Effects of Thiourea and KNO3 on flower Bud Burst in Durian, durio zibethenus Murr. After Paclobutrazol Use

Abstract

Flower buds in durian might not be normally developed unless the variable factors are most prevailed. A small amount of rainfall occur at dot stage of flower bud normally induce cessation of development. Escapers of such event may exhibit uncommercial threashold scale of developed flower buds, which leads to difficult subsequent mangement of the crop. Influence of thirourea on flower bud burst in counteract with the effect of the rain was then studied at various districts of Chanthaburi province.
In 1988/1989, thiourea at the rates of 500 1,000 and 1,500 ppm were sprayed on branches of durian threes pretreated by 1,000 ppm paclobutrazol at the first stage of flower bud development. thiourea can intensify the number of inflorescences per unit length of branceh, ruslting in higher number of flowers per tree. A positive correlation (r=0.661**) between thiourea rates and flower density was not9iced. An increase of 75% in the number of flowers per tree was observed in teees treated with 1,500 popm thiourea when compared with the trees pretreated with paclobutrazol.
In the year 1989/90, thiourea rates of 1,000 1,500 2,000 3,000 ppm and the mixture of 1,500 ppm KNO3 were sprayed on branches of durian trees pretreated with paclobutrazol. All teatments can intensify the number of inflorescences as compared with untreated trees. However, thiourea and KNO3 failed to increase the efficiency of paclobutrazol when there was continuous rainfall exceeded 35 mm per day.
To improve the efficiency of paclobutrazol during high rain, thiourea at 1,500 and 3,000 ppm and the mixture of thiourea with dextrose, humic acid anda 15-30-15 foliar fertilizer or thiourea at 1,500 ppm with NAA 11.25 ppm or 22.50 ppm and a 15-30-15 foliar fertilizer or thiourea at 1,500 pm with Florigen per day in the year 1990/1991. Thiourea alone at 3,000 ppm and thiourea mixed with other chemicals can increase the number of inflrescences compared with paclobutrazol alone.
The treatments used in 1990/91 were applied to durian trees in 1991/92. Opposite results were detected because the amount of rainfall during dot stage was less than 10 mm per day. Thiourea alone or mixed with other chemicals could not intensify the number of inflorescences compared with paclobutrazol alone.