Susceptibility of citrus species to Alternaria alternata, the causal agent of the Alternaria brown spot

Alternaria alternata, the causal agent of Alternaria brown spot (ABS), causes necrosis on leaves, twigs, and fruit, reducing the productivity and quality of fruits. Tangerines and their hybrids are highly susceptible to the disease. Species, hybrids, and cultivars of Citrus from the germplasm bank of the Estação Experimental de Citricultura de Bebedouro, São Paulo, Brazil, were evaluated in 2004 and 2005 with respect to their resistance to A. alternata, both through natural infection and by inoculation. Detached leaves were also used to demonstrate susceptibility or resistance to the disease. Ten cultivars of Satsumas (Citrus unshiu), and 14 cultivars of Clementine mandarin (C. clementina) did not show any symptoms of the disease in their leaves, either through natural infection or when inoculated in the field. The Burguess SRA-412, Wallent SRA-438, Carvalhais, Ampefy SRA-459, Ananas SRA, and Macaque SRA-426 mandarin hybrids (C. reticulata) did not show symptoms of the disease under natural or artificial infection in the field. Some cultivars of C. deliciosa, C. tangerina, C. erythrosa, and C. temple showed symptoms of the disease, even though no previous record of their susceptibility to Alternaria brown spot had been previously reported. The hybrids Fairchild, Nova, Page, Fortune, and Sunburst were susceptible to the disease. However, Fremont mandarin (a crossing between C. clementina and C. reticulata), Encore (C. nobilis × C. deliciosa), and Fallglo (C. reticulata × C. paradisi) did not show symptoms in field, and few symptoms were verified in detached leaves. These materials are promising for the cultivation of tangerines, and will enable genetic improvement for the development of cultivars resistant to Alternaria brown spot.     

Tree performance and fruit yield and quality of ‘Okitsu’ Satsuma mandarin grafted on 12 rootstocks

The citriculture in Brazil, as well as in other important regions in the world, is based on very few mandarin cultivars. This fact leads to a short harvest period and higher prices for off-season fruit. The ‘Okitsu’ Satsuma (Citrus unshiu Marc.) is among the earliest ripening mandarin cultivars, and it is considered to be tolerant to citrus canker (Xanthomonas citri subsp. citri Schaad et al.) and to citrus variegated chlorosis (Xylella fastidiosa Wells et al.). Despite having regular fruit quality under hot climate conditions, the early fruit maturation and absence of seeds of ‘Okitsu’ fruits are well suited for the local market in the summer (December through March), when the availability of citrus fruits for fresh consumption is limited. Yet, only a few studies have been conducted in Brazil on rootstocks for ‘Okitsu’. Consequently, a field trial was carried out in Bebedouro, São Paulo State, to evaluate the horticultural performance of ‘Okitsu’ Satsuma mandarin budded onto 12 rootstocks: the citrandarin ‘Changsha’ mandarin (Citrus reticulata Blanco) × Poncirus trifoliata ‘English Small’; the hybrid Rangpur lime (Citrus limonia Osbeck) × ‘Swingle’ citrumelo (P. trifoliata (L.) Raf. × Citrus paradisi Macfad.); the trifoliates (P. trifoliata (L.) Raf.) ‘Rubidoux’, ‘FCAV’ and ‘Flying Dragon’ (P. trifoliata var. monstrosa); the mandarins ‘Sun Chu Sha Kat’ (C. reticulata Blanco) and ‘Sunki’ (Citrus sunki (Hayata) Hort. ex. Tanaka); the Rangpur limes (C. limonia Osbeck) ‘Cravo Limeira’ and ‘Cravo FCAV’; ‘Carrizo’ citrange (Citrus sinensis × P. trifoliata), ‘Swingle’ citrumelo (P. trifoliata × C. paradisi), and ‘Orlando’ tangelo (C. paradisi × Citrus tangerina cv. ‘Dancy’). The experimental grove was planted in 2001, using a 6 m × 3 m spacing, in a randomized block design. No supplementary irrigation was applied. Fruit yield, canopy volume, and fruit quality were assessed for each rootstock. A cluster multivariate analysis identified three different rootstock pairs with similar effects on plant growth, yield and fruit quality of ‘Okitsu’ mandarin. The ‘Flying Dragon’ trifoliate had a unique effect over the ‘Okitsu’ trees performance, inducing lower canopy volume and higher yield efficiency and fruit quality, and might be suitable for high-density plantings. The ‘Cravo Limeira’ and ‘Cravo FCAV’ Rangpur limes induced early-ripening of fruits, with low fruit quality. ‘Sun Chu Sha Kat’ and ‘Sunki’ mandarins and the ‘Orlando’ tangelo conferred lower yield efficiency and less content of soluble solids for the latter rootstock.     

Production and characterization of new triploid seedless progenies for mandarin improvement

Eighty-six triploid Citrus plants were recovered from interploid crosses between a natural tetraploid selection of the tangerine ‘Dancy’ (Citrus reticulata Blanco, cultigroup ‘Tangerine’), used as the pollen parent, and two seedy selections of diploid mandarins (C. reticulata Blanco) as well as one clementine (Citrus clementina Hort. ex Tan.): ‘Fortune’ mandarin, ‘Wilking’ mandarin and ‘Monreal’ clementine. Flow cytometric analysis was used for screening the triploid plantlets and the ISSR-PCR technique was used to characterize the obtained triploids through a double approach, confirming the hybrid nature of the offspring and allowing the analysis of the genetic pool obtained. Selection among triploid genotypes generated from elite seedy parents will give us a better chance to obtain superior mandarin cultivars characterized by true seedlessness.     

Cybrid/hybrid plants regenerated from somatic fusions between male sterile Satsuma mandarin and seedy tangelos

Somatic hybridization provides an alternative for transferring mitochondria-encoded cytoplasmic male sterility (CMS). Herein, symmetric protoplast electrofusion was conducted between embryogenic callus protoplasts of Citrus unshiu Marc. cv. Guoqing No. 1 (G1), a CMS cultivar, and mesophyll-derived protoplasts of seedy ‘Page’ tangelo [C. reticulata Blanco × (C. reticulata Blanco × C. paradisi Macf.)] or ‘Nova’ tangelo [C. reticulata Blanco × (C. reticulata Blanco × C. paradisi Macf.)], to transfer CMS trait. Flow cytometry analysis showed that 14 plants recovered from G1 + ‘Page’ tangelo that displayed typical morphological character of ‘Page’ were diploid, and 6 plants regenerated from G1 + ‘Nova’ tangelo were tetraploid. Genetic compositions of regenerated plants from the two fusions were determined by SSR, CAPS and chloroplast-SSR analysis. Cybrid nature of diploids from G1 + ‘Page’ tangelo with nuclear DNA from ‘Page’, mitochondrial DNA (mtDNA) from the G1 and chloroplast DNA (cpDNA) derived from either parent was confirmed. Tetraploid plants from G1 + ‘Nova’ tangelo were identified as somatic hybrids with random cpDNA inheritance. The regenerated cybrid and hybrid plants hold great potential for Citrus seedless breeding at diploid or triploid levels.     

QTL analysis and regression model for estimating fruit setting in young Citrus trees based on molecular markers

This study was conducted to assess the genetic basis and develop a regression model for a QTL trait, fruit setting of a full sib population of 164 hybrids obtained between ‘Clementine’ mandarin (Citrus reticulata Blanco ‘Clementine) and ‘Orlando’ tangelo’ (Citrus paradisi Macf. ‘Duncan’ × C. reticulata Blanco ‘Dancy’). Fruit setting of a 164 full sib population field-planted in 2007 was evaluated by visual counting of fruits in 2008, 2009, and 2010. We estimated linkage groups and effects of QTLs by using MapQTL5. Based on interval mapping, seven linkage groups of the maternal and eight linkage groups of the paternal maps harboured QTLs of the fruits setting, covering a total 300 of 1744 cM Citrus map. Only three segments were associated with all three-year data (one in ‘Clementine’ and two in ‘Orlando’ map) spanning 60 cM of 1744 cM of Citrus linkage map. Twenty-seven (17%) and 13 (8%) hybrids consistently produced less than 5 fruits and the highest number of fruits (≥50) in their 2nd, 3rd, and 4th ages. Based on BACKWARD elimination procedure of PROC REG option nested in SAS program, regression models constructed for 2008, 2009, and 2010s fruit setting explained 35, 81, and 38% of the total phenotypic variation (R²) observed in the 164 full-sib hybrids, respectively (P ≤ 0.05). This study indicated that early fruit setting was a complex trait affected by many QTLs and the regression model developed in this study might be used to predict performances of hybrids with similar genetic background.     

Evaluation of ‘Hamlin’ sweet orange + ‘Montenegrina’ mandarin somatic hybrid for tolerance to Xanthomonas axonopodis pv. citri and Xylella fastidiosa

Asiatic citrus canker (ACC), caused by Xanthomonas axonopodis Starr & Garces pv. citri (Hasse) Vauterin et al., and citrus variegated chlorosis (CVC), caused by Xylella fastidiosa Wells et al., are considered the main diseases affecting sweet orange scion varieties in Brazil. Among commercial varieties, mandarins and tangerines are recognized as tolerant to these pathogens. We report herein the production of ‘Hamlin’ sweet orange (Citrus sinensis L. Osbeck) + ‘Montenegrina’ mandarin (Citrus deliciosa Ten.) allotetraploid somatic hybrid plants by protoplast fusion with improved disease tolerance that could be used as a donor of resistance genes in interploid hybridisation. Somatic hybridisation was confirmed by leaf morphology, flow cytometry and RAPD analyses. The somatic hybrid was propagated by grafting and cultivated in a screenhouse for tolerance assays. For X. axonopodis pv. citri assays, buds were collected from both ‘Hamlin’ sweet orange and the somatic hybrid and grafted onto ‘Cleopatra’ mandarin (Citrus reshni hort. ex Tanaka). As a negative control, buds from ‘Mexerica Tardia’ mandarin (C. deliciosa) were collected and grafted onto ‘Cleopatra’ mandarin. Two-month old plants with at least one young vegetative flush were individually spray-inoculated with a 10⁶ CFU mL⁻¹X. axonopodis pv. citri suspension and incubated in a growth chamber, at 27 °C, under 16-h photoperiod. The somatic hybrid showed a statistically significant reduction in susceptibility to ACC 30 days after inoculation. Compared to ‘Hamlin’ sweet orange, disease severity was reduced by 70%, with similar tolerance to that of the mandarin negative control. For X. fastidiosa assays, buds were collected from the somatic hybrid and its parental plants and grafted onto ‘Rangpur’ lime (Citrus limonia Osbeck). The developed plants were needle-inoculated with a X. fastidiosa suspension (8.7 × 10¹⁰ CFU mL⁻¹) into the new growth flush stem. Bacterial population was quantified both at 4 (at the inoculation point) and 8 months (50 cm above the inoculation point) after inoculation. The first evaluation detected X. fastidiosa in 63% of ‘Hamlin’ sweet orange and ‘Hamlin’ + ‘Montenegrina’ mandarin samples. In the second evaluation, X. fastidiosa was detected in 47.4% of ‘Hamlin’ sweet orange and 10.5% of ‘Hamlin’ + ‘Montenegrina’ somatic hybrid samples, suggesting that bacterial movement was restricted in the somatic hybrid. X. fastidiosa was not detected in both evaluations in samples collected from leaves of ‘Montenegrina’ mandarin. These results indicate that the ‘Hamlin’ sweet orange + ‘Montenegrina’ mandarin somatic hybrid has potential for improved disease tolerance that should enhance its value regarding future use in citrus breeding programs.     

Horticultural performance of ‘Folha Murcha’ sweet orange onto twelve rootstocks

Despite its outstanding position, the Brazilian citriculture is established on a very limited pool of varieties that limits its expansion and restricts the fruit availability throughout the year. This situation determines the urgent necessity of developing alternative scion and rootstock cultivars, with good performance under local conditions. ‘Folha Murcha’ sweet orange (Citrus sinensis (L.) Osbeck) is a late-harvest cultivar, suitable both for the juice processing industry and the fresh fruit market, being described as tolerant to citrus canker (Xanthomonas citri subsp. citri Schaad et al.), and less affected by citrus variegated chlorosis (Xylella fastidiosa Wells et al.). A study was conducted in Bebedouro, São Paulo State, Brazil, to evaluate the horticultural performance of ‘Folha Murcha’ sweet orange budded onto 12 rootstocks: the citrandarin ‘Changsha’ mandarin (Citrus reticulata Blanco) × Poncirus trifoliata ‘English Small’; the hybrid ‘Rangpur’ lime (Citrus limonia Osbeck) × ‘Swingle’ citrumelo (P. trifoliata (L.) Raf. × Citrus paradisi Macfad.); the trifoliates (P. trifoliata (L.) Raf.) ‘Rubidoux’, ‘FCAV’, and ‘Flying Dragon’ (P. trifoliata var. monstrosa); the ‘Sun Chu Sha Kat’ mandarin (C. reticulata Blanco); the ‘Sunki’ mandarin (Citrus sunki (Hayata) Hort. ex. Tanaka); the ‘Rangpur’ limes (C. limonia Osbeck) ‘Cravo Limeira’ and ‘Cravo FCAV’; ‘Carrizo’ citrange (C. sinensis × P. trifoliata), ‘Swingle’ citrumelo (P. trifoliata × C. paradisi), and ‘Orlando’ tangelo (C. paradisi × Citrus tangerina cv. ‘Dancy’). The experimental grove was planted in 2001, using a 7 m × 4 m spacing, in a randomized block design, with five replications and two plants per plot. No supplementary irrigation was applied. Fruit yield, canopy volume, tree tolerance to drought and to citrus variegated chlorosis, and fruit quality were assessed for each rootstock. Trees grafted onto the ‘Flying Dragon’ trifoliate were smaller in size, but had largest yield efficiency when compared to those grafted onto other rootstocks. Lower alternate bearing index was observed on trees budded onto ‘Cravo FCAV’ ‘Rangpur’ lime. Both ‘Rangpur’ lime rootstocks and the ‘Sunki’ mandarin induced higher tree tolerance to drought. The ‘Flying Dragon’ trifoliate induced better fruit quality and higher tolerance to citrus variegated chlorosis (CVC) to ‘Folha Murcha’ trees. A cluster multivariate analysis identified three groups of rootstocks with similar effects on ‘Folha Murcha’ tree performance. Among the 12 evaluated rootstocks, the ‘Flying Dragon’ trifoliate has a unique effect on plant growth, tolerance to drought and CVC, fruit yield and fruit quality of ‘Folha Murcha’ trees, and may be better suited for high-density plantings.     

Chitinase and β-1,3-glucanase enzymatic activities in response to infection by Alternaria alternata evaluated in two stages of development in different tomato fruit varieties

Chitinase (ChA) and β-1,3-glucanase (GA) activity had been related with plant defense mechanism against pathogen attack in vegetative tissues. Scarce information is available about the behavior of these enzymes in response to different stages of development and fungi infection in fruits. The changes in ChA and GA activities in response to Alternaria alternata infection were evaluated in mature green (MG) and red ripe (RR) developmental stages of Sunpride, Geronimo and Charleston varieties of tomato fruit. Tomato fruits were inoculated with a conidial suspension of A. alternata and stored for 10 days at 25 °C and 90–92 H.R.%. The degree of fruit infection was measured by a hedonic scale every 2 days. ChA activity was determined fluorometrically by quantifying the release of 4-methylumbelliferyll (4-MU) from 4-methylumbelliferyll β-d-N,N′N″-triacetylchitotrioside, and GA activity was measured quantifying the release of glucose from β-1,3-glucan (laminarin) by HPLC. Tomato fruit in RR stage was more susceptible to fungi infection than MG stages. Geronimo was the most resistant variety, whereas Sunpride was the most susceptible for both stages of development (MG and RR). Higher levels of ChA and GA activities were observed for mature green stage in Charleston variety at the end of the storage period. An induction in ChA and GA in response to infection by A. alternata was observed in all varieties. Particularly high levels of ChA were found for inoculated Geronimo in RR stage and inoculated Charleston in MG stage which correlated with low levels of fungi infection. Higher levels of GA induction in response to fungi infection were recorded for Sunpride variety in RR stage, whereas no substantial induction was observed for Geronimo and Charleston varieties at the same stage of development. This GA induction correlated negatively with the resistance showed by the different varieties to fungi infection. We concluded that chitinase and β-1,3-glucanase induction are part of the tomato fruit defense mechanism against A. alternata infection with a different behavior depending upon stage of development and variety.     

Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent. I: GA3 increases the yield of commercially valuable ‘Nules’ Clementine Mandarin fruit only in the off-crop year of an alternate bearing orchard

Worldwide, gibberellic acid (GA₃) is used routinely to increase fruit number and size of seedless mandarins. The efficacy of seven combinations of GA₃ concentrations and application times to maximize total yield and yield of commercially valuable fruit (diameter 57.2–76.2 mm) of ‘Nules’ Clementine mandarin (Citrus reticulata Blanco) was determined in a commercial orchard. GA₃ applied during the period of intense flower abscission failed to reduce the total number of abscised flowers in both the light off- and heavy on-bloom years. No GA₃ treatment reduced fruit abscission when trees were setting the low yield off-crop. However, all trees receiving GA₃ in the high yield on-crop year had fewer abscised fruit than untreated control trees (P = 0.0188) and GA₃ applied 10 days after 75% petal fall and in July increased the number of fruit retained on tagged branches >20% compared to control trees (P = 0.0005). Maximum air temperature was not related to flower or fruit abscission. In the off-crop year (548 fruit per untreated control tree), it was necessary to apply 15 or 25 mg L⁻¹ GA₃ at 60% bloom, 90% bloom, 75% petal fall and 10 days after 75% petal fall to significantly increase the number of fruit per tree and yield of commercially valuable fruit (kilograms and number per tree) (P < 0.0001) above that of control trees, with no reduction in total kilograms per tree. In the following on-crop year, it was better not to apply GA₃: no treatment increased total yield or fruit size and five of seven GA₃ treatments tested reduced total yield as kilograms and number of fruit per tree (P = 0.0003). The results provide strong evidence that GA₃ efficacy is crop load-dependent and dictate that crop load should be considered when using GA₃ to increase fruit set or fruit size of mandarins.     

Confirmation of Clematis hybrids using molecular markers

The hybrid origin of progeny from crosses of Clematis tubulosa and Clematis brevicaudata was investigated using randomly amplified polymorphic DNA (RAPD) and single nucleotide polymorphisms (SNPs) from sequence analysis of chloroplast rbcL, accD genes, and the C. brevicaudatamatK gene. Plants collected from three and four populations of C. brevicaudata (C. brev) and C. tubulosa (C. tubu), respectively, from Mt. Songshan, Beijing, China were used as parents for hybridization. Morphological characters of pollen, seeds, and leaves were recorded in 2007. DNA from leaf samples of both parents and of C. brev × C. tubu and C. tubu × C. brev were extracted, and used for RAPD and SNPs from sequence data. A dendrogram was constructed by the branching neighbor-joining (IB-NJ) method. Proportionate population scores were generated by the admixture model using the STRUCTURE software. Based on morphological characters, C. brevicaudata was quite uniform. However, variations were detected in C. tubulosa. Hybrids of C. brev × C. tubu and C. tubu × C. brev showed intermediate morphological characters of the parents. Accessions of C. tubu × C. brev were clustered into 2 groups, with the majority of hybrids belonging to group IV b in the RAPD dendrogram, suggesting that this resulted from variations within C. tubulosa. In general, the hybrid origin of all progeny characterized by morphological characters was supported by the RAPD and SNPs data. These results indicate that RAPD results supported by SNPs data will be useful tool to verify hybrids.     

Production of mandarin + pummelo somatic hybrid citrus rootstocks with potential for improved tolerance/resistance to sting nematode

Sting nematode (Belonolaimus longicaudatus Rau) has become a primary factor limiting citrus production in localized regions of the central Florida sandridge citrus production area, making the development of resistant rootstocks a new breeding objective. In efforts to develop a replacement rootstock for the widely adapted sour orange, our focus has been on somatic hybridization of selected mandarin + pummelo combinations [Grosser, J.W., Gmitter, Jr., F.G., 1990. Protoplast fusion and citrus improvement. Plant Breed. Rev. 8, 339–374; Ananthakrishnan, G., Calovic, M., Serrano, P., Grosser, J.W., 2006. Production of additional allotetraploid somatic hybrids combining mandarins and sweet oranges with pre-selected pummelos as potential candidates to replace sour orange rootstock. In Vitro Cell. Dev.: Plant 42, 367–371], since sour orange is probably an introgression hybrid of mandarin and pummelo as suggested by molecular marker analyses [Nicolosi, E., Deng, Z.N., Gentile, A., La Malfa, S., Tribulato, E., 2000. Citrus phylogeny and genetic origin of important species as investigated by molecular markers. Theor. Appl. Genet. 100, 1155–1166; Gulsen, O., Roose, M.L., 2001. Lemons: diversity and relationships with selected Citrus genotypes as measured with nuclear genome markers. J. Am. Soc. Hort. Sci. 126, 309–317]. Somatic hybrid plants were produced from four new mandarin (C. reticulata Blanco) + pummelo (C. grandis L. Osbeck) parental combinations by fusing embryogenic suspension culture-derived protoplasts isolated from selected mandarins with leaf protoplasts of pummelo seedlings previously selected for tolerance/resistance to the sting nematode (B. longicaudatus Rau) as follows: Amblycarpa mandarin + ‘Liang Ping Yau’ (seedling) pummelo seedling SN7; Amblycarpa mandarin + ‘Hirado Buntan Pink’ (HBP) pummelo seedling SN3; Murcott tangor + pummelo seedling SN3; and Shekwasha mandarin + pummelo seedling SN3. Somatic hybridization was verified by ploidy analysis (via flow cytometry) and RAPD analyses. Mandarin parents were selected for wide soil-adaptation and ability to produce friable embryogenic callus lines. Pummelo seedlings used as leaf parents were identified from a previous screen of large seed populations (200 each) from four pummelos for resistance to sting nematode as follows: ‘Hirado Buntan Pink‘; ‘Red Shaddock‘; ‘Large Pink Pummelo’ and a seedling pummelo of ‘Liang Ping Yau‘. Ten resistant/tolerant pummelo seedlings were selected from the 800 pummelo seeds planted in the screen for further study. The four new somatic hybrids have been propagated to evaluate their horticultural performance and resistance to the sting nematode. These potential somatic hybrid rootstocks should also have potential to control tree size due to polyploidy.     

Agrobacterium tumefaciens-mediated genetic transformation and plant regeneration from a complex tetraploid hybrid citrus rootstock

Agrobacterium-mediated genetic transformation of a tetraploid “tetrazyg” citrus rootstock selection ‘Orange #16’ [Nova mandarin (Citrus reticulata Blanco) + Hirado Buntan pummelo (Citrus grandis L. Osbeck)] × [Cleopatra mandarin (C. reticulata Blanco) + Argentine trifoliate orange (Poncirus trifoliata (L.) Raf.)] was performed. Juvenile epicotyl segments were transformed with a construct containing a bifunctional egfp–nptII fusion gene under the control of an enhanced double CaMV 35S promoter. Our protocol resulted in a reasonable transformation efficiency of 18%. Stable integration of the transgene was confirmed by visual observation of EGFP expression, PCR and Southern blot hybridization. The purpose of this work was to investigate the amenability of novel citrus rootstock germplasm being developed for improved tree size control, soil adaptation, and disease resistance, to existing transformation technologies. Seed trees of such transgenic tetraploids also have potential as trap plants containing potent insecticidal transgenes, due to their inedible fruit and inherent crossing barriers with conventional commercial diploid scion cultivars, and could be planted around producing citrus groves.     

Physicochemical changes in Mazafati date fruits incubated in hot acetic acid for accelerated ripening to prevent diseases and decay

A method was developed and optimized for the accelerated ripening of date fruits of cultivar ‘Mazafati’ to prevent diseases and decay. The date fruits were incubated in hot acetic acid solution 0.5% at 40 + 1 °C for 72 h. During the process some physicochemical changes in the fruits were studied and were found to be comparable with the changes in the fruits that naturally ripened on the tree. Fruit firmness, water insoluble solid (WIS), protein, pH, L*a*b* and E decreased during accelerated ripening whereas in control samples at 4 °C increased. Total solid (TS), total soluble solid (TSS) and acidity were slightly higher in treated fruits compared to control fruits. The greatest loss of fruit firmness occurred during the first 12 h of incubation. Organoleptic tests also showed little difference between the naturally ripened fruits on trees and accelerated ripened fruits in hot acetic acid. Overall there was no difference between the fruits and were readily acceptable to consumers.     

Evaluation of the effectiveness of soil-applied plant derivatives of Meliaceae species on nitrogen availability to peach trees

We assessed the effect of soil-applied derivatives of melia (Melia azedarach L.) and neem (Azadirachta indica A. Juss) on nitrogen (N) soil availability, root uptake and peach (Prunus persica L.) growth. First we evaluated the effectiveness of experimentally prepared amendments made with fresh ground melia leaves or commercial neem cake incorporated into the soil as nitrification inhibitors, then we evaluated the effect of fresh ground melia fruits and neem cake on growth and N root uptake of potted peach trees, and on soil microbial respiration. Soil-applied fresh ground melia leaves at 10 and 20 g kg⁻¹ of soil as well as commercial neem cake (10 g kg⁻¹) were ineffective in decreasing the level of mineral N after soil application of urea-N as a source of mineral N, rather they increased soil concentration of nitric N and ammonium N. The incorporation into the soil of fresh ground melia fruits (at 20 and 40 g kg⁻¹) and neem cake (at 10 and 20 g kg⁻¹) increased N concentration in leaves of GF677 peach × almond (Prunus amygdalus) hybrid rootstock alone or grafted with one-year-old variety Rome Star peach trees. An increase in microbial respiration, leaf green color and plant biomass compared to the control trees were also observed. The Meliaceae derivatives did not affect, in the short term (7 days), N root uptake efficiency, as demonstrated by the use of stable isotope ¹⁵N, rather they promoted in the long term an increase of soil N availability, N leaf concentration and plant growth.     

Pollination with laser-irradiated pollens breaks cross-incompatibility between zicaitai (Brassica campestris var. purpurea) and ornamental kale (Brassica oleracea var. acephala) to produce hybrids with the aid of ovule culture

The objective of this study was to produce interspecific hybrids between an Ogura-cytoplasmic male sterile (CMS) line of zicaitai (Brassica campestris var. purupurea, 2n = 20) and cultivars of ornamental kale (Brassica oleracea var. acephala, 2n = 18) to develop a CMS system for hybrid seed production. Pollination with pollen grains of ornamental kales irradiated at a power output of 9.0 mW with a He–Ne laser for 3 min could overcome the cross-incompatibility between the species concerned. Intact hybrids could be efficiently produced from ovules cultured on Murashige and Skoog media supplemented by 0.2 mg l⁻¹ 6-benzyladenine. Chromosome number of hybrids was confirmed to be 2n = 19. Hybrids resembled ornamental kales in leaf morphology and in vernalization response. Pollens of hybrids had a sterile appearance. Moreover the hybridity of the putative hybrids was confirmed by RAPD data on a DNA fragment of 820 bp.     

Responses of eight chile peppers to saline water irrigation

Salt tolerance of five cultivars of Capsicum annuum L. Early Jalapeno, Golden Treasure, NuMex Sweet, NuMex Joe E. Parker, and Santa Fe Grande, two cultivars of C. chinense Jacq. Habanero and Pimienta De Chiera, and one accession of C. annuum, NMCA 10652, were evaluated in a field study. Seedlings were transplanted in late May to field raised beds containing loamy sand soils in a semi-arid environment. Plants were well irrigated throughout the experiment. Three saline solution treatments, prepared by adding NaCl, MgSO₄, and CaCl₂ to tap water at different amounts to create three salinity levels of 0.82 dS m⁻¹ (control, tap water), 2.5 dS m⁻¹, and 4.1 dS m⁻¹ electrical conductivity (EC), were initiated on 15th June and ended in late August. Among the eight varieties, NMCA 10652 had the highest survival percentage at 100% in the 4.1 dS m⁻¹ treatment, followed by ‘Early Jalapeno’, ‘NuMex Sweet’, ‘Pimienta De Chiera’, ‘Santa Fe Grande’, ‘Golden Treasure’, and ‘NuMex Joe E. Parker’. ‘Habanero’ had the lowest survival at 28%. Compared to control, final shoot dry weight of the plants irrigated with saline solution at 4.1 dS m⁻¹ was reduced by 92% in ‘Habanero’, followed by ‘Golden Treasure’ at 80%. For fruit fresh weight in 4.1 dS m⁻¹ vs. control, ‘Habanero’ had the highest reduction at 86%, followed by ‘Golden Treasure’ at 74%, while NMCA 10652 and ‘Santa Fe Grande’ had the least at 26% and 19%, respectively. NMCA 10652, the most tolerant to salinity, had the lowest leaf Na⁺ accumulation, while ‘Habanero’, the most sensitive to salinity, had the highest Na⁺ in the leaves. For leaf Cl⁻, ‘Early Jalapeno’ had the highest, while ‘Habanero’ had the lowest Cl⁻ accumulation in the leaves. Generally, sensitive varieties accumulated more Na⁺ and/or Cl⁻ in leaves, except for ‘Early Jalapeno’, which was relatively tolerant to salinity but had high Na⁺ and Cl⁻ accumulation in leaves.     

Hybrid detection and characterization of Curcuma spp. using sequence characterized DNA markers

The tropical flower Curcuma alismatifolia of the family Zingiberaceae is widely valued as a cut flower and potted plant due to its range of vibrant colors and large long-lasting inflorescences. Much of this diversity has been cultivated through extensive hybridization of wild varieties since hybrids often exhibit dramatic phenotypic differences from the parents. This phenotypic diversity though has led to difficulties identifying and classifying the relatedness of Curcuma varieties particularly between hybrids. One Curcuma variety called ‘Patumma’ is of particular importance since it has strong stalks, large symmetric inflorescences, is moderately resistant to fungal blight, has a high yield, and has been used to produce numerous high quality hybrids. Since Patumma is one of the key Curcuma varieties from which many hybrid crosses and induced mutation varieties were developed, we chose it as a target to be characterized using a molecular marker. Starting with a set of 11 unique decamer primers, polymorphic bands ranging from 100 to 2500 base pairs were used to examine 20 Curcuma varieties from which banding patterns of interest were selected for conversion to the more reproducible and robust sequence characterized amplified region (SCAR) markers. In particular, one SCAR marker amplified a region 600 bp in length which was conserved in all Patumma varieties and hybrids and as an independent test did not amplify an additional series of 24 distinct Curcuma varieties. Since new varieties of Curcuma are often dissimilar from their progenitors, this genomic analysis allows a cost-effective morphologically independent characterization of Curcuma hybrids.     

Leaf development,net assimilation and leaf nitrogen concentrations of five Prunus rootstocks in response to root temperature

Rootstocks differentially influence tree physiology and these differences may be due to varying responses to root zone temperature (RZT). To determine if this is the case, the physiology, leaf development and nitrogen relationships of five different Prunus rootstocks with chill requirements between 100 and 1100 h were examined during and after growth at RZTs of 5, 12 and 19 °C for 6 weeks. RZT correlated positively with leaf numbers, expansion rates and final leaf area, and significant differences existed among the rootstocks in the magnitude of these parameters at different RZTs. In particular, leaf expansion and area were less affected at low RZT in the low chill varieties. Net assimilation (A_n), leaf nitrogen (N%) and photosynthetic nitrogen use efficiency (A_n/N) also correlated positively with RZT: again, there were differences in the magnitude of these parameters among the rootstocks. No associations amongst A_n, N% or A_n/N could be found for the rootstocks; hence, they all differed in their physiological responses to RZT. Low RZT alone was sufficient to reduce A_n and decreased both leaf area and photosynthetic activity. Leaf expansion was related to N%, as the varieties with the lowest N% also had the lowest expansion rates. Infrared thermography of the cv. Golden Queen showed a negative correlation between RZT and leaf temperature with leaves of plants at the lowest RZT being 2 °C warmer than ambient whilst those at the highest RZT were 2 °C cooler than ambient. These differences were due to transpiration, as transpiration for the variety used decreased with reducing RZT. Transpiration from the other rootstock varieties was lowest at the 5 °C RZT but, depending on variety, at 12 °C was either higher, lower or the same as that from plants whose roots were at 19 °C. Together, the results of this study explain some of the rootstock-induced changes in tree growth and suggest the need to incorporate seasonal changes in RZT into development models for peaches.     

Yield performance,quality characteristics and fruit storability of winter squash cultivars in sub-humid areas

This research investigated the quality traits of eight winter squash cultivars (Cucurbita maxima, C. moschata, C. pepo and interspecific hybrids of C. moschata × C. pepo) during three years, but only ‘Tetsukabuto’ and ‘Violina’ were tested each year. In 2005 these two varieties were compared to ‘Butternut’; in 2006 to ‘Red Kury’, ‘Tan Cheese’ and ‘Kabosha’; in 2007 to ‘Red Kury’, ‘Mooregold’, and ‘Winter Luxury’. The characteristics recorded were: fruit yield, storage ability, chemical composition and sensory quality. Following harvest and sorting of marketable winter squash, 50 fruits for each cultivar were stored at 12 °C for 12 weeks the 1st year, and for over 20 weeks in 2nd and 3rd years, during which rotten fruits were counted. Compositional analyses regarding sugar concentration, starch, carotenoids and dry matter content at harvest and after storage were carried out; a panel test was organised to assess sensory traits. The most interesting cultivars were ‘Tetsukabuto’ for yield, ‘Tetsukabuto’ and ‘Mooregold’ for storability, ‘Red Kury’ and the same ‘Tetsukabuto’ particularly for soluble sugars and carotenoids and sensory appreciation.     

Hybrids sugary × sugary enhancer of sweet corn: A valuable option for cool environments

Sugary (Se1Se1) sweet corn hybrids do not have a high quality for human consumption according to the preferences of today's consumers, although they have a good stand establishment in cool environments. On the contrary, sugary enhancer (se1se1) hybrids have a high table quality, but a poor stand establishment in areas with a cool growing season. Sugary × sugary enhancer (Se1se1) sweet corn genotypes could be a valuable alternative for cool environments, but no information is available about the performance of sugary × sugary enhancer hybrids under such conditions. The objective of this paper is to evaluate the potential of sugary × sugary enhancer sweet corn genotypes in cool environments in comparison with sugary and sugary enhancer genotypes. Eight sugary lines and eight sugary enhancer lines were used as the parental lines of 15 sugary, 12 sugary enhancer, and 57 sugary × sugary enhancer hybrids that were evaluated in three different cool environments. The results of this work show that sweet corn cultivars with the Se1se1 genotype are an appropriate alternative for cool areas because they have better plant and ear types and a better eating quality than the Se1Se1 genotypes, and better emergence, early vigor, and shorter flowering time than se1se1 genotypes.