2 8 2 5 2 8 2 5 ::: 11111 . _ 11111 . :~ 11111 . 11111 . -.-1.0 1.0 -- I~ l~t3~ .2 I~ ~1113.2 2.2 I:': I~ ~ I~ ~ I~ L:.i. I.:,; ~ i~ I!J I~ I 2.0 ...'"' ~ ..."" ~ 1.1 L.II..:.~ 1.1 LlL:.Li. - 111111.25 111111.4 111111.6 111111.25 111111.4 111111.6 MICROCOPY RESOLUTION TEST CHART MICROCOPY RESOLUTION TEST CHART NATlON~l BUREAU 0; STANDARDS·1963.A NATIONAL BUREAU OF STANDARDS-1963-A US3 -/ :it 141 Of TIlE BIOLOGY 'OF ;t POOR SEED PRODUCTION IN TEPHROSIA VOGELII '" REFERE/\ 'rl'" DO I'(,-c:. ~ . NOT LOAN >. ,Y ... ~ Teclmical Bulletin No. 1419 >t .....D d a ~ r-­ c.;I 0 en :.= E-4 .D '. .... co .. rn ~= 0 ~ ~ ~ ~ ! ',~ Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE ,, " Contents Pap .• Summary . .,.- ",. - ... _-- .. - ~------------------------------ 1 Introduction _._--------------------------------------- 1 Floral biology . ~---~--------~----------------- 2 Morphology and life cycle of the flower _ __ _ __ __ _ _ __ __ 2 Pollen development, abo.rtion, and germination .. _ _ __ _ _ 4 Self-pollination 7 Role of insects in pollination ... _ .. ___________ . 10 Abscission, pod drop, and pod shape 13 Effects of hormone treatments 15 Pod and seed yields 17 Factors affecting seed yield ... -- ... ___ r_ ...... _,. ___ _ _ 17 Effects of weather changes 18 Correlation of climatic variables with pollen production and self-pollination . __ __ __ ______ . 24 Effects of modified environments 25 Varietal and species comparisons 29 ~ j 1 Discussion ! - ~-.- ... ~, ... _"'------ .. 31 ~. Evolutionary status of Teph1'osiu vogelii 31 Causes of poor seed production 32 Recommendations for seed production and further study.. 33 Literature cited 34 Washington, D.C. Issued April 1970 For sale by thc Supct"intendcnt of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 20 cents ".. .. 1 THE BIOLOGY OF POOR SEED PRODUCTION IN TEPHROSIA VOGELII By FRANKLIN W. MARTIN, plant geneticist, and EUGENIO CABANILLAS, agri~ultural 1'esearch technician, Crops Reseu1'ch Division, Agriculturc:~ Resea1'ch 3e1'vice SUMMARY Tephrosia vogelt:'i Haak. f. is a patential saurce af the insecti­ cide ratenone. This plant flawers well, but sets pods and seeds paarly in Puerto. Rica. Variaus factars cause paar fert!Jity, princi­ pally pallen abartian and failure of anthers to dehisce. Abartion is assaciated with weather canditions and may result if moderate temperatures and high humidities do nat accur during the week .­ preceding anthesis. Althaugh self-pallinatian is aften accomplished without exter­ nal agents, large bees increase the amaunt af self-pollination by changing the relatianship af pallen and stigma. In additian, bees may passibly damage the stigmatic surface and thus make it mare receptive to pallen germinatian. The stigma is seldom expased and rarely crass-pallinated. Insect activity may limit seed praduc­ • tian. The fertilized avary may abscise before maturity, princi­ pally during the early part af the flawering season, but also dur­ ing hat, very dry weather later in the season. Harmone treat­ ments benefit pad and seed set when abscissian is a prablem. Minar causes af paar seed set include floral abnarmalities, in­ sect damage, and paar flawer develapment near the <,md of the f1awering seasan. A caal, maist enviranment, high nutritional levels, and insect­ cO"ltrol measures may maximize seed productian. Varietal differ­ ences in fertility suggest that seed praductian can also be in­ creased thraugh breeding. INTRODUCTION Plants af the genus Tephl'osicL frequently cantain ratenaid com­ paunds useful far killing insects and undesirable fish (9).:1 Hawever, few species contain enough rotenone to justify their use as insecticide crop plants (5). Because of its high rotenone content, large size, rapid growth, and adaptation to some re­ gions of the United States, Teph?'osia vogelii Hook. f. has been se­ lected for study and for development as a new crop species. Stud­ ies of this species in Puerto Rico showed that mature plants flow­ ered as day lengths decreased during the fall (6). However, in most parts of the United States plants do not mature sufficiently or are killed by frost before flowering. Therefore, although T. vo­ l Italic numbers in parentheses refer to Literature Cited, p. 34. 1 It 2 TECHNICAL BULLETIN 1419, U.S. DEPT. OF AGRICULTURE gei:i;i can be grown as an insecticide pla."!lt in tho continental United states, it requires a tropical location for sefid production, as well as for breeding and improvement (1). ~., During the Tephrosw, breeding program at the Federal Experi­ ment Station in Puerto Rico, investigators observed that plants bloomed freely but set seed poorly. Various aspects of this seed­ setting problem had been investigated, but the results were incon­ , clusive and were not published. In 1965 .more extensive studies on the reproductive processes of T. vogeli-i were undertaken to deter­ I ~ mine the principal causes of poor seed set. The results of these ! investigations are summarized here. FLORAL BIOLOGY Morphology and Life Cycle of the :Flower The typical flower of the family Papilionaceae (Fabaceae) is hermaphroditic and strongly zygomol'phIc. One petal, the stand­ ard, is often enlarged and vertical. The two lateral petals are usually extended as wing3. The two lower petals are united into a structure called the keel, which envelops the stamens and the pis­ til. The stamens are partially or entirely united in a tube sur­ rounding the ovary (4). Flowers are adapted to either of two kinds of breeding systems. In self-pollinated species (soybeans, lespedeza, some field beans) the pollen is usually shed directly onto the stigma before or as soon as the flower opens. In cross-pollinated species (clover, al­ falfa) various agents, chiefly insects, promote exchange of pollen. Self-fertilization of such species is often impeded by full or par­ tial seif-incompatibility. Three typical means of pollen dispersal include exposure of anthers and stIgma, pumping- of pollen from a cavity in the keel to the outside with the pistonlike action of the stamens, and explosive release of pollen coupled with exsertion of the staminal column. All these mechanisms depend on the depres­ sion of the keel by visiting insects (8). The flower of Teph7'osia vogel'ii is typical of the Papilionaceae (fig. 1). It is large, with a standard 2.5 cm. high and 3 cm. wide, keel and 'wings ~ cm. long, and wings extending 1.8 to 2.4 cm. to the sides. The flowers are borne in compact racemes of 50 to 200 flowers, which bloom over a 3- to 6-week period. Each flowering .L node bearing two flowers is subtended by a fugacious bract that leaves a scar. The flowers are either purple with white markings or entirely white. Anthesis of the normal flower may begin at any hour but is more frequent during the mornhg. It begins as a splitting of the suture of the standard below the keel. About the time that the standard unfolds, the anthers dehisce. Usually dehiscence is com­ plete by the time the standard has fully expanded. However, one or more anthers may fail to dehisce. They do not dehisce later. The pollen grains are somewhat glutinous and are aggregated to­ gether. After a short time these aggregations break up and indi­ vidual grains fall. .. ;(-.: -.".... "', .. ~ " •.Jr...... :" .," ",.,.. ... ,.. ........ '. "..,..' .~ ... '" '" .' "'tI o ~ i ~o Z~ ..... Z ;J "'tI ::x:: o~ ~ >­ ~ ~..... B:-:-35490, BN-35493, BN-45491, BN-35492 FIGURE I.-Flower of Tephrosia vogelii: A, Side view of newly opened flower; B, variations in keel structure' (anthers caught in upper suture of one flower); C, anther position and stamen length in old, intermediate, and young flowers; V, normal style (left) and three abnormal styles. x 1.25. <:0 4 TECHNICAL BULLETIN 1419, U.S. DEPT. OF AGRICULTURE Certain abnormalities of the flower occur at low frequency (1-5 percent). These include failure of the banner to open, inclu­ sion of a wing in the keel, and adhesion of the upper edges of the ~.' wings. Other more s17btle, more frequent, and probably more im­ portant abnormalities also occur. The stigma is sometimes so tightly enfolded by the :.:eel that self-pollination is impossible. The style is sometimes bent at an angle of 45° to 90° so that the stigma is not among the anthers. The .:lffect of these abnormali­ ties is to reduce the chances of self-pollination and in some in­ stances to make cross-pollination virtually impossible. During 1966 these abnormalities tended to vary in intensity as the flower­ ing season progressed (table 1). However, the percentage of ab­ nOlmal flowers was never high enough to account for all the poor pod set. As the flower ages, the upper suture of the keel may split. Less frequently the short leg of the L-shaped keel ruptures. The floYver begins to fade. The two wings become appressed to the keel. As wilting occurs, abscission also takes place. The life of an unpolli­ natedflowel' is 48 to 56 hours during the rainy season. However, in dry weather flowers wilt and abscise in 30 hours (table 1). If the pod is set, the flower usually does not abscise. The elongating ovary ruptures the wilted keel the third or fourth day after polli­ nation. One week after anthesis the pod is 2.5 to 5 cm. long, and in 3 weeks it is mature and 7 to 13 cm. long. Fertilized and unfer­ tilized ovules can be distinguished by size at about 7 days after anthfJsis. The pods mature, dry, and eventually dehisce. Pollen Development, Abortion, and Germination The chromosome number of T. vogelii is 22, the most common number in its genus (8). The genus is characterized by regular chromosomal behavior. In five typical, partially sterile lines stud­ ied, the chromosome number was 22.