Leaf counting: an effective seed production technique of ensuring flowering sychronization of hybrid rice parents

Producing enough seeds from hybrid seed production areas is a bottleneck in achieving sufficient supply of hybrid seeds for commercial cultivation. Because parental lines of rice hybrids usually differ in their growth duration, obtaining a well synchronized flowering is a major problem. Synchronization of flowering is key in achieving high seed yield in hybrid seed production. However, synchronization of flowering is difficult to achieve and highly dependent characteristics of both the parents (particularly maturity) and highly affected by external factors such as fertilizer and water management, and even stresses. Usually, synchronization is improved by manipulating planting dates (staggered sowing), fertilizer management water management, and GA sub 3 application . A new and improved technique called 'leaf number determination' was developed by Chinese breeders to optimize synchronization of flowering of hybrid parents. The study was conducted at PhilRice CES. Specifically, it aims to determine the number of leaves that coincide with the initial heading for both parents and improve flowering synchronization of PhilRice-bred hybrids. A total of six parent lines composed of three CMS and three restorer (IR80559A x PR34302, IR79128A x PR31559 and IR68897A x IR73013), were established in replicated trial by row crossing method of AxR seed production. Leaf counting started when first true leaf emerged up to flag leaf emergence. Leaf number was recorded every three days to 10 sample plants per entry. Only main culm leaves were counted. Analysis of variance for number of leaves at flag leaf emergence revealed significant differences among parent lines. Across combinations, IR80559A x PR34302 had 0.7 leaf difference, 0.59 for IR79128A x PR31559 and 1.5 leaf difference was observed to IR68897A x IR73013 cross combination. The result can be the basis of sowing interval in AxR seed production. Leaf count method can be instrumental in flowering synchronization of hybrid parent lines.