Rice variety development is a long-term research endeavor. It normally takes 4-5 years from when the initial cross is made to develop a new population, until superior progeny from that population are uniform enough to be entered into yield trials. The initial yield testing program is called the Preliminary Yield Tests. These are primarily two-replication tests, though a number of lines are evaluated each year in single-plot tests. These trials are planted in late March/early April on the Rice Research Station. This will allow sufficient growing season to evaluate first and ratoon (second) crop performance. A “plot” in the Rice Breeding Project is seven drill rows spaced 8 inches apart and is 16 feet long (or approximately 75 square feet). This represents approximately 0.17% of an acre.

We use these small plots to keep the overall test as small as possible to minimize environmental variations that might have influence on the performance of genotypes (breeding lines) in the tests. In other words, we try to have any differences expressed in these trials (yield, milling quality, height, etc.) a result of true genetic differences and not caused by differences such as soil type, fertility or water depth.

Approximately three weeks after the preliminary yields trails are planted, we will plant a seed increase/purification block which will include 10 head rows from each of the lines included in the yield trial. This block is planted later than the test to provide time to analyze data after harvesting the yield trial to determine which lines may be advanced and thus which headrow populations should be harvested. Before harvest, these lines are evaluated. Any segregating rows are removed from the population, 25 panicles are picked from a representative row and then the remaining seed is bulk harvested. This will serve as a pure seed source for this line for further advanced testing.

A typical preliminary yield test will have 750 entries (replicated twice) for a total of 1,500 plots. These tests also include the currently grown varieties so that the performance of the experimental lines can be compared to these as well as to each other. This size test will take approximately 5 acres. If everything goes without a hitch, this test can be planted in less than a day with our specialized planting equipment. However, preparing the seed for this planting (cleaning, cataloging, weighing, labeling and filling seed envelopes, laying out packets in planting order, etc.) is the result of many months of meticulous work during the winter. In addition, there is a great deal of data entry and record keeping involved as lines move from one generation to the next.

After planting, this yield trial is handled as any other rice field to optimize production and uniformity throughout the test area. This includes timely water management, fertilization, and weed and insect control. We do not use fungicides in the breeding program because relative disease resistance is evaluated at every step of the variety development process.

These trials are evaluated at least twice weekly during the growing season, and data is collected for the following traits; 1) emergence date, 2) seedling vigor, 3) tillering characteristics, 4) heading date, 5) plant height at maturity, 6) disease susceptibly (any diseases present), 7) lodging characteristics and 8) harvest maturity date. When a plot reaches harvest maturity, a hand-harvested sample is taken for use in milling quality evaluation. This sample is cut with a sickle. It is threshed using a stationary thresher, aspirated and then dried on our specialized sample drier. This sample is taken this way because the test will later be combined harvested with our small-plot combine when all plots have reached harvest maturity. Since there may be up to 10 days difference in maturity among lines in these trials, taking a sample from each plot at harvest maturity puts all lines on an equal footing for milling quality evaluation.

Before harvest, Dr. Don Groth will evaluate all the plots for relative susceptibility to major and minor rice diseases. Because we often do not have consistent disease pressure in these tests, Dr. Groth will also plant each of these lines in disease nurseries where disease pressure is maximized by inoculation (sheath blight) and the use of highly susceptible spreader varieties (blast).

When all lines in a trial have reached harvest maturity, the trial is harvested using a specialized small plot combine. This combine has a 6-foot header width so it fit these plots perfectly. The combine has the capability to harvest a plot, then automatically obtain the grain weight and grain moisture for the rice from that plot. The seed can then be bagged and tagged for identification. Under ideal conditions, the 1,500 plot test can be harvested in two days.

In the late summer and fall we will mill the hand-harvested samples, which will provide data on whole and total milled rice. In addition, these samples are evaluated for uniformity, chalkiness, grain shape and any other characteristic that might be a factor in the acceptability of the line as a commercial variety.

We will then analyze the multitude of data collected to decide which lines will be entered into advanced trials the following growing season. We will discuss the numerous advanced trials conducted in Louisiana each year as well as our cooperative tests with breeding program in other states in next month’s issue.