Amparo García-Luis

The influence of explant orientation and contact with the medium on the pathway of shoot regeneration in vitro in epicotyl cuttings of Troyer citrange

The effect of orientation as regards to gravity, and that of contact with the medium of culture, on shoot regeneration at the cut edges of epicotyl explants of Troyer citrange (Citrus sinensis (L.) Osbeck×Poncirus trifoliata (L.) Raf.) have been separated. The shoot regeneration pathway was not affected by the orientation of the explants as regards to gravity, and was determined by explant polarity and the contact with the culture medium. At the apical edge of the explants, the contact with the medium shifted the pathway of shoot regeneration from a direct one to an indirect one, with formation of a callus. This callus formation was cytokinin-dependent, but the change in the pathway of organogenesis was not caused by the increase in cytokinin availability resulting from the contact with the medium. In contact with the media, regeneration at the basal edge of the explants occurred through an indirect pathway after callus formation. No regeneration occurred, at the basal edge, if the contact with the media was prevented. The orientation of the explants as regards to gravity affected shoot formation through the direct pathway of organogenesis. The number of buds differentiated, and that of growing shoots increased when the orientation of the explants departed from the vertical upright position.

Low temperature storage of corms extends the flowering season of saffron (Crocus sativus L.)

Summary Conditions for the cold-storage of saffron crocus (Crocus sativus L.) corms to delay flowering have been characterised. Storage of corms at 2ºC after flower initiation resulted in a time-dependent abortion of those flowers already initiated. The more advanced the stage of flower initiation at the beginning of cold-storage, the faster the rate of flower abortion. Overall, no benefit resulted from cold-storing corms after flower initiation. Corms stored in the cold before flower initiation, formed flowers when incubated after storage at 21º–25ºC. The number and size of flowers formed, and the yield of spice saffron per corm, depended both on the duration and conditions of cold-storage. Storage at freezing temperatures (0º or –1ºC) damaged the corms. Flowering could be induced in corms stored between 0.5º–2ºC. Within this range, temperature had little effect on the subsequent behaviour of corms. Flower number and flower size decreased gradually with increasing duration of cold-storage. This decrease was slower when storage was performed in 1% oxygen than in a normal atmosphere (21% oxygen). Corms lifted after leaf-withering, and stored at 2ºC in 1% oxygen for 70 d, could be forced to flower from early December until the end of January with the same yield of spice saffron as non cold-stored corms.These results complement previous findings on the control of saffron flowering. Taken together, they allow saffron flowering without loss of spice yield from early September to the end of January. Flowering could be further delayed until May by extending the duration of cold-storage, but this delayed flowering resulted in a significant reduction in spice saffron yield.

The anatomy of the fruit in relation to the propensity of citrus species to split

The anatomy of the fruit has been compared in three prone-to-split mandarin hybrids (Nova, Ellendale and Murcott), several cultivars of clementine mandarin (Fino, Clementina de Nules and Orogrande), and in Owari satsuma mandarin. The fruit of the hybrids is oblate to subglobose and usually presents an open stylar end disrupted by a navel formed by the floral meristem, which is conserved near the apex of the fruit. In the non-prone-to-split clementines as well as in Owari satsuma, the floral axis protrudes inside the style, and the flower meristem is lost through abscission shortly after petal fall. The abaxial side of the carpels fuses with the flower axis forming at the stylar end of the fruit a solid tissue which externally has a small scar at the place of style abscission. Most of the fruits in these cultivars have no navel. In addition, the fruit of clementine is slightly oblate or globose. The relevance of these anatomical characteristics as regards to splitting is supported by the differences between the split and non-split fruits in Nova, the split fruit being more oblate in shape and having a bigger navel than non-split fruit. However, the effect of applied growth regulators on fruit splitting could not be correlated with their effect on the anatomy of the fruit. Additional factors not contemplated in the study also influence fruit splitting.

Effects of applications of gibberellic acid on late growth, maturation and pigmentation of the Clementine mandarin

Gibberellic acid (GA3) applications were performed periodically from late September to late November on seedless Clementine mandarin (Citrus clementina Hort. ex Tanaka) trees, and their influence on the fruit growth and pigmentation determined. Irrespective of the time of application, GA3 had no effect on the growth of the fruit and its anatomical parts nor on juice content and composition, but early GA3 applications reduced peel thickness at maturation. The pigment changes in the peel were retarded by GA3, and this response was maximal when GA3 was applied during the 10 day interval between the onset of chlorophyll degradation and the onset of carotenoid accumulation.

Seasonal variation in the competence of the buds of three cultivars from different Citrus species to flower

The role of bud competence in the determination of flowering seasonality was studied in three Citrus cultivars, Bearss lime (Citrus latifolia Tan.), Fino lemon (C. limon [L.] Burm. f.) and Owari satsuma (C. unshiu (Mak.) Marc.), which differ in their adaptation to hot climates and their propensity to produce off-season blooms. Potted plants were kept in a greenhouse under non-inductive conditions (minimum temperature higher than 20°C), and periodically the flowering response was determined of a group of trees exposed for 30 days to an inductive temperature regime (15/8°C). A seasonal change in bud competence was demonstrated, and both bud sprouting and flower formation were highest when the low temperature regime was imposed during February and March. During the summer months, the low temperature regime resulted in a small increase in bud sprouting as compared to non-chilled trees, but only vegetative buds developed and no flowers were formed. The influence of environmental factors on the determination of bud competence was further studied. No effect of photoperiod was found, but raising the minimum air temperature above 25°C during 60 days, eliminated bud competence in Owari satsuma. In Bearss lime trees, the buds reacquired the competence after 4 months at 25/20°C, a temperature regime that does not induce flower formation. The reacquisition of competence was much faster at a lower temperature (15/8°C). A consistent relationship between the flowering response and DNA methylation in buds could not be demonstrated in all cultivars.

Colonisation and histological changes in muskmelon and autumn squash tissues infected by Acremonium cucurbitacearum or Monosporascus cannonballus

Muskmelon (Cucumis melo cv. Temprano Rochet) and autumn squash (Cucurbita maxima) seedlings were inoculated either with Acremonium cucurbitacearum or Monosporascus cannonballus, two of the soil-borne fungi implicated in ‘melon collapse’. Inoculation was achieved in two different ways: by growing the plants in pots containing infested soil to study the histological changes produced in the infected tissues using light microscopy and by growing seedlings in Petri dishes together with fungal colonies in order to observe the colonisation of the plant tissues using scanning electron microscopy. Both muskmelon and autumn squash roots infected with A. cucurbitacearum showed a suberised layer in the epidermis and the outermost layers of the parenchymatic cortex, but these symptoms developed earlier in the muskmelon plants. Muskmelon plants infected by this fungus also presented hypertrophy and hyperplasia, which led to a progressive separation of the vascular bundles in the lower stems of the affected plants. This response was not observed in autumn squash during the study. On the other hand, few histological changes were observed in tissues infected with M. cannonballus and only a slight increase in the size of cortical intercellular spaces was noted in the lower stems of muskmelon plants, and infected autumn squash tissues remained free of these symptoms throughout the study. The scanning electron microscope observations revealed that both fungi were able to colonise the tissues of the two host plants which were studied. A. cucurbitacearum colonised the epidermis and cortex of both muskmelon and autumn squash. The hyphae grew both inter- and intracellularly, and the density of the colonisation decreased within the endodermis. The same colonisation of host plants was observed as a result of M. cannonballus infection. The xylem vessel lumina of both muskmelon and autumn squash showed hyphae and tylose formation as a result of both fungal infections. However, non-fungal structures were detected in the hypocotyl vascular tissues. The present study demonstrates that both fungi are capable of infecting the tissues of a species which is resistant (autumn squash) and a species which is susceptible (muskmelon) to melon collapse.

The World Saffron and Crocus collection: strategies for establishment, management, characterisation and utilisation

Since 2007, the European Commission AGRI GEN RES 018 “CROCUSBANK” action has permitted the creation of the alleged World Saffron and Crocus Collection (WSCC), a unique collection which contains a representation of the genetic variability present in saffron crop and wild relatives at global scale. At present the germplasm collection, housed at the Bank of Plant Germplasm of Cuenca (BGV-CU, Spain), consists of 572 preserved accessions representing 47 different Crocus species (including saffron Crocus) and is expected to increase up to more than 600 accessions by the end of CROCUSBANK action (May 2011). The preserved biodiversity of saffron (Crocussativus L.) covers a wide range of the genetic variability of the crop and currently consists of 220 accessions from 15 countries: 169 of these come from European cultivation countries, 18 from commercial areas in non EU countries, 26 from regions of minimal or relict production and/or from abandoned fields and 7 from commercial nurseries. The non-saffron Crocus collection currently comprises 352 accessions: 179 collected from the wild in 12 countries of natural distribution, 24 from donations of public and private institutions, 91 from commercial nurseries and 58 acquired from BGV-CU collection management. Here we provide a record of collections, activities concerns and current strategies for documentation, conservation, characterisation, and management of the collection as important tools for researchers with interest in these valuable genetic resources.

The World Saffron and Crocus collection: Strategies for establishment, management, characterisation and utilisation

Since 2007, the European Commission AGRI GEN RES 018 “CROCUSBANK” action has permitted the creation of the alleged World Saffron and Crocus Collection (WSCC), a unique collection which contains a representation of the genetic variability present in saffron crop and wild relatives at global scale. At present the germplasm collection, housed at the Bank of Plant Germplasm of Cuenca (BGV-CU, Spain), consists of 572 preserved accessions representing 47 different Crocus species (including saffron Crocus) and is expected to increase up to more than 600 accessions by the end of CROCUSBANK action (May 2011). The preserved biodiversity of saffron (Crocussativus L.) covers a wide range of the genetic variability of the crop and currently consists of 220 accessions from 15 countries: 169 of these come from European cultivation countries, 18 from commercial areas in non EU countries, 26 from regions of minimal or relict production and/or from abandoned fields and 7 from commercial nurseries. The non-saffron Crocus collection currently comprises 352 accessions: 179 collected from the wild in 12 countries of natural distribution, 24 from donations of public and private institutions, 91 from commercial nurseries and 58 acquired from BGV-CU collection management. Here we provide a record of collections, activities concerns and current strategies for documentation, conservation, characterisation, and management of the collection as important tools for researchers with interest in these valuable genetic resources.