Chapter 9: Crop Plants and Exotic Plants


Chapter 9: Crop Plants and Exotic Plants


TEPHROSIA
Tephrosia vogelii Hook. f., family Leguminosae

Tephrosia is a potential source of rotenone, an important nonresidual insecticide, and also a material useful in killing undesirable fish (Blommaert 1950). It is maintained as a semicultivated plant in dooryards in some primitive areas where it is used for poisoning fish. Seeds are saved and planted, and the plants are tended, yet the plant also occurs in the wild state. It has not been grown commercially, although recent tests (Barnes et al. 1967, Gaskins et al. 1972) indicate that production might be economically feasible if the culture and handling of the crop could be similar to that of some hay crops. Other species of Tephrosia native to the United States have also been tested and show some promise as sources of rotenone (Sievers et al. 1938).

Plant:

Tephrosia is a short-lived, slow-growing, herbaceous, frost- susceptible perennial. Barnes et al. (1 967) suggested that for commercial production of rotenone, which is derived largely from the leaves, the plants should be grown at the rate of 30,000 to 37,000 per hectare. Barnes and Freyre (1969) reported that when plants were spaced 1.0 to 8.9 m apart, the seed yield per plant ranged from 1.1 to 8.9g, with the highest-yielding line producing at the rate of only 70 kg seed/ha.

Many individual plants produce good seed yields, whereas others are poor, indicating that considerable improvement through breeding for seed production is possible. Based on variations among accessions in seed set and others agronomic traits, Martin and Cabanillas (1970) suggested that cross-breeding procedures might result in improved seed production.

Gaskins et al. (1972) stated that seed production is impeded by the flowering requirements of the species, by a naturally occuring system of sterility, and by frequent shortages of pollinating insects.

Inflorescence:

The flower is typically papilionaceous (fig, 183), about an inch across, and purple with white markings or white. The flowers are borne on compact raccemes that bloom over a 3- to 6- week period. There may be 20 to 30 flowers per raceme with up to 200 flowers per plant (Gaskins et al. 1972). Pods usually contain 8 to 16 seeds. The flowers have a faint but definite pleasant aroma and bees visit them freely for both nectar and pollen. Flowering occurs on decreasing day-lengths. If the plant is grown in the United States, it is likely to be killed by frost before flowers appear, therefore the plant requires a tropical home for seed production. The flower may last about 2 days during cool or rainy weather but only 30 hours during dry weather (Martin and Cabanillas 1970)

[gfx] FIGURE 183. - Flowering stems of a tephrosia plant.

Pollination Requirements:

The plant is considered to be self-pollinated. The stigma appears to be receptive to pollination at anthesis. Often it is in contact with dehisced anthers, particularly if the stamens are long. Furthermore, data indicate that self-pollination generally occurs, because recessive white flowered selections grown next to dominant purple flowered ones never produce purple-flowered offspring. Also, flowers bagged before anthesis frequently produce some pods with seed; however, when viewed from an agronomic standpoint the seed set ispoor, and large differences in seed production occur in different locations. Martin and Cabanillas (1970) showed that pollination is a factor by comparing plants in the open, plants caged with bees, and plants caged without bees. The results showed that from 10.8 to 22.8 percent of the pods set in open plots, 17.4 percent set in the cage with bees, but only 0.8 to 3.7 percent of the pods set in cages without bees. There were also fewer seeds per pod in the cage without bees.

Knowing that visiting bees, largely honey bees or carpenter bees, caused scratches on the stigmas, possibly making them more receptive to pollination, some stigmas were intentionally damaged with a needle before pollination. Others were pollinated as gently as possible. The results were significant: a 50 percent increase in pod set and more than 100 percent increase in seed set were obtained from flowers with damaged stigmas.

Pollinators:

Martin and Cabanillas (1970) concluded that "bees appear to have a role in pollinating tephrosia." Honey bees were the most frequent visitors. Some were nectar-seeking bees that visited only "younger" flowers and usually did not touch the stigma. Pollen-seeking bees, on the other hand reportedly visited chiefly older flowers. They forced open the upper suture or short leg of the keel to remove pollen, but the effect of the bee behavior on the flower was not visibly discernable but did not "appear to lead to pollination." How the authors arrived at this conclusion is not clear. They concluded that carpenter bees (Xylocopa brazilianorum L.) were the principal pollinators. Gaskins et al. (1972) concluded that insects facilitate self-pollination but contribute little to cross-pollination. They considered the honey bee too small to trip the flowers, yet they reported that most flowers had scratches on the stigma but were not tripped. A high percentage of these untripped flowers were found to be self-pollinated. Thus, they concluded, bees facilitate self-pollination by changing the relative position of keel, stigma, and pollen, without tripping, preparing the stigma for pollinatin by breaking up the stigmatic surface.

Pollination Recommendations and Practices:

Martin and Cabanillas (1970) recommended that plantings be made close to weedy areas and in abandoned fields where dead trees or legume plantings occur. (They also recommended that research be conducted on methods of increasing natural populations of carpenter bees.) Their discussion of the pollination of this crop is so reminiscent of the early history of alfalfa pollination that one is led to wonder if flooding the field of tephrosia with honey bees might not have the same beneficial effect it has had on alfalfa seed production.

LITERATURE CITED:

BARNES. D. K., and FREYRE, R. H.
1969. SEED PRODUCTION POTENTIAL OF TEPHROSIA VOGELII IN PUERTO RICO. Puerto Rico Univ. Jour. Agr. 53(3): 207-212.

FREYRE, R. H., HIGGINS, J. J., and others.
1967. ROTENOID CONTENT AND GROWTH CHARACTERISTICS OF TEPHROSIA VOGELII AS AFFECTED BY LATITUDE AND WITHIN ROW SPACING. Crop Sci. 7: 93-95.

BLOMMAERT, K. L. J.
1950. THE PLANT TEPHROSIA VOGELII HOOKER, AS A FRESH WATER FISH POISON. Roy. Soc. So. Africa Trans. 32: 247-263.

GASKINS, M. H., WHITE, G. A., MARTIN, F. W., and others.
1972. TEPHROSIA VOGELII: A SOURCE OF ROTENOIDS FOR INSECTICIDAL AND PISCICIDAL USE. U.S. Dept. Agr. Tech. BuI. 1445, 38 pp.

MARTIN, F. W., and CABANILLAS, E.
1970. THE BIOLOGY OF POOR SEED PRODUCTION IN TEPHROSIA VOGELII. U.S. Dept. Agr. Tech. BuI. 1419, 34 pp.

SIEVERS, A. F., RUSSELL, G. A., LOWMAN, M. S., and others.
1938. STUDIES ON THE POSSIBILITIES OF DEVIL'S SHOESTRING (TEPHROSIA VIRGINIANA) AND OTHER NATIVE SPECIES OF TEPHROSIA AS COMMERCIAL SOURCE OF INSECTICIDE. U.S. Dept. Agr. Tech. BuI. 595, 40 pp.


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