitochondria and peroxisomes of a cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species L. pennellii (Lpa) was studied. Salt stress induced oxidative stress in Lem mitochondria, as indicated by the increased levels of lipid peroxidation and H(2)O(2). These changes were associated with decreased activities of superoxide dismutase (SOD) and guaiacol peroxidases (POD) and contents of ascorbate (ASC) and glutathione (GSH). By contrast, in mitochondria of salt-treated Lpa plants both H(2)O(2) and lipid peroxidation levels decreased while the levels of ASC and GSH and activities of SOD, several isoforms of ascorbate peroxidase (APX), and POD increased. Similarly to mitochondria, peroxisomes isolated from roots of salt-treated Lpa plants exhibited also decreased levels of lipid peroxidation and H(2)O(2) and increased SOD, ascorbate peroxidase (APX), and catalase (CAT) activities. In spite of the fact that salt stress decreased activities of antioxidant enzymes in Lem peroxisome, oxidative stress was not evident in these organelles.     

Marker-assisted transfer of acylsugar-mediated pest resistance from the wild tomato,Lycopersicon pennellii,to the cultivated tomato,Lycopersicon esculentum

Acylsugars exuded from type IV trichomes mediate the multiple pest resistance found in the wild tomato species, Lycopersicon pennellii. A marker-assisted selection breeding program was used to attempt the transfer of the ability to accumulate acylsugars to cultivated tomato. RFLP and PCR-based markers were used through three backcross generations to select plants containing 5 target regions associated by QTL analysis with acylsugar accumulation. The BC1F1 plant selected possessed all 5 target regions and accumulated acylsugars at a moderate level similar to that of the interspecific F1 control. The BC2F1 and BC3F1 selections contained complementary subsets of the 5 target regions and did not accumulate acylsugars. BC3F1 plants with complementary subsets of the 5 target regions were intermated to produce populations segregating for the 5 target regions. From 1000 BC3F1-intermated plants, three plants were found which accumulated acylsugars at low levels and contained 3 to 5 of the target regions. The recovery of acylsugar accumulation in progeny of the intermated BC3F1 plants supports the involvement of at least some of the 5 target regions in acylsugar biosynthesis. However, since the levels of acylsugars accumulated by these plants were lower than that of the interspecific F1, it is likely that another, as of yet unidentified, region is necessary for accumulation of higher levels of acylsugars.     

Salt stress induces up-regulation of an efficient chloroplast antioxidant system in the salt-tolerant wild tomato species Lycopersicon pennellii but not in the cultivated species

The response of the chloroplastic antioxidant system of the cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species L. pennellii (Lpa) to NaCl stress was studied. An increase in H₂O₂ level and membrane lipid peroxidation was observed in chloroplasts of salt-stressed Lem. In contrast, a decrease in these indicators of oxidative stress characterized chloroplasts of salt-stressed Lpa plants. This differential response of Lem and Lpa to salinity, correlates with the activities of the antioxidative enzymes in their chloroplasts. Increased activities of total superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), glutathione-S-transferase (GST), phospholipid hydroperoxide glutathione peroxidase (PHGPX) and several isoforms of non-specific peroxidases (POD) were found in chloroplasts of salt-treated Lpa plants. In these chloroplasts, in contrast, activity of lipoxygenase (LOX) decreased while in those of salt-stressed Lem it increased. Although total SOD activity slightly increased in chloroplasts of salt-treated Lem plants, differentiation between SOD types revealed that only stromal Cu/ZnSOD activity increased. In contrast, in chloroplasts of salt-treated Lpa plants FeSOD activity increased while Cu/ZnSOD activity remained unchanged. These data indicate that salt-dependent oxidative stress and damage, suffered by Lem chloroplasts, was effectively alleviated in Lpa chloroplasts by the selective up-regulation of a set of antioxidative enzymes. Further support for the above idea was supplied by leaf discs experiments in which pre-exposure of Lpa plants to salt-treatment conferred cross-tolerance to paraquat-induced oxidative stress while increased oxidative damage by paraquat-treatment was found in salt-stressed Lem plants.     

The effect of salt stress on lipid peroxidation and antioxidants in the leaf of the cultivated tomato and its wild salt‐tolerant relative Lycopersicon pennellii

The possible involvement of the antioxidative system in the tolerance to salt stress was studied in the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (M82) and its wild salt‐tolerant relative L. pennellii (Corn) D'Arcy accession Atico (Lpa). All analyses, except that of monodehydroascorbate reductase (MDHAR), were performed of the youngest fully‐expanded leaf of control and salt (100 m M NaCl) stressed plants, 4, 7, 10, 14, 18 and 22 days after completing the stress treatment. In Lpa, constitutive level of lipid peroxidation and activities of catalase (CAT) and glutathione reductase (GR) were lower while the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were inherently higher than in M82. Relative to M82, lipid peroxidation was much lower and the activities of SOD, CAT and APX were higher in Lpa at 100 m M NaCl. The activity of DHAR decreased more in Lpa than in M82 under salt stress, and the activity of MDHAR, which was lower in Lpa than in M82 under control conditions, increased much more and to a higher level in salt‐treated Lpa plants. GR activity decreased similarly in the two species under salt stress. The results of these analyses suggest that the wild salt‐tolerant Lpa plants are better protected against active oxygen species (AOS), inherently and under salt stress, than the relatively sensitive plants of the cultivated species.     

Up-regulation of the leaf mitochondrial and peroxisomal antioxidative systems in response to salt-induced oxidative stress in the wild salt-tolerant tomato species Lycopersicon pennellii

The response of the antioxidative systems of leaf cell mitochondria and peroxisomes of the cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species Lycopersicon pennellii (Lpa) to NaCl 100 mM stress was investigated. Salt-dependent oxidative stress was evident in Lem mitochondria as indicated by their raised levels of lipid peroxidation and H2O2 content whereas their reduced ascorbate and reduced glutathione contents decreased. Concomitantly, SOD activity decreased whereas APX and GPX activities remained at control level. In contrast, the mitochondria of salt-treated Lpa did not exhibit salt-induced oxidative stress. In their case salinity induced an increase in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione-dependent peroxidase (GPX). Lpa peroxisomes exhibited increased SOD, APX, MDHAR and catalase activity and their lipid peroxidation and H2O2 levels were not affected by the salt treatment. The activities of all these enzymes remained at control level in peroxisomes of salt-treated Lem plants. The salt-induced increase in the antioxidant enzyme activities in the Lpa plants conferred cross-tolerance towards enhanced mitochondrial and peroxisomal reactive oxygen species production imposed by salicylhydroxamic acid (SHAM) and 3-amino-1,2,4-triazole (3-AT), respectively.     

Potassium utilization and fluxes in wild salt-tolerant relatives of the cultivated tomato

The growth of the wild tomato species Lycopersicon peruvianum (L.) Mill, and L. pennellii (Correll) D'Arcy, was compared with that of the cultivated tomato, L. esculentum Mill. cv. VE 234, under conditions of reduced K⁺ supply. Growth was impaired less in the wild than in the cultivated species. The higher efficiency of K⁺ utilization in the wild species was not associated with more efficient JC uptake from the medium. The rate of K⁺ uptake by whole plants was similar in the three species, but the rate of uptake by detached root tips was lower in the wild species. The permeability of the plasma membrane to K+ was apparently similar in root tips of the three species, but the tonoplast permeability was much lower in the wild than in the cultivated species.     

Copper affects the enzymes of the ascorbate-glutathione cycle and its related metabolites in the roots of Phaseolus vulgaris

The involvement of the ascorbate-glutathione cycle in the defence against Cu-induced oxidative stress was studied in the roots of Phaseolus vulgaris L. cv. Limburgse vroege. All the enzymes of this cycle [ascorbate peroxidase (APOD), EC 1.11.1.11; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; dehydroascorbate reductase (DHAR), EC 1.8.5.1; glutathione reductase (GR), EC 1.6.4.2] were increased, and the total ascorbate and glutathione pools rose after a 15 μ M root Cu treatment. In the first hours after the start of the experiment, the accumulation of dehydroascorbate (DHA), formed as a result of a Cu-mediated direct oxidation of ascorbate (AA), was limited by a non-enzymatic reduction using glutathione (GSH) as the reductant. At 24 h, the enzyme capacities of both DHAR and GR were increased to maintain the redox status of the AA and GSH pools. After 72 h of Cu application, the DHAR capacity was inhibited and MDHAR was responsible for maintaining the AA pool in its reduced form. Although the GR capacity was enhanced after 72 h in the treated plants, the GSSG/GSH ratio was increased. This could be due to direct participation of GSH in the detoxification of Cu through reduction and complexation.     

QTL analysis of pest resistance in the wild tomato Lycopersicon pennellii: QTLs controlling acylsugar level and composition

Some accessions of Lycopersicon pennellii, a wild relative of the tomato Lycopersicon esculentum, are resistant to a number of important pests of cultivated tomato due to the accumulation of acylsugars, which constitute 90% of the exudate of type-IV trichomes in L. pennellii LA716. An interspecific F₂ population, created by the cross L. esculentum x L. pennellii LA 716, was surveyed for acylsugar accumulation and subjected to RFLP/QTL analysis to determine the genomic regions associated with the accumulation of acylglucoses, acylsucroses, and total acylsugars, as well as with acylglucoses as a percentage of total acylsugars (mole percent acylglucoses). Data were analyzed using MAPMAKER/QTL with and without a log₁₀ transformation. A threshold value of 2.4 (default value for MAPMAKER/QTL) was used, as well as 95% empirically derived threshold values. Five genomic regions, two on chromosome 2 and one each on chromosomes 3, 4 and 11, were detected as being associated with one or more aspects of acylsugar production. The L. esculentum allele is partially dominant to the L. pennellii allele in the regions on chromosomes 2 and 11, but the L. pennellii allele is dominant in the region on chromosome 3. Throughout this study, we report the comparative effects of analytical methodology on the identification of acylsugar QTLs. Similarities between our results and published results for the genus Solanum are also discussed.R. W. Doerge · S.-C. Liu · J. P. Kuai contributed equally to the paper, and we ordered randomly     

Comparison of mitochondrial ascorbate peroxidase in the cultivated tomato, Lycopersicon esculentum, and its wild, salt-tolerant relative, L. pennellii– a role for matrix isoforms in protection against oxidative damage

Mitochondria require robust antioxidant defences to prevent lipid peroxidation and to protect tricarboxylic acid cycle enzymes from oxidative damage. Mitochondria from wild, salt‐tolerant tomato, Lycopersicon pennellii (Lpa) did not exhibit lipid peroxidation in response to high salinity (100 mm NaCl), whereas those isolated from cultivated tomato, L. esculentum (Lem), accumulated malondialdehyde. The activity, intraorganellar distribution and salt response of mitochondrial ascorbate peroxidase (mAPX) differed dramatically in the two species. In Lem mitochondria, the majority (84%) of mAPX was associated with membranes, being located either on the inner membrane, facing the intermembrane space, or on the outer membrane. Total mAPX activity did not increase substantially in response to salt, although the proportion of matrix APX increased. In contrast, 61% of Lpa mAPX activity was soluble in the matrix, the remainder being bound to the matrix face of the inner membrane. Salt treatment increased the activity of all mAPX isoforms in Lpa, without altering their intramitochondrial distribution. The membrane‐bound isoforms were detected in mitochondria of both species by western blotting and found to be induced by salt in Lpa. These observations suggest that matrix‐associated APX isoforms could act in concert with other mitochondrial antioxidants to protect against salt‐induced oxidative stress.     

The response to NaCl of excised fully differentiated and differentiating tissues of the cultivated tomato, Lycopersicon esculentum, and its wild relatives, L. peruvianum and Solanum pennellii

The responses to NaCl of cultured leaf discs and leaflets derived from fully differentiated leaves and of shoot apices excised from the cultivated tomato Lycopersicon esculentum Mill. and its wild salt-tolerant relatives L. peruvianum (L.) Mill, and Solanum pennellii Cor were compared. The results suggest that the tolerance of the whole plant to salt depends largely on the tolerance of plant organs containing meristematic tissues rather than on tissues already differentiated. This suggestion is based on the positive correlation found between the response to NaCl of shoot apices and of the whole plant, i.e. both whole plants and apices of the wild species were more resistant to salt than those of the cultivated species. No difference was found among the species with respect to the responses of the fully differentiated parts. The ion balance (K⁺/Na⁺ and Cl⁻/Na⁺) in detached leaves and apices exposed to salt was different from the balance in the same parts while attached to the salt-treated plant. This difference may be due to the severance of the excised parts from the major sites controlling the balance of ions in the whole plant.     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸-谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明:外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

Identification of quantitative trait loci associated with acylsugar accumulation using intraspecific populations of the wild tomato, Lycopersicon pennellii

 Lycopersicon pennellii LA716, a wild relative of tomato, is resistant to a number of insect pests due to the accumulation of acylsugars exuded from type IV trichomes. These acylsugars are a class of compounds including both acylglucoses and acylsucroses. Intraspecific populations between L. pennellii LA716 and L. pennellii LA1912, the latter an accession that assorts for low-level acylsugar accumulation, were created to study the inheritance of type IV trichome density, acylsugar accumulation levels, percentage of acylsugars that are acylglucoses, and leaf area. The F₂ population was subsequently used to determine genomic regions associated with these traits. The relative proportion of acylglucoses and acylsucroses was found to be largely controlled by a single locus near TG549 on chromosome 3. One locus on chromosome 10 showed significant associations with acylsugar levels. In addition, 1 locus on chromosome 4 showed significant associations with leaf area. Ten additional loci showed modest associations with one or more of the traits examined, 5 of which have been previously reported. Received: 13 March 1997 / Accepted: 19 September 1997     

Introgression and DNA marker analysis of Lycopersicon peruvianum, a wild relative of the cultivated tomato, into Lycopersicon esculentum, followed through three successive backcross generations

 Segregation of the Lycopersicon peruvianum genome was followed through three generations of backcrossing to the cultivated tomato L. esculentum cv ‘E6203’ using molecular markers. Thirteen BC₁ plants were genotyped with 113 markers, 67 BC₂ plants with 84 markers, and finally 241 BC₃ plants were genotyped with 177 markers covering the entire genome and a BC₃ map constructed. Several segments of the genome, including parts of chromosomes 3, 4, 6, and 10, quickly became fixed for esculentum alleles, possibly due to sterility problems encountered in the BC₁. Observed overall heterozygosity and chromosome segment lengths at each generation were very near the expected theoretical values. Markers located near the top telomeric region of chromosome 9 showed segregation highly skewed towards the wild allele through all generations, suggesting the presence of a gamete promoter gene. One markers, TG9, mapped to a new position on chromosome 9, implying an intrachromosomal translocation event. Despite the great genetic distance between the two parents, overall recombination was only 25% less than that observed in a previous tomato cross, indicating that L. peruvianum genes may be more readily introgressed into cultivated germplasm than originally believed. Received: 9 April 1997 / Accepted : 20 May 1997     

Xv4-vrxv4: a new gene-for-gene interaction identified between Xanthomonas campestris pv. vesicatoria race T3 and wild tomato relative Lycopersicon pennellii

Strains of tomato race 3 (T3) of Xanthomonas campestris pv. vesicatoria elicit a hypersensitive response (HR) in leaves of Lycopersicon pennellii LA716. Genetic segregation of the resistance exhibited ratios near 3:1 in F2 populations, which confirmed that a single dominant gene controlled the inheritance of this trait. With the aid of a collection of introgression lines, restriction fragment length polymorphism, and cleaved amplified polymorphic sequence markers, the resistance locus was located on chromosome 3 between TG599 and TG134. An avirulence gene named avrXv4 was also isolated by mobilizing a total of 600 clones from a genomic DNA library of the T3 strain 91-118 into the X. campestris pv. vesicatoria strain ME90, virulent on L. pennellii. One cosmid clone, pXcvT3-60 (29-kb insert), induced HR in resistant plants. The avirulent phenotype of pXcvT3-60 was confirmed by comparing growth rates in planta and electrolyte leakages among transconjugants carrying a mutated or intact clone with the wild-type T3 strain 91-118. A 1.9-kb DNA fragment contained within a 6.8-kb active subclone was sequenced and was determined to carry an open reading frame of 1,077 bp. The predicted AvrXv4 protein exhibits high similarity to members of an emerging new family of bacterial proteins from plant and mammalian pathogens comprising AvrRxv, AvrBsT, YopJ, YopP, AvrA, and YL40.     

外源NO对铜胁迫下番茄幼苗根系抗坏血酸谷胱甘肽循环的影响

采用营养液培养方法,研究外源NO对铜胁迫下番茄(Lycopersicon esculentum Mill.)幼苗根系抗坏血酸(AsA)-谷胱甘肽(GSH)循环中抗氧化物质和抗氧化酶系的影响.结果表明：外施适量NO(硝普钠)可提高铜胁迫下番茄幼苗根系AsA、GSH含量和AsA/DHA(氧化型抗坏血酸)、GSH/GSSG(氧化型谷胱甘肽),降低DHA和GSSG含量.添加100 μmol·L^-1 BSO(谷胱甘肽合成酶抑制剂)处理下,外源NO可提高铜胁迫下番茄幼苗根系的AsA含量、AsA/DHA及抗坏血酸酶(AAO)、单脱氢抗坏血酸还原酶(MDHAR)和脱氢抗坏血酸还原酶(DHAR)比活性,降低DHA、GSH、GSSG含量及抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)比活性;添加250 μmol·L^-1 BSO处理下,外源NO提高了铜胁迫下番茄幼苗根系的AsA、GSH、GSSG含量、AsA/DHA及APX和GR比活性,降低了DHA含量及AAO、DHAR和MDHAR比活性.说明外源NO影响了铜胁迫下番茄根系的AsA-GSH代谢循环,并通过调节AsA/DHA、GSH/GSSG的变化来减轻氧化胁迫,从而缓解铜胁迫对番茄根系的伤害.     

Regulation of the ascorbate-glutathione cycle in wild almond during drought stress

In wild species of almond (Prunus spp.), the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), as well as the levels of ascorbate/glutathione pools and H₂O₂ were subjected to water deficit and shade conditions. After 60 days of water shortage, the species were subjected to a rewatering treatment. During water recovery, leaves exposed to sunlight and leaves under shade conditions of about 20–35% of environmental irradiance were sampled. After 70 days without irrigation, mean predawn leaf water potential of all the species fell from −0.32 to −2.30 MPa and marked decreases in CO₂ uptake and transpiration occurred. The activities of APX, MDHAR, DHAR, and GR increased in relation to the severity of drought stress in all the wild species studied. Generally, APX, MDHAR, DHAR, and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in sun-exposed leaves. The levels in total ascorbate, glutathione, and H₂O₂ were directly related to the increase in drought stress and subsequently decreased during rewatering. The antioxidant response of wild almond species to drought stress limits cellular damage caused by reactive oxygen species during periods of water deficit and may be of key importance for the selection of drought-resistant rootstocks for cultivated almond.     

Genetic analysis of resistances to races 1 and 2 of Fusarium oxysporum f. sp. lycopersici from the wild tomato Lycopersicon pennellii

Summary Resistance to race 3 of Fusarium wilt in the wild tomato Lycopersicon pennellii (LA 716) was previously found to be controlled by one major locus, I-3, tightly linked to Got-2 on chromosome 7. This accession was also found to carry resistance to races 1 and 2; a genetic analysis of these resistances is reported in this paper. This analysis proceeded in two steps. First, allelism tests demonstrated that race 1 and 2 resistances carried by L. pennellii were not allelic to the I and I-2 genes originally incorporated into L. esculentum from L. pimpinellifolium. Second, an interspecific backcross with L. pennellii (BC₁) was used to determine the mode of inheritance of these new resistances and their chromosomal location by segregation and linkage analysis. BC₁ responses to each of the races were determined using progeny tests (BC₁S₁). BC₁S₁ plants were inoculated with race 1 or 2 and evaluated after 1 month using a visual disease rating system; mean disease ratings were calculated for each BC₁ individual for each race based on the progeny scores. A bimodal frequency distribution of the BC₁ mean disease ratings was observed for both races, indicating that one major locus controlled resistance in each case. Statistical comparisons of the mean disease ratings of homozygous versus heterozygous individuals at each of 17 segregating enzyme loci were used to map the resistances to races 1 and 2. Tight linkage was detected between the enzyme locus Got-2 and resistances to both races, as was previously reported for the I-3 locus. Therefore, the Got-2 locus can be used as a selectable marker for resistances to all three races. The relationship of these resistances is discussed in the paper. In addition, as previously reported for race 3, significance was also detected for the chromosome segment marked by Aps-2 on chromosome 8 for both races. Currently many cultivars carry I and I-2 resistances to races 1 and 2. Incorporation of the LA 716 resistances to these two races into cultivars may reduce the likelihood of new race development.Florida Agricultural Experiment Station, Journal Series No. R-00205