Effect of Foliar Application of Triacontanol on the Growth and Yield of Rice Plants : I. Around the time of treatment

It is recognized in various species that triacontanol (TRIA) increases the growth of seedlings at very low concentrations. However, very fcw reports so far have actually shown increases in dry weight or yield in grain crops under field conditions. A field experiment was, therefore, carried out in 1983 and 1984 at the University Farm of Tokyo Univcrsity of Agriculture, Atsugi, Kanagawa Pref., using two cultivars of rice, with the aim to clarify the cffect of foliar-applied TRIA in colloidal dispersion at concentrations between 0.1 and 10 ppb. Main results obtained are as follows : 1. In 9 out of 16 TRIA-treated plots, increases of 5% to 14% (significant at 5% level in the latter) over control were found in the yield of hulled rice, i.e., brown rice (Tables 7 and 8). 2. As for the effect of TRIA on yield componcnts, increases in the number of ears and 1000-grain weight of hulled rice were often observed (Table 7). 3. The effective concentration of}TRIA for increasing the yield was found to be 0.2-10ppb and the most effective tilnc of application was at the early tillering stage or the end of nursery stage (Tables 7 and 8). 4. Plant length, total leaf area and total dry weight in early growth stages showed a tcndency to be slightly inhibited by TRIA-treatment at concentrations 0.2 to 10ppb (Tables 3 and 4). 5. At the activc ripening stage, however, not only the totalleaf area but also the total root mass were found to be larger in the TRIA-treated plants than in the non-treated control (Tables 4 and 5). It is highly possible that these characters have contributed heavily to increasing the yield through promoting the dry matter accumulation after heading (ΔW) in the TRIA-treated plants (Fi9. 1) . 6. It was found that ΔW was positively correlated with NAR (Fig.2) and that the latter in turn was negatively correlated with SLA (Fig. 3). These may be interpreted to suggest that photosynthetic rate during the active ripcning period was accelerated in the TRIA-treated plants, thus leading to arl increased yield.