CHROMOSOME NUMBERS ANDINCIDENCE OF POLYPLOIDYIN PANICOIDEAE (POACEAE)FROM PAKISTAN'S. M. Nadeem Ahsan,2 Ahsan A. Vahidy,3and S. I. Ali2ABSTRACT Chromosome numbers in 126 accessions representing 58 taxa belonging to 27 genera of Panicoideae from Pakistanare reported. Chromosome numbers of three species viz. Panicum atrosanguineum (n = 18), Pennisetum lanatum(n = 18), and Elionurus royleanus (n = 10) are new determinations. New cytotypes are reported for Isachnehimalaica (tetraploid) and Setaria intermedia (tetraploid). Chromosomal counts for 30 other species are new to theflora of Pakistan. More than two-thirds of the species investigated were found to be polyploid in nature. Members of Poaceae have been of great interestfrom both evolutionary and cytotaxonomic pointsof view. The role of polyploidy in the evolution anddiversification of grasses has been exceptionallylarge. Nearly ail genera and a majority of speciesin this family possess chromosome numbers whichare multiple of the original basic number. Accord-ing to Stebbins (1950, 1956), polyploidy has playedan important role in the production of a wide rangeof chromosome numbers in grasses. Further, heestimated nearly 70-75% of grass species to bepolyploid. Sharma (1985) estimated 63.41% poly-ploidy in the Himalayan grasses. Baquar (1976)observed only 30.40% polyploidy among membersof the family Poaceae from Pakistan. In the presentstudy the level of polyploidy is discussed in thelight of available information about the chromo-some counts of Panicoideae from Pakistan.MATERIALS AND METHODS For meiotic preparations young, unopened in-florescences were fixed in 1:3 acetic alcohol andstored at -4"C, and the anthers were squashed in1.8% aceto-orcein. For mitotic preparations youngand healthy root tips from germinating seeds werepretreated with 0.002 M 8-hydroxyquinoline for4-6 hr., fixed in acetic alcohol (1:3) for 1 hr.,hydrolysed in 1 N HQ for 6-12 min. at 600C, andsquashed in 1.8% aceto-orcein. The slides wereanalyzed and photographs were taken before mak-ng them permanent in euparal or Canada balsam.OBSERVATIONS AND RESULTS Table 1 lists chromosome numbers for 126 re-cords representing 58 taxa of 27 genera. Countsnew to science and new to the flora of Pakistanare specified on the basis of survey of IPCN (Fe-dorov, 1974; Goldblatt, 1981, 1984, 1985, 1988;Moore, 1973, 1974; Ornduff, 1967). Ploidy levelwas inferred from the lowest known diploid numberin the genus. Out of a total of 58 taxa investigated, 39(67.24%) were found to be polyploid. The majorityof the polyploids were at the tetraploid level. Onlyeight hexaploids, five octoploids and one decaploidtaxa were observed. In Table 1 the genera are arranged in tribesfollowing Cope (1982), and the species are ar-ranged alphabetically within genera. Voucher spec-imens, identified with the help of Flora of Pakistan(Cope, 1982), are deposited in Karachi UniversityHerbarium (KUH).DISCUSSION The investigated species belong to three tribesof Panicoideae. In Pakistan the tribe Isachneae isrepresented by a single species, Isachne himalaica(Fig. 19). Previously the pentaploid of this specieswith 2n = 50 was reported by Mehra (1982) andParkash (1979). The report presented here is thefirst of a tetraploid (n = 20) cytotype in this species. The tribe Paniceae is one of the largest tribes SWe thank M. Qaiser and ZA.A. Razaq of Departent of Botany, University of Karachi, for their help indentification of vouchers. We also thank A. Ghafoor, S. Orner, T. Ai, Z. A. Razaq, Moinuddin, and B. Jahan of theDepartment of Botany, University of Karachi, for collecting cytological material. This paper is part of the workUpported by National Science Foundation grant INT 8510318. 2 Department of Botany, University of Karachi, Karachi-75270, Pakitan. SDepartment of Genetcs, University of Karachi, Karachi-75270, Pakistan. ANN. MISSOURI BOT. GARD. 81: 775-783. 1994.