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Studies to Minimize Seed Coat Color Darkening in Pinto Bean
April 13, 2004

In order to evaluate darkening of the seed color of pinto beans, three experiments were conducted at different North Dakota Locations. The objectives of these experiments are: to determine the effect of the harvesting date on the seedcoat color, to determine the effect of nitrogen fertilization on the seedcoat colors, and to determine the effect of the relative humidity during the growing season on seedcoat color of pinto beans.

1. Effects of harvesting date on pinto bean seedcoat
Twenty pinto beans varieties (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 on May 29th 2003 at two locations in North Dakota, Fargo and Prosper, and they were harvested at four different times Sept 2nd, Sept 16th, Sept 30th , and Oct 14th. The experimental design was RCBD with three reps in a split-plot arrangement. Varieties constituted the main plot, while the harvesting dates constituted the subplots. Seed color was evaluated for each sample using a Agtron Color Quality Meter.

As a preliminary results from one year data we found significant differences among harvest date (Color Score Fargo = 45.3 (Sept 02) -34.2 (Oct 14) Color Score Prosper = 39.5 (Sept 02) -32.2 (Oct 14)). Significant differences among varieties were also found (Color Score Fargo Sept 2nd: GTS-900 = 40.2, Kodiak= 53.2; Oct 14th : Kodiak = 29.7, Montrose = 36.6) (Color Score Prosper Sept 2nd: Rally = 36.4, Remington = 42.2; Oct 14th : Rally = 28.3, Fargo = 35.9)

Significant differences in the interaction variety x harvest date were also found.

In General beans harvested on the first harvest date (Sept 2) had the lightest color across all varieties. Beans harvested on the last harvest date (Oct 14) had the darkest color across all varieties. In average color score reduce 3 point in each harvest date. There are differences in seed coat color among the harvest dates. In earliest harvest dates the seed coat color is lighter.

The longest the pinto beans are exposed to the environment the darker the color of the seed coat.

Since there is difference in the seed color among varieties under the same environments, genetic effect could be involve in darkening of seed coat color. As a general recommendation we could say that pinto beans should be harvested as soon is possible.

Further steps:
Repeat the trial on 2004. We are making crosses among the lighter and darker color varieties and we will plant F1s in the field to determine if there is a genetic effect involve in the darkening of seed coat color of pinto beans.

2. Nitrogen fertilization effect on seedcoat color.
Three pinto beans varieties (Maverick, Montrose, and Othello), planted at Erie (May 25th) and Hatton (June 4th). Four rates of nitrogen were used (0, 35, 70, and 105 lb/a) to determine the effect of nitrogen fertilization on the seedcoat color pinto beans. The experimental design was RCBD with three reps in a split-plot arrangement. Varieties constituted the main plot, while the nitrogen rates constituted the subplot. Seed color was evaluated using a Agtron Color Quality Meter. Nitrogen was applied on July 22nd at Erie and on July 8th at Hatton. The experiments were harvested on September 23rd at Erie and on September 11th at Hatton.

No significant differences were found in seed color coat among the different nitrogen rates.

The color score ranged from 37.3 to 35.8 at both locations. We probably will repeat this experiment this year at different locations.

3. Effect of Relative Humidity in Pinto Bean Seedcoat Color (Growth Chamber)
Ten pinto beans varieties (Bill-Z, Buster, Chase, GTS900, Maverick, Montrose, Othello, Remington, UI114, and Winchester) are being grown in a growth chamber at 25 C and four different relative humidities (RH). The RH are 45, 65, 75, and 85% respectively. The experimental design is RCBD with two replications. The first replication of the treatments at 45, 65 and 75% RH had been already evaluate, and the seed color was determined using an Agtron Color Quality Meter. At this moment we are harvesting the second rep of 65 and 45 % relative humidity treatments. The statistical analysis to determine if the relative humidity have a significant effect on the seedcoat color of pinto beans will be perform after completion of the study.


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Northarvest Bean Growers Association | 50072 East Lake Seven Road | Frazee, MN 56544
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