Cytologia 51: 527-547, 1986

Karyomorphology of Different Strains of Maydeae

J. S. P. Sarma1 and A. K. Sharma

Department of Botany, Centre of Advanced Study (Cell and Chromosome Research), University College of Science, University of Calcutta, 35, Ballygunge Circular Road, Calcutta-700 019, India

Accepted February 22, 1985

Maize (Zea mays L.) is the third most important cereal crop of the world (F.A. O. 1976) and a considerable acerage is under maize cultivation in India, mostly centered around the Indo-Gangetic plains (Wealth of India 1976, Wilkes 1981). Its asssociation with several pre-Columbian civilizations of America has been discussed (Brewbaker 1979). It is adaptible to a wide range of climates and soils and has a genetic plasticity that results in the production of innumerable varieties. Hybrid maize may be regarded as one of the most spectacular achievements in applied biology of this century. The modern maize is very productive, highly het erozygous and genetically complex, whose basic biology has been considerably altered through artificial hybridization and selection. Maize, along with some other American and oriental genera blelongs to Maydeae, one of the substribes of , a major tribe of Gramineae. Of the subtribe Maydeae, in addition to maize which is used for various pur poses, teosinte Euchlaena mexicana (Schrad.) Kuntze is cultivated for use as food and fodder (Wilkes 1967, 1972, 1977a). , more commonly known as Job's tears, is a minor cereal in North Eastern India, Burma, Indonesia, etc. and is used for food, fodder, thatching, personal adornment, preparation of beer and other purposes (Arora 1977, Jain and Banerjee 1974). Since maize is an obligate cultigen with no clearly discernible wild ancestor, the phylogeny of the Maydeae is still an unsolved issue. The tribe Andropogoneae was considered (Bews 1929, Hartley 1960) to be the most highly specialized of the grasses. Only a few disagree with the inclusion of the small group Maydeae within the tribe, which is only a natural extension through specialization of the Andro pogoneae (Celarier 1956). "Botanically , the Maydeae are characterized by the presence of unisexual spi kelets, the staminate and pistillate spikelets placed in separate portions of the same infloresence,the staminate above; sometimes the spikelets are placed in totally sepa rate inflorescences as in maize; the staminate spikelets are placed in pairs or in threes; they are two flowered, with the lower floret imperfect; the pistillate spikelets are placed usually single, also two flowered, the lower floret sterile. They are en closed in an osseous involucre. The Zea is anomalous; the pistillate spikelets are crowded in a much thickened axis" (Henrad 1941).

1 Present address: Department of Botany, C. S. R. Sarma College, Ongole-523 001, Andhra Pradesh, India. 528 J. S. P. Sarma and A. K. Sharma Cytologia 51

For a hundred years or more, it was customary while classifying the grasses, to place Zea, Euchlaena, , Coix, Sclerachne, Chionachne, Trilobachne and in the Maydeae (Weatherwax 1955). Several contradictory opinions were expressed (Doebley and Iltis 1980, Randolph 1976, Reeves and Mangelsdorf 1942) regarding the taxonomic composition of the subgroup, which have been discussed in the later part. Geographically, the Maydeae are divided into two distinct groups, the American and the Oriental Maydeae. The former group comprises maize, teosinte and Tri psacum and the latter, the rest of the genera. Maize attained a panglobal distribution and has a tremendous racial diversity (Brown and Goodman 1977, Goodman 1978). Teosinte is found along the western escarpment and central plateau of Mexico and Guatemala. Wilkes (1967, 1972, 1977a, b) highlighted the geographic and variation patterns of annual teosinte. The centre of variation for Tripsacumtoo, is the western escarpment of central Mexico (Wilkes 1977a); however, it is also distributed in South America (de Wet et al. 1981) and for the first time has been reported from India (Wilkes 1981). Coix is a minor cereal crop cultivated by the tribes of various ethnic groups, chiefly on the hill tracts of South East Asia (Arora 1977, Bor 1960, Jain and Banerjee 1974, Koul 1973, Uphof 1968). It also occurs wild or as an escape from cultivation throughout all tropical and warm regions of the world (Venkateswarlu and Chaganti 1973, Weatherwax 1926). The details of morphology and development of maize are too wellknown to be dealt with at length and the interested reader is referred to the publications of Bonnett (1954), Galinat (1977), Lyte (1978), Mangelsdorf (1958), Sass (1977) and Weatherwax (1955). Except for maize and maize alone, in the whole of the gigantic tribe of the Andropogoneae, polystichy of any sort is totally unknown and distichy is the universal rule (Doebley and Iltis 1980). To sum up the salient morphological features of different members of the May deae, "all genera of the group usually have unisexual flowers borne on the same plant; all except maize have forms with clustered spikes; all except Tripsacum tend to have their female spikes enclosed in at least one leaf sheath; all except maize and the male spikelets of all Maydeae usually have single female spickelets although the sessile female spikelet may be paired with a sterile pedicel in the Oriental Maydeae, all usually have a suppressed lower floret within the functional female spikelet and all except maize usually have an indurated organ that forms a fruit case" (Galinat 1977). Kuwada (1911, 1915, 1919, 1925) who made extensive chromosome counts in maize observed that the somatic chromosome number was not the same in different races. He found that sweet varieties often would have more than 20 chromosomes, whereas most field varieties, 20 chromosomes. Subsequent studies by Fisk (1925, 1927), Kiesselbach and Petersen (1925), Longley (1924, 1927), Randolph (1928a, b) and Reeves (1925) confirmed Kuwada's findings and established that the chromo somes present in excess of 20 were replicas of a supernumerary chromosome, which was designated by Randolph as B-chromosome, to distinguish the same from A-chromosomes, the members of the normal complement. McClintock (1933) first 1986 Karyomorphology of Different Strains of the Maydeae 529 demonstrated the importance of pachytene analysis in the identification of chromo somes of maize. No other stage of division, meiotic or mitotic , provides the detail ed picture as is available at pachytene in maize. There had been only a few studies dealing with different aspects of mitotic an alysis, such as banding (Sachan and Tanaka 1977, Vosa et al. 1972, Vosa and Mogford 1980, Ward 1980), somatic association (Horn 1970, 1971, Horn and Walden 1978, Miles 1968, 1970), karyotype vs. translocations (Filion and Walden 1973), endo sperm cytology (Lin 1977) etc. The relatively insignificant work done with the mitotic material is attributable to several technical problems, such as the difficulty of securing uniform one-celled thick squash in view of the very hard nature of the root tip and very heavy cytoplasmic content. Filion (1968) further has pointed out that the maize chromosome arms are not spread very widely and as such it is difficult to locate accurately the centromere and define the limits of arms. Colchicine, 8 hydroxyquinoline and a mixture of colchicine and a-bromonaphthalene were stip ulated to be used as pretreating agents (Brown 1966, 1967, Chen 1969, Hadlaczky and Kalman 1975). A mixture of pectinase and cellulase (Sachan and Tanaka 1976), glusulase (Lin 1977) and only pectinase (Chen 1968) were suggested as macerating chemicals. In view of the lacunae in our knowledge in understanding the mitotic chromo somes of maize and also in view of the immense potential of improved methods of chromosome analysis, it was deemed worthwhile to make an attempt to unravel the variation patterns of somatic chromosomes of maize. The present paper comprises a detailed investigation of somatic chromosomes of a representative cross section of the cytological diversity, existing in maize (mostly from Indian sources). A cultivar of teosinte and another of Coix lacrymajobi L. were included for comparison and examination of intergeneric relationships.

Meterial and methods

The present investigation comprises a detailed cytological analysis of twenty four cultivars of the Maydeae, which include twenty two cultivars of maize and two cultivars, one each of teosinte and Coix lacryma jobi L. Indian cultivars were re latively less worked out than their American counterparts. So, it was aimed at including mostly Indian cultivars in the present report.

The root tips were pretreated with a mixture of a-bromonaphthalene and col chicine, fixed in 1:3 acetic-ethanol, macerated in 5% pectinase solution, cleared in

45% acetic acid and stained in 1% aceto-orcein. For Feulgen staining the pre treated, fixed and macerated root tips were hydrolysed in IN HCl at 60•Ž for 15 min and then stained in Feulgen solution for a period of 2 hrs. Alternatively, the macer ration might also be carried out after staining, but at room temperature and for shorter duration.

The morphology of a chromosome may be appropriately described by two major features, its total length and the position of the centromere. The centromeric index

(C or F%) is given by the following equation, wherein the letters 'p' and 'q' represent the lengths of short and long arms of the chromosome respectively (Chicago Con 530 J. S. P. Sarma and A. K. Sharma Cytologia 51

Figs. 1-8: Idiograms of the different cultivars of maize. 1, Nal-Tel (Yucatan-7). 2, Comfite Morocho. 3, Tema Flint. 4, Sikkim Primitive. 5, Kalimpong Local 6, Sonada Local. 7, Warangal Local. 8, CM-104. 1986 Karyomorphology of Different Strains of the Maydeae 531

Figs. 9-16. Idiograms of the different cultivars of maize (contin.). 9, CM-105. 10, CM-114. 16, Globe Hybrid. 11, CM-115. 12, CM-201. 13, CM-206. 14, Ganga-5. 15, Ganga Safed-2. 532 J. S. P. Sarma and A. K. Sharma Cytologia 51 ference 1966). p/ C=F%= •~100 p+q Depending upon the centromeric index, the centromere may be described as median, submedian or subterminal. The total chromatin length of the haploid com plement and the total centromeric index (T. F%) were calculated by applying the following formulae. ƒ°(p+q) Total chromatin length of the haploid complement= / 2

(ƒ°p)•~100 Total centromeric index= /ƒ°(p+q)

Results

Based on the nature of primary and secondary constrictions, the chromosomes

of the cultivars studied were classified under three types. A-type: Chromosomes with two constrictions. Three subtypes were recog

nized in A-type.

Al-type: Median to nearly median primary constriction and submedian

to nearly submedian secondary constriction

A2-type: Median to nearly median primary constriction and subterminal to nearly subterminal secondary constriction

A3-type: Submedian to nearly submedian primary constriction and sub

terminal to nearly subterminal secondary constriction

B-type: Median to nearly median primary constriction

C-type: Submedian to nearly submedian primary constriction

Eventhough B and C-type chromosomes would actually form one type, they

were classified basing on the centromeric index. The details of the comparative karyomorphology of the different cultivars studi

ed have been presented in Table 1. The qualitative features of the idiograms (Figs.

1-24) are relatively uniform. The karyotype is graded. The karyotypes of teosinte

and Coix lacryma jobi L. do not differ more than those of cultivars of maize.

B-chromosomes were present in cultivars such as Nal-Tel (Yucatan-7), Warang

al Local, Stowell's Ever Green and Diara, which were confirmed by Feulgen staining also (Fig. 35). Their number ranges upto a maximum of five, although one or two

is the most frequently encountered number. The longest chromosome measures

7.92ƒÊ in length and the shortest chromosome, 1.32ƒÊ. The total chromatin length

of the haploid complements varies form 56.76ƒÊ in case of CM-105 to 22.82ƒÊ in

case of Synthetic-B23. Maximum TF value is 43.71 in Coix lacryma jobi and the

minimum TF value is 36.29 in the cultivar Diara; however, the variation in TF

values is relatively less compared to that of the total length of the haploid comple

ments. Chromosomes with secondary constriction are always two in number and

Figs. 17-24. Idiograms of the different cultivars of maize and other members of the Maydeae (contin.). 17, Golden Bantom. 18, Stowell's Ever Green. 19, Vijay. 20, Diara. 21, Synthetic B19. 22, Synthetic-B23. 23, Euchlaena mexicana. 24, Coix lacryma-ffjobi. 1986 Karyomorphology of Different Strains of the Maydeae 533 534 J. S. P. Sarma and A. K. Sharma Cytologia 51

Figs. 25-32. Somatic metaphase plates of different cultivars of maize. 25, Nal-Tel (Yucatan-7),

2n=20+3B. •~2000. 26, Tema Flint. •~3500. 27, Sikkim Primitive. •~5000. 28, Kalim

pong Local. •~2500. 29, Kalimpong Local, cell of a haploid root. •~2500. 30, CM-115, •~ 3500. 31, CM-201. •~4000. 32, CM-206. •~4000. 1986 Karyomorphology of Different Strains of the Maydea e 535

A2 is the most frequent type encountered , occurring in sixteen of the twenty four cultivars studied, followed by A3 and Al types in six and two cultivars respectively . More frequently, it is the 6th chromosome in order of length , as is the case within the pachytene complements . The chromosome length within an individual com plement ranges gradually from the longest to the shortest chromosome and no abrupt change in the chromosome length was observed . The features of the idio grams analysed are more or less uniform. The number of B-type pairs is either 4 , 5 or 6 and that of C-type pairs , 3, 4 or 5, except in case of Coix lacryma-jobi, where

Figs. 33-38. Somatic metaphase plates of different cultivars of maize and other members of

Maydeae. 33, Ganga-5. •~4165. 34, Ganga Safed-2. •~4165. 35, Stowell's Ever Green,

Feulgen stained, 2n=20+2B. •~2000. 36, Diara, 2n=20+IB. •~2500. 37, Diara, a plate showing heteromorphy of satellited chromosomes. •~2500. 38, Teosinte. •~3500. there are 7 pairs of B-type and 2 pairs of C-type. Some other variations were also observed, such as the presence of heteromorphic satellited chromosomes in Diara (Fig. 37) and the occurrence of haploid roots in Kalimpong Local (Fig. 29).

Discussion In the present study, seven races (Nos. 1-7), six inbreds (Nos. 8-13), three hy brids (Nos. 14-16), two varieties (Nos. 17 and 18), two composites (Nos. 19 and 20) and two synthetics (Nos. 21 and 22) of maize were included. One cultivar of teosinte (No. 23) and another of Coix lacrymajobi L. (No. 24) were also analysed to examine intergeneric relationships within the Maydeae. The results of the pre sent investigation may be conveniently dealt with under two heads. Table 1. Comparative karyomorphology of different cultivars of Maydeae

a: I. A. R. I., New Delhi. b: Haringhata Farm, Mohanpur. W.B. c: Dungra Fodder Farm, Kalimpong. d: Personal collection from Sonada, Dist. Darjeeling. e: Maize Research Station, Amberpet, Hyderabad. f: National Seeds Corporation, Calcutta. g: Globe Nursery, Calcutta. h: Suttons & Co., Calcutta. is Ghose & Co., Darjeeling. j: Bidhan Chandra Krishi Viswa Vidyalaya, Kalyani. k: Gujarat Agricultural Universi ty, Anand. 1: Botanical Surey of India, Sibpur, Howrah. 1986 Karyomorphology of Different Strains of the Maydeae 537

1. Variation within maize The essential uniformity in the gross features of the karyotype of maize are clearly evident by the comparative karyomorphological study of different cultivars. Chen (1969) and Horn and Walden (1978) have remarked that the ten pairs of chro mosomes of maize can be distinguished from each other by the combination of their relative lengths, arm ratios and cytological markers such as the statellite on chromo some 6, based on the former's study of a total number of 38 cells. The results of the present investigation are not comparable to those of Chen, as his analysis was based on measurements only from a single cultivar. The normal somatic chromo some number of the various cultivars is uniformly twenty. The karyotype of maize belongs to a graded type. There is a gradual decrease of length from the longest to the shortest chromosome with no abrupt change in size. The chromosome mor phology is more or less similar in different cultivars. The number of chromosomes with secondary constriction also does not vary, being one pair. More frequently, it is the 6th chromosome in order of length. The nonsatellited chromosomes are only of two types. The centromeres are either nearly median or nearly submedian in position. Notwithstanding the general uniformity of the somatic karyotype of maize, a few minute variations are observed in the chromosome complements of the various cultivars studied. Three types of chromosomes with secondary constriction are recognized, based on the relative variation in the position of primary and secondary constrictions. The primary constriction varies from median to nearly submedian position, whereas the secondary constriction, from nearly submedian to extremely subterminal position. The most frequent type is A2, encountered in fifteen of the twenty two cultivars studied, followed by A3 in five and A1 in two cultivars. The number of B-type pairs ranges from four to six and that of C-type pairs from three to five. In addition to the karyotypic variation mentioned, some other exceptions to the uniformity in chromosomal complements of maize are observed, such as the presence of B-chromosomes in cultivars such as Nal-Tel (Yucatan-7), Stowell's Ever Green (Fig. 35), Warangel Local and Diara, the occurrence of heteromorphic satellited chromosomes in Diara (Fig. 37) and the occurrence of haploid roots in Kalimpong Local (Fig. 29). The unravelling of these minor variations in the mitotic complements of the different cultivars has been made possible only with the adoption of improved techniques of chromosome analysis. The pachytene cytology of maize is most ex tensively worked out. This indicates that in addition to pachytene analysis, somatic karyomorphology too may be utilized to bring out elear differences among cultivars, if properly carried out by adequate techniques. The fact that the same karyotype has been consistently recorded in all dividing cells of the same cultivar clearly establishes that the karyotypic differences between cultivars, as observed here, are in fact genetic characters. Ono and Suzuki (1956) reported six different pachytene karyotypes in sixty nine accessions from Nepal. Evidences of gross chromosomal aberrations including reciprocal transloca tions are rather rare. This fact was essentially unravelled by the failure of Cooper and Brink (1937) to find any interchange heterozygosity in sixty eight varieties from 538 J. S. P. Sarma and A. K. Sharma Cytologia 51

Canada, Mexico, Central America, Peru and Bolivia and by that of Rhoades and

Dempsey (1953) to find the same in eighty five Latin American strains. The ab

normal chromosome 10 (Rhoades 1952, 1955) and various spontaneous aberrations,

such as inversion in 8S (McClintock 1933) were considered as random exceptions to

the chromosome uniformity of maize (Carlson 1977). These aberrations occur at

random and do not characterize any natural race. It is generally agreed that the

genomes of different races are more or less homologous, notwithstanding the dif ferences in their knob constitutions and allelic frequencies (Galinat 1977). These

conditions possibly preclude any large scale contribution of aberrations to the

karyotypic variations.

Most of the cultivars exhibit intimately synapsed pachytenes and regularly form

ten bivalents. This fact may suggest that minor alterations either do not affect

pairing of chromosome segments or may have attained homozygosity during con tinued selection even though there is overall heterozygosity characteristic of maize.

There has been judicious selection leading to the differentiation of modern cultivars

of this crop. The effects of selection in maize are wellknown (Beadle 1972, 1980, Doebley and Iltis 1980, Mangelsdorf 1974). In fact, the gross chromosomal uni

formity of maize is considered to be a consequence of human selection for only well

filled ears and kernels (Galinat 1977). It may, however, be noted that evidences

of minor alterations were observed by Blanco (1948), Clark (1942) and Rhoades

(1955) following selfing and subsequent crossing. In addition to the minor karyotypic variations, the total chromatin lengths of

the haploid complements of the different cultivars are found to vary considerably

from each other. The longest complement is that of CM-105, measuring 56.76ƒÊ

in length and the shortest is that of Synthetic B23, measuring 22.82ƒÊ. This wide

variation in total chromatin length in different cultivars of the same crop species is

remarkable, notwithstanding the basic uniformity of the karyotype. The number

of cultivars within the length ranges of <30ƒÊ, 30-40ƒÊ, 40-50ƒÊ and >50ƒÊ are 9,

6, 5 and 2 respectively. The longest chromosome measured is 7.92ƒÊ and the shortest,

1.32ƒÊ. This indicates that the minute differences in the karyotype and the total

chromatin length, taken together, may serve to characterize and identify the vari ous cultivars. But it is observed that they have much less variable total centromeric

indices and this points to relatively less variable ratios, when compared to total

lengths.

Undoubtedly minor structural changes account for karyotypic variation, but

causes for the wide differences in chromatin lengths of the complements require

analysis.

Maguire (1962) pointed out that the knobs would not detectably influence the

variability in arm length and would not contribute measurably to length. This

statement holds good generally, as is evidenced by pachytene observations of some

of the cultivars. The correlation, if any, of the chromatin length with the presence

and number of knobs is not observed. However, the establishment of relationship

between knobs and chromatin length can be accurately worked out provided pachy tene analysis and mitotic karyotype analysis are carried out on the same plant. The

other prerequisite is that the materials should be well established inbreds or races, 1986 Karyomorphology of Different Strains of the Maydeae 539 because with the modern cultivars like hybrids, synthetics and composites the hy bridity, selection and bulking often tend to result in heterogeneity in cell populations. The recent significant attempts to highlight the racial diversity of maize are those of Brandolini (1971), Brown and Goodman (1977), Goodman (1978), Goodman et al. (1977) and those to analyse the chromosomal diversity are those of Blumenschein (1973), Kato (1975) and McClintock (1978), which reveal the migration patterns of certain definitive knobs and knob-complexes. It is possible that the chromosomes may have inherent variability in their length patterns. Maguire (1962) suggested that the chromosomes may have two kinds of variability, one which apparently contributes uniformly per unit length throughout the genome and the other, which is, possibly a characteristic property of each chro mosome, unrelated to length in any way. She also further observed that the chro mosomes of a cell would tend to be either consistently longer or shorter than the average. The chromosomes with larger arm ratios have inherently more variable arm ratios and in each chromosome the short arm is apparently more variable in length than the long arm. She also analysed the possible effects of genotype on chromosome variation. The nature of origin of the different cultivars studied may possibly account for the genotypic variation. The materials included in the present investigation are quite heterogeneous comprising different races, varieties, hybrids etc. These are formed by adopting different breeding procedures and hybridity, selection and bulking tend to alter the genotypic constitution of the different cultivars. Differences in degree of condensation in various cultivars may possibly result in length variations to a considerable extent. Some cultivars may have relatively less specialized chromosomes than those of the others. It is to be pointed out that the degree of condensation is under genotypic control. The addition of nucleotypic DNA may be another possible factor contributing towards length variation. In view of the remarkable consistency, which char acterizes the modern cultivars of maize, it is to be pointed out that the addition of nucleotypic DNA resulting in tandem duplications, if at all occurred, did not involve the structural genes. It is well known that chromosomes are capable of internal precise duplication of genes (Britten and Davidson 1971, Flamm 1972, Price 1976). It is a well realized fact that duplication of base sequences, genes and chromo some segments has played a significantrole in the evolution of maize under domesti cation (Carlson 1977). These duplications are naturally occurring and some of them seem to involve duplications of single cistrons. Compound loci that consist of tandem repeats have been found at the R locus (Dooner and Kermicle 1971, Emmerling 1958, Stadler and Neuffer 1953),A locus (Laughnan 1949, 1952a, b) and Adh locus (Schwartz and Endo 1966). Certain duplications have been identified by RNA-DNA hybridization techniques in case of 18s and 28s-rRNA genes, followed by cytological confirmation (Phillips et al. 1971). Several other factors may contribute to chromosome length such as the dif ferential response of various cultivars to the uniform processing, the differences in growth phase and the internal differences in cellular environment. Such factors 540 J. S. P. Sarma and A. K. Sharma Cytologia 51

were given due consideration by Jain (1967), Rees (1958), Swanson (1943), Wilson and Boothroyd (1944) and others. It is quite likely that several factors such as minor aberrations, inherent length variability, genotypic differences, differences in degree of condensation, addition of nucleotypic DNA and other miscellaneous factors may act individually and in teract with each other to produce the wide variation observed in the chromosome length of the different cultivars, analysed in the present investigation. A detailed study of chromosome condensation patterns and variations, if any, may further lead to an understanding of the causes for the wide variation in chro mosome characteristics. However, the observed fact that the different cultivars of maize have a basically uniform karyotype with minor changes indicates the impor tance of structural alterations in the differentiation and evolution of maize under domestication. 2.Variation betweenmaize, teosinte and Coix The karyotypes of maize and teosinte are almost indistinguishable from each other. The chromosome number is the same in both the cases. Both the species have one pair of chromosomes with no apparent difference in the morphology of their secondary constrictions. The range of length of teosinte chromosomes does not exceed that of maize chromosomes. Even the chromosomes with primary constriction are alike in their morphology. This indicates that the karyotype of teosinte does not vary much more than those of the cultivars of maize. Opinions differ with regard to the congeneric nature of maize and teosinte and the role which teosinte is assumed to have played in the origin and evolution of maize. This is well reflected in the different taxonomic treatments which teosinte is subjected to. Teosinte was regarded as a separate genus (Euchlaena)from maize (Brieger 1952, Randolph 1952, 1955, 1959, Weatherwax 1955). More recently Randolph (1976) tabulated the various differences of both the taxa warranting their retention as separate genera, who emphasized their continued maintenance as distinct entities despite their sympatric existence and ready hybridization, permitting normal gene exchange. It was transferred to the same genus Zea as maize independently by Kuntze in 1904 (cited by Wilkes 1967)and by Reeves and Mangelsdorf (1942). Reviewing the opinions expressed by various authors such as Celarier (1956), Darlington (1956), and others, Reeves and Mangelsdorf (1959) concluded that there was a general agreement with regard to at least the congeneric status of both . This view has recently been supported by deWet et al. (1976), Galinat (1977, 1978) and Mangels dorf (1974). Annual teosinte was consisdered to be even a subspecies of Zea mays (Beadle 1972, 1980, Darlington 1956, Doebley and Iltis 1980, Iltis 1972). Bird (1978) has coined a new specificname, Zea luxurians for the Guatemala race of annual teosinte. Considering all the above facts Iltis and Doebley (1980) have proposed the modern classification of the genus Zea. It has been divided into two sections: (1) Luxuri antes with three species-(a) Zea perennis, (b) Zea diploperennis and (c) Zea luxuri ant, and (2) Zea consisting a single species, Zea mays with three subspecies-(i) 1986 Karyomorphology of Different Strains of the Maydeae 541 mays, (ii) mexicana and (iii) parviglumis. The essential similarity of the mitotic karyotypes of maize and teosinte is quite remarkable. The chromosome complement of teosinte does not vary more than that of a cultivar of maize. This situation does not warrant the segregation of the two taxa into separate genera, as maintained by Randolph (1976). On the other hand, the karyotype similarity presents no serious obstacle to consider both of them to be conspecific, as has been proposed by Beadle (1980), Doebley and Iltis (1980) and others. The morphological dissimilarities between maize and teosinte (Galinat 1971, 1977) are attributed to the power of human selection (Beadle 1972, 1978, 1980). Iltis (1972, 1974) and Iltis and Doebley (1980) have suggested the use of anthro pogenically neutral characters, as taxonomic criteria. Galinat (1963, 1975) estab lished the relationship between the two based on cupule and phytomer organization. However, the structural and functional attributes of their chromosome complements are similar to a great extent (Beadle 1932, Longley 1937, 1939, Galinat 1977, 1978, Ting 1964, Kato 1976, Smith, Goodman and Kato-cited by Smith et al. 1981, Mangelsdorf 1974). Their hybrids are fully fertile and exhibit synaptic and allelic relationships (Emerson and Beadle 1932). Nevertheless, interpretational discre pancies of archaeological data resulted in widely divergent conclusions (Man gelsdorf et al. 1967, Mangelsdorf 1974, Galinat 1978, Randolph 1976, Wilkes 1977b, Flannery and Schoenwelter 1970). Comparative palynology (Galinat 1973, Barghoorn et al. 1954, Bartlett et al. 1969, Banerjee and Barghoorn 1972) contributed to resolve certain disputes of phylogeny (Mangelsdorf 1974). Serology, poly acrylamide gel electrophoresis (Smith and Lester 1980, Waines 1972), comparative fl avonoid spectra (Gray and Perkins 1973), organelle DNA patterns (Levings et al. 1978, Timothy et al. 1979) and ultimately DNA hybridization studies (Hake and Walbot 1980) establish the close similarity of maize and teosinte. The present in vestigation falls in line with the data from different disciplines indicating the sim ilarity of the two taxa. The karyomorphology of Coix is slightly different from that of maize and teosinte. The chromosome number, range in length and the number of pairs of chromosomes with secondary constriction are similar. However, the number of B-type chromosomes is maximum and number of C-type chromosomes is mini mum, manifesting in its maximum T. F. value and indicating a tendency towards a more symmetrical karyotype. Conflicting opinions were expressed regarding the systematic treatment of the Maydeae. The subtribe was considered to be a valid taxonomic offshoot from the Andropogoneae (Anderson 1945, Celarier 1957, Hitchcock and Chase 1950, Stebbins 1956) inspite of the inclusion of several American and oriental genera, whereas several authors regarded the same to be an artificial assemblage (Chaganti 1965, Chandravadana and Galinat 1976, Smith and Lester 1980, Weatherwax 1954). The American Maydeae were believed to form the subtribe Tripsacineae, as distinct from the oriental Maydeae (deWet et al. 1976). So far as can be observed in the present investigation, the karyotypes of maize and Coix are similar to a great extent and both of them may possibly be regarded 542 J. S. P. Sarma and A. K. Sharma Cytologia 51

as belonging to a natural group. Even though there are minor differences, it is too farfetched to consider the Maydeae as an artificial assemblage.

Summary

The present investigation was undertaken with a view to explore the variational patterns of the mitotic chromosomes of maize and to examine the intergeneric re lationships within the Maydeae. Twenty two cultivars of maize, mostly of Indian origin and one each of teosinte and Coix were analysed, employing the refined techniques of chromosome analysis. A wide variation was observed in the total chromatin lengths of the haploid complements. The cultivar CM-105 has the longest complement while Synthetic - B23 has the shortest complement. The karyotype is graded. The qualitative features of the ideograms are relatively uniform. The position of primary constric tion varies from median to nearly submedian. Three types of chromosomes with secondary constriction were recognized, depending on the relative position of the two constrictions. Certain other variations were observed such as heteromorphic satellited chromosomes and haploid chromosome number in roots. The karyo types of teosinte and Coix do not differ more than those of cultivars of maize. The gross chromosome uniformity of maize is well known and is the resultant of judicious human selection. The presence of gross chromosomal aberrations as the possible cause of the wide range of length variation in the chromosome comple ments can be ruled out. Addition or deletion of nucleotypic DNA during the for mation of the cultivars might possibly have played a role in causing the observed variation. Differential condensation patterns of the chromosomes, reflecting dif ferent degrees of genetic activity have also been suggested to result in alterations of chromosome characteristics. In addition, several other factors such as minor aberrations, genetic differences, inherent length variability, nature of formation of the cultivars and differential response to the treatment may have acted individually and interacted with each other to produce the wide variation. Thus it has been shown that mitotic chromosome analysis, when carried at with appropriate tech niques, brings out significant differences in maize. Evidences from several fields such as pachytene cytology, archaeology, paly nology and comparative biochemistry indicate the close similarity of maize and teosinte. The present investigation does not warrant the segregation of maize and teosinte into distinct genera. The observations further support the inclusion of maize, teosinte and Coix in the Maydeae.

Acknowledgment

The wishful cooperation of Dr. Mrs. Mandira Sharma and Dr . Miss S. Sen is thankfully acknowledged. Our thanks are due to the authorities of various agencies , from whom the materials were received. One of the authors (J. S.P .S.) acknowledges the award of teacher fellowship by the University Grants Commission , New Delhi. 1986 Karyomorphology of Different Strains of the Maydeae 543

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