Environmental effects on stunting and the expression of a tiller inhibition (tin) gene in wheat

A recessive gene (tin) that inhibits tillering in wheat (Triticum aestivum L.), and that may be important in the redirection of assimilate from unproductive to productive tillers, has been reported. However, this gene has also been associated with a fatal condition known as 'stunting'. The severity of this phenomenon has been shown to increase when plants are grown under long photoperiods and at low temperatures. The objectives of this study were to observe how the expression of the tin gene varied in different genetic backgrounds, in addition to obtaining a better understanding of environmental factors that may affect both tillering and stunting in lines with the tin gene. Plants were grown outdoors in Canberra, Australia, at various times throughout the year, as well as under controlled conditions where photoperiod, temperature and light intensity were varied. The inhibition of tillers resulting from the presence of the tin gene was most extreme in summer, autumn and spring (up to 90% reduction in tillering). However, when sown in late autumn and winter, tillering was reduced by between 30-50% for the tin lines compared with their near-isogenic parents. Reduced tillering in the tin lines was due to an earlier cessation of tillering rather than a reduced rate. Stunting was frequently observed in some lines more than others when plants were grown under long days and when temperatures were low. The daily minimum temperature, rather than the average daily temperature, was associated with stunting. The duration of the dark period also influenced stunting, with a longer dark period reducing the incidence of stunting from almost 100% to 0%. In all experiments where irradiance was increased, stunting also increased. In addition, elevated CO2 also increased growth characteristics associated with stunting. It is concluded that stunting is associated with a high assimilate supply to the main stem shoot apex before the time of floral initiation. This is caused by an inhibition of tillering and a high photothermal quotient. Leaf length was found to be a good indicator of stunting severity, with stunted plants producing shorter leaves than those plants which failed to stunt. Measurements of leaf length indicated that stunting is induced when the second leaf is expanding.