Rice Variety Development – Early Stages
H. Rouse Caffey Rice Research Station/Southwest Region
The rice breeding program at the H. Rouse Caffey Rice Research Station has been in existence since the station was first established in 1909. Since its beginnings, the breeding program has had the goal of continually providing new, superior varieties to the Louisiana rice industry to foster that industry’s productivity and viability. Initially, the program was primarily involved in bringing in rice lines from other regions and testing them to see if they might have value for production under Louisiana’s rice growing environment. Later, the program began to make crosses in efforts to create adapted varieties. Making crosses involves artificial hybridizations that combine genetic material from two different rice lines. Making crosses is the backbone of the program today.
The rice plant has a perfect flower because it contains both the male and female parts in each floret. Under normal conditions, the pollen will pollinate the stigma within the same floret. So, to make a cross, one needs to remove the male flower parts (anthers) from a rice floret prior to pollination. Later, pollen from a different rice line is used to pollinate that floret to create a cross seed that contains DNA from both the plant where the anthers were removed and the pollen bearing plant. During the next growing season, this cross seed is planted to produce what is called an F1 plant. Seed harvested from the F1 plant is then planted at a very low density so each plant can be observed. This F2 population is segregating, which means it is showing many different plant types representing traits from each of the original parents used in the cross. The F2 generation has the maximum amount of segregation, and each subsequent generation has segregation decreased by approximately half.
When these plants are mature, breeding project personnel walk through the F2 plots and pick panicles or heads off selected plants that bear desirable traits. Typically, about 100 panicles are selected from each population that shows desirable characteristics. These panicles are then individually threshed and used to plant what are called panicle rows the following growing season, which would be considered the F3 generation. A panicle row describes a short row (about 6 feet) of rice that has plants originating from the same rice panicle. From this point on, each generation of all breeding populations are grown as panicle rows. As the panicle rows reach maturity, breeders then select some for advancement and discard the rest. Those selected appear to have the combination of characteristics desirable for a rice variety in Louisiana. There are many traits that the breeder is looking for, but some of the more significant and evident ones would be apparent. These include yield potential, tiller number, grain shape and size, plant height, and length of time from planting to maturity. Other more subtle characteristics include general plant architecture, plant color, leaf shape dimensions and alignment. Of course, all of these evaluations are subjective. Also, under certain environments, disease resistance can be evaluated as well. All of the selected F3 rows will then have 10 panicles harvested from individual plants within the row.
To expedite this process, the winter nursery in Puerto Rico is typically used for production and selection of a number of the F2 and F3 populations during one winter growing season there. This is accomplished by planting the cross seed that will produce the F1 plants in the greenhouse each year in mid-February. When it warms up enough for good rice growth and development in the field (typically late March), these plants are then transplanted into the field with a good head start. Because of this head start, these plants are normally mature by mid to late July. These plants are harvested, and the F2 seed is processed and loaded for planting. This seed is then shipped to Puerto Rico and planted as soon as possible, which we hope is late July to early August. A grow-out in Puerto Rico takes about four months. At maturity, which is normally late November to early December, the breeding crew heads down to Puerto Rico to make selections just as they would at the Rice Station. After harvesting, this seed is dried, threshed and loaded for planting, then planted as soon as possible. With a great deal of hard work and long hours, all of this can be accomplished within two days for about 120 populations. These F3 populations will also take about four months to mature, so the breeding crew will head back down in April to harvest these populations. This seed will be returned to the Rice Station for planting in late April to early March.
Regardless of whether this occurs in Puerto Rico or at the Rice Station, the five panicles harvested from an F3 row are used to plant F4 rows with the remainder held in reserve. Again, at maturity, breeders select the superior rows, and the process is repeated. At some point in this process, when a superior selected row shows a high level of uniformity, that row might be bulked after the 10 panicles have been harvested. When a row is bulked, all of the seed from that row is harvested and combined. This is the seed used to begin yield testing of those lines that appear to have favorable characteristics from field evaluations as well as additional evaluations in the labs, which will evaluate grain characteristics, cereal chemistry and seedling vigor.
Next month we will address later stages involved in variety development and release.
This project was partially supported by USDA National Institute of Food and Agriculture.
Permission granted March 15, 2016 by B. Leonards (LA Farm & Ranch) to republish article on www.lsuagcenter.com.