Genomic Classification in Guizotia (Asteraceae)
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_??_1995 The Japan Mendel Society Cytologia 60: 67-73, 1995 Genomic Classification in Guizotia (Asteraceae) H. N. Murthy, S. C. Hiremath and A. N. Pyati Department of Botany, Karnatak University, Dharwad-580 003, India Accepted March 10, 1995 Guizotia Cass. is a small genus, comprising of six species, of the family Asteraceae. Guizotia abyssinica (L. f.) Cass. is an important oil-seed crop cultivated in India and east Africa. Baagoe (1974) revised the taxonomy of the genus and based upon morphological similarities, she noted that G. abyssinica (L. f.) Cass., G. scabra (Vis.) Chiov. and G. schimperi Sch. Bip. are closely related species. Further, she merged G. schimperi under the subspecific rank of G. scabra. Prior to our earlier work (Hiremath and Murthy 1992, Hiremath et al. 1992), cytological study was undertaken to ascertain the taxonomic position of these three species. Materials and methods Guizotia abyssinica, G. scabra and G. schimperi, were used for the present karyomorphologi cal study. For karyotype study, root apices excised from the potted plants were pretreated with 2mM 8-hydroxyquinoline for two hours (14-15•Ž) and fixed in 1:3 acetic alcohol. They were stained with Lillie's Schiff's reagent. Levan et al's (1964) system was followed to classify the chromosomes. For karyotype description and comparision of chromosomes they were catego rized into: A: SAT chromosome with median centromere A•Œ: SAT chromosome with submedian centromere A••: SAT chromosome with subterminal centromere B: Chromosome with median centromere C: Chromosome with submedian centromere D: Chromosome with subterminal centromere Results The species investigated alongwith their collection number (s), source, life form and chromosome count (s) (present and previous) are given in Table 1. Table 2 shows the karyomorphological data of the three species. 1. Guizotia abyssinica (L. f.) Cass. Thirteen collections were studied and all of them showed 2n=30 chromosomes, confirm ing the earlier reports of Gelin (1934), Richharia and Kalamkar (1938), Shetty (1967), Harriman (1978) and Patel et al. (1983). The somatic chromosomes of Coll. No. 89 are shown in Fig. 1. The karyotype formula is 2n=30=2A+28B. The karyotype consists of single pair of satellited median chromosomes and fourteen pairs of chromosomes having median centromere. The satellite measured about 0.4ƒÊm. The chromosome length ranged from 1.8 to 3.4ƒÊm with an absolute length of 36.4ƒÊm. The karyotype formulas in Coll. No. 59 and Coll. No. 63 are similar to that of Coll. No. 89 (Table 1). The somatic chromosomes of Coll. No. 51 (Fig. 2) are of three types. The karyotype 68 H. N. Murthy, S. C. Hiremath and A. N. Pyati Cytologia 60 Table 1. Source, collection number, life form and chromosome counts present and previous in Guizotia species formula is 2n=30=2A+26B+2C. They are one pair of satellited median chromosomes and a single pair of chromosomes having submedian centromere and thirteen pairs of median chromosomes. Satellite measured about 0.2ƒÊm. The chromosome length varied from 1.5 to 2.6ƒÊ m with an absolute length of 33.9ƒÊm. The karyotype formulas of Coll. No. 61, 67, 71 (Fig. 3), 74 (Fig. 4), 98 (Fig. 5), 121 (Fig. 6), 122 (Fig. 7) and 123 are basically similar to that of Coll. No. 51. The somatic chromosomes of Coll. No. 69 also contained three types of chromosomes and satellites were present on submedian chromosomes (Fig. 8). 2. G. scabra (Vis.) Chiov Chromosome number 2n=30 was determined in six collections of G. scabra thus confirm ing the earlier chromosome count of Renard et al. (1983). Somatic chromosomes of Coll. No. 128 are shown in Fig. 9. Karyotype formula is 2n=30=2A'+26C+2D. It has three types of chromosomes with one pair of satellite on short arm, thirteen pairs of submedian chromosomes, and one pair of chromosomes having subterminal centromere. The satellite measured 0.4ƒÊm. Chromosome length ranged from 1.5 to 2.3ƒÊm and with absolute length of 29.2ƒÊm. The karyotype formulas of Coll. No. 107 and 131 were similar to Coll. No. 128. Although the karyotype formulas of Coll. No. 105, 127, 134 were similar to that of Coll. No. 128, the number of chromosomes having submedian and subterminal centromere was different (Figs. 10-12). 3. G. schimperi Sch. Bip. Five collections were studied and all of them showed 2n=30 chromosomes. Somatic chromosomes of Coll. No. 135 (Fig. 13) had two types with karyotype formula of 2n=30= 1995 Genomic Classification in Guizotia 69 Table 2. Karyomorphological data in Guizotia species 2A+28B. The complement had 15 pairs of chromosomes with median centromere, out of which one pair was satellited. The satellite measured 0.2ƒÊm. Chromosome length varied from 1.7 to 3.2ƒÊm with absolute length of 35.4ƒÊm. Karyotype formulas of Coll. No. 137, 136 and 158 (Figs. 14, 15, 16 respectively) were similar to that of Coll. No. 135. Somatic chromosomes of Coll. No. 129 had three types of chromosomes, different from other collections by having submedian chromosomes. Discussions Karyomorpholigical studies reveal that chromosomes in Guizotia species are medium in size. The size difference between longest and shortest chromosomes in the complement is small. They form a gradual series. All the collections of G. abyssinica showed symmetrical karyotype with predominantly median chromosomes. But karyotype heteromorphism was observed in several collections. Karyotype of G. scabra is asymmetrical with submedian and subterminal chromosomes. Remarkably, median chromosomes are absent. The polymorphism of karyotype in different collections is due to the variation in the number of submedian and subterminal type of chromosomes, satellite size and total chromosome length. In G. schimperi five collections contained medium chromosomes. Satellite size and range of chromosome length were almost similar in all collections. Thus, karyomorphologically it can be said that this taxon is homogenous and symmetrical and showes little polymorphism. These observations make it amply clear that there exists interspecific karyotype variation in different collections of the same species and chromosomal repatterning is wide spread in the genus Guizotia. Such karyotypic 70 H. N. Murthy, S. C. Hiremath and A. N. Pyati Cytologia 60 Figs. 1-8. Somatic metaphase chromosomes of Guizotia abyssinica. [Fig. 1. Coll. No. 89; Fig. 2. Coll. No. 51; Fig. 3. Coll. No. 71; Fig. 4. Coll. No. 74; Fig. 5. Coll. No. 98; Fig. 6. Coll. No. 121; Fig. 7. Coll. No. 122 and Fig. 8. Coll. No. 69]. (•~1000). 1995 Genomic Classification in Guizoti a 71 Figs. 9-12. Somatic metaphase chromosomes of Guizotia scabra [Fig. 9. Coll. No. 128; Fig. 10. Coll. No. 134; Fig. 11. Coll. No. 105; Fig. 12. Coll. No. 127]. (•~1000). Figs. 13-16. Somatic metaphase chromosomes of Guizotia schimperi [Fig. 13. Coll. No. 135; Fig. 14. Coll. No. 137; Fig. 15. Coll. No. 136; Fig. 16. Coll. No. 158]. (•~1000). 72 H. N. Murthy, S. C. Hiremath and A. N. Pyati Cytologia 60 heteromorphism is also evident in plant species due to chromosomal reorganizations brought about by unequal translocations and pericentric inversions (Stebbins 1971). Although G. schimperi was described as an independent species, Baggoe (1974) clubbed into subspecies of G. scabra. Morphologically these two species and G. abyssinica are similar and closely related. Nevertheless they can be distinguished from each other by several diagnostic characters. Guizotia scabra can be easily distinguished from G. schimperi by its perennial habit, outer involucral leaves exceeding disk center, ray florets 8-16 and disk florets more than 50. Cytologically G. scabra is advanced in having asymmetrical karyotype, i.e., chromosome complement of this taxon predominantly subterminal and submedian type of chromosomes. In contrast, G. schimperi is annual weed in the cultivation of G. absyssinica and possesses symmetrical karyotype having only median and/or submedian chromosomes. Thus it is tempting to think that G. scabra with asymmetrical karyotype might have originated from G. schimperi with symmetrical karyotype. However, such a derivation seems unlikely because G. schimperi is an annual weed. It is well-established that annuals are mostly derived from pernnial taxa (Stebbins 1950). The other way round is also not possible, i.e., derivation of G. schimperi with symmetrical karyotype from G. scabra having asymmetrical karyotype. Further more, there is no evidence of Robertsonian type of translocaiton to convert asymmetrical karyotype into symmetrical one. The most likely situation is that both G. schimperi and G. scabra might have descended from a common ancestor. Thus, from morphological and genomic point of view merger of these two taxa into single species as done by Baagoe (1974) is not sound. Guizotia schimperi is a weed in the cultivation of G. abyssinica. Both these taxa are morphologically alike and their karyotype are similar. Genome analyses work of Murthy et al. (1993) reveals that genomes of these two taxa are homologous and G. schimperi might be progenitor of domesticated G. abyssinica. Thus G. schimperi cannot considered as subspecies of G. scabra as proposed by Baagoe (1974). Guizotia schimperi is genetically conspecific with the cultivated G. abyssinica. Harlan and de Wet (1971) discussed the problem of taxonomic classification of cultivated plants and related wild species. Following their guidelines, we are tempted to propose that G. abyssinica and its progenitor G. schimperi be merged into a single species G. abyssinica (L. f.) Cass. with subspecific ranks. They may respectively be treated as G. abyssinica (L. f.) Cass. ssp. abyssinica and ssp. schimperi. All cultivated races, varieties, etc. of G. abyssinica may be included in ssp. abyssinica whereas the progenitor taxon and its spontane ous races may be included in ssp. schimperi. In recent years taxonomic treatment of cultivated species and their progenitor taxa, forming primary and secondary gene pool are treated in this manner (Hilu et al.