High field grain yield and acceptable milling quality are very important objectives of our rice breeding program at the University of Arkansas Division of Agriculture. We are constantly investigating traits in our new cultivars that will maintain and improve both of these objectives.
One such trait can be characterized by a rice plant having dark green leaves and delayed leaf drying at grain maturity and is known as stay-green.
The stay-green trait was observed in Columbia in the 1950s and is thought to be responsible for higher amounts of chlorophyll in the leaves, which provides higher rates of photosynthesis, and the photosynthesis rates continue to remain high through grain filling. Plants lacking stay-green tend to begin leaf drying before or during grain filling, which is thought to decrease the duration and quality of grain filling.
Measuring chlorophyll amounts
When the leaf is young, it builds up nutrients and other materials that are transported to the growing parts of the plant during growth. Leaves turn yellow during aging because of the degradation of chlorophylls and proteins that are acquired during photosynthesis. In theory, the longer photosynthesis continues, the longer the plant stays green, and the longer the grains will fill. This is how the term “stay-green” came about.
Photosynthesis rates can be measured digitally by the use of a SPAD meter, which reads the amount of chlorophyll in a leaf. The higher the SPAD reading, the more chlorophyll in the leaf. The higher the SPAD reading, the more chlorophyll in the leaf.
We measured leaf chlorophyll content of two rice lines that were observed to be different in shades of green color in the field. We also made a cross between these plants and measured chlorophyll in the leaves of their progeny to see how this trait is inherited.
Knowing how the trait is inherited will help rice breeders in their selection methods. Breeders will know what ratios to expect in progenies and can predict the gene action taking place.
The phenotypic ratios shown in all of the populations from the cross were representative of single dominant gene inheritance. More confident crosses can be made involving this trait that will perhaps lead to more stay-green rice varieties with higher yields and better grain quality.
Information for this article was provided by James Gibbons, Rice Breeder and Assistant Professor of Crop, Soil and Environmental Sciences, and Jerry D. Morgan, graduate
student, with the University of Arkansas Division of Agriculture.