SHAPES OF PINNULES OF LEUCAENA TAXA AND FI SPECIES HYBRIDS

Size: px

Start display at page:

Download "SHAPES OF PINNULES OF LEUCAENA TAXA AND FI SPECIES HYBRIDS"

Shanon Moody
5 years ago
Views:

Sorensson, C. T. Dept, of Agronomy and Soil Science, 1910 East-West Road, Honolulu, HI 96822. SHAPES OF PINNULES OF LEUCAENA TAXA AND FI SPECIES HYBRIDS Introduction.

1 Sorensson, C. T. Dept, of Agronomy and Soil Science, 1910 East-West Road, Honolulu, HI SHAPES OF PINNULES OF LEUCAENA TAXA AND FI SPECIES HYBRIDS Introduction. Leaf blade shapes are basic criteria in most plant taxonomic studies. This is principally because leaf shape is a highly visible plant trait which is relatively constant from one generation to the next. In leucaenas, whose leaves are bipinnately compound, pinnule shape is used. In most cases there is no question that more than one gene, working additively, controls leaf shape of plants. However, certain genes do affect leaf shape in nonadditive ways, be it via dominance, homozygous recessiveness, and/or epistasis. To those who believe taxonomy should mirror phylogeny, this is worrisome because a taxonomy/phylogeny based solely on pinnule shape will reach incorrect conclusions whenever non-additive gene action is involved. Phylogenetic analyses should utilize traits which are governed by many genes with additive effects, or even genes which can have "no" effects, e.g., DNA introns. The most recent effort to revise Leucaena systematics may have fallen prey to this problem. Zarate (1984) used the ratio of pinnule lengthiwidth to split the genus into two "natural" sections, leucaena and macrophylla. Unfortunately ploidy level, alloploidy, ecological adaptation, and other important considerations were left out of the study. This resulted, in my opinion, in at least one error - L. greggii and L. retusa were placed in separate sections. It is easy to support the claim that these species are closely related, as their geographic ranges overlap and both have the unusual qualities of frost resistance, yellow flowers, darkly striated bark, and difficulty nodulating with rhizobia strains developed for L. leucocephala. The point here is not to emphasize possible errors in the revision, but to recognize that the chances of producing a realistic phylogenetic classification using any single trait are low due to the many possible types of gene action, population drift, and varying rates of trait divergence/convergence. (Note: the author assumed that Zarate s division of the genus into sections had implied phylogenetic significance, if this is not so then my criticism is unfounded). The present study primarily illustrates pinnule shapes of Leucaena taxa and FI species hybrids by magnification of representative pinnules to a common scale. Trends in data, and hypotheses about the types of gene action involved, are also considered. Materials and Methods. Taxa illustrated herein were chosen to represent as comprehensively as possible the range in variation of shape known to exist in taxa and FI species hybrids. Pinnules were magnified to equivalent lengths using an enlarging photocopy machine, traced, and then reduced to meet page size restrictions. Pinnules of L. cuspidata were photocopied directly from a color photocopy of the type specimen by the US National Herbarium. The specimen was collected in May, 1911 by Purpus in Minas de San Rafael, San Luis Potosi, Mexico. Pinnules of L. lanceolata ssp. sousae were photocopied from an herbarium specimen made in February 1987 by C.E. Hughes of OFI at a site 40 km west of Puerto Escondido on the coastal plain of Oaxaca. The mutant form of L. macrophylla, labelled in Figure 1 as K158mu, was a mutant discovered among open-pollinated seedlings of K158, and was ruled out as a species hybrid using leaf analysis (Sorensson 1987). The L. leucocephala ssp. leucocephala was a naturalized strain common in Waimanalo. Pinnules of all other taxa and hybrids were sampled over a two-week period in August, 1990 at the Waimanalo Experiment Station. The species hybrids were produced by the author and

2 colleagues by hand pollinations. In addition to leaf analysis (Sorensson 1987) all but one of the 34 hybrids (Figure 2) were verified by analysis of pollen. L. pulverulenta x L. greggii had not flowered yet, but was verified using petiolar gland number and shape (Sorensson 1987). Results and Discussion. Leucaena Taxa. Pinnules of Leucaena taxa shown in Figure 1 range in shape from ellipses (e.g., L. retusa K502) to "teardrops" (e.g., L. macrophylla K836). The shapes seem to fit into a continuum rather than into easily separable categories. Most taxa have nearly bisymmetrical pinnules, and have their major vein inserted off-center at the pinnule s base b 14b 14a 12 K745 K--- K445 K465 K769 K502 Figure 1. Representative pinnule shapes (variable magnification) and actual pinnule lengths (bars) of recognized and tentative Leucaena taxa. la) L. collinsii ssp. collinsii 8a) L. macrophylla ssp. macrophylla lb) L. collinsii ssp. "zacapana" 8b) L. macrophylla ssp. nelsonii 2) L. cuspidata 9) L. multicapitula 3a) L. diversifolia ssp. trichandra 10a) L. pallida 3b) L. diversifolia ssp. diversifolia 10b) L. pallida ( = L. "paniculata") 4a) L. esculenta ssp. esculenta 11) L. pulverulenta 4b) L. esculenta ssp. matudae 12) L. retusa 5) L. greggii 13) L. salvadorensis 6a) L. lanccolala ssp. lanccolata 14a) L. shannonii ssp. "magnifica" 6b) L. lanceolata ssp. "sousae" 14b) L. shannonii ssp. shannonii 7a) L. leucocephala ssp. glabrata 15) L. sp. ( = L. "confertiflora") 7b) L. leucocephala ssp. leucocephala 16) L. trichodes

3 diploid triploid te tra p lo id

4 Figure 2. (opposite page) FI species hybrid crossing diagram of leucaena pinnules shapes, broken into five artificial parental categories. Taxa illustrated include the following: Top row across: I = L. lanceolata K393, II = L. greggii K859, III = L. salvadorensis K746, IV = L. pulverulenta K75, V=L. esculenta K138. Left row down: I = L. macrophylla K158, II = L. retusa K502, III(2x) = L. shannonii K445, III(4x) = L. leucoccphala K8, IV(2x) = L. diversifolia K399, IV(4x) = L. diversifolia K156, V = L. pallida K748. Row I across: 1x1 = L. macrophylla K158 x L. lanceolata K393, IxIII = L. lanceolata K393 x L. shannonii K445, M V = L. lanceolata K410 x L. diversifolia K409. Row II across: IM = L. retusa K280 x L. lanceolata K10, IM I = L. retusa K502 x L. greggii K859, IMII(left) = L. retusa K502 x L. shannonii K445, IMII(right) = L. retusa K502 x L. salvadorensis K746, IMV(left) = L. retusa K280 x L. diversifolia (2n=4x=108), IMV(right) = L. retusa K280 x L. pulverulenta K881, IIxV=L. retusa K280 x L. esculenta K138. Row III(2x) across: IIM = L. shannonii K445 x L. lanceolata K10, IIMI = L. shannonii K445 x L. retusa K502, IIIxIII = L. shannonii K445 x L. salvadorensis K746, IIIxIV(left) = L. shannonii K445 x L. collinsii K740, IIMV(right) = L. shannonii K445 x L. diversifolia (K408xK409), IIIxV = L. shannonii K445 x L. esculenta K138. Row III(4x) across: IIIxI = L. leucocephala K8xL. trichodes K738, IIMI = L. leucocephala K636 x L. retusa K280, L. leucocephala K636 x L. sp. K745, L. leucocephala K8 x L. pulverulenta K75, L. leucocephala K8 x L. esculenta K138. Row IV(2x) across: IVxI = L. collinsii K180 x L. lanceolata K410, IVxII = L. pulverulenta K881 x L. greggii K867, IVxIII = L. diversifolia K409 x L. shannonii K405, IVxIV(left) = L. pulverulenta K75 x L. collinsii K450, IVxIV(right) = L. diversifolia K423 x L. collinsii K180, IVxV = L. diversifolia K821 x L. esculenta K810. Row IV(4x) across: IVxI = L. diversifolia K156 x L. lanceolata K10, IVxIII = L. diversifolia K156 x L. shannonii K445, IVxIV = L. pulverulenta K19 x L. diversifolia K156, IVxV = L. diversifolia K156 x L. esculenta K138. Row V across: VxI = L. pallida K748 x L. lanceolata K393 (2n=4x=104ca.), VxIII=L. esculenta K138 x L. shannonii K445, VxIV=L. pallida K748 x L. diversifolia K165.

An apparent relationship exists between pinnule length and vein placement. Probably this is related to the greater importance of structural strength in large pinnules to withstand winds.

5 An apparent relationship exists between pinnule length and vein placement. Probably this is related to the greater importance of structural strength in large pinnules to withstand winds. Three taxa with short pinnules stand out as having centrally located pinnule veins, L. cuspidata, L. greggii and L. retusa. This relationship may be more than coincidental, indications suggest they are the only frost-resistant species in the genus. Pinnules of some taxa are noticeably curved, either at the tip, or throughout the pinnule. Both diploid and polyploid L. diversifolia have pinnules with off-centered tips. L. collinsii (both subspecies) and L. pulverulenta also have curved pinnules, but their tips are more bisymmetrical. Pinnule shapes within taxa are fairly constant. The greatest range in shape within a taxa is in the diversifolia complex, as previously noted (Pan 1985). L. lanceolata also has highly variable pinnule shapes. An interesting comparison is that between L. macrophylla K158 and its mutant. The mutant has wider pinnules, similar to those like other L. macrophylla, suggesting the K158 is an offtype population. This is not unexpected as it is geographically isolated in Veracruz from other L. macrophylla. Range of pinnule size within Leucaena taxa is also relatively constant. L. shannonii K465 is an exception, as it has very diminutive pinnules. Its pinnule shape is similar, however, to other L. shannonii, like K769, which have larger pinnules. Species Hybrids. The crossing diagram (Figure 2) illustrates pinnules of FI species hybrids. For this purpose, five artificial categories were constructed to represent the range of parental pinnule shapes. Category I included taxa with teardrop-shaped pinnules (L. lanceolata, L. macrophylla, L. multicapitula, and L. trichodes). Category II included taxa whose pinnule veins were bisymmetrically placed (L. greggii and L. retusa). Category V included species with thin, straight pinnules (L. esculenta and L. pallida). Categories III and IV included the remaining taxa. Category IV included taxa with thin and curved pinnules, whereas category III included taxa with broader pinnules. Few relationships arc apparent from Figure 2 except that additive gene interaction is the primary force controlling shape of hybrid pinnules. Trends in length:width ratios of pinnules are apparent, but these were already modelled (Sorensson 1987). This study was inadequate to delineate dosage effects on pinnule shape, other than their effects on length:width ratios as previously noted (Sorensson 1987). Conclusions. Additive gene interaction was probably the major type of gene interaction controlling pinnule shapes of Leucaena taxa and hybrids in all but two instances. These were narrow (e.g., K158) and dwarf (e.g., K465) pinnules traits. The narrow pinnule gene(s) could be responsible for the visually significant, but possibly evolutionarily insignificant, differences between shapes of several potentially related taxa, like common and giant L. leucocephala, L. retusa and L. greggii, and L. salvadorensis and L. shannonii. Traits which may deserve further study include pinnule vein location and pinnule curvature. Acknowledgement. This research was supported financially by Mclntyre-Stennis Forestry Funds. References: Pan, F.J Systematics and genetics of the Leucaena diversifolia (Schlecht.) Bentham complex. Ph.D thesis, University of Hawaii. 244 p. Sorensson, C.T Interspecific hybridization in Leucaena Bentham. M.Sc. thesis, University of Hawaii. 274 p. Zarate Pedroche, S Taxonomic revision of the genus Leucaena Bentham from Mexico. Bull. Int. Group for the Study of Mimosoideae (IGSM). No. 12: University Paul Sabatier, Toulouse, France.

Edited by Dolores R. Piperno, Smithsonian Institution, Washington, DC, and approved July 13, 2007 (received for review March 18, 2007)

Edited by Dolores R. Piperno, Smithsonian Institution, Washington, DC, and approved July 13, 2007 (received for review March 18, 2007) Serendipitous backyard hybridization and the origin of crops Colin E. Hughes*, Rajanikanth Govindarajulu, Ashley Robertson*, Denis L. Filer*, Stephen A. Harris*, and C. Donovan Bailey *Department of Plant