Thursday, 22 August 2013

Modification of rice heading date with photoperiod-sensitive genes

An IRRI Seminar

By Tsutomo Ishimaru
Senior Scientist, Plant Breeder
Plant Breeding, Genetics, and Biotechnology Division

Thursday, 22 August 2013
Havener Auditorium, IRRI

Rice is a short-day plant but it grows in an extremely wide latitudinal range—from 53oN to 40oS. Adjustment of its heading date to an appropriate time is a key determinant for its wide adaptability. Many quantitative trait loci (QTLs) for heading date (Hd) have been identified and recent genetic studies reveal that breeders have used Hd genes to develop local varieties with good yield and quality under a local environmental condition.

Hd1 is a major photoperiod-sensitivity QTL in rice. It functions to promote heading under short-day conditions and to inhibit it under long-day conditions. Nucleotide polymorphisms observed in Hd1 among Asian varieties suggest that Hd1 might be a main cause for the diversity of heading dates in rice in the region.

Japan is located at one of the northernmost areas for cultivated rice in the world. In the highest-latitude area of Japan (approximately 45oN), rice has to be cultivated under a long natural day length during a very short summer period. Only early-heading varieties with extremely low photoperiod sensitivity can be cultivated. The use of loss-of-function Hd5 in a local breeding program was critical in developing extremely early-heading rice that is adaptable to conditions in the northern limits of the rice area.

A recent effort was made to develop climate-resilient rice with an Hd gene in Japan. High temperatures during grain-filling increase chalkiness in the grains and low acceptability in the rice market. To avoid grain-filling happening during the hottest period of summer, lines with late heading were developed.

Are Hd genes useful in the development of climate-resilient and crop-intensified indica-type rice? The IRRI-Japan collaborative research project has attempted to modify the heading date of the photoperiod-insensitive indica-type rice variety IR64 by introgressing Hd genes from several accessions. Although the breeding program for the days-to-heading (DTH) trait was just recently launched, some near-isogenic lines (NILs) for DTH have been developed. Further efforts are being made to build a wider variation of DTH in IR64.

In this seminar, Dr. Ishimaru will share about the ongoing breeding program on the development of DTH lines through the IRRI-Japan collaborative research project. He will also discuss the application of DTH lines in rice ecosystems that are changing as a consequence of climate change.

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