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IX. Allelic Series at the Maturity Gene Loci

IX. Allelic Series at the Maturity Gene Loci

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TABLE XV

Frequency Distribution of Flowering of Parental and FZPopulations of Combine Hegari X 1 W a y Milo and

Combine Hegari X Hegari Grown at Plainview, Texas, in 1965



CH X H

MalMazmaJbfas

Days to

flower

56

58

60

62

64

66

68

70

72

74

76

78

80

82

84

86

88

90

92

94



Hegari (H)

MalMeMaamar

I



12

6

5

2

1

2



-



-



-



X



MalM@Mama,

3



3

4



4

6

-



2

1



3

6

15

20

20

18

2

-



Combine

Hegari (CH)

MalMazmaaMm

10

15

7



C H X lOOM

MalMa2maJta4



x



lOOM



MalMazMaaMaa



Ma,Ma-JMa&fad



-



-



-



1

-



-



-



-



2

5

10

23

17

30

15

6



-



-



-



-



-



-



f



2

0



m



3



cn



8

cn

$2



8K



-



-



8

27

6

-



M



2



292



J. R. QUINBY



The dominant at locus 1 in Combine Hegari ( M a , M a , ma3M a , )

probably came from Hegari, and the dominant at locus 2 must have

come from Hegari. Dominant M a , in Combine Hegari must have come

from Milo, Hegari is M a , M a , M a , m a , and 100-day Milo is M a , Ma,M a , Ma,. The latest genotype. in each F, population is homozygous

dominant at all 4 loci, In the latest plants of the F, of CH x lWM, at

least one dominant at each locus would have come from Milo. In the

F, of CH x H, all dominants at loci 1, 2, and 3 came from Hegari and

only dominant M a , came from Milo. The latest plants in the F2 of

CH x lOOM flowered in 90 to 92 days, The latest plants in the F, of

CH X H flowered in 84 to 86 days, a difference of 6 days. These data

indicate that dominants at loci 1, 2, and 3 from Milo interact to cause

more lateness than dominants at loci 1,2, and 3 from Hegari.

Texas Milo originated from one Periconia root-rot resistant plant

that was selected along with more than 1,oO others from a diseased

field in Runnels County, Texas (Quinby and Karper, 1949). All the

selections were grown at Chillicothe, Texas, and, although all the

progenies looked like Dwarf Yellow Milo, small differences in maturity

existed among them. Finney Milo originated at the Garden City, Kansas,

Experiment Station as one of two Periconia root-rot resistant plants

found in a diseased plot (Wagner, 1936). Both Finney and Texas Milo

are of the genotype M a , maz ma, Ma,, but Finney Milo heads about 2

days later than Texas Milo. The difference in maturity between the two

varieties is thought to be due to an allelic difference at one locus, probably locus 1. Similar small differences in maturity exist among strains

of Blackhull Kafir that were found growing on farms in Texas, Oklahoma,

and Kansas in the 1920’s and are still preserved in sorghum nurseries.

These small differences in maturity are thought to be allelic and not to

be due to modifiers.

Allelic designations were not assigned to the genes in Table XIV

but will be in the discussions that follow.



B. ALLELFSAT



THE



FIRSTMATURITY

Locus



The recessive maturity alleles at the first locus in grain varieties of

American origin came from Early White Milo, Blackhull Kafir, Red

Kafir, Pink Kafir, or Feterita. The Red and Pink Kafirs and several sorgos

from South Africa, the Feteritas and Durras from the Sudan, the Durras

from the Middle East, and the Kaoliangs of Manchuria were all recessive

at the first locus when they arrived in the United States. The recessives

at the first locus in the Sooner Milos and in Blackhull Kafir probably

occurred as mutations in the United States.

The following are the designations of the known alleles at locus 1:



MATURITY GENES OF SORGHUM



293



MalM-from Milo and in Fargo

MalH-from Hegari and in Early Hegari

malM-from Milo

malF-from Bonita and Combine Bonita that come originally from

either Feterita or Blackhull Kafir

malB1-from Texas Blackhull Kafir

malc-from Combine Kafir-60 but of unknown origin

malB2-from Redlan but originally from Blackhull Kafir C171

malP1-from Pink Kafir CI432, arid in Kalo and Early Kalo

malK-from Red Kafir PI19492

malp2-from Pink Kafir PI19742

malE-from Combine 7078 and probably in TX414 but of unknown

origin

malB3-from Caprock but originally from Dawn Kafir

malD-from Durra PI54484

The allelic series at the first locus must be much longer than shown

because the recessives in the Kaoliangs of Manchuria, the numerous Feteritas and Durras of the Nile Valley, and the many sorgos from South

Africa must all be different. Likewise, the dominants at locus 1 in

many tropical varieties must be unlike the dominant Mu;s from Milo

and Hegari.



C. ALLELESAT THE SECONDMATURITY

Locus

Of all the varieties identified for maturity, only SMW, SM80, 60M,

8OM, Kalo, and Fargo are recessive at the second locus and the recessive is the same in each of them, For this reason the only known recessive allele at the second locus is the one in the Milos. The dominant

alleles at locus 2 are more numerous and those that are known are listed

below:

MatM-from

MatH-from

MatF-from

MatB1-from

MatB2-from

Matc-from

MatK-from

MazPz-from

MatP1-from

MatE-from

MatB3-from

MatD-from

mazM-from



Milo

Hegari

Bonita but originally from Feterita or Blackhull Kafir

Texas Blackhull Kafir

Redlan but originally from Blackhull Kafir C171

Combine Kafir-60

Red Kafir PI19492

Pink Kafir PI19742

Pink Kafir (21432 and probably in Early Kalo

Combine 7078

Caprock but originally from Dawn Kafir

Durra, PI54484

Milo and in Fargo and Kalo



294



J. R. QUINBY



When Periconia root-rot resistant strains of Milo were being picked

up on farms in the 193(Ys, plants of the following maturity genotypes

were found: Mal maz ma, Ma,, M a , ma2M a , Ma,, and mal M a , Ma, Ma,.

It is probable that the first two genotypes did not originate at the same

time and there are probably two recessive mutations preserved in Milo

at the second locus.

Many varieties from different areas of Africa and Asia are dominant

at locus 2 and it is likely that the many dominant Ma:s are not identical.



D. ALLELESAT



THE



THIRD

MATURITY

Locus



A mutation to early maturity at locus 3 in Milo occurred before

1905 because the genotype M a , maz ma, M a , was being grown in Texas

by that time. An allelic series at maturity locus 3 has been reported

previously (Quinby and Karper, 1961). Early Hegari is recessive at

locus 3, and because of its different origin, recessive ma3 from Early

Hegari should be unlike recessive ma, from Milo. Recessive ma3 in

Bonita probably came from Feterita. Because Milos have been one of

the parents of many crosses, the recessive ma, in many varieties of

American origin came from some Milo. The known alleles at locus 3

follow:

M~3~-frornMilo

M ~ 3 ~ - f r o mHegari and-in Combine Bonita

M~3~l-frorn Texas Blackhull Kafir

M~3~~-frorn

Redlan but originally from Blackhull Kafir C171

Ma?'-from

Pink Kafir CI432 and in Kalo and Early Kalo

M ~ ~ ~ - f r o rRed

n Kafir PI19492

M ~ ~ ~ ~ - f rPink

o m Kafir PI19742

M ~ 3 ~ ~ - - f r oCaprock

rn

but originally from Dawn Kafir

M ~ 3 ~ C f r osome

m Blackhull Kafir and in Fargo

rn~3~-fromSooner Milo

rn~3~-from Ryer Milo

rn&-frorn

Early Hegari

rn~~~-from

Bonita

rn~3~-from Durra PI54484

rn~~~-from

Combine Kafir-60

rn~3~-frorn Combine 7078

Many tropical and many temperate zone varieties that have been

introduced into the United States are dominant at locus 3; the dominants

are not identical so the allelic series at locus 3 must be long.



MATUFUTY GENES OF SORGHUM



E. ALLELESAT



THE



295



FOURTH

MATURITY

Locus



Recessive mu4 was found in Hegari and occurs in Early Hegari also

but has not been found elsewhere. Dominant Ma, occurs in the Milos

and in many other varieties and so the allelic series at locus 4 must be

long. The known alleles at locus 4 are the following:

M ~ ~ ~ - f r oMilo

m and inrCombine Hegari

M ~ ~ ~ - f r oBonita

m

but originally from Feterita or Blackhull Kafir

M ~ ~ ~ - f r o Combine

m

Kafir-60

M~~~'--from

Texas Blackhull Kafir

M ~ ~ ~ ~ - f rRedlan

o m but originally from Milo or Blackhull Kafir C171

Ma4P1-from Pink Kafir (21432

Ma4K-from Red Kafir PI19492

Ma4p2-from Pink Kafir PI19742

7078

M ~ ~ ~ - f r oCombine

m

M~$~-from Caprock but from either Milo or Dawn Kafir

M ~ ~ ~ - f r oDurra

m

PI54484

ma4H-from Hegari and in Early Hegari



F. ALLELESAND RESPONSE

TO TEMPERATURE

SM100, Combine Bonita, Texas Blackhull Kafir, Redlan, Early Kalo,

Caprock, and Pink Kafir CI432, all have the same genotype for maturity

as far as dominants and recessives at the four maturity gene Ioci are

concerned. Yet they vary in days to flower from 56 to 70 days. Likewise,

SM90, Bonita, Combine Kafir-60, PI54484, Combine 7078, and TX414 are

genetically identical as far as dominants and recessives at the four gene

loci are concerned. Nevertheless, they vary in time of flowering by as

much as 6 days.

Within the first group that has the genotype ma, Mu, M a , Ma4,

SM100, Combine Bonita, and Early Kalo are quite sensitive to photoperiod. Texas Blackhull Kafir and Redlan are relatively insensitive to

photoperiod and the response of Caprock and Pink Kafir CI432 is unknown. Within the second group that has the genotype mal Ma, ma, Ma4,

SM90 and Bonita are sensitive to photoperiod. Combine Kafir-60 and

Combine 7078 are less sensitive, and Combine Kafir-60 is later in flowering in Jamaica in the winter than varieties that are much later in flowering in Texas in the summer.

The inferance here is that the differences that exist in time of flowering among varieties within a genotype are allelic and that different

alleles differ in response to temperature, some alleles being more temper-



296



J. R. QUINBY



ature sensitive than others. If this is true, it is logical to assume that the

four maturity gene loci control response to photoperiod and that alleles

that differ in temperature response influence the response to photoperiod

differently. How photoperiod and temperature interact to control time

of floral initiation is still not known, but it seems obvious that both

photoperiod and temperature operate through the same gene loci.

As shown in Table XIV, interaction of dominants and recessives

at four gene loci result in times of flowering that spread from 44 to 90

days. Because only four gene loci have been found and because multiple

allelic series must exist at each locus, it seems unnecessary to assume

the existence of numerous gene loci to account for the continuous variation seen in time of flowering in the sorghum species.

Winter and spring growth habits in cultivated barley, Hordeum

sativum Jess., have been attributed to 3 gene loci by Takahashi and

co-workers in work that has been reviewed by Takahashi (1955).

Variation in time of flowering among the varieties with spring growth

habit or differences in low temperature requirement for removal of the

winter nature were attributed to different multiple alleles of the spring

gene.

Barley is a long-day species whereas sorghum is a short-day species.

Nevertheless, the genetics of maturity in the two species is similar, and

it is likely that maturity in all plant species is controlled by a few gene

loci and allelic series at those loci.

X.



Influence



of Time of Floral Initiation on Plant Size



Under 10-hour photoperiods in the field at Chillicothe, 2-dwarf

genotypes of the Sooner 90, 60-day, 80-day, and 90-day Milos initiated

heads at the same time and flowered simultaneously. In this short-day

environment, the several genotypes were obviously similar in size and

were quite small. Under 14-hour photoperiods, the four genotypes were

quite dissimilar in size, the earliest in maturity being the smallest and

the latest, the largest. Part of the data obtained from a planting at

Chillicothe, Texas, in 1944 is shown in Table XVI. The data show that

dominance in the 90-day genotype Ma, Ma, ma3M a , as contrasted to

recessiveness at the first locus in the SM90 genotype, ma1 Ma, ma3Ma,,

increased duration to flowering by 53 days, leaf number by 92 percent,

height by 77 percent, and more than doubled total dry weight of plant.

When growing conditions are favorable, there is correlation of early

maturity with low yield and late maturity with high yield. The positive

regression of grain yield on maturity in sorghum hybrids has been discussed by Dalton (1967). In most tests under favorable conditions, each

increase of one day in duration to flowering increases grain yield by



297



MATURITY GENES OF SORGHUM



TABLE XVI

Influence of Dominance or Recessiveness a t Locus 1 on Plant Growth in Milo

Grown under Normal Photoperiods a t Chillicothe, Texas, from a Planting Made

on June 20, 1944a

Genotype

Parameter



mu1Mazma,Ma4



MalMazmasMaa



Number of days to anthesis

Number of leaves

Height of plant, cm.

Length of leaf, cm.

Weight of heads, g.

Weight of plant, g.



49

16

86

54

109

195



102

32

152

78

122

440



Data from Quinby and Karper (1945).



about 100 to 200 pounds of grain per acre. Because of this regression,

days to flower must be considered in evaluating hybrids using the results

of yield trials.

XI.



Maturity Gene Loci and Heterosis



No critical data exist in sorghum to show that hybrids grow faster

than varieties, but it has been shown that hybrids grow to be more than

50% larger than parent varieties in a few days less time (Quinby, 1963).

For this reason, it is reasonable to assume that rate of cell division must

be greater in hybrids.

Greater tillering is a manifestation of heterosis in sorghum (Quinby,

1963), and heterozygosity at one maturity locus has been reported to

cause greater tillering and greater head yield (Quinby and Karper,

1946). Some of the data are presented again in Table XVII. In 1942,

plants in a row segregating only for maturity were harvested and grown

the next year to identify the homozygous and heterozygous plants. The

TABLE XVII

Effect of Heterozygosity a t Locus 1 on Time of Flowering, Amount of Tillering, and

Weight of Heads of Homozygous and Heterozygous Milo Plants a t

Chillicothe, Texas, in 1942c

~



Genotype



_



_



_



_



Days to

flower



Number of

stalks

per plant



Head weight

per plant

(9)



95

93



1.7

2.7



150

240



MalMalMa2M(~ma3ma3Ma*Mu~

MalmalMa&azma3ma3Mafia4



~



Data from Quinby and Karper (1946).



~~



_



~



~



~



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IX. Allelic Series at the Maturity Gene Loci

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