The effect of leaf exudates on the spore germination of phylloplane mycoflora of chilli (Capsicum annuum L.) cultivars

Summary Ninetten aminoacids, twelve sugars, eleven organic acids and ten phenols were detected in the leaf exudates of three cultivars of chilli. The number of aminoacids, sugars, organic acids and phenols increased as the plants grew older. More aminoacids and sugars were detected in the exudate from the susceptible cultivar (Malwa). More organic acids and phenols were detected from the resistant cultivar (Simla). The leaf exudate of the resistant cultivar (Simla) inhibited spore germination of the pathogen (Alternaria solani) while that of susceptible (Malwa) stimulated spore germination. The cultivar ‘Patna’ which is moderately resistant, occupied an intermediate position. Spore germination of the isolated fungi was enhanced in leaf exudate of susceptible cultivar (Malwa), while leaf exudates of the moderately resistant (Patna) and resistant (Simla) inhibited spore germination of the majority of fungi isolated. Most of the antagonistic fungi were not isolated from the susceptible cultivar and the percentage spore germination of these fungi was less in leaf exudate of the susceptible cultivar, while leaf exudates of resistant cultivars enhanced the percentage spore germination of antagonistic fungi,viz Aspergillus flavus, A. fumigatus, A. versicolor, Penicillium citrinum, P. restrictum andTrichoderma viride.     

Dissolution of ferric phosphate by alfalfa (Medicago sativa L.) root exudates

Alfalfa (Medicago sativa L.) was grown in hydroponic culture to investigate adaptation to Fe-deficiency. Root exudates released into the nutrient solution from Fe-deficient plants were trapped and condensed on an amberlite XAD-4 resin column. The diethyl ether fraction of these exudates dissolved ferric phosphate remarkably. The dissolving capability was about 62 times higher than that of root exudates obtained from Fe-sufficient plants in complete nutrient solution. The Fe-dissolving compound was separated and identified. It was a new natural compound with molecular formula C₁₄H₁₀O₅ and was identified as 2-(3,5-dihydroxyphenyl)-5,6-dihydroxybenzofuran by means of mass spectrometry and ¹H-nuclear magnetic resonance. This new compound worked as a phytoalexin and inhibited completely the fungal growth of Fusarium oxysporum f. sp. phaseoli.     

Silver nitrate promotes shoot development and plant regeneration of chile pepper (Capsicum annuum L.) via organogenesis

Summary Chile pepper (Capsicum annuum L.) plants were regenerated from cotyledon explantsin vitro in four major stages: bud induction, bud enlargement, shoot elongation, and root development. Bud induction medium contained 0.5 mg/L (2.9μM) indole-3-acetic acid and 2 mg/L (8.9 μM) N⁶-benzyladenine. Bud enlargement occurred, and an occasional shoot appeared when medium with 2 mg/L (6μM) gibberellic acid, 2 mg/L (8.9 μM) N⁶-benzyladenine, and 5 mg/L (29.4 μM) silver nitrate was used. Most shoots elongated after placement on a third medium without plant growth regulators or on fresh plates of bud enlargement medium. Incubations were for 2, 2, and 4 weeks, respectively, at 28.5°C and continuous light. Treatment with silver nitrate was necessary for multiple shoot production and elongation to occur in the third culture stage and was most effective when present in the second-stage medium but not in the bud induction medium. Sixteen to 26% of the shoots rooted in medium with 1 mg/L (5.4 μM) 1-naphthaleneacetic acid after 1 month. Additional shoots transferred to a second rooting medium with 0.1 or 1.0 mg/L (0.54 or 5.4 μM) 1-naphthaleneacetic acid developed roots, increasing the overall rooting efficiency to 70–72%. Most rooted shoots grew well and produced viable seeds when grown in the greenhouse. Other cytokinins tested for plant regeneration were zeatin and thidiazuron. Zeatin induced few shoots and fewer well-developed plants. Thidiazuron induced multiple shoots 4 months after culture began, but many were small and did not elongate further. Phytagar tissue culture grade proved superior to other agars tested, increasing bud induction frequency from 0-33% to 80–93% and eliminating explant hyperhydricity.     

Effect of solarization of soil within plastic bags on root rot of gerbera (Gerbera jamesonii L.)

Solarization of soil, (potting mix = coarse sand:Eucalyptus marginata fines = 1∶1) infested with 3 fungi pathogenic to gerbera (Phytophthora cryptogea, Fusarium oxysporum andRhizoctonia solani), for 3 to 4 weeks within transparent polyethylene bags controlled root rot of gerbera. Solarization for 2 weeks however, was less effective. All plants grown in the infested potting mix which had been kept in shade for 2, 3 or 4 weeks were severely attacked. Solarization of soil within plastic bags for 4 weeks also increased availability of nutrients such as NH₄ ⁺-N, PO₄ ⁻ and K⁺ in comparison to bagged soil kept in the shade for the same period.     

Biological activity and chemical isolation of root saponins of six cultivars of alfalfa (Medicago sativa L.)

Wheat, cheat and Trichoderma viride bioassays were used to establish the relationship between the content of biologically active saponins in the roots and the degree of winter dormancy and/or time of six cultivars of alfalfa over the period January to August, 1988. Wheat and cheat bioassay results indicated no significant difforences among cultivars, whereas T. viride was inhibited most by extracts of roots collected during months with high rainfall and rapid growth. Cheast seedling roots were inhibited 8–10% more than those of wheat seedling roots indicating that alfalfa root saponins were more effective as allelopathic compounds in preventing growth of cheat than that of wheat alone. An average of 14 different saponins per cultivar were separated by thin-layer chromatograms. Saponins, and the aglycones produced by acid hydrolysis of the May samples, were separated by thin-layer chromatography. The conclusion is that the amount, structure, and type of saponins present in alfalfa roots vary with time.     

Quantification of the geocarposphere and rhizosphere effect of peanut (Arachis hypogaea L.)

Roots and pods of field-grown peanut (groundnut) (Arachis hypogaea L.) were sampled at the R3, R5, and R7 developmental stages and examined in comparison to root- and pod-free soil for microbial population densities to assess the geocarposphere and rhizosphere effects. G/ S (no. geocarposphere microorganisms/no. soil microorganisms) and R/S (no. rhizosphere microorganisms/no. soil microorganisms) ratios were calculated for total fungi,Asperigillus flavus, spore-forming bacilli, coryneform bacteria, fluorescent pseudomonads, and total bacteria isolated on low- and high-nutrient media. A clear geocarposphere effect was evidenced by increased population densities of bacteria and fungi associated with developing pods compared to soil. G/S and R/S ratios were generally greater than 1.0 for all groups of microorganisms except bacilli. G/S ratios were greater for total bacteria than for total fungi at two of the three sample times, suggesting that bacteria were stimulated more than fungi in the zone around developing pods. In contrast, R/S ratios, were higher for total fungi than for total bacteria at two of three sample times. The preferential association of fungi and bacteria with early developmental stages of the pod indicates that some microorganisms are particularly well adapted for colonization of the peanut geocarposphere. These microorganisms are logical candidates for evaluation as biological control candiates forA. flavus.     

The effects of Penicillium digitatum and Fusarium oxysporum rots on nutritional content of pawpaw (Carica papaya L.)

Investigations were carried out on the effects of Penicillium digitatum and Fusarium oxysporum on the nutritional value of pawpaw (Carica papaya). Decreases were observed in ash content, phosphorus, sodium, reducing sugars and ascorbic acid levels of fruits infected with P. digitatum, but increases in calcium and potassium content. In fruits infected by F. oxysporium, there were decreases in phosphorus, calcium, sodium ascorbic acid and reducing sugar levels; but the levels of ash content increased. The total protein level increased in the fruits infected with both fungi. These results revealed a reduction in fruit quality.     

Efficient transformation of potato (Solanum tuberosum L.) using a binary vector in Agrobacterium rhizogenes

Summary We transformed three potato (Solanum tuberosum L.) genotypes by using A. rhizogenes or a mixture of A. rhizogenes and A. tumefaciens. Inoculations of potato stem segments were performed with Agrobacterium rhizogenes AM8703 containing two independent plasmids: the wild-type Ri-plasmid, pRI1855, and the binary vector plasmid, pBI121. In mixed inoculation experiments, Agrobacterium rhizogenes LBA1334 (pRI1855) and Agrobacterium tumefaciens AM8706 containing the disarmed Ti-plasmid (pAL4404) and the binary vector plasmid (pBI121) were mixed in a 11 ratio. The T-DNA of the binary vector plasmid pBI121 contained two marker genes encoding neomycin phosphotransferase, which confers resistance to kanamycin, and -glucuronidase. Both transformation procedures gave rise to hairy roots on potato stem segments within 2 weeks. With both procedures it was possible to obtain transformed hairy roots, able to grow on kanamycin and possessing -glucuronidase activity, without selection pressure. The efficiency of the A. rhizogenes AM8703 transformation, however, was much higher than that of the mixed transformation. Up to 60% of the hairy roots resulting from the former transformation method were kanamycin resistant and possessed -glucuronidase activity. There was no correlation between the height of the kanamycin resistance and that of the -glucuronidase activity in a root clone. Hairy roots obtained from a diploid potato genotype turned out to be diploid in 80% of the cases. Transformed potato plants were recovered from Agrobacterium rhizogenes AM8703-induced hairy roots.     

Pod development of groundnut (Arachis hypogaea L.) in solution culture

Normal pods (containing seed) of groundnut (Arachis hypogaea L.) (cv. TMV-2) were successfully raised in darkened, aerated, nutrient solution, but not in the light. The onset of podding was evident 7 to 8 d after gynophores were submerged in the darkened nutrient solution. An examination of pods and submerged portions of gynophore surfaces by scanning electron microscopy showed the presence of two distinctly different protuberances: unicellular root-hair-like structures that first developed from epidermal cells of the gynophores and developing pods; and branched septate hairs that developed later from cells below the epidermal layer. The septate hairs became visible only after the epidermal and associated unicellular structures had been shed by the expanding gynophore and pods. Omission of Mn and Mg from the podding environment increased pod and seed weight, whilst omission of Zn reduced pod and seed weight.     

黑曲霉菌剂不同处理对西瓜根际细菌群落及土壤理化性质的影响

【背景】针对我国设施栽培西瓜土传病害发生严重、土壤理化性质劣变等问题,探究微生物菌剂对西瓜根际土壤微生物群落调控及土壤营养改良的作用。【目的】研究黑曲霉菌剂不同处理方式对设施栽培西瓜根际细菌多样性、群落结构及土壤理化性质的影响。【方法】通过高通量测序分析黑曲霉菌剂不同处理对西瓜根际土壤细菌多样性和群落结构的影响;采用分析化学方法测定西瓜根际土壤理化性质并解析驱动西瓜根际细菌群落动态变化的主要理化因素。【结果】黑曲霉菌剂(Y)、氨基寡糖素水剂(A)及黑曲霉菌剂与氨基寡糖素水剂配施(YA)处理,细菌α多样性指数如Chao1、Ace和Shannon等较对照均有所增加;不同处理西瓜根际优势细菌在门水平包括变形菌门(Proteobacteria)、放线菌门(Actinobacteriota)、绿弯菌门(Chloroflexi)、酸杆菌门(Acidobacteriota)等,其中Proteobacteria相对丰度最高,依次为A (28.26%)>Y (26.74%)>YA (22.61%);黑曲霉菌剂处理西瓜根际土壤芽单胞菌科(Gemmatimonadaceae)和类诺卡氏菌科(Nocardioidaceae)相对丰度较对照明显提高到4.06%和2.43%,氨基寡糖素水剂处理中根际土壤假单胞菌属(Pseudomonas)丰度显著提高(P<0.05),不同处理组微枝形杆菌属(Microvirga)相对丰度较对照均有所提高;黑曲霉菌剂单独或与氨基寡糖素水剂配施处理,西瓜根际土壤全氮、全磷及速效磷含量明显提高;冗余分析(redundancy analysis, RDA)表明,土壤pH、全氮、速效磷、速效钾与西瓜根际细菌群落结构具有显著相关性(P<0.05);Spearman相关性分析表明,根际假单胞菌科相对丰度与土壤全氮、全磷、速效磷、速效钾呈显著或极显著正相关。【结论】黑曲霉菌剂在设施栽培西瓜种植中单独或与氨基寡糖素水剂配施处理,具有提高西瓜根际土壤细菌多样性、增加有益菌群相对丰度、改良土壤理化性质从而提高土壤肥力的作用,该结果为黑曲霉菌剂产品开发及在设施栽培西瓜种植中合理应用提供了科学依据。     

Effects ofin Planta gamma-irradiation on growth, photosynthesis, and antioxidative capacity of red pepper (Capsicum annuum L.) plants

We investigated the effects of low-dose inplanta irradiation on red pepper plants treated with gamma rays of 2, 4, 8, and 16 Gy. Growth was stimulated at 2 and 4 Gy but inhibited at 8 and 16 Gy. Photochemical quenching (qP) increased slightly in all treatment groups for 1 d after irradiation (DAl), whereas non-photochemical quenching (NPQ) decreased more noticeably. These changes in qP and NPQ were transient and had almost recovered to the control level by 2 DAl. Although carotenoid pigments also fluctuated during the experimental period, chlorophylls were almost entirely insensitive to the gamma rays. Irradiation also partially protected leaves from a decrease in photochemical efficiency (Fv/Fm) under conditions of UV-B (2.2 W m^-2) and high light intensity (800 μmol m^-2 s^-1). This enhanced stress resistance could be partly explained by higher levels of SOD and APX activities, as well as ascorbate content. Our results demonstrate for the first time that the carotenoid pigments are the most radio-sensitive and fastest recovering compounds in plants, and that SOD, APX, and ascorbate are important inducible factors for improving stress resistance through the use ofin planta gamma-irradiation.     

Variation in the inheritance of expression among subclones for unselected (uidA) and selected (bar) transgenes in maize (Zea mays L.)

Variation in the inheritance of expression among subclones for an unselected (uidA) and a selected (bar) transgene was analyzed in two individual transformation events in maize. The unselectable gene (uidA) and the selectable gene (bar), on two separate plasmids, were transferred to maize (Hi-II derivative) by particle bombardment of embryogenic calli or suspension cells. A total of 188 fertile T1 plants were obtained from one transformant (transformation event BG which integrated uidA and bar). A total of 98 fertile T1 plants were obtained from a second transformant (transformation event B which integrated bar). Through self-pollination and/or cross-pollination in the greenhouse, approximately 10 000 T2 progeny were obtained from event BG, and more than 1000 T2 progeny were obtained from event B. Segregation of transgene expression was analyzed statistically in a total of 2350 T2 progeny from 40 T1 subclones of event BG and in 217 T2 progeny from six T1 subclones from event B. Variation in the inheritance of expression among subclones for the two transgenes (uidA and bar) was observed in the two transformants. A significant difference was observed between the use of the female or male as the transgenic parent in the inheritance of expression for the two transgenes in event BG. No inheritance through the pollen was observed in two of four T1 subclones analyzed in event B. Co-expression analysis of event BG showed that both transgenes were co-expressed in 67.7% of the T2 plants which expressed at least one of the two transgenes. Of the T2 expressing plants, 30.4% expressed only bar, and 1.9% expressed only uidA. Inactivation of the unselected (uidA) and the selected (bar) transgenes was observed in individual T2 plants.     

Effect of Tilemsi phosphate rock-solubilizing microorganisms on phosphorus uptake and yield of field-grown wheat (Triticum aestivum L.) in Mali

With the broad aim of biologically improving P uptake by wheat fertilized with Tilemsi phosphate rock (TPR), we investigated the effect of inoculation with TPR-solubilizing microorganisms isolated from Malian soils and with a commercial isolate of the arbuscular mycorrhizal (AM) fungus Glomus intraradices (Gi). AM root length colonization, and growth yield and P concentration of the cultivar Tetra of wheat were measured under field conditions in Mali. Experimental plots were established in Koygour (Diré) during the 2001–2002 cropping season. Inoculation treatments included two fungal isolates, Aspergillus awamori (C1) and Penicillium chrysogenum (C13), and an isolate of Pseudomonas sp. (BR2), used alone or in fungus-bacterium combinations in the presence or absence of the AM fungus Gi. In fertilized treatments, 0 or 30 kg P ha⁻¹ was applied as TPR or diammonium phosphate (DAP). In 45-day-old wheat plants, the highest root length AM colonization (62%) was observed with TPR fertilized wheat inoculated with Gi and BR2. Our results suggest that BR2 is a mycorrhizal-helper bacteria and a good plant growth-promoting rhizobacteria. In fact, inoculation of wheat Tetra fertilized with TPR with a combination of Gi, BR2 and C1 produced the best grain yield with the highest P concentration. This work shows that by inoculating seeds with TPR-solubilizing microorganisms and AM fungi under field conditions in Mali it is possible to obtain wheat grain yields comparable to those produced by using the expensive DAP fertilizer.     

In vitro efficacy of <Emphasis Type="Italic">Hyptis suaveolens</Emphasis> L. (Poit.) essential oil on growth and morphogenesis of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f.sp. <Emphasis Type="Italic">gladioli</Emphasis> (Massey) Snyder &; Hansen

Hyptis suaveolens L. (Poit.) essential oil was tested in vitro on the growth and morphogenesis of Fusarium oxysporum f.sp. gladioli (Massey) Snyder & Hansen, which causes Fusarium corm rot and yellows in various susceptible cultivars of gladiolus. The fungitoxicity of the oil was measured by percentage radial growth inhibition using the poisoned food technique (PF) and volatile activity assay (VA). The mycelial growth of the test fungus was completely inhibited at 0.998 and 0.748 μg ml⁻¹ concentration of oil in PF and VA, respectively. Essential oil was found to be fungicidal in nature at 1.247 and 0.998 μg ml⁻¹ concentration of oil in PF and VA, respectively. Determination of conidial germination in the presence of oil was also carried out and it was found that the oil exhibited 100% inhibition of conidial germination at 0.450 μg ml⁻¹ concentration. The effect of essential oil on the yield of mycelial weight was observed and it was found that at 0.873 μg ml⁻¹ concentration no mycelium was recorded and 100% inhibition was observed. The fungitoxicity of oil did not change even on exposure to 100°C temperature or to autoclaving, and the oil also retained its fungicidal nature even after storage of 24 months. The main changes observed under light microscopy after oil treatment were a decrease and loss of conidiation and anomalies in the hyphae such as a decrease in the diameter of hyphae and granulation of cytoplasm. The treatment of the oil also showed highly reduced cytoplasm in the hyphae, showing clear retraction of the cytoplasm from the hyphae and ultimately in some areas hyphae without cytoplasm were also found. GC-MS studies of the essential oil revealed that the oil consisted of 24 compounds with 1,8-cineole as major component accounting for 44.4% of the total constituents.     

Studies on the biosynthesis of tropane alkaloids in Datura stramonium L. transformed root cultures

The relative contributions made by the l-arginine/agmatine/N-carbamoylputrescine/putrescine and the l-ornithine/putrescine pathways to hyoscyamine formation have been investigated in a transformed root culture of Datura stramonium. The activity of either arginine decarboxylase (EC 4.1.1.19) or ornithine decarboxylase (EC 4.1.1.17) was suppressed in vivo by using the specific irreversible inhibitors of these activities, dl--difluoromethylarginine or dl--difluoromethylornithine, respectively. It was found that suppression of arginine decarboxylase resulted in a severe decrease in free and conjugated putrescine and in the putrescine-derived intermediates of hyoscyamine biosynthesis. In contrast, the suppression of ornithine decarboxylase activity stimulated an elevation of arginine decarboxylase and minimal loss of metabolites from the amine and alkaloid pools. The stimulation of arginine decarboxylase was not, however, sufficient to maintain the same potential rate of putrescine biosynthesis as in control tissue. It is concluded that (i) in Datura the two routes by which putrescine may be formed do not act in isolation from one another, (ii) arginine decarboxylase is the more important activity for hyoscyamine formation, and (iii) the formation of polyamines is favoured over the biosynthesis of tropane alkaloids. An interaction between putrescine metabolism and other amines is also indicated from a stimulation of tyramine accumulation seen at high levels of dl--difluoromethylornithine.Abbreviations ADC arginine decarboxylase - DFMA dl--dif-luoromethylarginine - DFMO dl--difluoromethylornithine - MPO N-methylputrescine oxidase - ODC ornithine decarboxylase - PMT putrescine N-methyltransferase We are indebted to Dr. E.W.H. Bohme of Merrell Dow Research Laboratories (Cincinnati, Ohio, USA) for kind gifts of DFMO and DFMA and to Dr. M.J.C. Rhodes for helpful advice and discussion.     

Antibacterial and antimycotic effect of a newly discovered secretion from larvae of an endoparasitic insect,Pimpla turionellae L. (Hym.)

Three analogues of the peptidyl pheromone, pheromone of Saccharomyces kluyveri, synthesized based on the amino acid sequence proposed by Sato et al. (Agric Biol Chem 45:1531–1533, 1981) were tested for both shmoo-inducing and agglutinability-inducing actions. Purified natural pheromone of the yeast showed the highest activity among the peptides tested. When methionine in the peptides was oxidized, the activity decreased significatly. Pheromone of S. kluyveri induced sexual agglutinability in a cells of Saccharomyces cerevisiae, and shmoo in a cells of S. cerevisiae and S. kluyveri. a Pheromone of S. kluyveri had no agglutinability-inducing action on cells of S. cerevisiae. a Cells of S. kluyveri inactivated only pheromone of the same species, but a cells of S. cerevisiae inactivated pheromones of both S. cerevisiae and S. kluyveri.     

Influence of BA and sucrose on the competence and determination of pepper (Capsicum annuum L. var. Sweet Banana) hypocotyl cultures during shoot formation

Summary The simultaneous presence of 6-benzyladenine (BA) and sucrose in a Murashige and Skoog medium (SIM) during the initial stages of shoot initiation have been found to be obligatory for high-frequency shoot formation in the Capsicum annuum L. var. Sweet Banana upper hypocotyl explants. The explants are determined for shoot formation following a minimum of 8 days of culture on SIM. Deprivation of exogenous sucrose from day 6 to day 20 of culture had no effect on the shoot forming response of the explants. BA and sucrose appear to act independently on different aspects of the competence of explants to respond to SIM during shoot initiation.Abbreviations BA N⁶-benzyladenine - MS Murashige and Skoog medium - SIM shoot induction medium - HFM hormone free medium - SUC sucrose minus medium