Early haploid identification markers for doubled haploid rice production

Overview

Doubled haploid (DH) rice production is a powerful technique for accelerating breeding programs, but a significant bottleneck is that 50–80% of plants produced are haploids that are typically discarded late in the production cycle. This proposal addresses that inefficiency by introducing novel, cost-effective markers for identifying haploids at a very early stage. By detecting haploids early, chromosome doubling efforts can be focused on the right plants, increasing the number of usable DH lines while avoiding the expense of maintaining haploids through to maturity.

The approach leverages three complementary markers: leaf tip morphology, early seedling vigor, and photosynthetic rate. Each marker is non-destructive, inexpensive, and easy to apply, making the method accessible to breeding programs operating under varied resource constraints.

Technical specifications

Key markers for early haploid identification:

• Leaf tip morphology: The leaf tip of haploid plants displays a distinct, visibly distinguishable shape compared to dihaploid plants. Observation and prediction of anther-derived plants from the rice hybrid KRH 4 and from a trait-introgressed rice line showed a perfect 100% correlation with haploidy versus dihaploidy status.
• Early seedling vigor: A vigor index based on plant height and total leaf area is significantly lower in haploids compared to DH plants, providing a reliable quantitative indicator at the seedling stage.
• Photosynthetic rate: DH plants, like diploids, record significantly higher photosynthetic rates than haploids, offering a physiological confirmation of ploidy status.

Advantages of the approach:

• Non-destructive and inexpensive compared to flow cytometry or chromosome counting
• Applicable at very early growth stages, before resource commitment to mature plants
• Suitable for screening large populations in breeding programs

Technology readiness level

The markers have been validated on anther-derived plants from the rice hybrid KRH 4 and from a trait-introgressed rice line, with leaf tip morphology showing 100% correlation with ploidy status. Future validation will expand the dataset by producing a greater number of haploid and DH plants across a wider range of genetic backgrounds and will confirm ploidy using flow cytometry rather than relying solely on sterility, fertility, or seed set observations. The technology is positioned for further refinement and broader validation in collaboration with rice breeding programs.