Effects of TIBA (2,3,5-triiodobenzoic acid) on growth and yield of Azuki bean, Vigna angularis.

Abstract

In soybean, TIBA treatment was reported to increase occasionally mainly due to greater pod set and/or improvement of leaf canopy shape, whereas almost no imformation is availble in azuki bean. Two azuki bean cultivars, Erimo-shozu, and Akane-dainagon which produces a larger seed and matures several days, later than Erimo-shozu, were grown in a spacing of 60×10cm in 1984 and 1985. TIBA was applied at initial flowering and at full flowering (in 1985 only) at the rate of 5g/10a and 2.5g/10a (in 1985 only). Growing season was rather dry in both experimental years, especially in 1984. 1. Main stem height was shortened remarkably and number of branches per plant and number of nodes on branches were increased by TIBA treatment at initial flowering. But these effects on branches were small or temporal and variable depending on years and cultivars (Figs. 1 and 2). Little effect was found on main stem height and branch development in the experiment where TIBA applied at full flowering. 2. The effect of TIBA on leaf area was also variable depending on years and cultivars. However, in general, leaf area index in TIBA treated plants, although it became higher temporally soon after the treatment in some cases, lower than those in control plants through reproductive period. The dry weight changes were generally similar to those of leaf area. Even in the early stage of seed development TIBA applied at initial flowering did not enhance the distribution of dry matter to seed (Fig. 3). 3. TIBA treatment resulted in vertical leaf structure of plant comunity unfavorable for light intercepting efficiency (Fig. 4), because the upper internodes on main stem became short and petioles moved downward, curved or distorted. Such abnormal arrangement of petioles and leaves was observed more frequently with 5g/10a TIBA treatment at both initial and full flowering. 4. Number of pods and number of seeds per pod were decreased by TIBA treatment mainly on main stem, although 100-seed weight was slightly increased (Tables 1 to 3). Although the extent of response was different in yield components, seed yield finally decreased by TIBA treatment irrespective of years, cultivars, and application methods (Table 4). Thus, in azuki bean, the effects of TIBA on growth and yield are considerably different from soybean reported previously. Plant form modified by TIBA treatment seemed to be unfavorable for photosysthesis, and probably this resulted in retard of reproductive growth. However, it is also probable that TIBA gave direct effect on the flowering and/or fertilization in azuki bean since decrease occurred in both pod number and seeds per pod.