Rajendra Agricultural University

Callusing and rhizogenesis--response of inbreds and their hybrids

--A. Kumar, H. Kumar and S. K. T. Nasar

Some selected inbreds, Tuxp124-1, Tuxp162-1, Tuxp46-6, Tuxp237-2, Tuxp104-2, MS1DR-120, PKMS1-49, and hybrid genotypes, Tuxp162-1xTuxp237-2, Tuxp162-1xTuxp124-1, Tuxp237-2xTuxp124-1, Tuxp104-2xTuxp46-6, MS1DR-120xPKMS1-49, which were never exposed to tissue culture experiments, were subjected to callusing and rhizogenesis.

The seeds were germinated on Murashige and Skoog's (MS) basal medium. Hybrid genotypes Tuxp162-1xTuxp237-2 and MS1DR-120xPKMS1-49 showed a greater number of roots as well as longer root length than their inbreds, while one hybrid, Tuxp104-2xTuxp46-6, showed an intermediate response. For shoot growth all hybrid genotypes showed better response than their inbred genotypes except for the hybrid genotype MS1DR-120xPKMS1-49.

The MS basal medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D), indole butyric acid (IBA), indole 3-acetic acid (IAA) and kinetin (KN) in different concentrations either singly or in combinations of two, were used for callusing and rhizogenesis. The explants used for callusing were root segments taken from seeds germinated on MS basal medium, while for rhizogenesis the callus formed on root segments was also used.

Callus formation from root segments was best achieved on the medium MS + 2,4-D (5.0mgL-1) + IAA (2.0mgL-1), with 88.88% of the cultures showing very good callusing response, followed by a response of 77.00% on the medium MS + 2,4-D (5.0mgL-1) + IBA (2.5mgL-1). The hybrid genotypes Tuxp162-1xTuxp237-2, Tuxp162-1xTuxp124-1 and Tuxp237-2xTuxp124-1 showed a response inferior to their inbreds with respect to the frequency of callus formation and callus growth. However, the other hybrid genotypes, Tuxp104-2xTuxp46-6 and MS1DR-120xPKMS1-49, showed better response than their inbreds. This was true for most of the media combinations having 2,4-D, IBA, and IAA that favoured good callus formation. The media combinations with KN showed minimum callus formation, but the calli were compact and green, with globular structures.

Rhizogenesis was achieved in many media combinations and in most of the genotypes. Roots were differentiated directly from the explant as well as through the formed callus, but the frequency of callus mediated rhizogenesis was more in most of the cases except for the media with IBA. The hybrid genotypes MS1DR-120xPKMS1-49 and Tuxp104-2xTuxp46-6 showed better response over their inbreds for the percentage of cultures showing rhizogenesis. The other hybrid genotypes were inferior to their inbreds in this aspect. However most of the hybrid genotypes showed better response than their inbreds for the number of differentiated roots per culture.

Most of the hybrids showed heterotic performance for mean root and shoot length, but some of them failed to overshoot the 'high' parent in the case of in vitro germination and thus failed to show a positive heterotic effect. For callusing and rhizogenesis also, although intergenotypic differences were observed, the hybrids did not always show positive heterotic effects. Thus the maize hybrids that were positively heterotic for yield have not always shown similar performance for tissue culture responses. This difference of performance of hybrids may be because of the different genic x environmental interactions for yield and tissue culture responses.

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