Steps towards mitigating challenges in the micropropagation of tropical and subtropical fruit and nut crops in South Africa

摘要

Micropropagation was developed as a tool for the rapid propagation of elite plant material. Subsequently, the last half-century has seen a variety of regeneration systems being developed, with application in plant breeding and improvement programmes for a wide range of plant species. Unfortunately, both clonal multiplication and the use of in vitro manipulation as tools in breeding and improvement programmes of tropical and subtropical fruit crops, are hampered by many challenges. Not only do aspectssuch as plant physiological status, genotype and environmental factors play a role in successful initiation and subsequent manipulation, but characteristics including (but not limited to) high levels of secondary metabolites (e.g., phenolic compounds),tissue texture, the presence of trichomes, as well as exogenous and endogenous pathogens, all play a role in preventing the successful application of in vitro manipulation. Tropical and subtropical crop fruit improvement programmes (citrus, mango, avocado, guava, granadilla, banana, macadamia, pineapple, etc.) of the Agricultural Research Council in South Africa focus on the development of selections and cultivars with improved marketable characteristics, tolerance to pests and/or diseases and resilience to suboptimal cultivation conditions. While extensive research is carried out using conventional breeding and selection methods, in vitro manipulations are hampered by the factors listed above. Strategies towards the successful initiation and manipulation of field-grown clonal material include pre-induction fungicide, heat and anti-phenolic treatments, while initiation treatments also include various sterilisation agents. An overview of the successes and challenges of tropical and subtropical fruit crop initiation and micropropagation for each of nine crops is presented.