Current Science 46(14): 499-501 (July 20, 1977)
ON THE OCCURRENCE OF ALTERNATIVE GERMINATION IN THE GENUS PHASEOLUS L (PAPILIONACEAE)
Bir Bahadur, N. Pratap Reddy, P. Vijaya Kumar and M. Madhusudana Rao

THE importance of seedling characters have lately been realized and it is only relatively recently that information on seedling characters began to be used for identification purposes1-4,5 and even for genetic studies4.

The latter author surveyed 58 genera and 200 species for the germination charactger and has shown the occurrence of both types of germination in Papillionaceae and Caesalpinae. In the former, hypogeal germination being more common than epigeal, and the reverse in the latter, while Mimosae shows epigeal type of germination only.

In this communication, the authors report the occurrence of alternative germination in the genus Phaseolus whose epigeal germination is well known.

In Table I data pertaining to different species of Phaseolus investigated with regard to the type of germination are listed. Out of the 9 species investigated P. angularis and P. multiflorus show hypogeal germination and Phaseolus vulgaris (Fig. 1-3) as also the six other species show epigeal germination. It may be further noted that even the large number of seedlings tested under the different varieties of P. mungo, P. vulgaris and P. aureus included in the present study show only epigeal type of germination though transitional forms are known to occur". To find out whether the epigeal and hypogeal type of germination has any functional significance to the species, we looked for the presence of stomata on the flat, smooth, inner and outer convex surfaces of the cotyledons. The outer surface of the cotyledons of the epigeal seedlings was found to be stomatiferous while the stomata were totally absent in hypogeal cotyledons. The inner smooth surface in both the epi- and hypogeal seedlings was devoid of stomata and the epidermis was made of rectangular cells in the former and elongated to polygonal cells in the latter. The mature stomata are anomocytic with 5-6 surrounding cells and measure 14.5 X 10.5µ with an ellipitic stomatal pore. The guard cells are typically kidney shaped with their inner walls thicker than the outer and with several chloroplasts in them and hence functional. Yet another interesting observation is that the epigeal cotyledons are rough and wrinkled with linear striations externally while the hypogeal cotyledons re smooth. We are unable to offer any explanation for this behaviour but it is probable that it may be functionally related to the stomatiferous epigeal cotyledons.

TABLE 1 List of Phaseolus species showing type of germination

S1.
No.
Species/Variety Type of
germination
Number of
seedlings tested
Source of material
1. Phaseolus angularis
C 87897
Hypogeal 113 N.B.P.I., Reg. Stn., Simla
2. Phaseolus multiflorus
PLB 190-2
do. 99 do.
3. Phaseolus lunatus
EC 18199
Epigeael 102 do.
4. Phaseolus vulgaris
PLB 141
do. 83 do.
  Phaseolus vulgaris
PLB K 1
do. 78 do.
  Phaseolus vulgaris
(Local)
do. 109 Agric. Market, Warangal
  Phaseolus vulgaris
Premier
do. 59 Commercial, Hyderabad
5. Phaseolus aureus
(Local)
do. 2142 Agric. Res. Stn., Warangal
  Phaseolus aureus
PLM 629
do. 35 D.P.I., IARI, New Delhi
  Phaseolus aureus
Pusa Baisakhi 100
do. 102 Commercial, Hyderabad
  Phaseolus aureus
Von G 65
do. 63 Agric. Res. Inst., Hyderabad
  Phaseolus aureus
PR-16
do. 131 Commercial, Hyderabad
6. Phaseolus mungo
PLM-221
do. 28 D.P.I., IARI, New Delhi
  Phaseolus mungo
(Local)
do. 2980 Agric. Market, Warangal
  Phaseolus mungo
U-30
do. 45 A.R.I., Hyderabad
  Phaseolus mungo
US-132
do. 64 do
  Phaseolus mungo
Krishna-11
do. 102 do.
7. Phaseolus atroperpolius
EC 276115
do. 16 D.P.I., IARI, New Delhi
8. Phaseolus aconitifolius
(Local)
do. 22 Kakatiya University Campus,
9. Phaseolus trilobus
(Local)
do. 23 do.

Kalyansundaram4 regards hypogeal germination in the Leguminosae as ancestral and the epigeal as derived from it. But according to Eames3 hypogeal germination is 'clearly advanced' and epigeal germination primitive. The occurrence of alternative type of germination just described, to our knowledge, is not on record for the genus Phaseolus. In view of the controversial opinions expressed the present observations are significant and may serve as taxonomic pointer in delimiting species. The occurrence of alternative germination in the genus Phaseolus thus raises phyletic problems and until further work is carried out it would be premature to regard a given Phaseolus species as primitive or advanced merely on the germination criteria alone.

FIGS. 1-3. Fig 1. Phaseolus vulgaris showing epigeal seedlings. Figs. 2-3. P. angularis and P. multiflorus showing hypogeal seedlings.
N.B. Longitudinal striations on cotyledons of epigeal cotyledon can be seen while the hypogeal cotyledons are smooth.

We are grateful to the Directors of the various Agricultural Research Stations, for kindly providing the seed material of various species investigated and to Prof. U. B. S. Swami, for giving us facilities and encouragement.

Kakatiya University, Warangal 506 009 (A.P.), January 25, 1977. BIR BAHADUR.
N. PRATAP REDDY.
P. VIJAYA KUMAR.
M. MADHUSUDANA RAO.
  1. Burger, Hzn, D., Seedlings of Some Tropical Trees and Shrubs Mainly of S.E. Asia, Translated from Dutch, by G. Burgan and S. Festing, Centre for Agric. Pub]. and Documentation, Wageningen, 1972.
  2. Crow, L. K., "Seedling characters," In Teaching Genetics, Eds., C. D. Darlington and A. D. Bradshaw, Oliver and Boyd, London, 1966.
  3. Eames, A. J., Morphology of the Angiosperms, McGraw-Hill, N.Y., 1961.
  4. Kalyansundaram, S., "On the hypogeal and epigeal germination of seeds in the family Leguminosae," Proc. 45th Indian Sci. Congr., Part III, 1958. p. 308. (Abstract).
  5. Koller, D., "Germination," Sci. Amer., 1959, 200(4), 75.

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