Differentiation of Meloidogyne incognita and M. arenaria novel resistance phenotypes in Lycopersicon peruvianum and derived bridge-lines

Lycopersicon peruvianum PI 270435 clone 2R2 and PI 126443 clone 1MH were crossed reciprocally with three L. esculentum-L. peruvianum bridge-lines. The incongruity barrier between the two plant species was overcome; F₁ progeny were obtained from crosses between four parental combinations without embryo-rescue culture. Hybridity was confirmed by leaf and flower morphology and by the production of nematode-resistant F₁ progeny on homozygous susceptible parents. Clones of the five F₁ bridgeline hybrids were highly resistant to Mi-avirulent root-knot nematode (Meloidogyne incognita) at both 25°C and 30°C soil temperatures. However, only clones from PI 270435-3MH and PI 126443-1MH, and hybrids from PI 126443-1MH, were resistant to Mi-virulent M. incognita isolates at high soil temperature. Clones and hybrids from PI 270435-2R2 were not resistant to two Mi-virulent M. incognita isolates at high soil temperature. A source of heat-stable resistance was identified in bridge-line EPP-2, and was found to be derived from L. peruvianum LA 1708. Accessions of the L. peruvianum Maranon races, LA 1708 and LA 2172, and bridge-line EPP-2, segregated for heat-stable resistance to Mi-avirulent M. incognita, but were susceptible to Mi-virulent M. incognita isolates. Clone LA 1708-I conferred heat-stable resistance to M. arenaria isolate W, which is virulent to heat-stable resistance genes in L. peruvianum PI 270435-2R2, PI 270435-3MH, and PI 126443-1MH. Clone LA 1708-I has a distinct heat-stable factor for resistance to Mi-avirulent M. arenaria isolate W, for which the gene symbol Mi-4 is proposed. A Mi-virulent M. arenaria isolate Le Grau du Roi was virulent on all Lycopersicon spp. accessions tested, including those with novel resistance genes.     

Relationships between Meloidogyne incognita resistance genes in Lycopersicon peruvianum differentiated by heat sensitivity and nematode virulence

Resistance to Meloidogyne incognita (Kofoid and White) Chitwood in clones of Lycopersicon peruvianum (L.) Mill. PI 126443-1MH, 270435-2R2 and 2704353MH, their F₁, a field-produced F₂, and their test-cross (TC₁) populations, was evaluated based on egg masses and eggs produced on root systems. Reactions to M. incognita isolates differing in virulence to gene Mi were determined at 25°C (Mi expressed) and 32°C (Mi not expressed). PI 126443-1MH, 270435-2R2, 270435-3MH, and their F₁ progenies were resistant to Mi-virulent and Mi-avirulent isolates. At 32°C with a Mi-avirulent isolate and at 25°C with a Mi-virulent isolate, four TC₁ generations segregated into resistant: susceptible (RS) ratios close to 31. These results indicated resistance to Mi-(a)virulent M. incognita isolates is conferred by different non-allelic dominant genes in PI 126443-1MH, 270435-2R2 and 270435-3MH. The F₂ progeny of PI 126443-1MH x EPP-1, challenged with Mi-avirulent M. incognita at 32°C and with Mi-virulent M. incognita at both 25°C and 32°C, segregated with a ratio of 31 (RS), indicating expression of a single dominant resistance gene in PI 126443-1MH in each case. In dual screenings on clones of the same individual plants from the TC₁ and F₂ segregating populations, some individual plants were susceptible at 32°C to a Mi-avirulent isolate but resistant to the Mi-virulent isolate, and vice versa, suggesting that different but linked genes confer heat-stable resistance to Mi-avirulent M. incognita and resistance to Mi-virulent M. incognita. We propose the symbol Mi-5 for the gene in PI 126443 clone 1MH and the symbol Mi-6 for the gene in PI 270435 clone 3MH which both confer resistance to Mi-avirulent M. incognita isolates at high temperature. We propose the symbol Mi-7 for the gene in PI 270435 clone 3MH and the symbol Mi-8 for the gene in PI 270435 clone 2R2 that both confer resistance to the Mi-virulent M. incognita isolate 557R at moderate (25°C) temperature. The novel resistance genes are linked and reside in a genomic region in each parental clone that is independent from the Mi locus.     

Inheritance of heat-stable resistance to Meloidogyne incognita in Lycopersicon peruvianum and its relationship to the Mi gene

Summary The inheritance of heat-stable resistance to the root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, was studied in crosses between different accessions and clones of Lycopersicon peruvianum L. F₁, F₂ and BC₁ generations were evaluated for their index of resistance based on numbers of eggs and infective second-stage juveniles (J₂) per gram of root, and the segregation ratios were determined in experiments carried out at constant soil temperatures of 25 °C and 30 °C. L. peruvianum P.I. 270435 clones 3 MH and 2R2 and P.I. 126443 clone 1 MH, all heatstable resistant, were crossed with L. peruvianum P.I. 126440 clone 9 MH, which is susceptible at both 25 °C and 30 °C. All F₁ progeny were resistant at 25 °C and 30 °C; F₂ and BC₁ generations at 25 °C gave resistant: susceptible (RS) ratios of 151 and 31, respectively, which suggests that resistance is conditioned by two independently assorting genes. However, at 30 °C, RS ratios of 31 and 11 were observed for the F₂ and BC₁ generations, respectively. These results indicate that heat-stable resistance is conferred by a single dominant gene expressed at 30 °C, while the second resistance gene is heat unstable and not expressed at 30 °C. P.I. 270435 clones 2R2 and 3 MH and P.I. 126443 clone 1 MH were crossed with P.I. 128657 clone 3 R4 (source of gene Mi), which is resistant at 25 °C but susceptible at 30 °C. All of the F₁ progeny were resistant at 25 °C and 30 °C.TC₁ progeny of 270435-2 R2 x 128657-3 R4, 270435-3 MH x 128657-3 R4 and 126443-1 MH x 128657-3 R4 crossed with susceptible 126440-9 MH were all resistant at 25 °C and segregated in a 11 ratio at 30 °C. These results also suggest that the heat-stable resistance is monogenic and that it is non-allelic to gene Mi. The non-segregation of TC₁ progenies at 25 °C, suggests that the heat-unstable resistance factor in L. peruvianum P.I. 270435 clones 2 R2 and 3 MH and in P.I. 126443 clone 1 MH is allelic to or the same as gene Mi. We propose the symbol Mi-2 for the gene in P.I. 270435 that confers heat-stable resistance to M. incognita.     

Mapping a novel heat-stable resistance to Meloidogyne in Lycopersicon peruvianum

 The root-knot nematode heat-stable resistance locus from L. peruvianum LA2157 was mapped on chromosome 6. All wild tomato LA2157 entries and the LA2157 S₁ progeny tested were resistant to Mi-avirulent Meloidogyne spp. isolates at 32°C, indicating that the self-compatible accession is homozygous for heat-stable nematode resistance. The novel resistance locus was mapped on a RFLP linkage map; this map was based on a segregating F₂ population obtained from the interspecific F₁ between L. esculentum cv ‘Solentos’ and L. peruvianum LA2157. The inheritance of the heat-stable resistance was evaluated in 100 F₃ lines derived from one F₁ interspecific hybrid. The genotype of the resistance locus of the individual F₂ plants was based on the phenotypic classification of their F₃ lines, and the data were used to map the resistance locus on the arm of chromosome 6 with the closest linkage to TG178. The position of the novel heat-stable resistance of LA2157 was localized in the resistance genes’ cluster close to the location of gene Mi-1. Cuttings of the F₃ lines expressed resistance to Mi-1-avirulent M. incognita and M. javanica biotypes at 25°C and at 32°C (a temperature at which Mi-1 resistance is not expressed). There was no difference in the segregating population for expression of heat-unstable resistance and heat-stable resistance to Mi-1-avirulent Meloidogyne spp. However, LA2157 and cuttings of the above F₃ lines were susceptible to a Mi-1-virulent M. incognita isolate at 30°C and to a M. hapla isolate at 25°C. Received: 6 July 1998 / Accepted: 28 July 1998     

Resistance in Lycopersicon peruvianum to Isolates of Mi Gene-Compatible Meloidogyne Populations

Root-knot nematode resistance of F₁ progeny of an intraspecific hybrid (Lycopersicon peruvianum var. glandulosum Acc. No. 126443 x L. peruvianum Acc. No. 270435), L. esculentum cv. Piersol (possessing resistance gene Mi), and L. esculentum cv. St. Pierre (susceptible) was compared. Resistance to 1) isolates of two Meloidogyne incognita populations artificially selected for parasitism on tomato plants possessing the Mi gene, 2) the wild type parent populations, 3) four naturally occurring resistance (Mi gene)-breaking populations of M. incognita, M. arenaria, and two undesignated Meloidogyne spp., and 4) a population of M. hapla was indexed by numbers of egg masses produced on root systems in a greenhouse experiment. Artificially selected M. incognita isolates reproduced abundantly on Piersol, but not (P = 0.01) on resistant F₁ hybrids. Thus, the gene(s) for resistance in the F₁ hybrid differs from the Mi gene in Piersol. Four naturally occurring resistance-breaking populations reproduced extensively on Piersol and on the F₁ hybrid, demonstrating ability to circumvent both types of resistance. Meloidogyne hapla reproduced on F₁ hybrid plants, but at significantly (P = 0.01) lower levels than on Piersol.     

Mapping a new nematode resistance locus in Lycopersicon peruvianum

Accessions of the wild tomato species L. peruvianum were screened with a root-knot nematode population (557R) which infects tomato plants carrying the nematode resistance gene Mi. Several accessions were found to carry resistance to 557R. A L. peruvianum backcross population segregating for resistance to 557R was produced. The segregation ratio of resistant to susceptible plants suggested that a single, dominant gene was a major factor in the new resistance. This gene, which we have designated Mi-3, confers resistance against nematode strains that can infect plants carrying Mi. Mi-3, or a closely linked gene, also confers resistance to nematodes at 32°C, a temperature at which Mi is not effective. Bulked-segregant analysis with resistant and susceptible DNA pools was employed to identify RAPD markers linked to this gene. Five-hundred-and-twenty oligonucleotide primers were screened and two markers linked to the new resistance gene were identified. One of the linked markers (NR14) was mapped to chromosome 12 of tomato in an L. esculentum/L. pennellii mapping population. Linkage of NR14 and Mi-3 with RFLP markers known to map on the short arm of chromosome 12 was confirmed by Southern analysis in the population segregating for Mi-3. We have positioned Mi-3 near RFLP marker TG180 which maps to the telomeric region of the short arm of chromosome 12 in tomato.     

Effect of salinity on photosynthetic activity of Nodularia spumigena

The aim of the study was to determine the influence of total dissolvedsolids/salinity (mg L^-1 TDS) on photosynthetic activity of Nodularia spumigena strain 001E isolated from Lake Alexandrina, SouthAustralia, using photosynthesis-irradiance (PI) curves. N. spumigena001E cultures were grown in ASM medium at a range of TDSconcentrations (360, 6,600, 13,200, 19,800, 26,400 mg L^-1)at an irradiance of 30 mol m^-2 s^-1 (PAR, 400–700 nm) at 25 °C. The PI relationship was determined at 25 °Cfor irradiances between 0 and 500 mol photon m^-2s^-1 (PAR). The initial slope of PI curve, , a function of lightharvesting efficiency and photosynthetic energy conversion, decreasedproportionally with an increase in salinity from 360 to 26,400 mgL^-1 TDS. The maximum rate of photosynthesis (P_max),occurred at 6,600 mg L^-1 TDS. No influence of salinity onI_k, the irradiance at which P_max was measured, or on R_d, the dark respiration rate, was identified.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: Recovery and its dependence on temperature

Recovery of photoinhibition in intact leaves of shade-grown kiwifruit was followed at temperatures between 10° and 35° C. Photoinhibition was initially induced by exposing the leaves for 240 min to a photon flux density (PFD) of 1 500 mol·m^-2·s^-1 at 20° C. In additional experiments to determine the effect of extent of photoinhibition on recovery, this period of exposure was varied between 90 and 400 min. The kinetics of recovery were followed by chlorophyll fluorescence at 77K. Recovery was rapid at temperatures of 25–35° and slow or negligible below 20° C. The results reinforce those from earlier studies that indicate chilling-sensitive species are particularly susceptible to photoinhibition at low temperatures because of the low rates of recovery. At all temperatures above 15° C, recovery followed pseudo first-order kinetics. The extent of photoinhibition affected the rate constant for recovery which declined in a linear fashion at all temperatures with increased photoinhibition. However, the extent of photoinhibition had little effect on the temperature-dependency of recovery. An analysis of the fluorescence characteristics indicated that a reduction in non-radiative energy dissipation and repair of damaged reaction centres contributed about equally to the apparent recovery though biochemical studies are needed to confirm this. From an interpretation of the kinetics of photoinhibition, we suggest that recovery occurring during photoinhibition is limited by factors different from those that affect post-photoinhibition recovery.Abbreviations and symbols F _o, F _m, F _v instantaneous, maximum, variable fluorescence - K _D, K _F, K _P, K _T rate constants for non-radiative energy dissipation, fluorescence, photochemistry, transfer to photosystem I - K(PI), k(R) rate constants for photoinhibition and recovery - PFD photon flux density - PSI, II photosystem I, II - _i photon yield of photosynthesis (incident light)     

Resistance of maize to Meloidogyne arenaria and Meloidogyne javanica

Summary A diallel cross of eight maize, Zea mays L., inbred lines was analyzed for reaction to two species of root-knot nematodes, Meloidogyne arenaria (Neal) Chitwood and M. javanica (Treub) Chitwood. Egg production following inoculation of F₁ hybrid seedlings with nematode eggs was determined in a greenhouse experiment. Data were analyzed using Griffing's Method 4, Model I. General combining ability was a significant source of variation in egg production of both M. arenaria and M. javanica; specific combining ability was not a significant source of variation for either. The correlation between egg production of the two nematode species on the 28 F₁ hybrids was highly significant. Hybrids with Mp313 or SC213 as one parent were the most resistant to both species. This indicates that germ plasm is available for developing inbred lines and hybrids with resistance to both M. arenaria race 2 and M. javanica.This article is a contribution of the Crop Science Research Laboratory, U.S. Department of Agriculture, Agricultural Research Service, in cooperation with the Mississippi Agricultural and Forestry Experiment Station, Journal No. J-7481.     

Combining cry1Ac with QTL alleles from PI 229358 to improve soybean resistance to lepidopteran pests

A QTL conditioning corn earworm resistance in soybean PI 229358 and asynthetic Bacillus thuringiensis cry1Ac transgene from therecurrent parent Jack-Bt were pyramided intoBC₂F₃ plants by marker-assisted selection. Segregatingindividuals were genotyped at SSR markers linked to an anitbiosis/antixenosisQTL on linkage group M, and were tested for the presence ofcry1Ac. Marker-assisted selection was used during andafter the two backcrosses to develop a series of BC₂F₃plants with or without the crylAc transgene and the QTLconditioning for resistance BC₂F₃ plants that werehomozygous for parental alleles at markers on LG M, and whicheither had or lacked cry1Ac, were assigned to one of fourpossible genotype classes. These plants were used in no-choice, detached leaffeeding bioassays with corn earworm and soybean looper larvae (Lepidoptera:Noctuidae) to evaluate the relative antibiosis in the different genotypeclasses. Resistance was measured as larval weight gain and degree of foliageconsumption. Few larvae of either species survived on leaves expressing theCry1Ac protein. Though not as great as the effect of Cry1Ac, the PI229358-derived LG M QTL also had a detrimental effect on larval weights of bothpest species, and on defoliation by corn earworm, but did not reduce defoliation bysoybean looper. Weights of soybean looper larvae fed foliage from transgenicplants with the PI-derived QTL were lower than those of larvae fed transgenictissue with the corresponding Jack chromosomal segment. This work demonstratesthe usefulness of SSRs for marker-assisted selection in soybean, and shows thatcombining transgene-and QTL-mediated resistance to lepidopteran pests may be aviable strategy for insect control.     

A mechanism of chlorotoluron resistance in Lolium rigidum

Many biotypes of Lolium rigidum Gaud, (annual ryegrass) have developed resistance to herbicides; however, few have developed resistance to phenylurea herbicides. Two biotypes with different histories of herbicide selection pressure were six to eight times less sensitive to the phenylurea herbicide, chlorotoluron, than a susceptible biotype. Resistance was not due to differences in the herbicide target site as oxygen evolution by thylakoids isolated from resistant and susceptible biotypes was similarly inhibited by diuron and chlorotoluron. There was no difference in the uptake and distribution of chlorotoluron into resistant and susceptible plants. There was a twofold greater rate of chlorotoluron detoxification in resistant plants with N-demethylation being a major detoxification reaction. Resistant plants treated with a 3-h pulse of 120 M chlorotoluron recovered net carbon fixation after 42 h, half the time taken by susceptible plants. The mixed-function oxidase inhibitor 1-aminobenzotriazole (70 M) intensified the effects of chlorotoluron in resistant plants when applied in combination with the herbicide for 7 d. 1-Aminobenzotriazole also inhibited the metabolism of chlorotoluron in both resistant and susceptible plants. The cytochrome P-₄₅₀ inhibitor, piperonyl butoxide piperonyl butoxide, interacted with chlorotoluron when applied to plants growing in soil. Chlorotoluron applied with reduced plant dry weight to a greater extent than chlorotoluron alone. It appears, therefore, that enhanced detoxification is the major mechanism of resistance to chlorotoluron in the resistant biotypes studied.Abbreviations ABT 1-aminobenzotriazole - VLR1 Victorian L. rigidum biotype 1 — herbicide susceptible - VLR69 Victorian L. rigidum biotype 69 — herbicide resistant - WLR2 Western Australian L. rigidum biotype 2 — herbicide resistant M.W.M.B, was supported by an Australian Postgraduate Research Award and a supplementary scholarship from the Grains Research and Development Corporation. We are very grateful to Dr. E. Ebert, Ciba Geigy, Basal, Switzerland for providing [¹⁴C]chlorotoluron and standards of chlorotoluron metabolites. We express our gratitude to Dr. John Huppatz of the CSIRO Division of Plant Industry for providing ABT. We also thank Ciba Geigy Australia for providing technical-grade chlorotoluron and formulated phenylurea herbicides.     

Resistance to powdery mildew (Oidium lycopersicum) in Lycopersicon hirsutum is controlled by an incompletely-dominant gene Ol-1 on chromosome 6

The inheritance of resistance to powdery mildew (Oidium lycopersicum) in Lycopersicon hirsutum was investigated by disease tests in segregating populations obtained by hybridising tomato (L. esculentum) cv Moneymaker with the wild relative L. hirsutum G1.1560. One incompletely dominant gene Ol-1 was found to largely control resistance to the disease. To map Ol-1, DNA pools from seven resistant and ten susceptible F₂ plants were analyzed for random amplified polymorphic DNA (RAPD). With 32 primers tested, one RAPD, primed with the sequence 5-GACGTGGTGA-3, was observed between the susceptible and the resistant bulks, which cosegregated with resistance in the F₂ population of L. esculentum × L. hirsutum G1.1560. This RAPD was mapped on chromosome 6 by using an F₂ (L. esculentum × L. pennellii) already mapped for 49 RFLPs. RFLP analysis of the F₂ from L. esculentum cv Moneymaker × L. hirsutum G1.1560 demonstrated that Ol-1 maps near the Aps-1 region on chromosome 6, in the vicinity of the resistance genes to Meloidogyne spp. (Mi) and to Cladosporium fulvum (Cf-2/Cf-5).     

High resolution RFLP map around the root knot nematode resistance gene (Mi) in tomato

Summary In the 1940's the root-knot nematode resistance gene (Mi) was introgressed into the cultivated tomato from the wild species, L. peruvianum, and today it provides the only form of genetic resistance against this pathogen. We report here the construction of a high resolution RFLP map around the Mi gene that may aid in the future cloning of this gene via chromosome walking. The map covers the most distal nine map units of chromosome 6 and contains the Mi gene, nine RFLP markers, and one isozyme marker (Aps-1). Based on the analysis of more than 1,000 F₂ plants from four crosses, we were able to pinpoint the Mi gene to the interval between two of these markers — GP79 and Aps-1. In crosses containing the Mi gene, this interval is suppressed in recombination and is estimated to be 0.4 cM in length. In contrast, for a cross not containing Mi, the estimated map distance is approximately 5 times greater (ca. 2 cM).Using RFLP markers around Mi as probes, it was possible to classify nematode resistant tomato varieties into three types based on the amount of linked peruvianum DNA still present. Two of these types (representing the majority of the varieties tested) were found to still contain more than 5 cM of peruvianum chromosome — a result that may explain some of the negative effects (e.g. fruit cracking) associated with nematode resistance. The third type (represented by a single variety) is predicted to carry a very small segment of peruvianum DNA (<2 cM) and may be useful in the identification of additional markers close to Mi and in the orientation of clones during a chromosome walk to clone the gene.     

N 5,N 10-Methenyltetrahydromethanopterin cyclohydrolase from the extremely thermophilic sulfate reducing Archaeoglobus fulgidus: comparison of its properties with those of the cyclohydrolase from the extremely thermophilic Methanopyrus kandleri

Archaeoglobus fulgidus and Methanopyrus kandleri are both extremely thermophilic Archaea with a growth temperature optimum at 83°C and 98°C, respectively. Both Archaea contain an active N ⁵,N ¹⁰-methenyltetrahydromethanopterin cyclohydrolase. The enzyme from M. kandleri has recently been characterized. We describe here the purification and properties of the enzyme from A. fulgidus.The cyclohydrolase from A. fulgidus was purified 180-fold to apparent homogeneity and its properties were compared with those recently published for the cyclohydrolase from M. kandleri. The two cytoplasmic enzymes were found to have very similar molecular and catalytic properties. They differed, however, significantly with respect of the effect of K₂HPO₄ and of other salts on the activity and the stability. The cyclohydrolase from A. fulgidus required relatively high concentrations of K₂HPO₄ (1 M) for optimal thermostability at 90°C but did not require salts for activity. Vice versa, the enzyme from M. kandleri was dependent on high K₂HPO₄ concentrations (1.5 M) for optimal activity but not for thermostability. Thus the activity and structural stability of the two thermophilic enzymes depend in a completely different way on the concentration of inorganic salts. The molecular basis for these differences are discussed.Abbreviations H₄MPT tetrahydromethanopterin - MFR methanofuran - CH₃–H₄MPT N ⁵-methyl-H₄MPT - CH₂=H₄MPT N ⁵,N ¹⁰-methylene-H₄MPT - CH₂H₄MPT N ⁵,N ¹⁰-methenyl-H₄MPT - CHO–H₄MPT N ⁵ formyl-H₄MPT - CHO-MFR formyl-MFR - cyclohydrolase N ⁵,N ¹⁰-methenyltetrahydromethanopterin cyclohydrolase - MOPS 3-(N-morpholino) propane sulfonic acid - TRICINE N-tris (hydroxymethyl) methyl glycine - 1 U=1 mol/min     

Properties and regulation of ribulose diphosphate carboxylase from Thiobacillus novellus

Ribulose-diphosphate carboxylase from Thiobacillus novellus has been purified to homogeneity as observed by polyacrylamide gel electrophoresis and U. V. light observation during sedimentation velocity analysis. The optimum pH for the enzyme with Tris-HCl buffers was about 8.2. Concentrations of this buffer in excess of 80 mM were inhibitory. The apparent K _m RuDP was about 14.8 M with a Hill value of 1.5, for HCO ₃ ^- the apparent K _m was about 11.7 mM with an n value of 1.18 and for Mg²⁺ about 0.61 mM. The enzyme was specific for this cation. Relatively high concentrations of either Hg²⁺ or pCMB were required before significant inhibition was observed. Activity declined slowly during a 4-hr incubation period in either 3.0 M or 8.0 M urea. Incubation for 12 hrs resulted in complete loss of activity which was not prevented by 10 mM Mg²⁺ and was not reversed by dialysis and subsequent addition of 10 mM cysteine. Polyacrylamide gel electrophoresis revealed a loss of the major band and the appearance of 2 new bands. SDS polyacrylamide gel electrophoresis gave an average M.W. of 73 500±2500 for the slower moving band and 12250 ±2500 for the faster moving. However, incubation in urea for up to 40 hrs revealed a decrease in the M.W. of the slower moving band to about 60000. The E _a for the enzyme was calculated to be about 18.85 kcal mole^-1, with the possibility of a break between 40 and 50°C. The Q ₁₀ was 3.07 between 20 to 30°C whereas between 30 to 40°C it was 3.31. Only phosphorylated compounds caused significant inhibition of enzyme activity. They included ADP, FDP, F6P, G6P, PEP, 6PG, 2-PGA, R1P, R5P and Ru5P.Abbreviations ATP adenosine-5-triphosphate - FDP fructose-1,6-diphosphate - F6P fructose-6-phosphate - G6P glucose-6-phosphate - GPDH glyceraldehyde-3-phosphate dehydrogenase - NADH nicotinamide adenine dinucleotide (reduced) - OAA oxalacetate - pCMB parachlormercuribenzoate - PEP phosphoenolpyruvate - 6PG 6-phosphogluconate - 2-PGA 2-phosphoglycerate - 3-PGA 3-phosphoglycerate - PGK 3-phosphoglyceric phosphokinase - R1P ribose-1-phosphate - R5P ribose-5-phosphate - RuDP ribulose-1,5-diphosphate - Ru5P ribulose-5-phosphate - SDS sodium dodecyl sulfate     

Effects of R-(1-amino-2-phenylethyl)phosphonic acid on glyceollin accumulation and expression of resistance to Phytophthora megasperma f.sp. glycinea in soybean

(R)-(1-Amino-2-phenylethyl)phosphonic acid (R-APEP), an inhibitor of phenylalanine ammonia-lyase (PAL), was applied to the tap root of 42-h-old soybean (Glycine max. (L.) Merrill cv. Harosoy 63) seedlings during inoculation with zoospores of the incompatible race 1 of Phytophthora megasperma f.sp. glycinea (Pmg1) for 2 h and during a subsequent incubation period. In contrast to L-2-aminooxy-3-phenylpropionic acid, R-APEP was not toxic to the zoospores which remained virulent in presence of the inhibitor. A 50% inhibition of PAL activity in vitro was observed with 4.2 M R-APEP and with 36 M of the S-enantiomer. When R-APEP at 330 M was applied for a total of 36 h to the seedlings, resistance against Pmg 1 was abolished. Such seedlings were indistinguishable in appearance from those seedlings which had been inoculated with the compatible race 3 of Pmg. Roots treated with R-APEP at 330 M showed a reduction of about 47% in glyceollin content when measured 12 h after inoculation, and with 1 mM a 67% reduction. In contrast, treatment with S-APEP (1 mM) caused only a 20% reduction in glyceollin content. As determined by indirect immunofluorescence of fungal hyphae in cryotome cross-sections of roots, the growth pattern of the incompatible race 1 of Pmg changed to that of the compatible race 3 under conditions where R-APEP caused loss of resistance against Pmg 1. The results support the concept of an important role of glyceollin in resistance of soybean against incompatible races of the fungus.Abbreviations R-APEP, S-APEP R.S enantiomers of (1-amino-2-phenylethyl)phosphonic acid - L-AOPP L-2-aminooxy-3-phenylpropionic acid - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - Pmg 1 Phytophthora megasperma f.sp. glycinea race 1 - Pmg 3 Phytophthora megasperma f.sp. glycinea race 3     

Genetics and mapping of adult plant rust resistance in soybean PI 587886 and PI 587880A

Two soybean accessions, PI 587886 and PI 587880A, previously identified as having resistance to Phakospora pachyrhizi Syd. (soybean rust, SBR) were used to create two populations (POP-1 and POP-2) segregating for SBR resistance. F₂-derived F₃ (F_2:3) families from each population were grown in a naturally SBR-infected field in Paraguay to determine inheritance and map resistance genes. Over 6,000 plants from 178 families in POP-1 and over 5,000 plants from 160 families in POP-2 were evaluated at R5 for lesion type: immune reaction (IR), reddish-brown (RB), or tan (TAN) colored lesions. Based on the lesion type present, each F_2:3 family was rated as resistant, segregating or susceptible and this classification was used to infer the F₂-phenotype and genotype. For both populations, the F₂ segregation ratios fit a 1:2:1 (resistant:segregating:susceptible) ratio expected for a single gene (P > 0.05). The RB lesions occurred almost exclusively in the heterozygous class, indicating incomplete dominance under the conditions of this study. Molecular markers flanking the locations of the known resistance genes were used to map the resistance gene in both populations to the Rpp1 locus. However, evaluation of PI 587886 and PI 587880A against eight P. pachyrhizi isolates indicated that the resistance allele in these two accessions was different from Rpp1. This test also demonstrated that these accessions were resistant to at least one P. pachyrhizi isolate collected in the southern US. This is the first report of using an adult plant field-screen with natural rust pressure to map SBR resistance.     

Solar heat gain in a desert rodent: unexpected increases with wind speed and implications for estimating the heat balance of free-living animals

We quantified metabolic power consumption as a function of wind speed in the presence and absence of simulated solar radiation in rock squirrels, Spermophilus variegatus, a diurnal rodent inhabiting arid regions of Mexico and the western United States. In the absence of solar radiation, metabolic rate increased 2.2-fold as wind speed increased from 0.25 to 4.0 m·s^-1. Whole-body thermal resistance declined 56% as wind speed increased over this range, indicating that body insulation in this species is much more sensitive to wind disruption than in other mammals. In the presence of 950 W·m^-2 simulated solar radiation, metabolic rate increased 2.3-fold as wind speed was elevated from 0.25 to 4.0 m·s^-1. Solar heat gain, calculated as the reduction in metabolic heat production associated with the addition of solar radiation, increased with wind speed from 1.26 mW·g^-1 at 0.25 m·s^-1 to 2.92 mW·g^-1 at 4.0 m·s^-1. This increase is opposite to theoretical expectations. Both the unexpected increase in solar heat gain at elevated wind speeds and the large-scale reduction of coat insulation suggests that assumptions often used in heat-transfer analyses of animals can produce important errors.Abbreviations absorptivity of coat to solar radiation - kinematic viscosity of air (mm²·s^-1) - reflectivity of coat to solar radiation - a r _B expected at zero wind speed (s·m^-1) - A _P projected surface area of animal on plane perpendicular to solar beam (cm²) - A _SKIN skin surface area (cm²) - b Coefficient describing change in r _B with change in square-root of wind speed (s^1.5·m^1.5) - d hair diameter (m) - d characteristic dimension of animal (m) - D _H thermal diffusivity of air (m²·s^-1) - E evaporative heat loss (W·m^-2) - I probability per unit coat depth that photon will strike hair - k constant equalling 1200 J·m^-3·°C^-1 - l _C coat depth m) - l _H hair length (m) - M metabolic rate (W·m^-2) - n density of hairs of skin (m^-2) - Q _A solar heat gain to animal (W·m^-2) - Q _I solar irradiance intercepted by animal (W·m^-2) - RQ respiratory quotient - r _A thermal resistance of boundary layer (s·m^-1) - r _B whole-body thermal resistance (s·m^-1) - r _E thermal resistance between animal surface and environment s·m^-1) - r _R radiative resistance (s·m^-1) - r _S sum of r _B and r _E at 0.25 m·s^-1 (s·m^-1) - r _T tissue thermal resistance s·m^-1) - T _AIR air temperature (°C) - T _B body temperature (°C) - T _E operative temperature of environment (°C) - T _ES standard operative temperature of environment (°C) - u wind speed (m·s^-1)     

Sulfate activation in Rhodobacter sulfidophilus and other species of the Rhodospirillaceae

Rhodobacter sulfidophilus, R. capsulatus, R. sphaeroides, Rhodospirillum rubrum, Rhodopseudomonas palustris, R. viridis and Rhodocyclus gelatinosus were found to be able to synthesize adenylylsulfate and 3-phosphoadenylylsulfate from sulfate and ATP. The presence of ATP sulfurylase was proven for the soluble protein fractions of all these species. ADP sulfurylase was not found. ATP sulfurylase was purified from R. sulfidophilus. Its molecular weight was 290,000. The enzyme is stabilized by magnesium ions and elevated salinities. The optimal pH was 8.0, activity was found between pH 6.8 and 9.4. The enzyme is inactivated at temperatures above 40°C. Kinetic studies resulted in K _m(ATP)=0.26 mM, K _m(sulfate)=0.33 mM; K _i(AMP)-2.1 mM, K _i(ADP)=1.15 mM; K _i(APS)=0.8 M; K _i(sulfite)=0.4. mM; K _i(sulfide)=0.66mM.Uncommon abbreviations APS adenylylsulfate - PAPS 3-phosphoadenylylsulfate - PEP phosphoenolpyruvate Dedicated to Professor Gerhart Drews on the occasion of his 60th birthday     

Evidence for simply inherited dominant resistance to Meloidogyne javanica in carrot

Root-knot nematodes (Meloidogyne spp.) are serious pests of carrot (Daucus carota L.) worldwide. While soil treatment with nematicides is the primary means for managing nematodes in carrot, there is a need to identify and introduce host plant resistance for crop improvement. This study was conducted to determine the inheritance of resistance to root-galling and reproduction by M. javanica (Treub) Chitwood in a selection (BR-1252) of carrot variety Brasilia. F₂, F₃, F₄, and BC₁ progenies from the cross BR-1252×B6274 (a susceptible inbred line) were screened in pot tests for reaction to M. javanica. The observed reactions based on galling and egg production on fibrous roots gave segregation patterns in all tests that were consistent with relatively simply inherited dominant resistance. Field testing in progress indicates that this resistance is very effective against both M. javanica and M. incognita. A single gene model fits the observed data acceptably well in F₃ generations. However, the range of 3% to 51% susceptible plants in segregating F₃ families and 1% to 47% in segregating F₄ families is much wider than the 25% expected with a single-gene model, and linked duplicate factors in the coupling phase could also explain the observed segregation patterns. The variation in percentage susceptibility among these families did not clearly cluster into three expected categories (25% S, 20.25% S, and 0.25% S for a 10-cM linkage distance, or 25% S, 16% S and 1% S for 20 cM), but it did tend to occur over the same range. Thus a 10-cM to 20-cM-linked duplicate factor model cannot be dismissed at this time. Egg production data in the F₂, F₃, and F₄ families provided evidence for slightly lower resistance expression in the heterozygous condition. Thus, while overall expressed in a dominant fashion, the resistance does exhibit some allelic dosage response. Received: 14 June 1999 / Accepted: 7 July 1999