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IV. Effect of Environment on Time of Flowering

IV. Effect of Environment on Time of Flowering

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272



J. R. QUINBY



Keulemans (1959) subjected two temperate zone and two tropical zone

varieties to 10-hour and normal photoperiods. All four varieties initiated

floral buds and flowered quickest in short days and tropical varieties

flowered later under long days than temperate zone varieties. To show

the influence of short-day treatment on time of floral initiation, data

from Lane (1963) are shown in Table 111.

TABLE I11

Influence of Photoperiod on Time of Floral Initiat'ion in Milo Genotypes"

Days to floral initiation

Genotype



10-hour days



14-hour days



SM90

60M

80M

lOOM



19

19

19

19



35

38

44

70



Data from Lane (1963).



In addition, Lane (1963) determined the length of the light period,

or critical photoperiod, needed to delay the floral initiation of four Milo

genotypes. The critical photoperiods of four Milo genotypes are shown

in Table IV, which was made from information published by Lane. All

four genotypes eventually flowered in continuous light. A difference in

TABLE IV

Critical Photoperiods of Milo Maturity Genotypesa

~



~~



Genotype



Day length necessary to

delay floral initiation



SMSO

60M

80M

lOOM



13 .O

12.5

12.5

12.0



Data from Lane (1963).



day-length treatment of half an hour was not short enough to separate

the 60M and 80M genotypes. These data show that different critical

photoperiods account for different times of flowering in sorghum. The

difference of 1 hour in critical photoperiod that distinguishes SM90 from

lOOM results in a difference of more than 30 days in time of flowering of

the two genotypes in the field in Texas.



273



MATURITY GENES OF SORGHUM



B. INFLUENCE

OF TEMPERATURE

Temperature affects duration of growth by influencing photoperiod

response, which in turn influences time of floral initiation. Under field

conditions in Texas, flowering of some varieties is hastened and of others

is delayed at higher elevations where night temperatures are lower.

Hegari, Early Hegari, and 100M, 60M, and SM60 Milos were grown

from earIy June plantings for many years at Chillicothe, Texas, and for

several years at Plainview, Texas, and their times of flowering were

observed. The two locations are at practically the same latitude so their

photoperiods are similar, but the two locations are separated by about

500 meters in elevation, which causes night temperatures to be about

2°C. lower at Plainview. The average minimum night temperature at

Plainview in June is about 16°C. The Hegaris and 1OOM Milo are

TABLE V

Influence of Temperature on Time of Flowering in Sorghum

Usual days to flower



Variety



Chillicothe



Plainview

(2'C. lower

temp.)



Hegari

Early Hegari

lOOM Milo

60M Milo

SM60 Milo



78

71

100

66

52



68

62

90

66

60



Influence of

lower temperature

on flowering

Hastened

Hastened

Hastened

Little change

Delayed



hastened in maturity at the higher elevation, 60M Milo is influenced

only slightly, but SM60 Milo flowers later at Plainview than at Chillicothe. To show this influence of temperature on flowering, some figures

are given in Table V.

It is apparent from information published earlier (Quinby and Karper, 1945) and from that already presented here that maturity in sorghum

is controlled by the genotype of the variety and that the expression of

the maturity genes is influenced by both photoperiod and temperature.

The influence of all three variables is apparent in the data shown in

Table VI where the duration to flowering of several varieties at Kingston,

Jamaica, and at Chillicothe, and Plainview, Texas, is presented. These

figures show that the very earliest varieties cannot be influenced very

greatly by the environment, that photoperiod-sensitive varieties whose

critical photoperiods have been met are early in maturity, and that a

variety like Feterita, FC811, even though it is known to be sensitive to



274



J. R. QUINBY



photoperiod at Chillicothe, Texas, is earlier at Plainview and Chillicothe

than at Kingston, Jamaica. Presumably, interactions between genotype,

temperature, and photoperiod bring about this result.

The sensitivity or insensitivity to photoperiod of several varieties

and hybrids was determined at Chillicothe, Texas (Quinby and Karper,

1947). Several varieties were found to be quite sensitive to photoperiod

as they all initiated heads 23 days from planting under 10-hour days,

but others were less sensitive and Japanese Dwarf Broomcorn was quite

TABLE VI

Effect of Environment on Days to Flowering of Certain Sorghum Varieties Grown in

Kingston, Jamaica, and a t Chillicothe and Plainview, Texas

Days to flower



Variety

38M Milo

SM60 Milo

60M Milo

lOOM Milo

Hegari

Combine Kak-60

Feterita FC811

Combine 7078



Kingston,

planted

Nov. 3, 1961



Chillicothe,

planted

May 25, 1961



Plainview,

planted

June 1, 1965



44

49

51

53

46

56

57

54



44

56

66

104

76

62

56

62



44

63

64

92

60

64

56

62



insensitive. The inference is that the thermal requirements of the sensitive varieties had been met, those of the less sensitive varieties had been

partially met, and those of insensitive varieties had not been met. Sensitivity to photoperiod was found to be dominant in inheritance, as all

hybrids with one sensitive parent were sensitive to photoperiod. Some

excerpts from the Chillicothe data are shown in Table VII.

Ayyangar et al. (1937) in India studied the inheritance of a gene that

caused “tall-late’’ plants in sorghum and assigned the symbol In in to the

factor pair. In their study, earliness was dominant to lateness. Their

studies were made in southern India during the rabi, or winter, season,

and the reversal of dominance is thought to be the result of the environment because In and M a , are likely to be the same gene.

Varieties bloom at slightly different times from year to year, and it is

apparent that differences of only 1 or 2°C. influence the time of floral

initiation. In June at Chillicothe, night temperatures are too high for

earliest floral initiation of some varieties, particularly Hegari and Early

Hegari.



275



MATURITY GENES OF SORGHUM



Coleman and Belcher (1952) have presented data that show the

influence of photoperiod and temperature on the flowering of five sorgo

varieties. The five varieties were grown at Meridian, Mississippi, in the

summer and at Canal Point, Florida, from several planting in the winter.

TABLE VII

Effect of Photoperiod on Time of Flowering of Sorghum Varieties

at Chillicothe, Texas, in 1941"

Days to flower

Variety



10-hour day



Texas Milo

Hegari

Feterita

Blackhull Kafir

Japanese D. Broomcorn

a



14-hour day



47

47

56

59

68



Data from Quinby and Karper (1947).



A small part of the data is shown in Table VIII. Hod0 is the latestmaturing variety in the summer but is an early-maturing variety in the

winter. Collier is of intermediate maturity in the summer but is much the

latest-maturing variety in the winter. Their data indicate that the thermal

requirements of a variety must be met before response to photoperiod

TABLE VIII

Days from Planting to Anthesis of 5 Sorgo Varieties at Meridian, Mississippi,

in the Summer and a t Canal Point, Florida, in the Wintera

Days from planting to anthesis



Variety



Meridian,

spring planting



Waconia Amber

Leoti

Collier

Honey

Hod0

a



60

67

88

98

108



Canal Point,

Dec. 6, 1948 planting

68

78

114

75

74



Data from Coleman and Belcher (1952).



can be manifested and that there are differences between varieties in

sensitivity to temperature. The cool weather in the winter in Florida did

not prevent early floral initiation of Honey and Hod0 even when the

daily mean temperature was below 70°F.

The optimum temperature for growth and the favorable temperature

for early floral initiation in sorghum are obviously different. Martin



276



J. R. QUINBY



(1941) has concluded that 45 to 50°F. is the minimum temperature for

germination and that 60°F. is the minimum for subsequent growth. The

optimum temperature for growth is not known, but Martin believes it to

be between 88 and 98°F. July temperatures of 80" to 85°F. have resulted

in record high yields. Temperatures above 100°F. are thought by Martin

to be detrimental to growth.

Floral initiation is the culmination of meristematic growth that consists largely of cell division. The grand period of growth in sorghum

follows the formation of a floral bud and consists largely of cell enlargement. The biochemical steps that lead to differentiation of a floral bud

are retarded by night temperatures as high as 70°F. that accompany

day temperatures as high as 88 to 98°F. at Chillicothe, Texas, which are

favorable for cell enlargement.

Stickler et al. (1962) were interested in the influence of temperature

on germination and seedling growth. Seeds of Kaoliangs that are native

to the high latitude of Manchuria germinated quicker and the seedlings

grew more rapidly than those of several other varieties. Their study and

those of Evans et al. (1961) were not concerned with the influence of

temperature on time of floral initiation but do show a difference in

response of sorghum varieties to temperature during germination and

the early stages of vegetative growth.

Critical data for sorghum to show a difference in response to temperature that influences time of floral initiation would be welcome.

Fryer et at. (1W)have recently reported the influence of temperature

on anthesis date in sorghum at 8 locations in Kansas using 6 varieties and

4 planting dates during 5 years. Their conclusions were that day-time

temperatures above 70°F. during the first 30 days of growth hastened

maturity, as did 80°F. temperatures after the first 30 days. Nighttime

temperatures in the 60's retarded maturity, but nighttime temperatures

either below 60°F. or above 70°F. hastened maturity. They could not

predict time of flowering with precision, using any of their temperaturesummation variables. Ranges in average temperature were quite limited,

and it was impossible to detect clear-cut differences among varieties in

response to temperature. They assumed that the time of flowering in

their studies depended chiefly on temperature. In view of the fact that

the varieties in their study were chosen because of differences in time of

flowering, genetic differences between the varieties must also have been

influencing their results. Based on a different assumption, their data

might have been analyzed and interpreted differently.

Hutchinson (1965) is of the opinion that numerous genes are involved

in determining maturity in sorghum because the distinct maturity classes

found in segregating populations in temperate zones do not always occur



MATURITY GENES OF SORGHUM



277



in the tropics. However, Ayyangar et al. (1937) did observe a simple

segregation for maturity at Coimbatore, India, although dominance was

the reverse of that observed in Texas. Furthermore, in the tropics, where

day length is below the critical photoperiod of most varieties, segregation for maturity similar to that observed in Texas in the summer would

not always be expected.

Because nights in the tropics are long enough to satisfy the photoperiod requirement of most varieties, the differences in maturity among

many tropical varieties must be due to a difference in temperature

response. The situation is the same in the temperate zone where differences in time of flowering among varieties with high critical photoperiods due t o being recessive ma, are caused by differences in response

to temperature.

However, Lane (1963) showed that differences in critical photoperiod as small as 30 minutes cause digerences in time of flowering.

Undoubtedly, some tropical varieties differ from one another in critical

photoperiod by as much or more than 30 minutes, and it is reasonable

to assume that differences in maturity in sorghum in the tropics, as in the

temperate zones, are due to differences in response to both photoperiod

and temperature.

Tropical varieties are being converted to early maturity and short

stature at Plainview, Texas, and Kingston, Jamaica, by backcrossing to

the tropical parent. The F, populations are grown in Texas, and simple

segregations for both maturity and height always occur.

V.



Control of l e a f Number by Time of Floral initiation



In sorghum, leaves continue to be laid down in the meristem until a

floral bud is initiated. If floral initiation is delayed, more leaves are

formed. Sieglinger (1936) first pointed out the relationship between leaf

number and maturity and observed that an additional leaf delayed heading by about 3 days. Sieglinger’s data also showed that varieties of about

the same maturity have different numbers of leaves indicating a difference in the rate at which varieties initiate leaves.

Keulemans (1959) found that successive leaves are laid down in the

meristem in 3 or 4 days. According to Tarr (1962), Reznik (1934) found

5 embryonic leaves in sorghum. Young (1950) examined the embryos of

Sooner Milo seeds microscopically and found 7 leaves in the seeds

before germination. L. E. Clark of the Texas Agricultural Experiment

Station in a personal communication told me that he found either 6 or

7 leaves in the embryos of seeds of Combine Kafir-€@, and the higher

number was found in the more mature seeds.

This information, along with data on number of leaves and time of



278



J. R. QUINBY



floral initiation, allows an estimate of the time needed for a sorghum

plant to lay down a leaf in the meristem. Table IX has been prepared

using data from Chillicothe (Quinby and .Karper, 1947). The figures

indicate that 3 to 6 days elapse between the differentiation of successive

TABLE IX

Usual Time Needed to Lay Down a Leaf in the Meristem of Sorghum

Assuming 7 Leaves in the Embryo"

Number of leaves



Variety

Sooner Milo

Texas Milo

Hegari

Kalo

Calif. W. Durra

Spur Feterita

Freed

Manko

Bishop

Sumac

Blackhull Kafir

Jap. D. Broomcorn

0



Number of

days to head

initiation



Total



32

39

48

39

34

36

32

47

39

39

39

39



13

18

18

17

14

19

12

17

17

16

16

15



Produced

after

germination

6

11

11

10



7

12

5

10

10

9

9

8



Days per

leaf

5

4

4

4

5

3

6

5

4

4

4

5



Data from Quinby and Karper (1947).



leaves in the meristems of growing sorghum plants. Obviously, some

varieties lay down leaves in the meristem faster than others. According

to Collier ( 1963), a sorghum seed is physiologically mature in 30 days,

more or less. Because embryonic leaves number 6 or 7 , leaves in the

embryo must be laid down at about the same rate as in the meristem.

VI.



Interaction of Maturity Genes in the Milos and Hegari



Dominants and recessives at the four maturity gene loci differ in

their effects on time of flowering and have important interactions. The

information in Tables I and I1 justifies the following conclusions about

the interaction of maturity alleles in the Milos and Hegari.

Dominant M a , interacts with dominants Ma,, Ma,, and M a , to

produce lateness. A strain dominant at all loci or even at only M a , and

Ma, could be considered to be tropical varieties. Extreme lateness never

occurs unless M a , and M a , are both dominant. Recessive ma, causes

earliness regardless of the dominant condition at the other three maturity

loci.



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