The Italian Plum Rootstock Trial: Results for Sicilian Environmental Conditions

Abstract

An increase of plum industry has been evident in Italy since the 1990s. This growth was in both area planted and production and it has been especially evident in the South of Italy, where the environmental conditions favor the development of plum orchards, particularly those adopting Japanese cultivars. The Myrobalan seedling was the main rootstock historically used in the south of the country for plum orchards, on account of its strong vigor, hardiness, longevity and adaptability to a wide range of soil types. The introduction of new scion cultivars and new rootstocks has stimulated new studies on the main technical aspects related to plum cultivation, to evaluate the wide number of rootstock genotypes which are today available for the plum species. The Italian Ministry of Agriculture has sponsored a National project which aims to evaluate the most recent rootstocks licensed and available for European and Japanese plum cultivars. A series of experimental orchards have been established in different regions representative of the main Italian plum growing areas. This paper reports on the vegetative and qualitative traits observed both for European and Japanese plum cultivars, respectively, 'Stanley' and 'Shiro', grafted onto five rootstocks. INTRODUCTIONFor at least the last 30 years the plum industry in Italy has been based on the cultivation of indigenous germplasm cultivars/varieties. In fact, there is a wide range of plum germplasm concentrated particularly in the south of the country; this scion germplasm is characterized by some interesting fruit traits -aroma, taste, flavor -which although partially linked to the cultivation areas, are thought to present considerable qualitative and productive potential. For this reason, considering the importance of this germplasm, interest has been expressed in these local cultivars, prompting some research studies.Since the 1990s new cultivars have been introduced, and this has lead to the development of a plum industry mainly based on the cultivation of Japanese cultivars (Sansavini et al., 1996). During the same period, new rootstocks were introduced; these should be less variable in terms of vegetative growth and production than the diffused plum seedling and seedling-raised 'Myrobalan' used as traditional rootstocks.In just a few years clonal 'Myrobalan 29C' has been rapidly adopted becoming the chosen rootstock in almost the 80% of the new plum plantings. The increase of interest on this facet of plum cultivation inspired the Italian Ministry of Agriculture to sponsor a National rootstock evaluation project (Mezzetti and Sottile, 2007). This aims to evaluate the most recent rootstocks, which are licensed and available for use with European and Japanese plum cultivars, by adopting a national network of experimental orchards. Actually, the recent advances in rootstock breeding and licensing appear very limited and few new genotypes have been licensed specifically for plum (Nicotra and Moser, 1997).

Unlocking Plum Genetic Potential: Where Are We At?

“…As a result, the progressive loss of old traditional cultivars and the increasing narrowing of the genetic base is occurring, with the consequence of inbreeding depression phenomena that undermines the potential for future breeding progress [25,26], and increases vulnerability to pests, diseases, and environmental change. In this context, plum germplasm accessions (old traditional cultivars, landraces, related or wild progenitor species, especially in the original centers of diversity), which may have been less subjected to artificial selection pressures [27], can play a crucial role in the gene-pool reservoir which might be exploited for breeding purposes, especially in areas of fruit quality, disease resistance, climatic adaptability, and new rootstocks selection [28][29][30][31][32][33]. Considering its present and future strategic role, this germplasm deserves, overall, special attention and coordinated efforts of conservation [34], evaluation and utilization for breeding purposes [35] by both conventional and innovative (genomic) approaches [36].…”