Albinism in Plants: A Major Bottleneck in Wide Hybridization, Androgenesis and Doubled Haploid Culture

Albinism is a common problem encountered in interspecificcrosses and tissue culture experiments including anther cultureand generation of doubled haploids. It is characterized by partialor complete loss of chlorophyll pigments and incomplete differentiationof chloroplast membranes. This in turn impairs photosynthesisand the plants eventually die at a young stage withoutreaching maturity. Environmental conditions such as light, temperature,media composition and culture conditions play somerole in determining the frequency of albino plant formation. Geneticfactors are even more important, and are major determinantsin albinism. Genetic studies in different crops show that itis a recessive trait governed by many loci. Both the nuclear andchloroplast genomes affect albinism and incompatibilities betweenthe two are a probable cause of many pigment defects in hybridprogenies. Such incompatibility has been reported in a large numberof angiosperms. The mechanisms behind these incompatibilitiesare poorly understood. Studies of plastid DNA inheritancetogether with observations using electron microscopy have establishedthat the transmission of plastids can bematernal, paternal orbiparental, even within the same genus, especially following widecrosses; contrary to the widespread belief that plastids are almostalways transmitted from the maternal parent. Albinism has beenovercome in some crop species through somatic hybridization anddevelopment of cybrids (cytoplasmic hybrids). However, the strictrequirement of efficient protoplast regeneration is a major limitationof these techniques. This review focuses on albinism followinginterspecific crosses or development of doubled haploids facilitatedby tissue culture experiments, underlying mechanisms, andthe possibilities for dealing with this important biotechnologicallimitation.