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Cultivar Differences in Shear Strength of Okra Pods

Jim E. Wyatt, Emily W. Gatch, Craig H. Canaday

 

Interpretative Summary

‘North and South’ and ‘Cajun Delight’ had high early and late season yields and the highest total yields. ‘Burgundy’, ‘Clemson Spineless’, ‘Clemson Spineless 80’, and ‘Perkins Dwarf’ had spineless pods. ‘Star of David’ and ‘Silver Queen’ had many spines, especially on the apical end of the pods. ‘Star of David’ and ‘Silver Queen’ were the easiest pods to remove from the plant. The most difficult to snap by hand were on ‘Burgundy’, Cajun Delight’, and ‘Dwarf Long Green Pod’. ‘Star of David’, ‘Clemson Spineless’ and ‘Clemson Spineless 80’ had the highest mean pod weight. On days 5 and 7 after anthesis, ‘Burgundy’ and ‘Perkins Dwarf’ did not differ significantly from those that produced the largest pods and also had significantly less shear strength. Most correlations of okra pod length and weight with shear force were significant.

Introduction

Okra pods are edible for a relatively short time after which the pods become too tough and fibrous for consumption. The optimum length for highest quality okra is from two to four inches. Pods of this size are produced approximately three to four days after anthesis under most conditions and have a low shear strength because of little or no fiber present in the pod. Okra for processing can have pods between 3½ and 5 inches long and still have a size classification of "medium" (USDA, 1976). If the time from anthesis to harvest could be extended by cultivar selection without a concomitant loss of quality from excessive fiber, the per-acre yield of okra could be increased.

This study was conducted to determine if okra cultivars differ in rate of development of pod fiber and to identify cultivars that produce large pods with lower shear strength.

Materials and Methods

Eleven okra cultivars and hybrids (hereinafter called "cultivars") were planted at the West Tennessee Experiment Station on May 14, 2003. Prior to planting, Diazinon insecticide at 4 qts/acre, trifluralin herbicide at 1½ pt/acre, and 15-15-15 fertilizer at 300 lbs/acre were broadcast and incorporated.

Each plot was 20 ft long and spaced 5 ft apart. Plots were over seeded and seedlings were thinned to an in-row spacing of about 1 ft. The experimental design was a randomized complete block with four replications. The test was grown using recommendations for okra production in Tennessee (Sams, 1984). Rainfall was supplemented as needed by drip irrigation.

Harvest began on July 7, 2003. Yield data were obtained by harvesting pods two to five inches long three times weekly for six weeks. Pods from each plot were rated two times for presence or absence of spines. Pods were rated on a subjective scale of 1 to 5 with 1=no spines and 5=many or heavy spines. Ratings were made on 13 and 25 August and data were averaged for analysis.

To obtain pods of known maturity, flowers were tagged on the day of anthesis (DOA) and pods were harvested at one day intervals for four days beginning at DOA + 4. Shear strength was measured on a Model T-1200-G Texture Test System using a Model CS-1 Standard Shear-Compression Cell with 10 blades (Food Technology Corp., Rockville, MD). Individual pods were weighed and the length measured. The "cap" (botanically, the receptacle) was removed and single pods were sheared perpendicular to the direction of the blades. If pods were over 2½ inches long after removal of the cap, the proximal 2½ inches were used for shear measurements.

In an associated study, three pods from each plot were grown for DOA + 6 and rated for ease of removal from the plant. The pods were scored on a scale of 1 to 5 with 1 = stem snapped easily and 5 = stem required cutting. Pods were weighed, seeds and placental tissue removed, and the remaining pod wall weighed. Pod walls were dried overnight at 100EC and dry weights were obtained.

Correlations of pod length with weight, pod length with shear force, and pod weight with shear force were calculated for each cultivar and with each pod age. Replicated data from plots were converted to per-acre yields and subjected to analysis of variance (ANOVA) using appropriate SAS procedures (SAS Institute Inc., Cary, N.C.). Means were separated using Duncan’s multiple range test at P#0.05, where applicable.

Results and Discussion

‘North and South’ and ‘Cajun Delight’ had the highest yields in the study (Table 1). They were also either the highest yielding cultivar in both the early and late portion of the harvest season, or were not significantly different from the highest yielding cultivar. The lowest yielding cultivars, ‘Burgundy’ and ‘Star of David’, are specialty types unlike most commercial cultivars commonly grown.

‘Burgundy’, ‘Clemson Spineless’, ‘Clemson Spineless 80’, and ‘Perkins Dwarf’ had no discernible spines on the pods (Table 1) while ‘Star of David’ and ‘Silver Queen’ had many spines which were very irritating to bare skin. If spines were present, their occurrence was usually on or near the pod sutures, and were more dense toward the blossom end of the pods.

The easiest pods to remove from the plant were on ‘Star of David’ and ‘Silver Queen’ while the most difficult to snap by hand were on ‘Burgundy’, Cajun Delight’, and ‘Dwarf Long Green Pod’ (Table 1). This is an important characteristic when harvesting because it is much easier and faster to snap off a pod by hand than to cut the stem with a knife.

Table 1. Seasonal yield distribution, total yield, and pod spine ratings of okra cultivars grown at the West Tennessee Experiment Station in 2003.

 

Cultivar

Yield (lbs/A)

Pod
spine
rating (1-5)x

 

Pod removal score (1-5)y

 

Earlyz

Latey

Total

 

 

Cajun Delight

1507aw

8142ab

9649ab

2.5e

4.8ab

Burgundy

740f

4737e

5477e

1.0f

4.9a

Star of David

412g

4745e

5157e

3.8b

1.5e

Silver Queen

1102cde

6933bcd

8035bcd

5.0a

1.6e

Clemson Spineless

957def

7831abc

8788bc

1.0f

3.4c

Clemson Spineless 80

1203bcd

7685abc

8888bc

1.0f

2.6d

Dwarf Long Green Pod

885ef

5613de

6498de

3.0cde

4.2abc

Annie Oakley II

1312abc

7392bc

8704bc

3.4bc

3.8c

Green Best

1411ab

6586cd

7997bcd

3.1cd

4.0bc

North and South

1444ab

9043a

10487a

2.6de

4.0bc

Perkins Dwarf

1203bcd

6619bcd

7822cd

1.0f

3.4c

zEarly = 7/7/03 to 7/21/03
yLate = 7/23/03 to 8/27/03
xSpine rating: 1=no spines; 5=many or heavy spines. Mean of two ratings.
wMeans in columns followed by the same letter are not significantly different, Duncan’s multiple range test (P# 0.05).

Table 2. Early, late, and total season mean okra pod weights from cultivars grown at the West Tennessee Experiment Station in 2003.


Cultivar

Mean pod wt (oz)

 

Earlyz

Latey

Season

Cajun Delight

0.49dex

0.44f

0.45g

Burgundy

0.53a-e

0.54c

0.53cd

Star of David

0.49cde

0.62a

0.61a

Silver Queen

0.52a-e

0.58ab

0.57abc

Clemson Spineless

0.57ab

0.61a

0.60a

Clemson Spineless 80

0.59a

0.60a

0.59ab

Dwarf Long Green Pod

0.54a-d

0.52cd

0.52de

Annie Oakley II

0.46e

0.45ef

0.45g

Green Best

0.55a-d

0.48de

0.49ef

North and South

0.51a-e

0.48ef

0.48fg

Perkins Dwarf

0.57abc

0.55bc

0.56bcd

zEarly = 7/7/03 to 7/21/03
yLate = 7/23/03 to 8/27/03
xMeans in columns followed by the same letter are not significantly different, Duncan’s multiple range test (P# 0.05).

When considering the data on pods harvested for yield, ‘Star of David’, ‘Clemson Spineless’ and ‘Clemson Spineless 80’ produced the largest pods of all the cultivars in the study (Table 2). During the early part of the season, we were learning about the characteristics of fruit development of the cultivars and were harvesting the ‘Star of David’ pods too early for optimum yield for this cultivar.

Pods harvested at 4, 5, 6 and 7 days after anthesis were uniform in size within each day but varied among cultivars (Tables 3 and 4). ‘Clemson Spineless’, Clemson Spineless 80’, ‘Burgundy’, ‘Perkins Dwarf’, and ‘Dwarf Long Green Pod’ had the largest pods in the study while ‘Star of David’, ‘Silver Queen’, and ‘Annie Oakley II’ had the smallest pods. This may be useful in selecting cultivars which produce pods which mature quickly and are ready to harvest soon after flowering.

The optimum condition would be to identify cultivars which do not differ significantly from those that produce the largest pods and also have significantly less shear strength. The only cultivars that meet this criteria are ‘Burgundy’ and ‘Perkins Dwarf’ on days 5 and 7 after anthesis (Tables 3 and 4).

Table 3. Pod length, weight, and shear strength at four and five days after anthesis.

 

Pod measurements, DOAz + 4

Pod measurements, DOA + 5

Cultivar

Pod len
(cm)

Pod wt
(g)

Shear
(lbs)

Pod len
(cm)

Pod wt
(g)

Shear
(lbs)

Cajun Delight

7.2bcdy

6.3d

164bc

11.2bc

14.0bc

265b

Burgundy

9.1a

9.0ab

191ab

14.8a

19.9a

261b

Star of David

3.8g

6.7cd

121d

5.0f

10.9c

198c

Silver Queen

5.5f

6.1d

117d

8.0e

12.3c

211c

Clemson Spineless

7.0cd

10.1a

212a

10.6cd

19.6a

317a

Clemson Spineless 80

6.6de

9.1a

191ab

10.2cd

19.8a

332a

Dwarf Long Green Pod

7.8b

8.5abc

198ab

11.9b

19.3a

321a

Annie Oakley II

6.3e

5.6d

150cd

9.7d

12.3c

259b

Green Best

7.2bcd

7.2bcd

184abc

10.5cd

13.9bc

276b

North and South

7.3bc

7.2bcd

167bc

11.2bc

14.5bc

271b

Perkins Dwarf

7.8b

9.0ab

187abc

10.9bcd

17.2ab

265b

zDay of anthesis
yMeans in columns followed by the same letter are not significantly different, Duncan’s multiple range test (P# 0.05).

Table 4. Pod length, weight, and shear strength at six and seven days after anthesis.

 

Pod measurements, DOAz + 6

Pod measurements, DOA + 7

Cultivar

Pod len
(cm)

Pod wt
(g)

Shear
(lbs)

Pod len
(cm)

Pod wt
(g)

Shear
(lbs)

Cajun Delight

14.4bcdy

23.0bcd

345bc

18.0cde

37.2b

468ab

Burgundy

19.7a

36.4a

375ab

22.7a

43.1ab

360c

Star of David

5.5f

13.4e

243d

7.6h

25.3c

430b

Silver Queen

10.4e

18.2de

285cd

12.4g

25.0c

324c

Clemson Spineless

13.5cd

30.3ab

405ab

16.8ef

47.6a

477ab

Clemson Spineless 80

13.3cd

30.4ab

436a

17.0ef

49.8a

514a

Dwarf Long Green Pod

15.9b

30.4ab

397ab

19.3bc

42.7ab

465ab

Annie Oakley II

12.7d

19.0cde

338bc

15.8f

29.3c

419b

Green Best

14.6bc

26.1bc

369b

17.4de

39.6b

514a

North and South

14.5bc

23.9bcd

353b

18.4bcd

38.5b

434b

Perkins Dwarf

15.3b

27.4b

340bc

19.3b

44.3ab

435b

zDay of anthesis
yMeans in columns followed by the same letter are not significantly different, Duncan’s multiple range test (P# 0.05).

Correlations of okra pod length and weight with shear force are presented in Tables 5 through 8. Most data are significant to highly significant, indicating an increase in shear force with increased pod length and weight. A few occasions were found where correlations were not significant, but these were not consistent from day to day for the same cultivar.

Table 5. Correlations of okra pod characteristics four days after anthesis.

 

Cultivar

 

N

Correlations (Pod size = day of anthesis + 4)

 

 

Pod length/
Pod weight

Pod length/
Shear force

Pod weight/
Shear force

Cajun Delight

12

0.96***

0.84***

0.93***

Burgundy

12

0.58*

0.56*

0.79***

Star of David

12

0.93***

0.97***

0.98***

Silver Queen

12

0.61*

0.72**

0.91***

Clemson Spineless

12

0.89***

0.85***

0.97***

Clemson Spineless 80

12

0.87***

0.88***

0.99***

Dwarf Long Green Pod

12

0.87***

0.79***

0.97***

Annie Oakley II

14

0.81***

0.89***

0.89***

Green Best

12

0.93***

0.93***

0.99***

North and South

12

0.97***

0.93***

0.96***

Perkins Dwarf

12

0.66**

0.49NS

0.76**

Total (all cultivars)

134

0.57***

0.70***

0.89***

NS, *, **,***Nonsignificant or significant at P# 0.05, 0.01, or 0.001, respectively.

Table 6. Correlations of okra pod characteristics five days after anthesis.

 

Cultivar

 

N

Correlations (Pod size = day of anthesis + 5)

 

 

Pod length/
Pod weight

Pod length/
Shear force

Pod weight/
Shear force

Cajun Delight

13

0.92***

0.81***

0.88***

Burgundy

13

0.95***

0.76**

0.85***

Star of David

12

0.95***

0.94***

0.99***

Silver Queen

12

0.85***

0.84***

0.89***

Clemson Spineless

12

0.55*

0.24NS

0.28NS

Clemson Spineless 80

12

0.94***

0.94***

0.96***

Dwarf Long Green Pod

12

0.33NS

0.13NS

0.89***

Annie Oakley II

12

0.83***

0.84***

0.82***

Green Best

12

0.88***

0.83***

0.94***

North and South

12

0.90***

0.07NS

0.13NS

Perkins Dwarf

13

0.68**

0.28NS

0.85***

Total (all cultivars)

135

0.66***

0.51***

0.82***

NS, *, **,***Nonsignificant or significant at P# 0.05, 0.01, or 0.001, respectively.

Table 7. Correlations of okra pod characteristics six days after anthesis.

 

Cultivar

 

N

Correlations (Pod size = day of anthesis + 6)

 

 

Pod length/
Pod weight

Pod length/
Shear force

Pod weight/
Shear force

Cajun Delight

12

0.93***

0.84***

0.90***

Burgundy

13

0.98***

0.85***

0.90***

Star of David

12

0.91***

0.89***

0.97***

Silver Queen

13

0.92***

0.84***

0.96***

Clemson Spineless

12

0.90***

0.67**

0.88***

Clemson Spineless 80

13

0.85***

0.79***

0.94***

Dwarf Long Green Pod

12

0.94***

0.92***

0.96***

Annie Oakley II

12

0.96***

0.84***

0.90***

Green Best

13

0.98***

0.93***

0.95***

North and South

12

0.93***

0.84***

0.92***

Perkins Dwarf

13

0.86***

0.57*

0.89***

Total (all cultivars)

137

0.82***

0.62***

0.86***

NS, *, **,***Nonsignificant or significant at P# 0.05, 0.01, or 0.001, respectively.

Table 8. Correlations of okra pod characteristics seven days after anthesis.

 

Cultivar

 

N

Correlations (Pod size = day of anthesis + 7)

 

 

Pod length/
Pod weight

Pod length/
Shear force

Pod weight/
Shear force

Cajun Delight

14

0.93***

0.82***

0.85***

Burgundy

13

0.79***

0.32NS

0.69**

Star of David

13

0.81***

0.83***

0.97***

Silver Queen

12

0.89***

0.86***

0.99***

Clemson Spineless

12

0.86***

0.46NS

0.72**

Clemson Spineless 80

12

0.88***

0.67**

0.65*

Dwarf Long Green Pod

13

0.60*

0.42NS

0.93***

Annie Oakley II

14

0.89***

0.86***

0.78***

Green Best

14

0.92***

0.81***

0.82***

North and South

13

0.68**

0.50NS

0.84***

Perkins Dwarf

12

0.81***

0.62*

0.92***

Total (all cultivars)

142

0.67***

0.22***

0.69***

Grand Total (all cultivars & all pod sizes)

548

0.88***

0.79***

0.92***

NS, *, **,***Nonsignificant or significant at P# 0.05, 0.01, or 0.001, respectively.

Literature Cited

Sams, David. 1984. Okra Production. The University of Tennessee. P&SS Information Sheet #77.
U. S. Department of Agriculture. 1976. United States standards for grades of okra for processing. U. S. Dept. Agr., Agr. Mktg. Serv., Wash., D. C.

Copyright © 1999 by The University of Tennessee. All rights reserved.

This research represents one season's data and does not constitute recommendations.  After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.

 

 

 

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