HEREDITARY CONTROL OF CALLUS FORMATION IN MAIZE ENDOSPERM CULTURED IN VITRO

Abstract

1. The growth response of maize endosperm excised from immature kernels was studied in vitro, using White's medium supplemented with yeast extract. The endosperm tissue excised 9 days post-pollination generally gave best growth.2. Of four inbred strains (two of starchy, one of waxy, and one of sugary type endosperm) of maize tested, callus tissue was formed only in the endosperm explants from the starchy strains (S41 and S42). The excised endosperm tissues of the F1 kernels obtained by the reciprocal crosses between S41 and S42 showed a better growth in vitro than those of either of the inbred parents. Histological observations of the endosperm in vivo failed to reveal any developmental or cytological differences between the F1 endosperm and the endosperms of the parental strains.3. Among the callus tissues obtained, only those from the strain S42 and S41×S42 have been cultured successfully for three years, while other cultures ceased to grow within a few months.4. Progeny tests of the S41×S42 hybrid suggested that the two strains could be different in two or more genetic factors concerning the callus formation in the endosperm explant, although the phenotypic expression is influenced by environmental and nutritional factors. Furthermore, the genetic study of the waxy strain S43 suggested that it possesses a genetic factor for inhibiting callus formation.5. None of indole-3-acetic acid, kinetin, and crude extracts of established tissue cultures gave a growth promoting effect on excised endosperm tissues, whereas the amino acid components of yeast extract were found to be essential for the callus formation in the explants.