Exploration for, and utilization of, collections of tropical pasture legumes

Agro-Ecosystems, 2 (1975, published 1976) 319--327 © Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands

319

E X P L O R A T I O N FOR, AND U T I L I Z A T I O N OF, COLLECTIONS OF T R O P I C A L P A S T U R E LEGUMES III. T h e distribution o f various Stylosanthes species with respect t o climate and p h y to g eo g r aphi c regions

R.L. BURT and R. REID Division of Tropical Crops and Pastures, Davies Laboratory, CSIRO, Private Mail Bag, TownsviUe, Qld. 4810 (Australia) (Received November 24th, 1975)

ABSTRACT Burt, R.L. and Reid, R., 1976. Exploration for, and utilization of, collections of tropical pasture legumes. III. The distribution of various 8tylosanthes species with respect to climate and phytogeographic regions. Agro-Ecosystems, 2: 319--327. The world distribution of certain species of Stylosanthes is examined in relation to climate and phytogeographic regions. Then on the basis of previous evaluation studies in northern Australia the regions most likely to yield material suitable for the Australian dry tropics are designated. Examinations of floras and climatic data are then used to extend the studies to other g e n e r a . The implications of this work in the operation of "genetic resources centres" is discussed

It has been estimated t h a t the tropics contain some 50 leguminous genera which could furnish new forage species f or the tropics; this includes some 2000 species n o t presently cultivated in any way (Williams et al., 1976). Although the i n t r o d u c t i o n process per se is relatively easy the ensuing evaluation processes are b o t h time consuming and costly. The main problems associated with plant i n t r o d u c t i o n are essentially concerned with selectivity. It is desirable th at we i n t r o d u c e only t h a t material m ost likely t o be useful and t h a t this material be evaluated at locations m o st likely to show its potential. We recognise th at the selectivity o f introductions would be less if large "gene banks" were t o be f o u n d e d ; distribution problems would then, however, be even greater. Luckily we can narrow t he range of material for i m p o r t in several ways. Not all genera contain species likely t o be of value (Williams et al. 1976) and we can largely restrict our search to those which do. Some areas of the world are floristically richer than others and thus m o r e likely to reward exploration

320 (Hartley, 1963). Some climates are much more likely to yield adapted material for a given Australian situation than others (see, for instance, Hartley, 1963; Butt et al., 1976). In the following sections we are attempting to delineate areas of the world most likely to furnish adapted pasture legumes for the t y p e of climates found in the Australian dry tropics. We begin (Section1) by examining the distribution of various Stylosanthes species in relation to climate and phytogeo~ graphic region. On the basis of previous studies we designate those areas, and those species, most likely to be of interest. Subsequently we detail those areas of the world which contain similar climates to those stipulated. The "floristic richness" of these areas is then examined and those likely to be of interest delineated. We conclude by examining, where possible, the performance of Australian introductions from these areas, thereby checking the validity of the conclusions. DISTRIBUTION OF VARIOUS STYLOSANTHES SPECIES WITH RESPECT TO CLIMATE AND PHYTOGEOGRAPHIC REGION.

Methods Several Stylosanthes species are of known value as sown pasture species in the dry tropics (see, for instance, Butt et al., 1971, 1974). Others are highly valued in native pastures in their country of origin (see, for instance, Skerman, 1970). These species are listed in Table I. Literature surveys, personal communication and the unpublished results of plant collecting trips have been used to examine the distribution of these species. A major source of information has been Mohlenbrock (1957), other references being omitted for the sake of brevity. To illustrate the types of climate in x~hich these species occur we have preferred to use the system devised by Reid (1973). This system defines climates in terms of their ability to support the growth of pasture species and is thus relevant for the present purpose. The phytogeographic regions referred to in the text are those delineated by Good (1964). Although a given species may be present in a given area or a given climate, it may occur only in certain climatically distinct environmental niches; this could be misleading for our present purposes. We have therefore attempted to to give some indication of the frequency with which the various species are found in a given region. Where a given species is listed as being c o m m o n in at least one area of a given climate type, it has been so designated. This does not imply that it is equally abundant in all regions having this type of climate; S. harnata, for instance, is dominant in many climatic types throughout the Caribbean b u t is absent from similar areas in Brazil.

(3)

(0)

X (0) XXX(0)

XX(0)

(0)

X

XXX(0)

X (1) XX(2)

X (0)

(3)

XX (2)

XXX(1)

(24)

X (0) XXX(0) X (0)

XXX(12) XXX(0) XXX(1) XX (9) XX (2)

(0)

XXX(O) XXX(0)

(19)

XX (3) XXX(3) XX (0)

X (6) XXX(7)

X

X

(17)

(0)

(15)

XXX(2)

(11)

X (1) X (0) XXX(0) XXX(7) XXX(1) XXX(0) XXX(2) XX (0) ~ (92)

XX (7) X (1)

XXX(60) XXX(4) XXX(6) XXX(14)

(11)

XXX(2) XXX(1) XXX(0) XXX(6) XXX(0) XX (0) XX (2) XX (0) X (0)

X X

(22)

(0) (0)

XXX(5) XX (0) XXX(0) XXX(IO) X (7)

m

202

82 8 7 68 19 0 14 4 0

*After Reid (1973) **Numbers in brackets refer to numbers of Australian accessions as listed in Edye et al. (1975), from these types of climates. Of the total collection of 237 is has been possible to define climate of origin for only 154. t " X " signifies present, " X X " common, " X X X " frequent (see text).

Total**

Wet tropical highlands Equatorial, extended rainfall Tropical, extended rainfall Tropical, seasonalrainfall Tropical, semi arid Hot, sub-tropical desert Sub-tropical, seasonalrainfall Dry tropical highlands Frosty tropical highlands

Distribution of various Stylosanthes spp. in relation to climate

TABLE I

o~ t~

322

Results and preliminary discussion We can see (Table I) that the various species differ markedly in their range of climatic adaptation. Some, such as S. viscosa, can be found over a very wide range of climates; others, such as S. humiUs, are more restricted. We can see further that Australian collections have been biased towards certain species and certain types of climate. Most collections were from wetter areas and a high proportion were of S. guyanensis. Perennial species suitable for dry tropical areas, S. scabra, S. fruticosa, S. hamata and S. viscosa, received scant attention. In a previous publication (Burt et al., 1976) we showed that plants adapted to the dry tropics of Australia came from even drier and somewhat hotter climates. These climates correspond to the h o t sub-tropical deserts and tropical semi-arid climates referred to in Table I. Within the hot, sub-tropical deserts only three species of Stylosanthes are known to occur. Until recently none of this material had been introduced into Australia and, even now, we have no introductions of S. sympodialis and only one of S. viscosa from such areas. A greater range of species can be found in the semi-arid regions. Of these we again have very restricted ranges of imported materials. In these dry conditions S. capitata and S. scabra are only to be found in the Caatinga regions in the highlands of eastern Brazil. Reasonable collections of this material have n o w been obtained. S. hamata is restricted to the Caribbean region; dry areas are found on the coasts of the islands. Introduction from the islands has been very limited. Reasonable collections of S. fruticosa are available. The highest deficiencies in the range of introduced material would n o w appear to be in S. syrnpodialis and S. viscosa. S. sympodialis is found only in the drier regions of Ecuador and the Galapagos. S. viseosa is found throughout many phytogeographic regions. Although some collections have been made in the Caatinga regions of north east Brazil, material has n o t been forthcoming from other dry areas referred to subsequently. T H E L O C A T I O N O F H O T SUB-TROPICAL D E S E R T A N D T R O P I C A L SEMI-ARID REGIONS THROUGHOUT THE WORLD.

These types of climate correspond closely to the 3.2 and 1.5 climatic regions designated b y Papadakis (1966) (R. Reid, unpublished data). As the Papadakis climatic maps are readily available we shall n o w use this system. In addition to these two climatic units, we shall also refer to h o t semi-tropical (4.3) and monsoonal sub-tropical (4.2) regions. These areas are of widespread occurrence in sub-coastal Queensland. They are somewhat wetter than the semi-arid tropical regions and experience lower temperatures in the dry season.. The only Australian introductions from this type of climate have shown considerable potential in the Australian dry tropics. We shall limit our discussion to these climatic types only as they occur in the Americas and the Caribbean, the areas of major interest for pasture le-

Monsoonal subtropical

Sub-coastal S o n o r a

N o r t h East Brazil

Tropical semi-arid

N u m b e r o f species

8 11

13 0

0

0 0

1 1 (humilis)

1 (viscosa)

4 2 5

0 1 2

1 (sympodialis) 2 (scubra, viscosa) 2 (guyanensis,

(5)

1. Shreve a n d Wiggins (1964). 2. R . L Burt (unpublished data).

(5)

(3)

6

6

3

6

4

2

3

1

1

10

8

9

4

(14)t

22

19

12

11

9

5

9

5

2

24

19

18

8

Macroptilium ** Total

B. G r o f , personal c o m m u n i c a t i o n , 1 9 7 2 . A r n o l d o (1964). Svenaon (1946). Wiggins a n d Porter (1971). B u r k h a r d t ( 1 9 5 2 a). De Martius ( 1 8 6 2 ) R.L. Burt (unpublished data).

(1)

5 5 (scabra, hamata,

humilis, viscosa, capitata )

7

2 6

4

macrosoma )

2

0

4

1

1 (humuta) 1 (sympodialis)

O

0

4 (viscose, hamuta, humilis, scabra )

0

0

3

Desmodium

0

3. 4. 5. 6. 7. 8. 9.

Centrosema

1 (viscosa)

Stylosanthes

* After G o o d (1964). ** Previously Phaseolus. t N u m b e r s in brackets refer to n u m b e r o f species f o u n d in region on a recent collecting mission.

(9)

(b) Highlands o f Eastern Brazil ( 8 )

Total n u m b e r of species

Monsoonal sub-tropical

N o r t h e r n A r g e n t i n a H o t semi-tropical Central Argentina

(a) G r a n d Chaco (7)

H o t sub-tropical desert Semi h o t tropical desert

Tropical semi-arid

Tropical semi-arid

Tropical semi-arid

Southern Brazilian

Ecuador

Curacao

Coastal Colombia a n d Venezuela

Zacapa

Galapagos

(4)

H o t semi-tropical

Coastal S o n o r a

T o t a l n u m b e r o f species

H o t sub-tropical desert

Climatic type

Central a n d S o u t h e r n Baja California

Geographical location

(a) Flanks of the Andes (5) (6)

Andean

(c) N o r t h e r n Colombia a n d N o r t h e r n (3) Venezuela

(2)

(b) G u a t e m a l a - P a n a m a

(a) Mexican lowlands and coast (1)

Caribbean

Phytogeographic region*

Floristic richness of various regions (see t e x t )

T A B L E II

Co to ~o

324 gumes. We note, however, that these climates are widely distributed throughout Africa and the latter areas could benefit by the importation of pasture legumes from equivalent regions of the Americas. Unlike Australia (see for instance, Papadakis, 1966) the tropical regions of the Americas contain relatively small areas of these climatic types. Hot subtropical deserts are found only in Baja California, the Guajira peninsula area of northern Colombia and parts of the Galapagos. Tropical semi-arid regions are found on northern coastal Colombia and Venezuela, Ecuador, the Caatinga regions of north east Brazil and a small region in Zacapa, Guatemala and some small Caribbean islands. Hot semi-tropical situations are found in north west Mexico and the Chaco region of northern Argentina. The only monsoonal subtropical region abutts onto the former region in northern Argentina. FLORISTIC RICHNESS OF THE AREAS SPECIFIED Methods Of the 22 tropical pasture legume cultivars listed by Barnard (1972), 14 belong to only four genera. In Table II we have listed the number of species present in these genera within the different regions previously specified. Sources of reference are referred to on the table, no data being available to the authors for north west Mexico. Where a given area contains two or more climates of interest it has been so divided. In one instance it has been possible to compare the species reputed to be present in an area with those actually collected during a recent visit. Results and preliminary discussion. We are concerned with certain types of climates within three phytogeographic regions and we begin by briefly comparing their floristic composition. The Caribbean region lacks Centrosema in the areas in which we are interested. It is, however, rich in Desmodium and Phaseolus. With the exception of northern Colombia and Venezuela it is generally deficient in Stylosanthes species. By contrast the Southern Brazilian region is generally rich in Stylosanthes and Centrosema but relatively poor in Phaseolus and Desmodium. The Andean region is floristically poor but is the only region to contain 8. syrnpodialis. Compilation of floristic richness within a given type of climate within a given region can give misleading results; some species, for instance, may only be found in environmentally favoured niches within the broad climatic region. In north east Brazil it seems likely that the number of Desmodium and Phaseolus species was overestimated in this way. Visits to two of these regions have shown, however, that the unexpected deficiency of some genera m a y be compensated for by the unexpected presence of other species or genera. Thus Centrosema brasilianum and Desmanthus virgatus, hitherto regarded by the

325

authors as plants to be found in wetter regions, were collected in the dry north east region of Brazil and the Zacapa region of Guatemala, respectively. Of the areas listed, t w o in particular have received scant attention from Australian plant collectors; these are the Mexican coastal lowlands and the Chaco region of Argentina. The similarity between these areas has been commented u p o n by several authors. Johnston (1940) gives examples o f species and paired species whose present distribution indicates a former floristic connection between the t w o continents. He also describes several plant characteristics which he deems to be adaptive to xeromorphic conditions and which occur in both regions. We cannot, of course, be certain that the plant material contained in these areas is sure to be agronomically desirable; some circumstantial evidence would, however, suggest that this is so. Firstly, we note that both regions contain species k n o w n to be of value -- Stylosanthes scabra, S. viscosa, S. guyanensis, Centrosema virginianum and Macroptilium atropurpureum (previously Phaseolus atropurpureus) in the Chaco and S. viscosa, Desmodiurn intortum and t w o species forms of M. atropurpureum in north west Mexico. Secondly we find the presence of plant attributes deemed to be of value in pasture species. Some geocarpic seed production coupled with the rhizomatous or stoloniferous habit are found in Phaseolus geophilus (Burkhardt 1952b) and in Arachis spp. in north east Argentina and in Phaseolus supinus in the Sonoran region (Wiggins and Rollins, 1943). We note that similar habits are found in herbaceous legumes in some of the other areas noted; in north east Brazil we have Centrosema arenarium, Phaseolus longepedunculatus and Arachis spp. and in northern Venezuela in Phaseolus peduncularis. NURSERY STUDIES Over a period of several years we have examined many legume introductions at Lansdown, in the seasonally dry tropics. The evaluation procedure includes a progression from a spaced plant, clean cultivated situation, through a phase where weed competition is severe, to a period of deliberate under and overgrazing. We believe that this process effectively delimits adapted introductions. Introductions which show promise under these conditions have been listed elsewhere (Annual Reports, CSIRO, Division of Tropical Agronomy, 1969 to 1974). They are contained in 14 genera and were collected in Africa, India and South and Central America. Where it is possible to stipulate the site of collection we find that all originated in dry sub-tropical, tropical or semi-arid or h o t sub-tropical desert conditions. Where several introductions of the same species had been tested those from the climates stipulated were best adapted to Lansdown. It seems probable, therefore, that the areas most likely to yield a range of leguminous genera suitable for the Australian dry tropics are those previously delimited on the basis of floristic studies and results with Stylosanthes.

326 DISCUSSION

The present studies From the data presented we have suggested areas most likely to furnish pasture legumes for the Australian dry tropics. Where collecting missions to these areas have already been made they have furnished us with a wide range of species and species forms, some of which were n o t previously considered as being suitable for dry tropical situations; many had n o t previously been imported. Collecting missions to the other regions could be equally valuable.

Genetic resources of tropical pasture species It is undeniably true that there is a very real need for the establishment of "genetic resource centres" for tropical pasture species. It is equally true that the value of such centres will be limited, n o t by their capacity to retrieve data, but by their ability to store the most useful forms o f data in the first instance. We believe that descriptions of the t y p e provided for Stylosanthes (see, for instance Butt et al., 1971; Edye et al., 1975) are useful for the purposes of plant introduction and evaluation. They provide, moreover, a framework on which the more specialised disciplines can work (see data quoted by Butt and Williams, 1975) to give a better appreciation of the material involved. Background climatic studies, linked with the results of evaluation programmes, enable us to delimit the areas of potential use of newly imported material. Climatic studies of the t y p e undertaken by Reid et al., (1976) and Reid (1973), when completed, should enable us to undertake distribution on a more routine basis. These studies are currently being expanded and refined using more complete data obtained from collecting missions. It is already obvious that soils, and soil mineral status, must be taken into account. We believe that the results of such studies could provide the information necessary for the efficient operation of genetic resource centres. ACKNOWLEDGMENTS Much of the work described is based on long term studies. The authors wish to acknowledge the help afforded by the Lansdown technical staff during the course of this period and the continued financial support of the Australian Meat Research Committee. We should also like to thank our numerous overseas contacts who have provided both seed and information over this prolonged period. Finally, thanks are due to numerous colleagues and for the able technical assistance of Mr. B.C. Pengelly.

327

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