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Recently, a breeding technology for hybrid pigeonpea [Cajanus cajan (L.) Millsp.] based on cytoplasmic-nuclear male sterility (CMS) and partial natural outcrossing was developed at ICRISAT. The limited number of experimental hybrids tested has shown the presence of a considerable amount of hybrid vigor for seed yield. In the present study, one extra-early- (120 d), two early- (150 d), and two late-maturing (180 d) pigeonpea hybrids were studied to generate information on the genetics of fertility restoration of the A 4 CMS system. In the extra-earlymaturing hybrids, pollen fertility was controlled by a single dominant gene, whereas in the earlyand late- maturing hybrids, male fertility was governed by two duplicate dominant genes. It was also observed that hybrids with two dominant genes produced a greater pollen load and expressed greater stability as compared with those carrying a single dominant gene. The information on the inheritance of fertility restoration will help in designing strategies for breeding elite hybrid parents, and it was concluded that for breeding hybrids with stable fertility restoration, the presence of two dominant genes is essential.

The presence of 1 and 10 mol m−3 proline in media containing 100 and 200 mol m−3 of NaCl, had little effect on the growth of salt-adapted callus of rice. However, in such callus proline accumulation was stimulated by 10 mol m−3 proline in the presence of 100 mol m−3 NaCl. On the other hand, with 100 mol m−3 NaCl, both 1 and 10 mol m−3 proline significantly increased both the growth and proline content of salt-unadapted callus. On replacing NaCl with KCl (100 and 200 mol m−3), growth of saltadapted as well as unadapted callus was inhibited, but the presence of 10 mol m−3 proline had an ameliorating effect. Abscisic acid (ABA) supressed the growth of both salt-adapted and unadapted callus of rice in the absence of salt stress. ABA inhibited the growth of callus adapted to and grown in 100 and 200 mol m−3 of NaCl or when it was replaced by equimolar concentrations of KCl. Growth of 100 mol m−3 NaCl adapted cells was inhibited when they were transferred to a medium containing 200 mol m−3 of NaCl, but in the presence of ABA it was stimulated. ABA increased the growth of unadapted cells when subjected to different salts. Also, ABA accelerated the adaptation of cells exposed to salt but not to water deficits imposed by nonionic solutes.

The activity during root and shoot initiation of key enzymes involved in aromatic amino acid metabolism was examined in rice (Oryza sativa L. cv. Bala) callus cultures. Increased activities of the enzymes quinate:NAD+ oxidoreductase (EC 1.1.1.24), shikimate kinase (EC 2.7.1.71), chorismate mutase (EC 5.4.99.5), anthranilate synthase (EC 4.1.3.27) and tryptophan synthetase (EC 4.2.1.20) were noticed in organ-forming callus compared to proliferating callus of rice, especially prior to the visible manifestation of form. These results suggest a correlation between organogenesis and the aromatic amino acid pathway.