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Seed Coat Integrity: Inheritance and Selection for Resistance to Mechanical Damage in Common Beans (Phaseolus vulgaris)

Soon J. Park and Terry Rupert

Agriculture and Agri-Food Canada Greenhouse and Processing Crops Research Centre, Harrow, Ontario N0R 1G0 Canada.
Email: parks@agr.gc.ca

Abstract

Common beans are chiefly consumed by humans in various forms of food, mostly processed as baked beans. Therefore, seed coat integrity of navy beans is extremely important for processing. Mechanical damage (MD) of seed also causes abnormal and reduced emergence and seedling vigor. This prompted an initial study into seed coat integrity of beans, resistance to MD and a subsequent search for resistant beans as there are variety differences. The second part of the study was carried out to determine genetic control of MD, to estimate heritability, and to apply these findings in development of MD tolerant bean cultivars. F4 and F4:5 recombinant inbred lines (RIL) of two crosses between resistant and susceptible navy bean lines, were tested. The study found that MD was under quantitative genetic control by multiple minor genes. Heritability, estimated by the parent-offspring regression method, was moderate. Correlations between the base population and selected progeny lines tested in two years suggested that selection for mechanical damage tolerance would be moderately effective and breeding is possible. Seed characteristics measured by using image analysis system found that MDI was correlated with seed length and surface area in one of the two crosses.

Media Summary

Beans are consumed by humans in mostly processed forms that require whole, sound beans. Inheritance and selection for resistance to mechanical damage was studied.

Key Words

Inheritance heritability selection correlation index combine

Introduction

Common beans (Phaseolus vulgaris) in Ontario are annually a $50 million industry with most of the beans consumed by humans in various forms of food, mostly processed as baked bean. Over 85% of Ontario’s bean crop is exported overseas for processing primarily into canned food items. Therefore, seed coat integrity (high quality wholesome bean) is extremely important in the competitive international trade. Mechanical damage also causes abnormal seedlings and reduced seedling vigor. These prompted an initial study into seed coat integrity of beans as resistance to MD and a subsequent search for resistant beans. We report results from the studies conducted in the field with direct combining of beans and in the laboratory with simulation devices. Results of progeny testing of RIL to verify breeding behavior, and some characteristics of seed and plant related to resistance are summarized.

Materials and Methods

Development of recombinant inbred populations: Two crosses between navy bean lines susceptible and resistant to MD were prepared by artificial hybridization. They are Cross 1, Envoy/OAC Laser and Cross 2, OAC Speedvale/Vista. The hybrids were grown at Harrow in 1999 and following two generations were advancing in single seed descent in a winter nursery to F4. Subsequent generations of inbred lines were tested in field trials.

Tests with F4 and F4:5 lines of the base populations in 2000-2001: About 130 F 4 plants of each of the populations were grown in plant rows at Harrow in summer of 2000. At maturity plants were pulled manually at fairly high seed moisture (close to 18%) to avoid seed coat damage. They were shelled with an Almaco plot thresher at 300 rpm with a wide open concave to avoid seed coat damage. In 2001, F4:5 RIL populations were grown at two sites, Harrow and St. Thomas, Ontario.

Progeny tests with selected F4:6 and F4:7 lines in 2002-2003: Thirty selected F4:6 RIL from each of the two crosses were grown in field plots at Harrow in 2002 and F4:7 lines at Harrow and St. Thomas in 2003. The lines were selected on the basis of average MDI of previous three trials conducted at Harrow and St. Thomas in two years by choosing low 10%, mid 10% and high 10% of each population. The plots were harvested by two methods: manually sampled for simulation testing (250-300 gr per plot) and the rest were directly combined by Hegi plot combine at 700 rpm cylinder speed at 18% seed moisture.

Sample preparation: Moisture of seed samples were adjusted to 13% and two sub-samples of 100 seed per line were prepared to subject to MD simulation device (pedal machine). The samples were dropped one at a time through the pedal machine to induce seed coat damage at 8.5 mm/sec (or 395 rpm). The seed samples were soaked in red food dye water solution for 30-40 seconds and scored visually for damage as 1 for whole bean (no damage), 2 for hair line crack, 3 for clearly visible crack, 4 for large crack and 5 for split beans. Mechanical damage index (MDI) was estimated by Sum[MD score x # of seed in each score]/total # of seed x 100.

Seed chracteristics were observed by using image analysis system. Digital image was taken on top and side surfaces for length and width, and the image was converted to numerical data by Sigma Scan pro@. Then, ratio of length (L)/width(W) and seed surface were estimated. Shape of seed was visually scored as 1 for round to 5 for oblong seed. Correlations between MDI and the seed characteristics were estimated.

Results and Discussion

A. Inheritance and Heritability of MDI

Frequency distribution of MDI. Frequency distribution of MDI of 132 RIL of cross 1 was continuous with a slight skewness toward the resistant side with a mean MDI of 75 (range of 25 to 181). MDI of parental lines were 62.7 for the resistant cv Envoy and 93 for susceptible cv OAC Laser. MDI distribution of 127 RIL of the cross 2 was continuous with fairly normal curve. (Fig. 2). Average MDI of the cross 2 was 60.7 (range of 22 to 142). MDI of the two parental lines were 27.8 for resistant cv OAC Speedvale and 55 for susceptible cv Vista. This clearly suggested that MD is inherited quantitatively by the control of multiple minor genes.

Heritability of MDI: Average MDI of F4:5 lines of cross 1 grown at the two locations in 2001 were regressed on F4 lines and mean heritability, estimated by the parent-offspring method, was 0.55. Similar results were also obtained in cross 2 with mean heritability estimate of 0.65 and its scatter diagram is presented in Fig. 2. These results suggest that selection against MD should be moderately effective though it is controlled quantitatively and that breeding for mechanical damage resistance may be possible.

B. Progeny Testing of Selected RIL

Agronomic performance and MDI estimated by simulation and direct combine: In 2002 the trials grown at Harrow, average seed yield was 2196 kg/ha for cross 1and 2111 kg/ha for cross 2. Lines performed better than average of the two parents were 12 in cross 1 and 5 in cross 2 (mean of the two parents was 2252 and 2340 kg/ha for crosses 1 and 2). In 2003 trials at two locations, average seed yield of cross 1 was 2002 kg/ha and 2140 kg/ha for cross 2.

Frequency distribution of mechanical damage index: Mean MDI of the base populations and selected low, medium and high progeny of the two crosses, grown at 3 sites in 2002-2003, are presented in Table 1. Mean and ranges of MDIs (simulated) and MDIc (combined) were generally maintained their relative rankings. Frequency distribution of both MDIc and MDIs of the two crosses grown at two locations were fairly normally distributed indicating the trait is quantitatively controlled for its inheritance

Correlation of MD by simulation and combine harvest: Relationship between MDIc and MDIs was examined by regressing MDIs on MDIc and estimated correlation coefficients for the two crosses tested at 2 sites in two years. (Table 2). Positive correlations in both crosses suggest that MDI estimated by both methods agrees fairly well. Also, the results suggested that simulation device to estimate MD would be an acceptable method for selecting resistant bean lines and it is repeatable over the years and locations as shown by an average correlation coefficients of 0.4 for cross 1 and 0.54 for cross 2.

Correlation of MD of the base population and selected progeny lines: MD of the parental base populations grown in three trials in 2000-2001 was compared with results obtained from the trials conducted in 2002 - 2003. The two crosses grown in both years showed significant average correlations with a range of 0.58 to 0.78 except MDIc of the cross 1 which had 0.24 (Table 2).

Overall MD are clearly separated by low, medium and high MDI groups of the base population and MDI estimated by both methods are scattered within the base population group. Correlations of each cross tested at each environments were mostly highly significant, suggesting that seed coat integrity of the progeny selected from the base populations were repeatable and selection for the characteristics may be practiced effectively. However, cross 1 showed consistently low level of correlations between the base population and the progeny for MDIc though it showed highly significant relations when measured by MDIs. This suggests that there is cross specific response for the trait.

Correlation between MD and characteristics of plant and seed: Plant and seed characteristics were segregating in the populations. Correlation coefficients between MDI and growth type were not significant. However, MDI and maturity was negatively correlated with r = - 0.364 for cross 1 and - 0.382 for cross 2, suggesting that late maturing lines tend to be more resistant to MD than those with early maturity. Seed characteristics were observed from both sides of the flat top and the side (length, width, length/width ratio, thickness) for the base population groups and two parental lines. The cross 1 showed closer association with both MDIc and MDIs and seed characteristics such as length, width and surface area than cross 2. Correlation between seed surface area and MDI, and seed shape and MDIc estimated by both methods were significant in cross 1. Some plant and seed characteristics may be used in selecting for resistance to MD but this relationship depends on parental variability and appears to be cross specific.

Summary

Our studies revealed that seed coat integrity measured as MD of seed coat had variety differences in navy bean and MD could be measured by a simulation device. The studies also found that MD is genetically controlled quantitatively with moderate level of heritablity. MDI estimated by direct combine and simulation device showed significant correlations. In progeny testing, the three selected progeny groups even significantly correlated with the base populations, by showing the similar seed coat damage ranges in both harvest methods. However, the simulated MDIs had a closer relationship between the base populations than MDIc of the direct combine. Some plant (i.e. maturity) and seed characteristics (i.e. shape, length and surface area) may be used for visual selection for resistance to MD. However, it should be noted that this association appears to be cross specific depending on parental seed characteristics. Our studies suggested that selection for mechanical damage resistance would be moderately effective and breeding is possible.

Figure 1. Frequency distribution of mechanical damage index (MDI) of Cross 2, at Harrow and St. Thomas in 2001.

Figure 2. Parent-offspring correlation of MDI of cross 2, OAC Speedvale/Vista, tested in 2000-2001.

Table 1. Mechanical damage index (MDI) of base poplulations in 2000-2001 and selected lines tested in 2002-2003 at St. Thomas and Harrow.

Cross/Class

2000-2001

2002 (Harrow)

2003 (Harrow)

2003 (St. Thomas)

B. Population

MDIc

MDIs

MDIc

MDIs

MDIc

MDIs

Cross 1 (Envoy/OAC Laser, n=10)

         

Low 10%

22.5

39.5

30.9

45.4

70.5

13.8

69.8

Mid 10 %

53.4

53.9

36.9

55

75.3

19

82.2

High 10%

90.5

47.9

46.7

61.1

102.8

17

116.2

Envoy

42

26.9

38.2

28.5

50

15.4

54.7

OAC Laser

88

90.9

55.8

28.17

66.7

29.1

95.3

Cross 2 (OAC Speedvale/Vista, n=9)

         

Low 10%

32

61.6

35.4

39.2

63.8

22.1

78.4

Mid 10 %

62.3

77.3

52.6

58.1

94.4

28.8

106

High 10%

97.4

87.9

75.4

62.2

108.7

49.8

142.7

Speedvale

28

27.8

22.8

58.4

101.2

9

59

Vista

86

68.2

54.5

55

128.8

37.9

100.1

Table 2. Correlation between mechanical damage index estimate by combine (MDIc) and simulation device (MDIs), and correlation between the base population MDIs and progeny MDI in 2002 - 2003.

Year/site

   

Base population MDIs

 
 

MDIc

vs. MDIs

With MDIc

With MDIs

 
 

Cross 1

Cross 2

Cross 1

Cross 2

Cross 1

Cross 2

 

(N = 32)

(N = 30)

(N = 30)

(N = 28)

(N = 30)

( N = 28)

 

2002 Harrow

0.503**

0.62**

0.16

0.34

0.45**

0.70**

 

2003 Harrow

0.407*

0.527**

0.31

0.71**

0.48**

0.68**

 

St. Thomas

0.287

0.476**

0.16

0.53**

0.76**

0.84**

 

Mean

   

0.33

0.74**

0.71**

0.89**

 

Average

0.40

0.54

0.24

0.34

0.60

0.78

 

*, ** signifigance at p = 0.05 and 0.1 level

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