Elisabetta Nicolosi

Citrus phylogeny and genetic origin of important species as investigated by molecular markers.

Abstract Citrus phylogeny was investigated using RAPD, SCAR and cpDNA markers. The genotypes analyzed included 36 accessions belonging to Citrus together with 1 accession from each of the related genera Poncirus, Fortunella, Microcitrus and Eremocitrus. Phylogenetic analysis with 262 RAPDs and 14 SCARs indicated that Fortunella is phylogenetically close to Citrus while the other three related genera are distant from Citrus and from each other. Within Citrus, the separation into two subgenera, Citrus and Papeda, designated by Swingle, was clearly observed except for C. celebica and C. indica. Almost all the accessions belonging to subgenus Citrus fell into three clusters, each including 1 genotype that was considered to be a true species. Different phylogenetic relationships were revealed with cpDNA data. Citrus genotypes were separated into subgenera Archicitrus and Metacitrus, as proposed by Tanaka, while the division of subgenera Citrus and Papeda disappeared. C. medica and C. indica were quite distant from other citrus as well from related genera. C. ichangensis appeared to be the ancestor of the mandarin cluster, including C. tachibana. Lemon and Palestine sweet lime were clustered into the Pummelo cluster led by C. latipes. C. aurantifolia was located in the Micrantha cluster. Furthermore, genetic origin was studied on 17 cultivated citrus genotypes by the same molecular markers, and a hybrid origin was hypothesized for all the tested genotypes. The assumptions are discussed with respect to previous studies; similar results were obtained for the origin of orange and grapefruit. Hybrids of citron and sour orange were assumed for lemon, Palestine sweet lime, bergamot and Volkamer lemon, while a citron × mandarin hybrid was assumed for Rangpur lime and Rough lemon. For Mexican lime our molecular data indicated C. micrantha to be the female parent and C. medica as the male one.

Relationships among cultivated Opuntia ficus-indica genotypes and related species assessed by cytoplasmic markers

The taxonomic classification of the genus Opuntia, which includes several cultivated species, is complicated mainly because of inadequate morphological descriptors, the common intra- and inter-generic hybridization and the relationships between phenotypic variation and ecological conditions. The phylogenetic relationships among 72 cultivated genotypes, either selected for fruit or forage production, and wild accessions belonging to approximately 15 different species of Opuntia were inferred using cytoplasmic markers. Previous studies indicated as the most important cultivated accessions for fruit production have a polyphyletic origin but polyploidy hampered their clear phylogenetic assignment based on nuclear markers. Cytoplasmic markers are considered helpful for their maternal inheritance and for overcoming the multiple gene copy problem in polyploid phylogenetics already reported in the Opuntia genus. In particular, we combined in this work capillary electrophoresis for newly designed cpSSRs and high resolution melting for SNV analyses to identify chloroplast (ndhF-rpl32, psbJ-petA, atpB-rbcL, matK, ycf1) and mitochondrial (rpl5) DNA markers in a selected group of genotypes. The results revealed the presence of polymorphisms in the predicted cpSSRs and SNVs and clearly evidenced that most of the studied genotypes were closely related to Opuntia ficus-indica (L.) Miller. Plastid markers identified 11 chlorotypes and 8 unique genotypes. Interestingly the analysis evidenced a multiple maternal phylogeny for the fleshy fruit varieties classified as O. ficus-indica. These results allow questioning of the reliability of the current classification based on morphological parameters and reveal the narrow genetic base of the most common cultivated opuntias for fruit production, while forage genotypes evidenced greater variability.

Recovery of Citrus Somatic Hybrids Tolerant to Phoma Tracheiphila Toxin, Combining Selection and Identification by RAPD Markers

Phoma tracheiphila is a pathogen that causes a serious tracheomycotic disease in commercial lemon cultivars. Somatic hybridization offers the possibility to transfer the trait for tolerance into susceptible cultivars. One of the limitations of this approach is selection and identification of nuclear hybrids at an early stage. Protoplasts isolated from calli of ‘Murcott’ tangor (tolerant) and ‘Messina’ lemon (susceptible) were fused (PEG treatment). Prior to fusion, ‘Murcott’ protoplasts were treated with 0.25 mM iodoacetate. Fusion treated protoplasts were plated in liquid medium for 40 days and then exposed to 0.6 μM of P. tracheiphila toxin. Total DNA was extracted from the selected calli and corresponding embryos and analyzed by RAPDs. With the selected primers, hybrids were successfully identified. In the survey of coculture with 1 μM toxin, the hybrid callus lines showed tolerance to the toxin. Immunoblot analysis of the recovered hybrid calli indicated the presence of chitinase among the extracellular proteins. The combined methods, selection and identification by RAPD markers, resulted in 90% recovery of nuclear hybrids tolerant to the P. tracheiphila toxin.

Influences of aspect and tillage on two winegrape cultivars on Mount Etna

ABSTRACT The effect of minimum tillage on two autochthonous Vitis vinifera L. varieties, namely Nerello mascalese and Carricante, established on the eastern and northern aspect slopes of the volcano Mount Etna in Sicily, was evaluated over two seasons. The objective was to determine whether conventional tillage and minimum tillage affect the vegetative growth, bud fertility, total leaf area, leaf nutritional status and fruit yield components. The ratio of bunches/retained buds was strongly influenced by aspect. Yield per vine was significantly different within cultivars and seasons depending on cultivar, tillage treatment and aspect. Due to its natural plasticity in marginal conditions, yields were consistently higher in Nerello mascalese. The yield reduction with minimal tillage was excessive in Carricante. As a consequence of the yield reduction in the second season, total soluble solids in particular were increased in Nerello mascalese. Linear discriminant analysis revealed the highest discrimination values for cultivar and the lowest ones for tillage.