Variation within and between land races of winged bean (Psophocarpus tetragonolobus (L.) DC.)

Field Crops Research, 3 (1980/1981) 359--364

359

Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

VARIATION WITHIN AND BETWEEN LAND RACES OF WINGED BEAN (PSOPHOCARPUS TETRAGONOLOBUS (L.) DC.)

W. ERSKINE* and T.N. KHAN**

Agriculture Faculty, University of Papua New Guinea, P.O. Box 4820 University Post Office (Papua New Guinea) *Present address: International Center for Agricultural Research in Dry Areas, P.O. Box 5466, Aleppo (Syria) **Present address: Department of Agriculture, South Perth, 6151 (Western Australia) (Accepted 12 August 1980)

ABSTRACT Erskine, W. and Khan, T.N., 1981. Variation within and between land races of winged bean (Psophocarpus tetragonolobus (L.) DC.). Field Crops Res., 3: 359--364. The overall variability in 14 land races of the winged bean collected in the Highlands of Papu New Guinea for three quantitative characters was partitioned between and within races, and measurements were also made of the percentage of polymorphic loci within races. The average percentage of polymorphic loci (four loci were evaluated) was 80.4 over all the races. There were significant differences between the land races for all the quantitative characters. Strong local preferences and a low level of cross-pollination between adjacent land races are probably major factors in the distribution of land races. The implications of the study to the planning of further collection of winged bean for germplasm conservation are discussed.

INTRODUCTION

The winged bean (Psophocarpus tetragonolobus (L.) DC.) has generated considerable interest in the tropical world as a potential protein source (Anonymous, 1975). The plant produces edible tubers, green pods, y o u n g leaves, flowers and seeds, all of which are a rich source of protein. Efforts to explore the variability of this autogamous crop have shown that Papua New Guinea is a centre of diversity, and have also resulted in the establishment of a germplasm collection (Khan, 1976). The overall variation of land races collected mainly in the Highlands of Papua New Guinea has been reported (Khan, 1976). This study partitions the overall variation in the germplasm between and within land races and also measures the extent of allelic polymorphism within individual land races.

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360 MATERIALS AND METHODS

The 14 land races of winged bean were all collected in the Highlands of Papua New Guinea from either fields or markets at the locations given in Table I. The collected seed of the races was grown as spaced plants in the Crop Garden of the University of Papua New Guinea, Port Moresby (9 ° 25'S, 148°8'E) during 1975. Observations were made on individual plants for the qualitative characters stem colour, pod wing colour, pod shape and pod specking (as defined in Khan, 1976). There is a single gene difference between purple and green stemmed plants. In addition, there are single gene differences between flat and rectangular p o d d e d plants, between green p o d d e d plants and those with purple specked pods, and between plants with purple p o d wings and those with green p o d wings (Erskine and Khan, 1977). The presence of allelic polymorphism within a land race was scored when both alleles at a locus were found amongst the plants of one land race (e.g. both purple and green stems within a race). The progeny of 88 o f these spaced plants, henceforth called families, were planted in single rows on 2 January 1976 in the Crop Garden of the University of Papua New Guinea. The number of families from each land race is given in Table I. An augmented randomized complete block design (Federer, 1956) was used with seven replicate blocks and three homozygous check varieties. The plants were grown on ridges 3 m long and 1 m apart, and were thinned to 25 cm apart giving 12 plants/family. All plants were supported on TABLE I T h e origin a n d n u m b e r o f families in t h e l a n d r a c e s

Land race

L o c a t i o n and province

Geographic location

No. o f families

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Mt. Hagen, W.H.P.* Mt. Hagen, W.H.P. K i n d e n g , W.H.P. K i n d e n g , W.H.P. Banz, W.H.P. Banz, W.H.P. K a r m a n g , W.H.P. K o n d e p i n a , W.H.P. Matuasa, E . H . P . * * G o r o k a , E.H.P. G o r o k a , E.H.P. H o t e r a b e , E.H.P. Aiyura, E.H.P. Aiyura, E.H.P.

5° 5 1 ' S 5°51'S 5° 5 2 ' S 5 ° 52rS 5° 4 7 ' S 5° 4 7 ' S 5 ° 48~S 5° 4 8 ' S 6° 0 3 ' S 6° 0 3 ' S 6° 0 3 ' S 6° 1 6 ' S 6 ° 19'S 6° 19'S

7 5 8 9 9 12 4 6 10 4 3 4 4 3

144 ° 1 3 ' E 144°13'E 144 ° 2 4 ' E 144 ° 2 4 ' E 144 ° 3 7 ' E 144 ° 3 7 ' E 144° 4 2 ' E 144 ° 2 8 ' E 145 ° 2 0 ' E 145 ° 2 4 ' E 145 ° 2 4 ' E 145° 4 9 ' E 145 ° 5 5 ' E 145 ° 5 5 ' E

*W.H.P. = Western Highlands Province. * * E . H . P . = E a s t e r n Highlands Province.

361

2 m high w o o d and string trellises. A d e q u a t e fertilizer and pest cont rol measures were provided during growth. Three quantitative characters measured on each family row were the time (days) f r o m sowing t o the opening of the first flower, the mean pod length (cm) o f 10 r a n d o m pods, and the weight (g) o f 100 random seeds. After a preliminary analysis of variance, the overall variation for these characters was partitioned into the variation bet w e e n land races and the variation between families within land races. T h e residual variance was derived from the check varieties. T h e variation between the families within individual land races was examined to see if land races which were particularly variable for one character were also variable f or the o t h e r characters. Accordingly the variances b e t ween families in all the races were arranged in a two-way table and an analysis o f variances under t a ke n. RESULTS

Detection o f allelic p o l y m o r p h i s m within land races T he occurrence o f allelic p o l y m o r p h i s m at each locus is shown in Table II f o r the land races. T h e average percentage o f p o l y m o r p h i c loci was high at 80.4% over all the races. In six races all f o u r loci were p o l y m o r p h i c . Every land race was p o l y m o r p h i c f or p o d wing c ol o ur and all but one for stem colour. This suggests t hat the gene frequencies for b o t h alleles for these t w o characters are high and show little variation across land races. However, this suggestion must be regarded as tentative in view of the small sample sizes involved. TABLE II P r e s e n c e of allelic polymorphism (*) in t h e land races

Land

Stem colour

Pod specking

1

*

2

*

3

*

race

Pod wing colour

Pod shape

*

*

*

*

*

*

*

*

*

4

*

*

*

*

5

*

*

*

*

6

*

*

*

7

*

*

8

*

9

*

10

*

11 12

*

*

*

*

*

*

*

*

*

13 14

* *

*

*

*

* * *

362

Variation in quantitative characters The mean values of the land races for the three quantitative characters are shown in Table III. The time to flower ranged from 51 to 62 days, pod length from 10.3 to 21 cm and 100 seed weight from 23.1 to 32.3 g. There were highly significant differences between the land races for all three characters (Table IV). The land races (1--14} were collected along a broadly East--West transect along the Highlands Highway, and some were collected at distances less than 1 km apart (Table I). There was no evidence of clinal variation along the transect, and the pattern of variability was mosaic (Fig. 1). It was also evident t h a t those races collected close together were no more similar than those collected further apart. Within land races there were significant differences between families for time to flower and 100 seed weight, but not for pod T A B L E III M e a n v a l u e s o f t h e l a n d r a c e s f o r the t i m e ( d a y s ) t o f i r s t o p e n f l o w e r , a v e r a g e p o d l e n g t h ( c m ) a n d 1 0 0 s e e d w e i g h t (g) Land race

Flowering (days)

Pod length (cm)

Seed weight (g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

60.3 55.2 57.3 56.6 58.2 62.4 51.0 59.0 54.3 57.3 58.3 53.8 57.0 57.7

15.2 21.0 13.4 14.8 17.3 18.6 18.6 13.5 12.9 14.2 14.0 13.7 10.3 11.8

27.5 32.3 25.8 27.2 26.9 31.8 28.6 24.1 25.6 23.8 29.2 27.7 23.1 24.3

± 2.7 ± 0.8 ± 1.7 ± 1.1 _+ 1 . 9 ± 2.3 ± 0.4 ± 2.7 ± 1.0 ± 1.9 ± 0.7 ± 1.3 ± 1.4 ÷ 2.4

± 1.5 -+ 2 . 2 ± 1.5 ÷ 1.0 + 0.8 ± 0.7 ± 2.8 + 0.8 ± 0.6 ± 2.1 ÷ 0.9 + 1.4 + 0.4 + 1.4

± ± ± ± ± ± ± ± ± ± ± ± ± ±

2.9 2.4 0.6 1.4 1.4 1.3 0.6 0.8 0.7 1.8 0.7 2.1 2.2 1.3

TABLE IV Mean squares from the analysis of variance of the days to flower, pod length (cm) and 100 s e e d w e i g h t (g) Source

d.f.

Mean squares Flowering

Pod length

Seed weight

49.4*** 10.0 5.7

52.6*** 16.7" 5.4

B e t w e e n land races

13

56.1"*

Within land races Residual

74 12

26.4* 10.7

*P < 0.05;**P

< 0.01;***P

< 0.001.

363 2 2O 31.

07

¥

29

¥

07

120 gO

e

27

4~11 3~ 08

£

9° 4~

1

0

1~3

14

~

11

25

14~8

14

55

~3

23 60

Flowering(days)

51

55

60

Flowering(days)

23

25

27

29

31

100 Seed Weight(g)

Fig. 1. Means of the land races (1--14) for days to first open flower, mean pod length (cm) and 100 seed weight (g). Land races collected at distances < 1 km apart are connected by lines, whose lengths indicate the similarity between races (e.g. the shortest lines would be between similar races).

length (Table IV). Land race 1 was the most variable for the t w o characters time to flower and 100 seed weight. DISCUSSION

The results show that there were large differences between the land races in time to flower, p o d length and 100 seed weight. Some of the variation was between land races collected less than 1 km apart. This suggests firstly that there must be large differences in the selection pressures acting on adjacent land races, and secondly that the gene flow between adjacent land races must be low or even lacking. The different selection pressures were probably largely governed by the preferences o f local farmers. Winged beans grown for tuber production are sometimes grown in a separate garden from those grown for their pods (Strathem, 1980). However, the distinction into pod and tuber types of winged bean is not the only classification used by the highland farmer in Papua New Guinea. A survey around Mt. Hagen has shown as many as 48 named winged bean land races (Powell et al., 1975). This classification was based on earliness, pod, seed and tuber characteristics, as well as cooking features. In particular, the tier form o f classification used by the Melpa people has been discussed by Strathern (1980). Although evidence of variation within locally classified races has been found in this study, the importance of the local system of classification should not be underestimated as it emphasizes the profound local knowledge o f the crop. Furthermore, it is within the framework of the local classification system that the selection pressures caused by local farmers must operate on land races. The differences between adjacent land races could only be maintained by a low level o f gene flow between races. Certain management practices dis-

364 courage the gene flow between land races. For example, winged beans are planted throughout the year, although the peak time of planting is June-August (Khan et al., 1977). This leads to staggered planting dates and a lack of synchrony between the flowering of adjacent land races. In addition, in the Western Higlands Province plots of winged bean are scattered around the valley floors. This spatial separation also discourages the cross-pollination by insects of adjacent land races. Thus, it appears that strong local preferences and a low level of cross-pollination between adjacent land races are two major factors affecting the micro-geographic distribution of the winged bean in the Highlands of Papua New Guinea. Land race 1 was the most variable for quantitative characters and was collected at Mt. Hagen, Western Highlands Province. It was also amongst the more variable land races for qualitative characters, with all the loci examined showing allelic polymorphism. This correlation of variability suggests that land races exhibiting particular variability for easily observable qualitative characters also contain considerable variation for quantitative characters. The individuality of winged bean land races highlighted in this study has implications in the planning of further collection of germplasm for genetic conservation. Clearly, collection must be made of as many different land races as possible. Furthermore, it is probable that additional variability for quantitative characters will be captured b y sampling extensively within those races which exhibit particular variability for easily observable qualitative characters like stem, flower and p o d colour. ACKNOWLEDGEMENTS

The authors wish to thank the Research Committee of the University of Papua New Guinea for financial support, and Dr. V. Kesavan for fruitful discussion during the course of this work. Assistance from Mr. J. Bohn and other officers of the Department of Primary Industry in travel arrangements and in interpretations was invaluable. REFERENCES Anonymous, 1975. The Winged Bean. A High Protein Crop for Tropics. National Academy of Sciences, Washington D.C., 54 pp. Erskine, W. and Khan, T.N., 1977. Inheritance of pigmentation and pod shape in winged bean. Euphytica, 26: 829--831. Federer, W.T., 1956. Augmented (or hoonuiku) designs. Hawaii. Plant. Rec., 55: 191--208. Khan, T.N., 1976. Papua New Guinea: a centre of genetic diversity in winged bean (Psophocarpus tetragonolobus (L.)DC.). Euphytica, 25: 693--706. Khan, T.N., Bohn, J.C. and Stephenson, R.A., 1977. Winged Bean: cultivation in Papua New Guinea. World Crops Livestock, 29: 208--214. Powell, J.M., Kulunga, A., Moge, R., Pono, C., Zimike, F. and Golson, J., 1975. Agricultural Traditions of the Mount Hagen Area. Occasional Paper No. 12. Department of Geography, University of Papua New Guinea, Port Moresby, 98 pp. Strathern, A., 1980. Ethnobotany and plant geography of the winged bean. In: Proceedings of the Workshop/Seminar on the Development of the Winged Bean. Philippines Council of Agriculture and Resources Research, Los Banos. (In press.)