Gamic propagation of globe artichoke for the production of F1 hybrids

Globe artichoke gives an important contribution to the Mediterranean agricultural economy. However, in the Mediterranean countries, where this crop was first grown and its cultivation developed and increased over the centuries, production has recently remained stagnant since the end of last century. The principal problems related to the development of globe artichoke as a modern cultivation consist in the irregularity both of production and commercialization calendar as well as in the traditionally adopted vegetative propagation system, which requires expensive agronomical practices and does not guarantee well-being propagation material. No intensive breeding programs have been carried out. The only real novelty in this sense is represented by the development of few seed propagated hybrids. Male sterility was used to allow production of many experimental F1 hybrids eliminating the long and expensive operation of floral emasculation. Seed-planted cultivars have the following major advantages: 1) labor saving and a cheap operation of the mechanical seed sowing; 2) conversion of globe artichoke into annually grown crops and introduction into crop rotation; 3) respect to vegetatively propagated plants, more efficient use of both moisture and fertilizers due to the long vertical tap roots penetrating into the soil deeper than the adventitious roots produced by planted suckers; 4) protection from pathogens and pests by annual cultivation coupled with crop rotation; 5) more vigorous and healthier growth of the plants with a low input of pesticides, fungicides and fertilizers, so making globe artichoke as a valid rotation choice in an organic cultivation system. For the development of globe artichoke as a modern crop, it is important to produce new stable seed propagated hybrids, but also to set up the techniques necessary to rationalize the cultivation system. In the process of F1 hybrid production, it needs to consider some aspects such as (i) the correct management of the cultural cycle, (ii) the adaptability of the new F1 hybrids to the different cultivation environments as well as to the different production and commercialization calendars, (iii) the economical production of F1 hybrid seed because the adequate pollination of male-sterile plants still remains difficult to achieve. IV During the three years of PhD program, a strategy of development of F1 hybrids was carried out in order to reach some objectives. The first one was to develop stable male and female parental lines, selecting the germplasm already available and trying to improve their stability. Some male sterile clones were selected and individuated as good female parents; some male fertile genotypes were selected as stable. Moreover, in order to deep the knowledge on the morphological and functional differences between male sterile and male fertile globe artichoke flowers, a study of the floral biology was carried out. The floral male and female structures were staged and studied in order to highlight the differences. The male sterile flowers showed either a normal development of the male reproductive structures or a normal meiosis in the cytological analyses of pollen formation. The block of pollen viability was post-meiotic and the low viability of the male sterile pollen was connected with a less developed external exine structure. Female organs of the male sterile flowers were more elongated than those of the male fertile flowers at the same stages. Different cross-combinations were developed either in Italy (2006 and 2007) or in USA 82008) in order to compare the different hybrids and to individuate the most homogeneous ones. A focal point of the project was to find an evaluation system capable of distinguishing which hybrids were more homogeneous than others. For this reason, an evaluation of all hybrids based on the morphological traits was carried out using the Protocol for Globe Artichoke European Union CPVO (2004) and some other traits chosen by Lopez Anido et al. (1998) both in Italy and in USA. In order to analyze the hybrids also from a molecular point of view, five F1 offsprings produced during the PhD program along with their parents and a commercial hybrid (Opal F1) used as a control were analyzed by ISSR markers. Molecular work was realized in the laboratory of the Dpto. Ciencia y Tecnologia Agraria of Universidad Politecnica de Cartagena (UPCT), Spain. Hybrids were all well differentiated by both the molecular and morphological analyses. The results of the molecular analysis were compared with those of the morphological one. The clustering of clones based on the morphological characters resulted consistent with that derived from the molecular analysis. The last focal point of the research was the development of an effective pollination technique for the production of F1 hybrids by comparing different pollination systems studied. Their potentialities in seed productivity of our male sterile lines were evaluated. In 2006, the field experiment were carried out at the Regional Agency for the Development and Innovation of Agriculture (ARSIAL), in Tarquinia (Viterbo, Italy) and V both manual pollination by brush and pollination by bumblebees (Bombus terresris) were compared with an open pollination control. In 2008, open field activities were carried out in the experimental fields of Big Heart Seed Company (BHSC), in Brawley (California, USA) and the effectiveness of honey bees (Apis mellifera) as pollinators was evaluated in order to verify if, changing the percentage of both male sterile and male fertile plants, there were some differences in the seed production. The results of the first year experiment should be repeated because highlighted interesting potentialities in the use of the bumblebees as valid alternative to the honey bees. Unfortunately, some environment problems reduced seed production and it was not possible to get some definitive results. The results obtained in the third year confirmed that the honey bees are less attracted by the male sterile flowers.Dottorato di ricerca in Ortoflorofrutticoltur