Formation of Jerusalem Artichoke Tubers in Sterile Culture

Abstract

DURING the development of shoots of Helianthus tuberosus L. in sterile in vitro culture, swollen, ellipsoidal structures bearing scale leaves, and producing roots, were formed. These structures resemble, and are considered to be, tubers. The shoot cultures were derived originally from the growth of sterilized ‘eyes’ of tubers (artichoke strain P 17 of Nitsch and Nitsch¹). From a leafy shoot growing in sterile culture, a section of stem 1 cm. long, including a single node with its pair of foliage leaves, was taken as explant, and was placed on a complex medium containing salts, 2 per cent sucrose, naphthalene-acetic acid (0.01 mgm./l.), casein hydrolysate, and coconut milk. The composition of the medium is given by Marsden and Wetmore², except that cysteine and urea were omitted. When kept at 25° C. in a 12-hr, day at the relatively low light intensity afforded by pairs of fluorescent lamps and tungsten lamps at a distance of about 1 m., one or both axillary buds of the explant grew out into elongated shoots bearing foliage leaves (referred to hereafter as long shoots). Tubers were first noticed forming sporadically in such cultures, either at the base, or in the axils at recently formed nodes, or at the shoot apex. Fig. 1A shows a culture of the latter type, in which roots are forming abundantly from the tuber even though it is wholly in the air. The tubers would continue to grow if the entire culture, or the portion bearing the tuber, were transferred to new medium at intervals of about a month, and they could attain lengths of several centimetres; some, however, ‘bolted’ after transfer, that is, the apex grew out as a long shoot.