[print this page]

Studies to Minimize Seed Coat Color Darkening in Pinto Beans
April 18, 2005

Principal Investigator

Gonzalo Rojas-Cifuentes, Research Associate

NDSU Department of Plant Sciences


Cooperating Scientists

Kenneth Grafton, Professor, Department of Plant Sciences

Dean College of Agriculture

Director N.D. Agricultural Experiment Stations, NDSU


Jean Robert Gelin

Research Associate, NDSU Department of Plant Sciences


Jody Vander Wal

Research Specialist, NDSU Department of Plant Sciences


Research Goals       

Evaluate factors affecting the seed coat color of pinto beans in a second year study.



1. Determine the effect of the harvest date on seed coat color.

2. Determine the effect of nitrogen fertilization on seed coat color.

3. Determine the effect of the relative humidity on seed coat color in a controlled environment.


Benefits to North Dakota and Minnesota Bean Growers

Seed coat color is an important trait in pinto beans. Consumers prefer pinto cultivars with bright and shiny mottle colored seed coat. Dark seed coat on pinto beans results in lost of market value. The results obtained in these studies will give the growers additional management practices to reduce the darkening of pinto bean seed coat.


Research methods

Effects of harvest date: Twenty varieties of pinto beans (Apache, Aztec, Bill-Z, Burke, Buster, Chase, Elizabeth, Fargo, Focus, GTS-900, Kodiak, Maverick, Montrose, Othello, Rally, Remington, Topaz, UI114, UI320, and Winchester) were planted at two locations in ND: Prosper on June 4 and Fargo on June 10. Fargo location was lost due to excessive rainfall. Prosper was harvested at four different dates Sept. 17, Oct. 1, 15, and 29. Seed color was evaluated for each sample using an Agtron Color Quality Meter (calibration: black = 0, white = 90).

Effect of Nitrogen fertilization: Three pinto bean varieties (Maverick, Montrose, and Othello), were planted at Hatton, ND on June 5th. Four rates of nitrogen were used (0, 35, 70, and 105 lb/a) to determine the effect of nitrogen fertilization on the seed coat color of pinto beans. The full rate of nitrogen was applied on July 12th at V4 stage. The experiment was harvested on October 11th (four months after planting). Seed color was evaluated using an Agtron Color Quality Meter.

Effect of Relative Humidity (Growth Chamber): Ten varieties of pinto beans (Bill-Z, Buster, Chase, GTS900, Maverick, Montrose, Othello, Remington, UI114, and Winchester) were used to evaluate the effect of relative humidity. Plants were grown in a growth chamber at relative humidities (RH) of 45, 75, and 85% at 25 °C, with a regime of 12 hours of light and 12 hours of dark.











Fig. 1. Seed color samples of Montrose of fpur harvest dates from Prosper, ND 2004.

Fig. 2. Seed color samples of Winchester of four harvest dates from Prosper, ND 2004.


Effects of harvesting date: Results from 2004 growing season at Prosper, ND show that harvest dates significantly affect seed coat color on pinto beans (Chart 1). Significant differences were observed among varieties. UI-320 and Winchester presented the darkest color on Sept. 17 and Oct. 29 respectively, Montrose presented the lightest color across all harvest dates. The higher the score the lighter the color of the seed coat.

In general late harvest had a negative effect on seed coat color across all varieties. Beans harvested on the first harvest date (Sept 17) had the lightest (higher score) color. Beans harvested on the last harvest date (Oct 29) had the darkest (lower score) color. On average, color score was reduced 6 points between the first and the last harvest date. The data obtained in 2004 season agree with the results from 2003 study.

This year differences among varieties were not consistent with the data obtained in 2003 growing seasons, with the exception of Montrose (Fig. 1), which showed an acceptable seed coat color at the last harvest date in both seasons. For instance, the variety Winchester, the best from 2003 data, resulted to be one of the darkest varieties this growing season (Fig. 2). The variety Kodiak which scored as the darkest seed coat color last year is in the middle range in seed coat color this season. As a general recommendation pinto beans should be harvested as early as possible, since the longest the beans are in the field exposed to the environment the darker the color of the seed coat.

Effect Nitrogen fertilization: Results in this study shown that nitrogen fertilization did not affect seed coat color at any rate. Similar results were observed in 2003 where no differences were found.

Effect of Relative Humidity (Growth Chamber): Relative humidity had a significant effect on seed coat color of pinto beans. Significant differences were found among varieties and relative humidities. Variety GTS-900 had the lower color score (darker color) and was the only one significantly different from all the rest. In general, seed gown under the 85% relative humidity treatment had the darkest color and was significantly different from the 45% relative humidity treatment, which had the lighter color.


Other Headlines

Email Newsletter icon, E-mail Newsletter icon, Email List icon, E-mail List icon Sign up for our Email Newsletter
For Email Marketing you can trust


Northarvest Bean Growers Association | 50072 East Lake Seven Road | Frazee, MN 56544
Ph: 218-334-6351 | Fax: 218-334-6360 | Email: