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IV. Production of Polyploid Types

IV. Production of Polyploid Types

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216



NAGIB M. A. NASSAR



microspores. Prakken and Swaminathan (1952) observed that diads (with two reduced microspores) and tetrads (with four reduced microspores) occur together in

the same plants of several Solanum species. This was confirmed later by several

workers using different crop plants (Roads and Dempsey, 1966). Nassar (1992) reported for the first time in cassava interspecific hybrids as a consequence of meiotic irregularity. Now, there is agreement that diads form due to spindle abnormalities which may be visible at meiotic metaphases I and II (Nassar, 1996).

Cassava clones grown in the germplasm bank of the Centro Agronomico Tropical de Investigacion y Ensenanza were used to prove the previously mentioned

hypothesis (Vasquez and Nassar, 1994). Floral buds were collected and fixed for

24 h in 3:1 ethanol:acetic acid mixture, transferred to 70% ethanol, and stored at

5ЊC. The anthers were squashed in a drop of 1% acetocarmine. Metaphase I was

used for chromosome counting and study of chromosome associations. The tetrad

stage was observed to determine the frequency of diads and triads. About 300

tetrads were counted in each clone. Photomicrographs were taken from temporary

preparations using the Zeiss standard research microscope.

Of the nine cassava clones studied, eight showed regular metaphase with complete pairing and formation of 18 bivalents. The ninth clone (No. 6477), known as

Chioriqui, showed a sectorial chimera in the inflorescence. One sector of inflorescence developed flowers with normal metaphase I and complete pairing of chromosomes. No laggards at anaphase I and no micronuclei at the tetrad stage were

observed. The other sector of the inflorescence had flowers with extreme abnormal metaphase I in all the flowers investigated. This was accompanied by the presence of empty anthers. The abnormality at metaphase I was due to lack of chromosome pairing asynapsis. In the 20 metaphases examined the chromosome

association was 11 or 12 bivalents instead of 18 normal bivalents. The remaining

chromosomes formed only univalents. This resulted in the formation of micronuclei at the tetrad stage. There were 1–15 micronuclei per tetrad (Table XXII). Apparently, this chimeral sector was due to a gene mutation in the second layer (LII)

of the apex of the growing shoot. Since only a lateral sector exhibits this abnormality, the chimera must be sectorial rather than mericlinal or periclinal. This is

the first report of a mutation which affects chromosome pairing in cassava. Since

cassava reproduces vegetatively, it is likely that this mutation has been preserved

for a long time in this indigenous Costa Rican clone. To trace unreduced microspore formation, diads and triads were checked among 300 tetrads of each

clone. The most interesting case was found in clone No. 11,965 which formed

11 diads per 300 sporocytes studied, indicating first meiotic restitution (Table

XXIII). No other clone showed diad formation. Regarding triad formation, four

clones, namely, 9959 (Mangi), 6429, Vegna Mochera, and 6399, formed triads in

the range of 1–1.3%. The clone 11,965, the only diad producer among the clones

studied, also produced triads with a frequency of 1%.

As can be seen from Table XXIII there is variation for 2n gamete production



217



CASSAVA, M. esculenta Crantz, GENETIC RESOURCES

Table XXII



Chromosome Association and Diad and Triad Frequencies in Investigated Germplasm

Diads

Cultivar

9,959 (Mangi)

6,417 (White)

10,861 (Num-4-RB)

6,429 (Negra Muchera)

11,965 (Sim Nombre)

6,379 (Amarilla-1)

6,473 (Vagana 4208)

6,477 (Chiriqui)

Chimera a

Chimera b



Triads



Chromosome

association



Frequency



2%



Frequency



2%



18II

18II

18II

18II

18II

18II

18II











11















3.7







4





4

3

3





1.33







1

1





18II

11II ϩ 14I



among the cassava clones. Several workers reported that in species with a tendency to form unreduced microspores, the frequency of such gametes may vary from

one line to another (Mok and peloquin, 1975). In the meantime, stable high 2n gamete production has been observed in 2n gamete producer lines (Ballington and

Galleta, 1976). Thus, the variation in the frequency of 2n gametes may be attributed mainly to their genotypic differences (Veilleux and Lauer, 1981). It seems that

unreduced microspore formation is gene controlled and not due to the disturbance

of chromosome asynapsis. However, it is agreed that this is due to the occurrence

of nonfunctional spindle, resulting in all the metaphase chromosomes remaining in

the center instead of separating to poles (Ramana, 1974; Vorsa and Bingham, 1979).

2. Unreduced Microspores in Interspecific Hybrids

The causes of unreduced microspores in plants are variable, ranging from simple recessive genes (Mok and Peloquin, 1975) to disturbed spindle function in in-



Table XXIII

Frequency of Diads and Five Kinds of Tetrads in the Sectorial Chimera of Clone 6477

(300 Tetrads Studied)



Parameter



Diad



Normal

tetrads



Frequency

%



1

0.3



18

6



Tetrads with different Nos. of

micronuclei

26

8.7



41

13.9



26

8.9



188

62.6



218



NAGIB M. A. NASSAR



terspecific hybrids. Nassar et al. (1995) suggested that the disturbance of meiotic

division in interspecific hybrids may lead to a higher frequency of aneuploid gametes, consequently making it possible to select polyploids among their progeny.

Brazilian Manihot species are believed to be progenitors of cassava, and Brazil

contains its centers of diversity (Nassar, 1978b). Interspecific hybridizations have

been carried out systematically by Nassar since 1980 and many interspecific hybrids have been produced (Nassar, 1989). Some of these, which represent different interspecific hybrids and cover a vast array of variation, were used by Nassar

in the current investigation. Ten interspecific hybrids and/or their progenies were

used in this investigation: F1 M. glaziovii ϫ cassava (3 genotypes), F2 M. epruiinosa ϫ cassava, F2 M. anomala ϫ cassava (3 genotypes), F3 M. pseudoglaziovii

ϫ cassava (two genotypes), and F4 M. pseudoglaziovii ϫ cassava. These hybrids

and progenies were chosen because they provide large genetic variation. Chromosome associations in meiotic metaphase I and the occurrence of dyads and triads and also pollen viability were studied. For the meiotic study, inflorescences

were fixed in a 3:1 mixture of absolute alcohol and glacial acetic acid and kept at

5ЊC for 24 h. The anthers were smeared in an acetocarmine stain. Chromosome

configurations at metaphase I, together with spared formation, were studied. For

the pollen viability study, one to three flowers per plant were selected, and their

pollen was crushed in acetocarmine and scanned. Pollen counts and the percentage of stained normal pollen were calculated.

Chromosome associations and their frequency in meiotic metaphase I of PMCs

of all interspecific hybrids have shown regular pairing of 18 bivalents except the

F2 progeny of M. glaziovii ϫ cassava (first genotype), which revealed the presence of two univalents in 5% of the cells examined. This genotype also showed a

high frequency (3.7%) of dyad formation and low pollen viability (42%). The

study of PMCs in the tetrad phase revealed the formation of abnormal tetrads having one to three micronuclei in all hybrids used in the experiment, except F1 M.

glaziovii ϫ cassava (second genotype). The abnormal tetrads ranged from 0.8%

in f1 M. glaziovii ϫ cassava (first genotype) to 94% in the F1 hybrid M. epruinosa

ϫ cassava (Table XXIV).

The high frequency of unreduced microspores in the F2 progeny of M. glaziovii

ϫ cassava will facilitate selection of this genotype and its progeny as a possible

progenitor of polyploids in the future. Apparently, the dyad formation is due to

meiotic restitution. The low pollen viability may be due to univalent formation and

the consequent irregular chromosome distribution leading to unbalanced gametes.

Cassava is a natural allopolyploid judging by its chromosome number and the

complete pairing of its meiotic metaphase chromosomes (Nassar, 1978b; Vásquez

and Nassar, 1994). If unreduced gametes were responsible for its natural polyploidization in the past, it is possible that one can detect them among wild relatives and their hybrids with cassava. The presence of unreduced microspores in the

hybrid progeny confirms this hypothesis.



Table XXIV

Frequency and Percentage of Diads and Triads in Different Sporads



Manihot hybrids



Triad



Tetrad



Abnormal tetrad



n (%)



n (%)



n (%)



n (%)



Pollen

examined



n (%)



1217

1168



10 (0.82)

43 (3.70)



8 (0.66)

8 (0.70)



1158 (95.15)

1107 (94.80)



41 (3.37)

10 (0.80)



2979

1713



1197 (40.18)

723 (42.21)



1044



0 (0.00)



4 (0.40)



1040 (99.60)



0 (0.00)



1463



1123 (76.76)



1252

1374

1145

1136

1416

1210

1138



0 (0.00)

1 (0.07)

1 (0.00)

1 (0.09)

0 (0.00)

0 (0.00)

1 (0.09)



0 (0.00)

0 (0.00)

0 (0.00)

0 (0.00)

0 (0.00)

0 (0.00)

0 (0.00)



1252 (100.00)

1326 (96.51)

1117 (95.56)

1106 (97.36)

1134 (95.62)

1207 (98.80)

1125 (98.80)



0 (0.00)

47 (3.42)

28 (2.44)

29 (2.55)

62 (4.38)

3 (0.20)

12 (1.05)



603

836

1297

801

1427

1130

1704



567 (94.03)

183 (21.89)

441 (34.00)

452 (56.43)

873 (61.18)

1034 (94.50)

862 (50.59)



491



2 (0.40)



3 (0.60)



476 (98.86)



10 (2.04)



1273



299 (23.49)



Microspores

examined



M. glaziovii ϫ cassava

F1 M. glaziovii ϫ cassava ϫ cassava

(1st genotype)

F1 M. glaziovii ϫ cassava ϫ cassava

(2nd genotype)

M. epriminoso ϫ cassava

F2 M. anomala ϫ cassava (1st genotype)

F2 M. anomala ϫ cassava (2nd genotype)

F2 M. anomala ϫ cassava (3rd genotype)

F3 M. pseudoglaziovii ϫ cassava

F4 M. pseudoglaziovii ϫ cassava

F1 M. dichotoma ϫ cassava

(1st genotype)

F1 M. dichotoma ϫ cassava

(2nd genotype)



Pollen

viability



Diad



220



NAGIB M. A. NASSAR



Vásquez and Nassar (1994) reported a high frequency of unreduced microspores

among cassava clones. It is believed, therefore, that this character is heritable and

genetically controlled. It was probably acquired by cassava from its wild ancestors (Nassar et al., 1995), representing an evolutionary remnant in cassava. The

significance of this phenomenon is that it provides direct evidence on polyploidization from lower ploidy levels through the mechanism of unreduced gametes and not through other types of somatic doubling (Harlan and de Wet, 1975;

de Wet, 1980). According to the genes of wild ancestors they have probably had

the opportunity to combine and produce larger rooted cassava (Nassar, 1992; Nassar et al., 1996a). It seems that this character is correlated with meiotic irregularities provided there is some univalent formation in the genotype producing unreduced microspores.

It is worth mentioning that this unreduced microspore-producing genotype is

a progeny of a natural hybrid of M. glaziovii with cassava. This natural hybrid

has been maintained by farmers for hundreds of years through vegetative reproduction. The unreproduced microspore gene has probably arisen through recurrent mutation and been maintained through vegetative reproduction. In other

germplasm that reproduces sexually, it would be eleminated by natural selection

due to the abortion of gametes which carry it.



B. INDUCTION OF A PRODUCTIVE ANEUPLOID

IN CASSAVA, M. esculenta Crantz

Within the wild Manihot species which have been evaluated and hybridized

with cassava by Nassar to transfer their useful genes (Nassar, 1978a, 1980, 1986),

two interspecific hybrids between cassava and wild Manihot species have been obtained and/or maintained in the Nassar program at the Universidade de Brasília.

One of the two interspecific hybrids was between cassava and M. pseudoglaziovii

Pax (Nassar, 1982); the second hybrid was between cassava and M. neusana Nassar (Nassar, 1989). These hybrids were cloned by vegetative reproduction and seed

produced by open pollination. Ten seeds were collected from each hybrid for germination studies. Four seeds from progenies of cassava with M. pseudoglaziovii

germinated, of which one plant was selected for vigor. Only two seeds of progenies of the hybrid of cassava with M. neusana germinated, of which one plant was

selected for vigor.

These three plants were cloned by vegetative propagation of cuttings. When the

plants flowered, the three clones and their parents were studied meiotically for

chromosome association in metaphase I, segregation in anaphase I, and pollen viability. Mitotic analysis was also performed on root tips taken from cuttings. After 9 months of growth, these clones were examined for root productivity. For the

study of meiosis, buds were fixed in a 3:1 mixture of ethyl alcohol and glacial



CASSAVA, M. esculenta Crantz, GENETIC RESOURCES



221



acetic acid for 24 h, transferred to 70% alcohol, and then smear stained with 1%

acetic carmin. For mitotic counting of chromosomes, root tips were treated with

0.2% colchicine for 2 h, washed in distilled water, transferred to the previously

mentioned fixative fluid for 24 h, treated with 1 N HCl for 10 min, and smear

stained with 1% acetic carmin.

Meiotic examination in metaphase I of the clone, progeny of the interspecific

hybrid of cassava with M. pseudoglaziovii (HPS), showed a mean of 16–19 bivalents, 154 trivalents, and 1.00 univalent for the 15 sporocytes examined. These

results suggested an aneuploid having a 2n ϩ 2 chromosome constitution. The

parental hybrid showed 2n ϭ 36, with a mean association of 17.42 bivalents and

1.58 univalents. Estimation of pollen viability revealed a viability percentage of

54% in 2917 aneuploid grains and 40% in 1350 of the parental hybrid. The hybrid

of cassava and M. neusana (HO1) had a mean of 1.86 trivalents, 16.13 bivalents,

and 0.13 univalents among 30 PCMs examined. The chromosome constitution was

2n ϭ 38. This was confirmed by chromosome counting at mitosis of root tip cells.

The second clone of this cross (HO4) showed a mean chromosome association of

1.63 trivalents, 12.41 bivalents, and 8.84 univalents in metaphase I. This clone also

had 2n ϭ 38. The parent had a mean of 17.42 bivalents and 1.58 univalents, which

means 2n ϭ 36. Pollen viability was found to be 35.8% in HO1, 17.7% in HO4,

and 36.8% in their parent.

The progeny of the interspecific hybrid of cassava with M. pseudoglaziovii had

a very large starched root with a mean of 6.1 kg per plant at 10 months for the 15

plants evaluated, compared to 3.7 kg for the cultivated cassava clones. The other

two aneuploids had fibrous roots.

These aneuploids apparently resulted from disturbance of meiotic division of

their interspecific hybrid parents. This disturbance was interpreted by Nassar et al.

(1995) as an inhibition of spindle function and chromosome asynapsis. Both have

led to laggard formation and unbalanced gametes. Thus, the origin of these aneuploids can be attributed to the fertilization of an n ϩ 1 egg by an n ϩ 1 male gamete based on the fact that gametes with this structure are more viable than gametes with n ϩ 2. The other possibility is the fertilization of an n ϩ 2 egg with an

external n male gamete because the plants were open pollinated. It was not possible to determine whether the male gamete came from selfing or from another pollinator plant. In various crops, interspecific hybridization has led to the disturbance

of meiotic division. Similar findings were reported in Trifolium pratense by Parrot and Smith (1984) and in Medicago spp. by Vorsa and Bingham (1979). No

aneuploids, however, were obtained in these crops.

The two additioinal chromosomes in clone HPS resulted in the production of a

large tuber root that is superior to normal root production in cultivated cassava

clones. In all likelihood this size increase in due to additive polygenes. These polygenes may be distributed on more than one chromosome.

Nassar (1978b) postulated the origin of cassava as a product of hybridization



222



NAGIB M. A. NASSAR



between two wild species, both having fibrous nonstarchy root as a result of an accumulation of additive polygenes derived from ancestral wild parents.



C. PRODUCTION OF TRIPLOID CASSAVA, M. esculenta

Crantz, BY HYBRID DIPLOID GAMETES

Through the Nassar program of cassava germplasm collection and utilization

in Brazil, a natural hybrid of M. pseudoglaziovii and cassava was collected in

1978 from Remigo county, Paraíba state, and grown in the living collection at

the Biological Experimental Station, Universidade de Brasília (Nassar, 1982).

This natural hybrid was identified by the marker genes of winged fruit which

came from cassava and peltated, pendurated leaf, two characteristic genes of M.

pseudoglaziovii overlaps cassava plantations. The hybrid was multiplied vegetatively and cloned 20 times to individuals maintained in the living collection

and used in this experiment. This clone was left for open pollination “entre si.”

Seeds collected were planted in 1980 and the progeny of 22 plants were produced. Evaluation of the progeny for root production was carried out in the following years.

The natural hybrid and its selected progeny were studied meiotically. The anthers were fixed for 24 h in a 3:1 solution of ethanol and acetic acid, transferred to

70% ethanol, and stored at 5ЊC. The anthers were squashed in 1% acetocarmine.

Pollen analysis was conducted by collecting pollen from undehisced natural anthers of a flower onto a microscope slide and staining with 1% acetocarmine.

Pollen grain diameter was assessed at 450x using an eyepiece micrometer. A minimum of 1000 stained grains per plant were counted. Pollen stainability was used

as a criterion for viability. Well-filled, darkly stained pollen grains were considered fertile and partially filled, and unstained ones were considered sterile. The frequency of mature 2n pollen grains was based on counts of 1000 pollen grains

stained with 1% acetocarmine. Classification of n vs 2n pollen was made by visual size discrimination of stained pollen, given that the latter should have twice the

nuclear volume of the former.

To obtain data on ploidy status, mitosis in root tips was examined and chromosome number was counted to confirm the plant’s chromosome constitution.

Screening the hybrid cloned plants for tuber formation showed them to have complete fibrous roots but they extended deep in the ground, almost 5 or 6 m in length.

The presumed progenitor, M. pseudoglaziovii grows in one of the driest pockets

of Paraíba state, Remigio county, where the wild species and the hybrid were collected. Apparently, the wild species had acquired this deep-rooted character as a

mechanism for removal of subterranean water. This character may be useful in subsequent improved generations for production of drought-tolerant cassava cultivars. Two years after planting, the hybrid reached 3 or 4 m in height. Its leaves



CASSAVA, M. esculenta Crantz, GENETIC RESOURCES



223



were peltate and frequently pendulous. These characters are typical of M. pseudoglaziovii and one of the striking features that distinguish this species from the other 98 species recognized by Rogers and Appan (1973). The hybrid carried few fruit

(4 or 5 fruits compared to 60–70 fruits in the pure M. pseudoglaziovii of the same

age). The fruit is winged, a marker gene characterizing cassava fruit (Nassar,

1989).

Cytological analysis of PMCs revealed a regular occurrence of 18 bivalents at

metaphase I. No multivalents were observed in 50 metaphase I cells studied. However, disturbed anaphases I was noted in 6 of the 30 anaphase I cells studied. Dyads

and triads were noted totalling 14, compared to 86 normal tetrads. Pollen viability as measured by stainability with acetocarmine was as low as 41%. Of these

viable pollen, 21% were small. The high percentage of sterility despite regular

pairing may be attributed to the maintenance of the hybrid through vegetative reproduction by farmers in Paraiba state. This mode of reproduction may have led

to the accumulation of sterility mutations which have not been eliminated by natural selection through the sexual cycle (Nassar, 1978c). Of the 20 plants cloned

from the hybrid, 82 fruits were collected. They gave 48 seeds with an average of

0.59 seeds per fruit. The average number of fruits collected per plant is 4.1 compared to 60 –70 fruits in the wild species plant. This low fertility is expected in

view of the high sterility of pollen grains.

By planting the seeds, 25 seedlings were obtained but all of them, with the exception of four plants that survived, were chlorotic or deformed and died. The

plants that survived were identified in the living collection by numbers 120 –123.

Of the four plants, three gave fibrous roots, but the fourth (No. 121) was very vigorous, resistant to stem borers, and produced large tuberated roots by the end of

the year. When multiplied vegetatively and compared with other cassava clones it

showed superiority in tuber formation by the age of 12 months. This superiority

reached approximately 28% more tubers than the Sonora clone, one of the best

commercial cultivars. Its production was 2.13 kg/plant compared with 1.67 for

Sonora. An evaluation of this selection under arid conditions was carried out during the years 1985 –1989 by the National Center for Tropical Semi-arid Region

and confirmed its superiority (Table XXV). The meiotic study of this plant showed

formation of trivalents, bivalents, and univalents in metaphase I with different frequencies (Table XXVI). The meiotic division triploid resulted from the fertilization of a 2n gamete with n gamete in the progenitor hybrid. Viability of pollen of

this triploid is as low as 19%. Seeds rarely formed. However, five seeds were collected and have been reproduced in our program.

The 2n pollen formation which led to production of this triploid is reported in

cassava by Nassar for the first time. The cytological mechanism of its formation

is probably inhibition of spindle at metaphases I and II judging from the triad

formation. In the literature, several mechanisms were reported. Clement and

Stanford (1961) and Tyagi (1988) attributed it to abnormal cytokinesis, whereas



224



NAGIB M. A. NASSAR

Table XXV



Average Productivity per Plant of the Triploid (Selection 121) and Other Cassava Clones under

Savanna and Semiarid Conditions

Clone

Triploid 121

Sonora

Triploid 121

Nagib 01/84

Nagib 02/84

Nagib 03/84

Nagib 04/84

Cigana



No. plants



Productivity



30

30

29

27

29

28

22

28



2.13

1.67

5.9

1.8

3.7

1.1

4.1

2.9



Region, location of trial, and harvest age (kg/plant)

Central Brazil, conducted at the experimental station, Univ. of Brasília; harvest age 12 months

Under semiarid conditions; trial conducted by the

CPATS, Petrolina, northeastern Brazil; harvest

age 18 months



Mendiburu and Peloquin (1977) proposed parallel spindle as an additional mechanism. The 2n pollen mutations were described in several plant species: Zea

mays (Roads and Dempsey, 1966), Solanum (Hogland, 1970), Medicago sativa

(Vorsa and Bingham, 1979), and Lolium (Sala et al., 1989). The vigor of Nassarselected triploid as seen in its productivity both under central Brazil conditions

and in the semiarid tropics adds evidence of the usefulness of this 2n gamete phenomenon as a powerful mechanism for transferring variability and fitness to

polyploid offspring. If a partially fertile type of triploid could be produced, it will

serve in establishing a founder population of a new chromosome race. Its progeny may rehybridize with new polyploids and diverse genotypes, producing additive heterotic potentialities. Since trivalent occurrence in this triploid is predominantly demonstrating gene exchange between wild and cultivated genomes,

it is likely that this will generate more variability in the progeny. The wild parent and its interspecific hybrid progeny are highly tolerant to drought as indicated by their deep roots. They normally survive the frequent years of drought in

their natural habitat. This triploid is a potential progenitor of cultivars adapted to

these conditions.



Table XXVI

Chromosome Associations at Metaphase I in the Triploid and Its Parent

Average chromosome association

Type

Natural hybrid

Triploid



No. PMCs examined

50

30



III



II



I





10.2



18

9.2





3.6



CASSAVA, M. esculenta Crantz, GENETIC RESOURCES



225



V. PROTEIN CONTENTS IN CASSAVA CULTIVARS

AND ITS HYBRID WITH WILD Manihot SPECIES

Tubers of 16 cassava clones, 8 months old and maintained in the germplasm collection at the Experimental Station, University of Brasília, were analyzed chemically for protein content. Total nitrogen and dry matter basis were determined by

the 1970 AOAC procedures (Nassar and Dorea, 1982). Percent protein was obtained by multiplying percent N by the factor 6.25. For every clone two samples

were analyzed, one from a small tuber (50 g) and the second from older tubers (200

g). Tubers were peeled, and protein was estimated in the coth peel and pulp. Tubers of hybrid between cassava clone Catelo and M. oligantha were analyzed in

the same way. Seed of cassava and wild Manihot species maintained in the living

collection at the University of Basília were analyzed for protein content by the

same procedures.

The concentration of protein in tubers of cassava clones and tubers of the hybrid is presented in Table XXVII. It can be seen that protein percent (N% ϫ 6.25

ϭ protein percent) ranged from 0.7 to 1.2% for larger tubers (Ͼ200 g), whereas

the range was 0.9 to 1.4% for tubers Ͻ50 g. In the same clone, protein content

of the pulp was higher in small tubers than in larger ones. These data agree with

those found by Akinrele (1964), who reported 0.7% for protein content in peeled

tuber on a dry matter basis, and Chada (1961), who found 1.2%. However, these

researchers did not pay attention to the effect of tuber size on protein content.

Jennings (1959) stated that protein in cassava root tends to be concentrated in the

outer zone of the root. This may explain why the small tubers have higher protein content since they have a larger proportion of the outer zone than do the older and larger ones. The very little variation of protein content among the 16

clones collected throughout Brazil shows that selection for this characteristic in

cassava clones will not bring any notable improvement. From Table XXVII it can

also be seen that protein is higher in peel than in pulp in all the examined samples and in all clones. This may be explained by the previously mentioned statement of Jennings that protein in cassava roots tends to be concentrated in the outer layers.

The analysis of hybrid tubers showed a notable increase in the hybrid of cassava with M. oligantha at 4.6%. In an earlier paper (Nassar and Costa, 1978),

the protein content in M. oligantha was reported to be 7.1% on a dry matter basis. Moreover, crosses of this species with cassava were highly fertile (Nassar,

1980). Nassar and Fitchner (1978) also showed a low HCN content in the wild

species M. oligantha. This may exclude any possibility that high protein content

in the species is due to HCN nitrogen. Table XXVIII shows the results of seed

analysis of some wild Manihot species maintained in our living collection. The

highest protein content is that of M. Brachyandra followed by M. alutacea.



226



NAGIB M. A. NASSAR

Table XXVII

Protein Content of Tubers of Cassava Clones



Clone

CBM 0206

EAB 348

BGM 188

CPM 0231

CPM 2002

CPM 0232

BGM 808

CPM 0225

BGM 204

CPM 1805

EAB 1156

EAB 484

BGM 048

BGM 020

CPM 1060

EAB 675

Hybrid



Approximate size (g)



Protein in peel (%)



Protein in pulp (%)



200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50

200

50



2.13

2.09

1.41

1.69



1.68



1.56



2.08

2.00

1.82

1.63



1.38

1.25

1.24



1.14

1.37

1.58

1.28

1.96



1.41

1.11

1.80

1.53



1.58

1.36

1.51

6.63

8.06



0.90

1.22

0.85

1.04



1.45



1.26



0.99

1.02

1.15

0.93



0.89

0.95

1.06



0.72

1.00

0.84

1.16

1.07



0.82

1.17

0.98

1.23



1.19

0.70

0.93

4.56

4.56



Manihot brachyandra is native to western Pernambuco and northern Bahia, two

of the driest areas in Brazil. Nassar (1980) reported that seed of wild cassava is

eaten by the population of these regions particularly in times of famine. Jones

(1959) reported that cassava seed is eaten in several parts of west and central

Africa. Thus, the discovery of the high protein content in native cassava hybrids

may open a new door to better protein-balanced food for people of the tropical

world.



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IV. Production of Polyploid Types

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