Micropropagation of Bulbous Crops: Technology and Present State

Conventional propagation of bulbous crops must be supplemented with micropropagation to satisfy the requirements of present-day horticulture with respect to fast production of disease-free, superior starting material. Adequate micropropagation protocols for bulbous crops are therefore a sine qua non. The successive steps in micropropagation of bulbous crops are reviewed: initiation, multiplication, bulb formation, dormancy breaking and planting. In the first two steps, new shoots or bulblets are generated by axillary bud outgrowth or adventitious regeneration. During initiation, endogenous contamination may be a severe problem since bulbs grow subterraneously and have often been propagated vegetatively in the field for many years. Other drawbacks are insufficient axillary branching, poor adventitious regeneration and inferior growth. The latter, inferior growth, is likely the most significant problem and is caused by poor translocation of medium ingredients to the growing regions within the explant. In micropropagation of bulbous crops, bulblets should be produced because of, among others, easy handling and acclimatization. For optimal performance after planting in soil, preparatory treatments are required in particular a dormancy breaking treatment. A phase-change from juvenile to adult and protective pretreatments are also profitable. It is concluded that when major problems like that of inferior growth have been solved, commercial micropropagation of bulbous crops will experience a second heyday. _____________________________________________________________________________________________________________