Ex vitro establishment and macropropagation of cassava (Manihot esculenta ‘Valencia’) to obtain disease-free rooted plants

Abstract

A common practice during cassava cultivation in Costa Rica is the use of stem cuttings coming from farmers' plantations as vegetative seeds. This system has widely spread diseases all over the country, especially the phytoplasm associated “Frog Skin” disease. At Tecnologico de Costa Rica we developed a protocol for rapid multiplication of disease-free plantlets. Terminal buds obtained from in vitro plants were grown in a MS (1962) medium under four different light treatments: 100% blue light (465 nm), 100% red light (630 nm), 50-50% red-blue light and white fluorescent light (as control), all of them with a light intensity (PPFD) of 70 μmol m-2 s-1. The best plantlets for acclimatization were obtained with blue light, which resulted in thicker stems and shorter internodes. In a second experiment, in vitro plants were transferred to the greenhouse for acclimatization, where five different substrates were evaluated: coco-coir, peat moss with perlite (75-25), mix of coco-coir with peat, sterile sand and sterile mix of soil+sand. The percentage of successfully acclimated plants was above 90% for those grown with coco-coir and peat moss, 86% for mix coco-coir+peat moss, 82% for soil+sand and 60% for sand-grown plants. Acclimatized plants were taken to a greenhouse and grown in pots with coco-coir during 8 weeks; after this time, plants became fully developed. Then cuttings of 10 cm length were obtained from the top of the plant and rooted using IBA (indolebutyric acid) in four concentrations: 0, 500, 1000 and 1500 ppm. The higher number and length of roots resulted in those cuttings treated with 1000 ppm. After three weeks, the rooted cuttings were taken successfully to the field, with a mortality of 4%.