Amelioration of chilling stress by paclobutrazol in watermelon seedlings

Paclobutrazol (PBZ) is a member of the triazole plant-growth inhibitor group that is responsible for inducing tolerance to number of biotic and abiotic stresses. An experiment was, therefore, conducted to test whether PBZ application at various concentrations (0, 25, 50 and 75 mg L⁻¹) through seed soaking or foliar spray would protect watermelon (Citrullus lanatus) seedlings, subjected to chilling stress. Thirty-five-day old plants were exposed to chilling 5 h/day at 4 °C for 5 days. PBZ improved growth rate of watermelon seedling subjected to chilling stress and increased relative leaf chlorophyll content (RLCC) and chlorophyll fluorescence ratio (Fv/Fm) compared with the control at the end of chilling stress. PBZ ameliorated the injury caused by chilling stress by inhibiting increases in proline and leaf electrolyte leakage, which suggested that PBZ ameliorated the negative effect of chilling stress. PBZ was most effective in increased chilling tolerance of watermelon seedling when applied using the seed soak method than as a foliar spray. The best protection appeared to be obtained from seedlings seed soaked with PBZ at 50 and 75 mg L⁻¹.     

Genetic transformation of Citrus sinensis cv. Hamlin with hrpN gene from Erwinia amylovora and evaluation of the transgenic lines for resistance to citrus canker

Transgenic Citrus sinensis (L.) Osb. cv. Hamlin plants expressing the hrpN gene were obtained by Agrobacterium tumefaciens (Smith and Towns) Conn-mediated transformation. hrpN encodes a harpin protein, which elicits the hypersensitive response and systemic acquired resistance in plants. The gene construct consisted of gst1, a pathogen-inducible promoter, a signal peptide for protein secretion to the apoplast, the selection genes nptII or aacC1 and the Nos terminator. The function of gst1 in citrus was evaluated in transgenic C. sinensis cv. Valencia harboring the reporter gene uidA (gus) driven by this promoter. Histochemical analysis for gus revealed that gst1 is activated in citrus leaves by both wounding and inoculation with Xanthomonas axonopodis Starr and Garces pv. citri (Hasse) Vauterin et al. Genetic transformation was confirmed by Southern blot hybridization in eight cv. Hamlin acclimatized plants. RT-PCR confirmed hrpN gene expression in seven cv. Hamlin transgenic lines before pathogen inoculation. Some hrpN transgenic lines showed severe leaf curling and abnormal growth. Six hrpN transgenic lines were propagated and evaluated for susceptibility to X. axonopodis pv. citri. RT-PCR confirmed gene expression in all six hrpN transgenic lines after pathogen inoculation. Several of the hrpN transgenic lines showed reduction in susceptibility to citrus canker as compared with non-transgenic plants. One hrpN transgenic line exhibited normal vegetative development and displayed very high resistance to the pathogen, estimated as up to 79% reduction in disease severity. This is the first report of genetic transformation of citrus using a pathogen-inducible promoter and the hrpN gene. Further evaluations of the transgenic plants under field conditions are planned. Nevertheless, the evidence to date suggests that the hrpN gene reduces the susceptibility of citrus plants to the canker disease.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Polyamines enhance chilling tolerance of cucumber (Cucumis sativus L.) through modulating antioxidative system

Cucumber chilling-resistant cultivar Changchun mici and -sensitive cultivar Beijing jietou were used in this study to investigate the effects of exogenous PAs on protection against chilling injury as well as on changes of physiological features, and the fluctuation of free PAs content in the leaves under chilling stress. Upon chilling treatment, free spermidine (Spd), spermine (Spm) and putrescine (Put) were remarkably induced in the leaves of cv. Changchun mici 1 day after treatment. The induction of Put declined thereafter, whereas Spd and Spm levels increased steadily. In the leaves of cv. Beijing jietou, Put content was increased only at 1 day after chilling while Spd content decreased significantly upon chilling treatment. Chilling reduced soluble protein content, and decreased the activities of antioxidant enzymes, including superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) only in Beijing jietou. However, these changes could be renovated by exogenous application of Put and Spd. It was also found that pretreatment with Put and Spd diminished the increased electrolyte leakage and malondialdehyde (MDA) content caused by chilling in the leaves of both cultivars. Pretreatment of methyglyoxal-bis-(guanylhydrazone) (MGBG), the PAs biosynthetic inhibitor cancelled the effects of PAs in most of the treatments. Moreover, histochemical staining and quantitative measurements showed that exogenous application of Put and Spd eliminated but MGBG exaggerated the hydrogen peroxide (H₂O₂) accumulation caused by chilling stress, especially in leaves of Beijing jietou. Interestingly, Changchun mici was found to contain higher endogenous free PAs contents compared to Beijing jietou. While no significant difference of SOD, POD and CAT activities was found between non-chilling Changchun mici and Beijing jietou seedlings, the former exhibited higher APX activity than the latter. These results suggest that PAs play important roles in the tolerance of cucumber against chilling stress, which is most likely achieved by acting as oxidative machinery against chilling injury.     

Breaking the intergeneric hybridization barrier in Carica papaya and Vasconcellea cauliflora

The present investigation was undertaken to develop PRSV (Papaya ringspot virus) resistant hybrids through intergeneric hybridization. Intergeneric hybridization was done involving nine Carica papaya cultivars as female and Vasconcellea cauliflora as male. To break the intergeneric hybridization barrier, various nutrient combinations were used. Among the combinations used, sucrose 5%, sucrose 5% + boron 0.5% and sucrose 5% + CaCl₂ 0.5% improved the fruit set and seed set percentage. A total number of 1197 flowers were pollinated and 308 fruits were obtained. On extraction, 721 seeds were obtained from CO 7, Pusa Nanha and CP 50. Out of 721 F₀ seeds (crossed seeds) sown, 419 seeds germinated and artificial screening for PRSV was carried out 27 days after sap inoculation. Out of 29 F₁ hybrid plants from CO 7 x V. cauliflora cross, only six plants namely CO 7V1 to CO 7V6 were found free from PRSV symptoms. Similarly, out of 55 F₁ hybrids from cross involving Pusa Nanha x V. cauliflora only 23 plants namely PNV1 to PNV23 were found free from the symptoms and 70 plants namely CPV1 to CPV70 out of 335 plants of CP50 x V. cauliflora cross were found free from PRSV symptoms. Among the crosses, Pusa Nanha x V. cauliflora had higher yield under PRSV infected conditions, however, total soluble solids and total sugars were found lesser than the CO 7 x V. cauliflora cross. The hybridity of the progenies were confirmed by using ISSR (Inter Simple Sequence Repeats) primers by the amplification of DNA from progenies and their parents. ISSR primers UBC 856, UBC807 and ISSR primer combinations UBC 856-817, UBC 810-817, UBC 861-817, UBC 856-810, UBC 861-810 and UBC 856-817 clearly amplified specific bands of the male parent, which were present in F₁ progenies, but it was absent in female parents.     

In vitro induced tetraploid of Dendranthema nankingense (Nakai) Tzvel. shows an improved level of abiotic stress tolerance

The tetraploid of Dendranthema nankingense (Nakai) Tzvel. was induced by the colchicine treatment using nodal segments. Ploidy level was determined by an analysis of flow cytometry and chromosome counting. The morphological characteristics such as the stomata, leaves, flowers and pollen grains of the tetraploid were significantly larger than those of the diploid. The tolerance responses of the diploid and tetraploid were compared under the imposition of heat, cold, drought and salinity stress. Semi-lethal temperatures suggest that cold tolerance is improved by polyploidization, but the heat tolerance is reduced. Under drought and salt stress, the activity of peroxidase (POD) and relative water content (RWC) in the tetraploid were higher than those in the diploid. Accordingly its malondialdehyde (MDA) content maintained a lower level. The content of chlorophyll (a + b) in the tetraploid was higher, and decrease of its content was postponed in tetraploid compared with the diploid under salt stress. It suggested that polyploidization could alleviate oxidative stress, maintain good water balance and higher chlorophyll (a + b) content, thereby enhanced the drought and salt tolerance in colchicine induced tetraploid.     

Development of seedless and Mal Secco tolerant mutant lemons through budwood irradiation

Mal secco (caused by Phoma tracheiphila (Petri) Kantsch. and Gik.) is the most destructive fungal disease of lemon plantations worldwide and seedless lemons would be preferred by most consumers. Five dosage levels, 0, 3, 5, 7, and 9 kiloradian (krad), of cobalt (⁶⁰Co) gamma irradiation were applied to budstick of ‘Kutdiken’ lemon (Citrus limon (L.) Burm. f.) clone KT-2A. Mutations were stabilized in three vegetative generations. Three hundred fifty-eight and 478 M1V3 (mutation one and vegetation three) plants were evaluated for seed number and mal secco tolerance in the field and the greenhouse, respectively. LD₅₀ was around 5 krad gamma irradiation for ‘Kutdiken’ lemon. The seed number varied from 0 to 34 per fruit. The level of mal secco tolerance also varied significantly among the plants from 1.0 (no symptom) to 4.3 (high level of disease occurance). The stable seedless and mal secco tolerant plants were obtained from 5 and 7 krad irradiation: the three mutants from 5 krad irradiation gave more lemon-like fruits, while 7 krad irradiation caused altered tree morphology and early maturation of fruits. This study shows considerable potential for lemon cultivar improvement aiming to obtain seedless and mal secco tolerant lemons.     

Towards crop improvement in bell pepper (Capsicum annuum L.): Transgenics (uid A::hpt II) by a tissue-culture-independent Agrobacterium-mediated in planta approach

Agrobacterium tumefaciens-mediated transformation has been one of the methods used to generate transgenic plants in bell pepper. An alternate transformation method that avoids/minimizes tissue culture would be beneficial for the improvement of bell pepper due to its recalcitrant nature. In this report, transgenic bell pepper plants have been developed by a tissue-culture-independent A. tumefaciens-mediated in planta transformation procedure. In the present study, two open pollinated varieties viz., Arka Gaurav and Arka Mohini were used for transformation. Agrobacterium strain EHA105 harboring the binary vector pCAMBIA1301 that carries the genes for β-glucuronidase (uid A) and hygromycin phosphotransferase II (hpt II) was used for transformation. GUS histochemical analysis of T₀ and T₁ plants at various stages of growth followed by molecular analysis using PCR, Southern analysis and RT-PCR allowed selection of transgenics. The method resulted in 17.8% and 11.4% of the T₀ plants in Arka Gaurav and Arka Mohini being selected as chimeric and 35.0% and 29.7%, respectively, were identified as stable transformants in the T₁ generation based on PCR analysis.     

Ethylene influences development and flowering of Ptilotus spp. in vitro and ex vitro

The genus Ptilotus has immense potential for ornamental horticulture but its commercial development has been hindered by propagation limitations. Poor seed quality and germination are reported. Cutting propagation is limited by cutting supply as the juvenile phase of Ptilotus is short. Micropropagation has been used in an attempt to overcome these difficulties but explants become floral in vitro and this causes plantlets to elongate. Ethephon has been used to control flowering of stock plants of many ornamental species. This study investigated the effect of ethephon applied to young (3-week-old, deflasked from tissue culture) and mature (1-year-old) Ptilotus plants in a greenhouse. A system of applying gaseous ethylene at 0, 100, 200 and 300 mg l⁻¹ to the headspace of in vitro plantlets in glass jars was developed and the response of in vitro plantlets to ethylene studied. One-year-old Ptilotus plants were treated with 500 mg l⁻¹ ethephon 2 days before pruning or 1 or 2 weeks after pruning. Ethephon application 2 days before pruning decreased the number of inflorescences and increased the number of shoots (compared to the control) but was phytotoxic. Ethephon applications of 150 or 300 mg l⁻¹ applied weekly or fortnightly to 3-week-old plants deflasked from tissue culture reduced plant height and number of inflorescences and at low concentrations increased the number of new shoots. A fortnightly application at 150 mg l⁻¹ is recommended. Previous reports on the effects of ethylene on inflorescence production on plantlets in vitro are limited. Our study showed that exposure of in vitro plantlets of P. nobilis to ethylene gas at 100 mg l⁻¹ for 1 h significantly increased the number of shoots and plant height but this did not occur for plantlets of P. spicatus. Plantlets of P. spicatus exposed to transient ethylene at 200 and 300 mg l⁻¹ showed significantly greater rooting (52.4%) than the control (13.6%).     

Production of transgenic sweetpotato plants resistant to stem nematodes using oryzacystatin-I gene

Stem nematode (Ditylenchus destructor Thorne) is one of most serious diseases limiting sweetpotato (Ipomoea batatas (L.) Lam.) production, and it is urgent to develop sweetpotato varieties resistant to this disease. In present study, we have developed transgenic sweetpotato (cv. Xushu 18) plants resistant to stem nematodes using oryzacystatin-I (OCI) gene with Agrobacterium tumefaciens-mediated transformation. A. tumefaciens strain EHA105 harbors a binary vector pCAMBIA1301 with OCI gene, uidA gene and hptII gene. Selection culture was conducted using 7 mg/l hygromycin. A total of 2119 plants were produced from the inoculated 1710 cell aggregates of Xushu 18 via somatic embryogenesis. GUS assay and PCR analysis of the regenerated plants randomly sampled showed that 92.8% of the regenerated plants were transgenic plants. Transgenic plants exhibited enhanced resistance to stem nematodes compared to the untransformed control plants by the field evaluation and the inoculation test with stem nematodes and stem nematode-resistant plants were selected from the transgenic plants. Stable integration of the OCI gene into the genome of resistant transgenic plants was confirmed by Southern blot analysis, and the copy number of integrated OCI gene ranged from 1 to 3. High level of OCI gene expression in the resistant transgenic plants was demonstrated by real-time quantitative PCR analysis. This study provides a way for improving stem nematode resistance of sweetpotato.     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Regeneration and transformation system in Mirabilis jalapa

Protocols for in vitro regeneration and production of in vitro-propagated plants and a transformation system were developed for Mirabilis jalapa (Nyctaginaceae). Among the types of explants and the different media tested, consistent shoot regeneration was obtained only from nodal segments grown in a regeneration medium consisting of Murshashige and Skoog medium supplemented with 2 mg l⁻¹ 6-benzyladenine, 2 mg l⁻¹ zeatin and 1 mg l⁻¹ indole acetic acid. Regeneration efficiency was dependent on the type of plant – white or pink flowers – used as the source of explants. Stable transformation was obtained following inoculation of nodal segments with Agrobacterium tumefasciens strain EHA105, which harbours the binary plasmid pAD1339 containing both nptII and gus genes under the control of the 35S promoter. Transformation was confirmed by PCR and Southern blot analysis of genomic DNA from mature regenerated plants. β-Glucuronidase (GUS) activity was observed only in tissues regenerated from in vitro-grown plants and not in tissues originating from greenhouse-grown plants. GUS expression was not uniform in regenerated leaves and showed a chimera pattern.     

Fruits are more sensitive to salinity than leaves and stems in pepper plants (Capsicum annuum L.)

The effects of NaCl stress on plant growth, gas-exchange, activity of superoxide dismutase (SOD), rate of lipid peroxidation, and accumulation of Na⁺ ion and sugar were investigated in leaves and fruits of pepper plants (Capsicum annuum L.). Especially, the gene expression of l-galactono-1,4-lactone dehydrogenase (GalLDH), which is the last enzyme of ascorbic acid (AsA) biosynthesis, and the relationships between AsA level and Na⁺ concentration in plant tissue were investigated with increasing salinity. Plants were treated with three treatments: the control (0 mM NaCl) and two salinity levels (50 and 100 mM NaCl) for 21 days under greenhouse conditions. Plant growth was markedly restricted due to the reduction of photosynthetic rate and the increase of Na⁺ accumulation in leaves with the increasing intensity of NaCl stress. Salinity had more effect on fruit growth comparing to leaf growth, suggesting that fruits could be more sensitive to salinity than leaves. In comparison with the control, salt stress significantly increased lipid peroxidation (as measured as malondialdehyde content) but decreased SOD activity in both fruits and leaves although the effect was larger in fruits; and the rate of the decrease in SOD activity was greater than that of the increase in lipid peroxidation. The AsA concentration transiently increased first 7 days but it slightly decreased from the initial level in the end of treatment day 21. The change in GalLDH gene expression was similar to AsA concentration. The accumulation of Na⁺, the reduction of AsA level at severe salinity stress were greater in fruits than in leaves; and AsA level had a negative relationship with Na⁺ concentration in both leaves and fruits. These results suggest that the difference in salt sensitivity between fruits and leaves in pepper plants can be related to the difference in inhibition of AsA synthesis, which in turn is probably due to the toxicity of extreme accumulation of Na⁺.     

Transformation of Brassica oleracea var. capitata with bacterial betA gene enhances tolerance to salt stress

The bacterial betA gene for biosynthesis of glycinebetaine was transferred to cabbage (Brassica oleracea var. capitata) cultivar ‘Golden Acre’ through Agrobacterium-mediated transformation of hypocotyl explants. Transgenic status was established through Southern hybridization and mRNA expression in the shoots. The transformants exhibited higher tolerance to NaCl stress compared to untransformed parent plants. In physiological assessment of salinity tolerance, transgenics showed better growth response and greater stability in maintaining plant water relations at increasing levels of salinity. These results demonstrate that engineering glycinebetaine biosynthetic pathway into cabbage can lead to enhanced salt tolerance.     

Cold tolerance and short day acclimation in perennial Gaura coccinea and G. drummondii

The use of related species to integrate important traits into cultivated crops is a common practice in plant breeding. Gaura coccinea and, potentially its derived species Gaura drummondii, could be donor species for introgressing cold tolerance into non-hardy G. lindheimeri. However, cold tolerance and acclimation has not been studied in these species, so protocols for determining these traits are required. The objectives of this study were to determine the relative cold tolerance of G. coccinea, G. drummondii and whether short day photoperiod is involved in cold acclimation. G. drummondii from Texas, USA and G. coccinea from Minnesota and Texas, USA were subjected to freezing tests using whole plant or electrolyte leakage after natural acclimation or non-acclimation conditions. Minnesota genotypes were able to withstand colder temperatures (−12 °C) than Texas genotypes (−9 °C). Acclimation capacity was determined for whole plant and electrolyte leakage assays using three different plant organs—stem, crown, and rhizome. Underground rhizomes were the best predictors of cold tolerance, however they were difficult to obtain. Stem sections of G. drummondii (Texas) and G. coccinea (Minnesota and Texas) were used to determine a shift in acclimation under short days. The Minnesota G. coccinea genotypes demonstrated greater cold tolerance after 3 weeks of short days while Texas G. coccinea, G. drummondii genotypes did not change even after 5 weeks.     

Osmotic adjustment,proline accumulation and cell membrane stability in leaves of Cocos nucifera submitted to drought stress

The role of drought-induced proline accumulation in coconut leaves is still unclear. With the objective of evaluating the impact of water shortage on leaf osmotic potential, proline accumulation and cell membrane stability in young plants of two Brazilian Green Dwarf coconut ecotypes from contrasting areas (Brazilian Green Dwarf from Una, Bahia, UGD, and from Jiqui, Rio Grande do Norte, JGD), a pot experiment was conducted under greenhouse conditions. Three drought cycles consisting of suspension of irrigation until the net photosynthetic rate (A) approached zero and rewatering until recovery of A to 85% of the irrigated control plants. Pre-dawn leaf water potential (Ψ_PD) reached −1.2 MPa at the point of maximum stress (PMS). Dry matter production and leaf area were severely reduced by drought treatment in the two ecotypes. Corrected values of osmotic potential were significantly reduced in stressed plants of the two ecotypes. Green dwarf coconut palm showed low osmotic adjustment (from 0.05 to 0.24 MPa) and significant accumulation of proline (from 1.5 to 2.1 times in relation to control) in leaflets in response to water deficit. Considering the growth reduction observed in both ecotypes, proline was not associated to osmoregulation. On the other hand, the absence of membrane damage, as indicated by electrolyte leakage method, suggests that the protective role of proline in this specie can be more important. The two ecotypes of Green dwarf coconut palm behaved similarly in the present experiment for most traits evaluated. Slight differences among the ecotypes were observed with respect to the response to treatments, such as higher proline accumulation in JGD.     

Response of Vitis vinifera L. plants inoculated with Phaeoacremonium angustius and Phaeomoniella chlamydospora to thiabendazole,resveratrol and sodium arsenite

The effect of some pesticides (sodium arsenite, thiabendazole and ziram) and the natural phytoalexin (resveratrol) on mycelial growth of Phaeomoniella chlamydospora and Phaeoacremonium angustius was studied. Several strains of these species were grown on malt extract agar (MEA) plates containing different concentrations of inhibitory compounds and colony diameters were measured. While sodium arsenite and ziram had little effect on the growth of both species, thiabendazole inhibited colony growth, at minimum concentrations of 6 μM for Ph. chlamydospora and 15 μM for P. angustius. Resveratrol at concentrations equal to or grater than 867 μM also inhibited colony growth of both species. To assay the effect of these substances on plant response to infection, in vitro grapevines were inoculated with Ph. chlamydospora or P. angustius spores and were grown in the presence of sodium arsenite (0–30 μM), thiabendazole (0–30 μM) or resveratrol (0–876 μM). Infected untreated plants and sodium arsenite-treated plants developed symptoms of senescence (reduced growth, increased membrane lipid peroxidation, and decreased chlorophyll content and fluorescence). In contrast, infected plants treated with thiabendazole (30 μM) or with resveratrol (876 μM) showed similar characteristics of fresh weight, malondialdehyde accumulation and chlorophyll fluorescence to those of uninfected plants. These results are promising with respect to the use of thiabendazole-containing pesticides as alternatives to currently used pesticides for control of esca in vines. Results also suggest that the presence of resveratrol in grapevines may be useful to induce resistance to these fungi.     

Factors affecting haploid induction through in vitro gynogenesis in summer squash (Cucurbita pepo L.)

Haploid production using in vitro ovule cultures has long been recognized as an important tool to produce haploid and homozygous double-haploid plants for genetic studies and plant breeding programs. In the present study, four experiments were carried out to study the influence of genotype, position of female flowers on plant stem, temperature and sucrose concentration on the in vitro gynogenesis induction of squash. (1) Ovules of 12 genotypes were excised from female flowers, 1 day before anthesis, and cultured onto MS medium containing 3% sucrose and 1 mg l⁻¹ from each of kinetin and 2,4-D (2,4- dichlorophenoxy acetic acid). Differences in response among genotypes were demonstrated. Raad F₁ showed the highest percentage of responding ovules and number of plantlets per dish with 48.8% and 15 plants, respectively. The results revealed that genotype is a key factor influencing the in vitro gynogenesis in squash. (2) Ovules were excised from first, second and third female flower of two hybrids (Giad and Raad) and cultured onto the mentioned above medium. The highest percentage of responding ovules and number of plantlets per dish were obtained from ovules excised from the second female flower on the plant stem. (3) Effect of temperature (4 and 32 °C) for 0, 4, 7 and 12 days on the ovule culture of Queen F₁ was studied. Ovules incubated at 4 or 32 °C for 4 days produced a better embryogenic response. (4) Three sucrose concentrations (30, 60 and 90 g l⁻¹) were tested with the ovule cultures of the local cultivar (Eskandrani). Differences among sucrose concentrations were statistically significant and ovules cultured on the MS medium containing 30 g l⁻¹ produced the best result. MS medium containing 90 g l⁻¹ did not produce gynogenic ovules.     

The inheritance of two novel subgynoecious genes in cucumber (Cucumis sativus L.)

Cucumber (Cucumis sativus L.), which is a vegetable crop, has served as the model system for sex expression in flowering plants, and the inheritance of sex expression in cucumber is well documented. However, the genetics of subgynoecism expression in cucumber had rarely been described. In this study, we investigated the inheritance of subgynoecious traits in cucumber plants with the inbred cucumber lines of subgynoecious (C. sativus L. var sativus cv 97-17 and S-2-98) as the materials. Genetic analysis had showed the two subgynoecious inbred lines were controlled by one pair of recessive gene and one pair of incompletely dominant gene, which were designated presently as mod-F2 and Mod-F1, respectively. Furthermore, the mod-F2 and Mod-F1 loci, which enhance the intensity of femaleness, also inherited independently with F and M genes.