Problems in breeding the legume Indigofera spicata for tropical pastures

Abstract

A survey of I. spicata introductions showed the majority to be tetraploid perennials and similar to each other with red stems, strongly stoloniferous habit, and poor seeding ability. The rest were green stemmed annuals or biennials which were either diploid or tetraploid and which were free seeding and almost non-stoloniferous.

Crosses were attempted using several green stemmed introductions as the female parents with a representative red stemmed one as the male. The ploidy of a diploid parent was raised with colchicine treatment before crossing. F₁ seed was obtained in all crosses except in that involving the induced tetraploid. The F₁ generations were sterile except for one cross from which a small quantity of F₂ seed was obtained. A high degree of sterility was maintained in the F₂ and F₃ generations but fertile F₃ selections produced mostly fertile progeny. The sterility could be followed by the percentage stained pollen and appeared to be controlled by genetic factors.

Normal types of distribution of the phenotypic classes for yield and stoloniferous development were obtained for the F₃ population which contained 26.3 per cent perennial plants. Two F₃ lines were obtained which combined the desirable characters of the two parents.

The effect of temperature and photoperiod on all introductions used as parents and the two promising lines was investigated in a phytotron. All types flowered at both the 8 hour and 16 hour photoperiods and temperatures 27°/22°C and 30°/25°C favoured flowering. The better flowering of the green stemmed parent had apparently been transferred to the selected F₃ lines. The highest plant dry weights occurred at 30°/25°C and the effect of photoperiod on yield was reversed as the temperature increased.