Legislatively Establishing a Health Certification Programme for Citrus

Abstract

Many countries have implemented plant material certification programmes to preserve or rebuild certain agricultural sectors. These programmes aim to produce and distribute high quality planting materials that are free from systemic diseases and pests. Certification programmes generally requirements for nurseries, growers and other purveyors of plants. Only those varieties of plants that have been registered and approved by the competent national authority; that have been evaluated, indexed and found free from any systemic diseases; and that thrive in the region may be certified. Generally, the agricultural ministry administers certification programmes, although the competent authority will vary by country. Many different crops throughout the world are subject to certification. Citrus is one of the major cultivated fruit crops in the world, grown in more than 100 countries throughout the tropical, sub-tropical and Mediterranean climate regions. For most of these countries, citrus is a significant export. South Africa, for example, exported over one million metric tonnes of oranges in the 2008/2009 marketing year, whereas the world export total was over three million tonnes. Citrus is also one of the crops most susceptible to and most easily harmed by pathogens transmitted through plant propagation, a type of plant reproduction whose object is to preserve the unique characteristics of a desirable plant from one generation to the next. Different types of plant propagation include grafting (uniting two plants to make them grow as a single plant by inserting one or more buds of one plant – the scion – into the rootstock or stock of the other) and budding (common for propagating young citrus trees: here the scion, consisting of a single bud, is attached just underneath the bark). As will be discussed in more detail below, citrus diseases range from prokaryotic (bacteria and mollicute, i.e. without a cell wall) to fungal (true fungi and oomycetes, i.e. pathogens that look like fungi but on a molecular level more closely resemble algae) to viral (true viruses and viroids, i.e. viruses without proteins). Some diseases, such as citrus tristeza, huanglongbing and witches’ broom, are so serious that they can cripple, debilitate or even destroy a citrus industry in a country or region. A citrus certification programme producing disease tested propagative material is one of the most efficient ways to eliminate or contain graft transmissible and other citrus diseases. This paper is designed as a resource for national or sub-national governments that are interested in designing and implementing a citrus certification programme. The paper first provides a background to the diseases and transmission vectors to which citrus species are susceptible. It then outlines examples of certification programmes, voluntary and mandatory, and then provides a detailed description of the specific elements of a certification programme and the legislation needed to put it in place.