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Relationship of yield components of main culms and tillers of grain sorghum
Field Crops Research, 8 (1984) 125--133
125
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
RELATIONSHIP OF YIELD COMPONENTS OF MAIN CULMS AND TILLERS OF GRAIN SORGHUM
H.A. BRUNS 1 and R.D. HORROCKS a
Department of Agronomy, University of Missouri, Columbia, M O 65201 (U.S.A.) tPresent address: Department of Agronomy, University of Maryland, College Park, MD 20740, U.S.A. 2Present address: Department of Agronomy and Horticulture, Brigham Young University, Provo, UT 84602, U.S.A. Journal Series No. 8651, Missouri Agricultural Experiment Station (Accepted 6 September 1983) ABSTRACT Bruns, H.A. and Horrocks, R.D., 1984. Relationship of yield components of main culms and tillers of grain sorghum. Field Crops R es., 8 : 1 2 5 - - 1 3 3 . An experiment was conducted in 1974 and 1976 at Columbia, MO (U.S.A.) to assess the relationship of grain yield components of main culms and lateral tillers of grain sorghum (Sorghum bicolor (L.) Moench.). TiUering was regulated by removing differing numbers of tillers at three stages of development (8-leaf, flag leaf visible, and 50% anthesis). Four levels of tillering were allowed at each stage: 0, 1, 2, and a variable number (control) of tillers per plant. Number of kernels produced by and weight of grains from main culm panicles decreased as number of tillers allowed to develop increased (15 and 9%, respectively). When increased intraplant competition interacted with moisture deficiency in late-planted plots, the deleterious effect on these components was exacerbated (19 and 12%, respectively). Yet, with increased competition, declines in number of kernels produced by main culm and kernal weight of grain from main and lateral tillers was more than compensated for by the total number of kernels produced. Time of tiller removal was important to main culm yield component expression if all tillers were removed. For number of kernels it was necessary to remove all tillers at the 8-leaf stage of development if a significant increase over the other removal treatments was to occur. On the other hand, kernel weight was not affected significantly unless removal was delayed until 50% anthesis. Allowing only one tiller to develop provided sufficient intraplant competition to negate any advantage in time of tiller removal within wach treatment. Yield components of lateral tillers were unaffected by removal of excess tillers at various stages of development.
INTRODUCTION
In crop plants of the Poaceae family development of the various components of grain yield (number of ears per unit area, number of kernels per ear, and weight per kernel) is affected by stress from the environement. But
0378-4290/84/$03.00
© 1984 Elsevier Science Publishers B.V.
126
because of the compensatory nature of these components, grain yield of sorghum (Sorghum bicolor (L.) Moench) usually remains relatively constant within a given environment (Bartel et al., 1935; Stickler and Pauli, 1961; Stickler and Wearden, 1965; Karchi and Rudich, 1966). The interrelationshipof yield components of main culms and tillers in sorghum is not well documented. The few reports to consider this matter have studied the effect of induced environmental stress on grain weight or number of grain produced per plant, not distinguishing the tillers from the main culms. For example, Fischer and Wilson (1975) reported that removal of neighboring plants at 10--15 days after floral initiation increased the number of grains per inflorescence 1.8- and 3.4-fold in medium and high density populations respectively, but removal at pre- and post-anthesis had little effect. On the other hand, removal at either of the latter two stages resulted in a 1.5-fold increase in grain weight. Castleberry et al. (1972) also reported that reduced post-anthesis competition resulted in a 17% increase in kernel weight. Numerous works have been published with regard to these relationships in small grains (Puckridge, 1968; Evans et al., 1972; Walpole and Morgan, 1973; Jones and Kirby, 1977; Kirby and Jones, 1977; Scott et al., 1977; Mohamed and Marshall, 1979; Frank, 1980) which, when coupled with additional sorghum research, will be useful in understanding the phenomena in grain sorghum. The purpose of this study was to further investigate the effects of tiller removal under varying conditions on yield components of both main culms and tillers. MATERIALS AND METHODS
This study was conducted at the University of Missouri's Agronomy Research Center near Columbia, MO in 1974 and 1976. Soil type was a Udollic Ochraqualf (Mexico silt loam ). Northrup-King grain sorghum hybrids 'NK277' and 'Savanna 2' were planted during two period each year: (1) the 1st week in May; and (2) 4 - 5 weeks thereafter. Individual plots consisted of four rows spaced 76 cm apart and 6 m long. Samples were drawn only from the two center rows. Uniform stands were obtained by over planting and subsequent hand thinning and transplanting to achieve a withing-row plant spacing of 38 + 8 cm (70176 plants ha-l). This plant density is approximately one half the recommended rate for the area (Cloninger et al., 1972) and was chosen to encourage filleting. Detillering treatments were removal of: (1) all lateral tillers (TR0); (2) all but one lateral tiller (TR1); (3) all but two lateral tillers (TR2); and (4) no lateral tillers (control, TRC). Each TR treatment was imposed at stages 3 (8 leaves), 4 (flag leaf visible in the whorl) and 6 (50% anthesis; Vanderlip and Reeves, 1972). New tiller growth was removed as it appeared after initiation of each treatment. At maturity, panicles of five randomly selected plants from each plot were
127 were harvested, weighed and dried at 55 ° C, reweighed, threshed, and the grain was cleaned. Weights were recorded for the grain and a 100-kernel sample. The number of kernels per panicle was determined from these data. This study was arranged experimentally as a split-split-plot with three replications. Planting dates were considered as main plot, hybrids as subplot, and tiller removal treatments as sub-sub-plot. When analyses were performed over years an additional split (in time) was added to the model. Procedures in line with basic assumptions of randomness required for analyses of variance were practised in designing and laying out the experiments. Statistical analyses were accomplished using Statistical Analysis Systems (SAS) programs compiled for a 4341 IBM c o m p u t e r (Helwig and Council, 1979). Significant differences mentioned t h r o u g h o u t the paper are at 0.05 alpha level. RESULTS AND DISCUSSION
Statistical significance None of the three- and four-way interactions were significant. Of the several possible two-way interactions the following were significant: date-ofplanting, season, and time-of-tillering removal × degree-of-tiller-removal. The only main effect means presented will be for hybrids, since all others were involved in significant interactions.
Seasons Grain sorghum is well adapted to central Missouri, particularly when precipitation patterns and amounts approximate the normal. Monthly precipitation amounts and deviations from normal are shown in Table I for the growing seasons of 1974 and 1976. The continuous deficit in 1974 preTABLE I Monthly precipitation and deviation from normal during the 1974 and 1976 growing seasons at Columbia, MO, U.S.A. Month
Precipitation(mm)
1974 May June July August Total
Deviation from normal
1976
Deviation from normal
93.5 45.5 6.1 5.4
--25.4 --71.1 --92.7 --74.6
196.9 149.6 36.3* 192.2
+78.0 +33.0 --62.5 +111.2
150.5
--264.8
619.4
204.1
*Irrigated 14 July (19.0 ram) and 16 July (25.4 ram).
128
vented normal plant development. In addition, an early fall frost abruptly stopped growth in early October of that same year. To prevent similar moisture stress from occurring in 1976, supplemental irrigation was applied on 14 and 16 July. Each irrigation was limited to 26 mm or less so as to not exceed the infiltration rate of the soil.
Main culm grain. Because of limited precipitation in 1974, the number of kernels did not differ for treatments with 0, 1, or 2 tillers per plant (Fig. la). Where unlimited tillering was allowed, the control or variable tiller treatment, the decline in number of kernels was large but kernel weight did not change. This indicates that interplant competition and insufficient moisture limited grain set and grain size. Precipitation amount and pattern in 1976 was considerably improved, and by contrast there was a progressive fall in both kernel number and weight as the number of tillers per plant increased. MAIN CULMS
60 -.
X
5,0 -
4.0-
~
3.0
-
0
-
19'47
Number Weight
~LSD J"
=030
2
Variable
:A
15
.'(0 ()
55
~
LATERAL TILLERS
tr ill
Number .....
Z
25
- 20
.........
tr UJ
I.L 0
=013
~"-. 1974 . . . . . . . . . . . . . _'::.==.~.=c . . . . . . . . . . . ~ --
~o --.I
w Z
• 30
"r ILSD
Iii Z
"4 0 0
- 3.0
I.L 0
i--
1974 ~
"7"
Weight
~'~
4.5
2.5
~
V "0'' C-.---ILSO ""?~
25
ILSD
1"
1.5
1974~-~~
B
o NUMBER
OF TILLERS
Fig. I. N u m b e r and weight of kernels from (A) main culm and (B) lateral tillerpanicles as influenced by growing season. Least significant difference (LSD) vMues were calculated for the year X degree-of-tiller-removalinteraction, thus they apply to all values within each variable.
129 If one tiller was present main culms produced 10% fewer kernels, two tillers effected a reduction of 12%, and variable tiUering (control) declined 15%.
Lateral tiller grain. The effect of environment on lateral tiller grain production and kernel size is shown in Fig. l b . In both seasons, as n u m b e r of lateral tillers allowed to develop per plant increased, the total n u m b e r of kernels produced by these tillers increased significantly. However, counteracting this increase was a decline in kernel weight of 52% in 1974 and 10% in 1976. The precipititous drop in 1974 was largely due to an early frost which arrested further development. Because of increased competition in the unrestricted tillering plots, lateral tiller grain was approximately 4--5 days later in development than other treatments. Since environmental control is nearly impossible in field studies, the decline in yield c o m p o n e n t expression in this study cannot be fully explained, but it appears to us that moisture stress is responsible. There is ample evidence that stress of any type causes a decrease in individual yield components. For example, Fischer and Wilson (1975) showed that additional competing sorghum plants at post-floral initiation resulted in large decreases in grain n u m b e r and weight. Other research with wheat and barley have also shown that environemntal stress at critical times will result in significant reductions in these components (Puckridge, 1968; Jenner, 1979; Fischer and Stockman, 1980; Frank, 1980; Lawlor et al., 1981). Cultivars The influence of cultivars on number if kernels per panicle and kernel weight of grain is presented in Table II. Savanna 2 produced significantly more kernels on the main culms than NK277 (8.6%), but there was no difference in kernel weight. The two cultivars differed significantly in the n u m b e r of kernels produced by lateral tillers; Savanna 2 produced 24% more kernels on fewer tillers, than did NK277. (The average number of tillers per plant was 2.45 and 2.75, respectively). But just as was the case with main culms, the weight of lateral tiller kernels did not differ significantly. TABLE II Number and w e i g h t s o r g h u m cultivars. Cultivar
NK277 Savanna 2
o f kernels
produced by main culm
and lateral tiller panicles
of two
1 0 0 - K e r n e l Weight (g)
Number of Kernels
Main Culm*
Lateral Tillers*
Total*
Main Culm*
Lateral Tillers*
Mean*
3506 b 3806 a
2361 b 2929 a
5867 b 6735 a
2.48a 2.44 a
1.49 a 1.55 a
1.98 a 2.00 a
* V a l u e s w i t h i n a c o l u m n f o l l o w e d b y t h e same letter do n o t differ significantly (~ = 0 . 0 5 ) .
130
Date of planting Main culm grain. With respect to planting date, the main effect showed significant differences (e = 0.05), but there were no significant interactions with other factors. Fig. 2a is presented to emphasize the linear decline, at both planting dates, in number of kernels and kernel weight of grain from main culm panicles as number of tillers allowed to develop increased. Delaying planting until June resulted in an average of 12.7% fewer and 9.5% lighter kernels over the four tillering levels. MAIN CULMS
-3.0
6.0TLSD
=0.09
-2.5
5.0-
................................. -~un-~ -2,0
4.0-
X
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.~ iii Z
n-
- -
Number
........
Weight
A
I"0 6
1
U5.0-
........
4.0-
- 3.0
........
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-2.5
--'~
LSD ~ 064
o 0
0 /
Weight
I
.-I W Z rt" W ~"
U.
S
-- Nurnbe'
ca
Variable
2
LATE.AL,,LLE
0
Z
~021
oi"
W
£E W
- 15 TLSD
June
3.0 -
- 2.0
T
B ,
0 1"
0
1
2
I" 0
Variable
NUMBER OF TILLERS
Fig. 2. Number and weight of kernels from (A) main culm and (B) lateral tiller panicles as influenced by planting date. Least significant difference (LSD) values were calculated for the date-of-planting × degree-of-tiller-removal interaction, thus they apply to all values within each variable.
Lateral tiller grain. As more tillers were allowed to develop, the total number of kernels produced by lateral tillers increased significantly (Fig. 2b). Planting in early May resulted in a 126% increase while planting in mid-June yielded an 80% increase. The development of more than two tillers did not enhance
131
total number of kernels produced when environmental stress was encountered in late-planted plots. This implied decrease in number of kernels per lateral tiller panicle with increased intraplant competition is typical of responses shown by other grasses in stress situations (Puckridge, 1968; Fischer and Wilson, 1975; Jenner, 1979; Fischer and Stockman, 1980; Frank, 1980; Lawlor et al., 1981). Regardless of whether planting occurred in early May or mid-June, kernel weight of lateral tiller grain declined by approximately 32% as competiion from additional tillers increased (Fig. 2b). These responses re-emphasize the importance of competition and stress in the expression of yield components. The greater the environmental stress (later planting} the more pronounced was the effect on number of kernels per panicle or plant and kernel weight. Tiller removal Number of kernels. The effect of tiller removal on kernel development on main culms is evident in Fig. 3. If competition effects were restricted by removing all tillers (TR0), then early removal was important. For example, removal of all tillers at the 8-leaf stage of development resulted in significantly more kernels being produced than if removal was delayed until the flag leaf was visible in the whorl -- a 10% decline. Thereafter, delaying tiller removal further resulted in a small decrease in number of kernels produced. 4.5
4.5 --
Number
.........
Weight
--
TRO
gO
4.0
4.0
X
._J LU Z
TFt2
~o .J
ILl
z rr
rr" 3.5
TRC
ILl LL
O rr
3.5 ---> -
-
-
-
-
~
~
0 0
3.0
-3.0
nI L S Dffi0 15
UJ
TR0 • 2.5
~---EZ . . . .
- - -- ~ ,
U.
0
l-"r"
2.5 Z
UJ
W
TRC TR2
o1"
Y
8-ieaf
flag'leaf in whorl
1"o
5'0% anthe~is
STAGE OF DEVELOPMENT
Fig. 3. N u m b e r and w e i g h t o f kernels f r o m main c u l m panicles as a f f e c t e d b y time and degree o f tiller removal ( T R 0 = 0 tiller remaining; T R 1 = I tiller; T R 2 = 2 tillers; TRC = u n c h e c k e d tillering or c o n t r o l ) . Least significant d i f f e r e n c e ( L S D ) values were calculated for the time-of-tiller-removal × degree-of-tiller-removal interaction, thus t h e y apply t o all values w i t h i n each variable.
132
Looking at the other individual lines where tillers were removed at the three stages of development (TR1 and TR2), it is evident that time of removal had no significant effect on number of kernels produced. It is important to note that under the conditions of this experiment, development of one tiller was sufficient to preclude any advantage of early tiller removal. Considering the situation where a differing number of tillers remained at the 8-leaf stage, we found an average decline, from TR0, of 12% in number of kernels produced by main culms if one tiller was present (TR1), a 15% decline if two tillers were present (TR2), and a 25% decline if unchecked tillering was allowed (TRC). When tiller removal was delayed until the flag-leaf stage, presence of one or two tillers (TR1 and TR2) resulted in approximately 7.5% fewer kernels. Control plants (TRC), because of unrestricted competition from tillers, produced significantly fewer kernels on main culms than other treatments. This is in accordance with the sorghum work of Castleberry et al. {1972) and Fischer and Wilson (1975) and the wheat studies by Puckridge (1968), Jenner (1979) and Mohamed and Marshall (1979). The total number of kernels produced by lateral tillers was not influenced by the stage of development at which tiller were removed.
Kernel weight. Interaction of number of tillers remaining and time of tiller removal was significant for main culm grain weight (Fig. 3). As the stage of development at which tillers were removed was delayed, removing all tillers (TR0) resulted in a linear increase in kernel weight. Other treatments (TR1 and TR2), however, maintained relatively constant kernel weights over time regardless of the relationship between time of floret initiation, approximately the 8-leaf stage of development (Castleberry et al., 1972) and competition among tillers. If tillers were not removed at the 8-leaf stage, thus ustaining higher competition, fewer florest were initially set. In those treatment where all tillers were initially at the flag-leaf or 50% bloom stage, fewer kernels had access to more photosynthates, thus larger kernels developed. Castleberry et al. {1972) similarly reported that grain sorghum responded to reduced competition with a 17% increase in kernel weight. Kirby and Jones (1977) and Walpole and Morgan (1973) have salso shown that lessened competition will result in an increase in the size of kernels formed by barley and wheat, respectively. Weight of kernels from lateral tillers was not influenced by time of tiller removal. REFERENCES Bartel, A.T., Martin, J.H. and Hawkins, R.S., 1935. Effects of tillers on the development of grain sorghum. J. Am. Soc. Agron., 27: 707--714. Castleberry, R.M., Eastin, J.D. and Clegg, M.D., 1972. The effects of thinning at specific growth stages on yield and yield components of sorghum. In: The Physiology of Yield and Management of Sorghum in Relation to Genetic Improvement. Annu. Rep. 6, Agricultural Experiment Station, University of Nebraska, Lincoln, NE, pp. 23--39.
133
Cloninger, F.D., Horrocks, R.D. and Heatherly, L.G., 1972. Missouri Crop Performance, 1972. Part If, Grain Sorghum. Spec. Rep. 149, Agricultural Experiment Station, Uni-
versityof Missouri,Columbia,M0, pp. 52--64. Evans, L.T., Bingham, J. and Roskams, M.A., 1972. The pattern of grain set within ears of wheat. Aust. J. Biol. Sci.,25: 1--8. Fischer, R.A. and Stockman, Y.M., 1980. Kernel number per spike in wheat (Triticum aestivum L.) responses to preanthesis shading. Aust. J. Plant Phys., 7 : 169--180. Fischer, K.S. and Wilson, G.L., 1975. Studies of grain production in Sorghum bicolor (L. Moench). IV. Some effects of increasing and decreasing photosynthesis at different stages of the plant's development on the storage capacity of the inflorescence. Aust. J. Agric. Res., 26: 25--30. Frank, R., 1980. Grain yield and ear development of spring barley as influenced by environmental conditions during early stages of plant development. Biol. Plant. (Praha), 22: 274--281. Helwig, J.T. and Council, K.A. (Editors}, 1979. SAS user's guide. SAS Institute Inc., Cary, NC, 494 pp. Jenner, C.F., 1979. Grain-filling in wheat plants shaded for brief periods after anthesis. Aust. J. Plant Physiol., 6 : 629--641. Jones, H.G. and Kirby, E.J.M., 1977. Effects of manipulation of number of tillers and water supply on grain yield in barley. J. Agric. Sci. (Camb.), 88: 391--397. Karchi, Z. and Rudich, Y., 1966. Effects of row width and seeding spacing on yield and its components in grain sorghum grown under drylandconditions. Agron. J., 58: 602--604. Kirby, E.J.M. and Faris, D.J., 1972. The effect of plant density on tiller growth and morphology in barley. J. Agric. Sci. (Camb.), 88: 381--389. Kirby, E.J.M. and Jones, H.G., 1977. The relations between the main shoot and tillers in barley plants. J. Agric. Sci. (Camb.), 88 : 381--389. Lawlor, D.W., Day, W., Johnston, A.E., Legg, B.J. and Parkinson, K.J., 1981. Growth of spring barley under drought: crop development, photosynthesis, dry-matter accumulation and nutrient content. J. Agric. Sci. (Camb.), 96: 167--186. Mohamed, G.E.S. and Marshall, C., 1979. Physiological aspects of tiller removal in spring wheat. J. Agric. Sci. (Camb.), 93: 457--463. Puckridge, D.W., 1968. Competition for light and its effect on leaf spikelet development of wheat plants. Aust. J. Agric. Res., 19: 191--201. Scott, W.R., Dougherty, C.T. and Langer, R.H.M., 1977. Development and yield components of high-yielding wheat crops. N.Z.J. Agric. Res., 20: 205--212. Stickler, F.C. and Pauli, A.W., 1961. Leaf removal in grain sorghum. I. Effects of certain defoliation treatments on yield and components of yield. Agron. J., 53: 99--102. Stickler, F.C. and Wearden, S., 1965. Yield and yield components of grain sorghum as affected by row width and stand density. Agron. J., 47 : 564--567. Vanderlip, R.L. and Reeves, H.E., 1972. Growth stages of sorghum (Sorghum bicolor (L.) Moench). Agron. J., 64: 13--16. Walpole, P.R. and Morgan, D.G., 1973. The effects of floret sterilization on grain number and grain weight of wheat ears. Ann. Bot., 37 : 1041--1048.
125
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
RELATIONSHIP OF YIELD COMPONENTS OF MAIN CULMS AND TILLERS OF GRAIN SORGHUM
H.A. BRUNS 1 and R.D. HORROCKS a
Department of Agronomy, University of Missouri, Columbia, M O 65201 (U.S.A.) tPresent address: Department of Agronomy, University of Maryland, College Park, MD 20740, U.S.A. 2Present address: Department of Agronomy and Horticulture, Brigham Young University, Provo, UT 84602, U.S.A. Journal Series No. 8651, Missouri Agricultural Experiment Station (Accepted 6 September 1983) ABSTRACT Bruns, H.A. and Horrocks, R.D., 1984. Relationship of yield components of main culms and tillers of grain sorghum. Field Crops R es., 8 : 1 2 5 - - 1 3 3 . An experiment was conducted in 1974 and 1976 at Columbia, MO (U.S.A.) to assess the relationship of grain yield components of main culms and lateral tillers of grain sorghum (Sorghum bicolor (L.) Moench.). TiUering was regulated by removing differing numbers of tillers at three stages of development (8-leaf, flag leaf visible, and 50% anthesis). Four levels of tillering were allowed at each stage: 0, 1, 2, and a variable number (control) of tillers per plant. Number of kernels produced by and weight of grains from main culm panicles decreased as number of tillers allowed to develop increased (15 and 9%, respectively). When increased intraplant competition interacted with moisture deficiency in late-planted plots, the deleterious effect on these components was exacerbated (19 and 12%, respectively). Yet, with increased competition, declines in number of kernels produced by main culm and kernal weight of grain from main and lateral tillers was more than compensated for by the total number of kernels produced. Time of tiller removal was important to main culm yield component expression if all tillers were removed. For number of kernels it was necessary to remove all tillers at the 8-leaf stage of development if a significant increase over the other removal treatments was to occur. On the other hand, kernel weight was not affected significantly unless removal was delayed until 50% anthesis. Allowing only one tiller to develop provided sufficient intraplant competition to negate any advantage in time of tiller removal within wach treatment. Yield components of lateral tillers were unaffected by removal of excess tillers at various stages of development.
INTRODUCTION
In crop plants of the Poaceae family development of the various components of grain yield (number of ears per unit area, number of kernels per ear, and weight per kernel) is affected by stress from the environement. But
0378-4290/84/$03.00
© 1984 Elsevier Science Publishers B.V.
126
because of the compensatory nature of these components, grain yield of sorghum (Sorghum bicolor (L.) Moench) usually remains relatively constant within a given environment (Bartel et al., 1935; Stickler and Pauli, 1961; Stickler and Wearden, 1965; Karchi and Rudich, 1966). The interrelationshipof yield components of main culms and tillers in sorghum is not well documented. The few reports to consider this matter have studied the effect of induced environmental stress on grain weight or number of grain produced per plant, not distinguishing the tillers from the main culms. For example, Fischer and Wilson (1975) reported that removal of neighboring plants at 10--15 days after floral initiation increased the number of grains per inflorescence 1.8- and 3.4-fold in medium and high density populations respectively, but removal at pre- and post-anthesis had little effect. On the other hand, removal at either of the latter two stages resulted in a 1.5-fold increase in grain weight. Castleberry et al. (1972) also reported that reduced post-anthesis competition resulted in a 17% increase in kernel weight. Numerous works have been published with regard to these relationships in small grains (Puckridge, 1968; Evans et al., 1972; Walpole and Morgan, 1973; Jones and Kirby, 1977; Kirby and Jones, 1977; Scott et al., 1977; Mohamed and Marshall, 1979; Frank, 1980) which, when coupled with additional sorghum research, will be useful in understanding the phenomena in grain sorghum. The purpose of this study was to further investigate the effects of tiller removal under varying conditions on yield components of both main culms and tillers. MATERIALS AND METHODS
This study was conducted at the University of Missouri's Agronomy Research Center near Columbia, MO in 1974 and 1976. Soil type was a Udollic Ochraqualf (Mexico silt loam ). Northrup-King grain sorghum hybrids 'NK277' and 'Savanna 2' were planted during two period each year: (1) the 1st week in May; and (2) 4 - 5 weeks thereafter. Individual plots consisted of four rows spaced 76 cm apart and 6 m long. Samples were drawn only from the two center rows. Uniform stands were obtained by over planting and subsequent hand thinning and transplanting to achieve a withing-row plant spacing of 38 + 8 cm (70176 plants ha-l). This plant density is approximately one half the recommended rate for the area (Cloninger et al., 1972) and was chosen to encourage filleting. Detillering treatments were removal of: (1) all lateral tillers (TR0); (2) all but one lateral tiller (TR1); (3) all but two lateral tillers (TR2); and (4) no lateral tillers (control, TRC). Each TR treatment was imposed at stages 3 (8 leaves), 4 (flag leaf visible in the whorl) and 6 (50% anthesis; Vanderlip and Reeves, 1972). New tiller growth was removed as it appeared after initiation of each treatment. At maturity, panicles of five randomly selected plants from each plot were
127 were harvested, weighed and dried at 55 ° C, reweighed, threshed, and the grain was cleaned. Weights were recorded for the grain and a 100-kernel sample. The number of kernels per panicle was determined from these data. This study was arranged experimentally as a split-split-plot with three replications. Planting dates were considered as main plot, hybrids as subplot, and tiller removal treatments as sub-sub-plot. When analyses were performed over years an additional split (in time) was added to the model. Procedures in line with basic assumptions of randomness required for analyses of variance were practised in designing and laying out the experiments. Statistical analyses were accomplished using Statistical Analysis Systems (SAS) programs compiled for a 4341 IBM c o m p u t e r (Helwig and Council, 1979). Significant differences mentioned t h r o u g h o u t the paper are at 0.05 alpha level. RESULTS AND DISCUSSION
Statistical significance None of the three- and four-way interactions were significant. Of the several possible two-way interactions the following were significant: date-ofplanting, season, and time-of-tillering removal × degree-of-tiller-removal. The only main effect means presented will be for hybrids, since all others were involved in significant interactions.
Seasons Grain sorghum is well adapted to central Missouri, particularly when precipitation patterns and amounts approximate the normal. Monthly precipitation amounts and deviations from normal are shown in Table I for the growing seasons of 1974 and 1976. The continuous deficit in 1974 preTABLE I Monthly precipitation and deviation from normal during the 1974 and 1976 growing seasons at Columbia, MO, U.S.A. Month
Precipitation(mm)
1974 May June July August Total
Deviation from normal
1976
Deviation from normal
93.5 45.5 6.1 5.4
--25.4 --71.1 --92.7 --74.6
196.9 149.6 36.3* 192.2
+78.0 +33.0 --62.5 +111.2
150.5
--264.8
619.4
204.1
*Irrigated 14 July (19.0 ram) and 16 July (25.4 ram).
128
vented normal plant development. In addition, an early fall frost abruptly stopped growth in early October of that same year. To prevent similar moisture stress from occurring in 1976, supplemental irrigation was applied on 14 and 16 July. Each irrigation was limited to 26 mm or less so as to not exceed the infiltration rate of the soil.
Main culm grain. Because of limited precipitation in 1974, the number of kernels did not differ for treatments with 0, 1, or 2 tillers per plant (Fig. la). Where unlimited tillering was allowed, the control or variable tiller treatment, the decline in number of kernels was large but kernel weight did not change. This indicates that interplant competition and insufficient moisture limited grain set and grain size. Precipitation amount and pattern in 1976 was considerably improved, and by contrast there was a progressive fall in both kernel number and weight as the number of tillers per plant increased. MAIN CULMS
60 -.
X
5,0 -
4.0-
~
3.0
-
0
-
19'47
Number Weight
~LSD J"
=030
2
Variable
:A
15
.'(0 ()
55
~
LATERAL TILLERS
tr ill
Number .....
Z
25
- 20
.........
tr UJ
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=013
~"-. 1974 . . . . . . . . . . . . . _'::.==.~.=c . . . . . . . . . . . ~ --
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• 30
"r ILSD
Iii Z
"4 0 0
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i--
1974 ~
"7"
Weight
~'~
4.5
2.5
~
V "0'' C-.---ILSO ""?~
25
ILSD
1"
1.5
1974~-~~
B
o NUMBER
OF TILLERS
Fig. I. N u m b e r and weight of kernels from (A) main culm and (B) lateral tillerpanicles as influenced by growing season. Least significant difference (LSD) vMues were calculated for the year X degree-of-tiller-removalinteraction, thus they apply to all values within each variable.
129 If one tiller was present main culms produced 10% fewer kernels, two tillers effected a reduction of 12%, and variable tiUering (control) declined 15%.
Lateral tiller grain. The effect of environment on lateral tiller grain production and kernel size is shown in Fig. l b . In both seasons, as n u m b e r of lateral tillers allowed to develop per plant increased, the total n u m b e r of kernels produced by these tillers increased significantly. However, counteracting this increase was a decline in kernel weight of 52% in 1974 and 10% in 1976. The precipititous drop in 1974 was largely due to an early frost which arrested further development. Because of increased competition in the unrestricted tillering plots, lateral tiller grain was approximately 4--5 days later in development than other treatments. Since environmental control is nearly impossible in field studies, the decline in yield c o m p o n e n t expression in this study cannot be fully explained, but it appears to us that moisture stress is responsible. There is ample evidence that stress of any type causes a decrease in individual yield components. For example, Fischer and Wilson (1975) showed that additional competing sorghum plants at post-floral initiation resulted in large decreases in grain n u m b e r and weight. Other research with wheat and barley have also shown that environemntal stress at critical times will result in significant reductions in these components (Puckridge, 1968; Jenner, 1979; Fischer and Stockman, 1980; Frank, 1980; Lawlor et al., 1981). Cultivars The influence of cultivars on number if kernels per panicle and kernel weight of grain is presented in Table II. Savanna 2 produced significantly more kernels on the main culms than NK277 (8.6%), but there was no difference in kernel weight. The two cultivars differed significantly in the n u m b e r of kernels produced by lateral tillers; Savanna 2 produced 24% more kernels on fewer tillers, than did NK277. (The average number of tillers per plant was 2.45 and 2.75, respectively). But just as was the case with main culms, the weight of lateral tiller kernels did not differ significantly. TABLE II Number and w e i g h t s o r g h u m cultivars. Cultivar
NK277 Savanna 2
o f kernels
produced by main culm
and lateral tiller panicles
of two
1 0 0 - K e r n e l Weight (g)
Number of Kernels
Main Culm*
Lateral Tillers*
Total*
Main Culm*
Lateral Tillers*
Mean*
3506 b 3806 a
2361 b 2929 a
5867 b 6735 a
2.48a 2.44 a
1.49 a 1.55 a
1.98 a 2.00 a
* V a l u e s w i t h i n a c o l u m n f o l l o w e d b y t h e same letter do n o t differ significantly (~ = 0 . 0 5 ) .
130
Date of planting Main culm grain. With respect to planting date, the main effect showed significant differences (e = 0.05), but there were no significant interactions with other factors. Fig. 2a is presented to emphasize the linear decline, at both planting dates, in number of kernels and kernel weight of grain from main culm panicles as number of tillers allowed to develop increased. Delaying planting until June resulted in an average of 12.7% fewer and 9.5% lighter kernels over the four tillering levels. MAIN CULMS
-3.0
6.0TLSD
=0.09
-2.5
5.0-
................................. -~un-~ -2,0
4.0-
X
3.0 -
.~ iii Z
n-
- -
Number
........
Weight
A
I"0 6
1
U5.0-
........
4.0-
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........
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-2.5
--'~
LSD ~ 064
o 0
0 /
Weight
I
.-I W Z rt" W ~"
U.
S
-- Nurnbe'
ca
Variable
2
LATE.AL,,LLE
0
Z
~021
oi"
W
£E W
- 15 TLSD
June
3.0 -
- 2.0
T
B ,
0 1"
0
1
2
I" 0
Variable
NUMBER OF TILLERS
Fig. 2. Number and weight of kernels from (A) main culm and (B) lateral tiller panicles as influenced by planting date. Least significant difference (LSD) values were calculated for the date-of-planting × degree-of-tiller-removal interaction, thus they apply to all values within each variable.
Lateral tiller grain. As more tillers were allowed to develop, the total number of kernels produced by lateral tillers increased significantly (Fig. 2b). Planting in early May resulted in a 126% increase while planting in mid-June yielded an 80% increase. The development of more than two tillers did not enhance
131
total number of kernels produced when environmental stress was encountered in late-planted plots. This implied decrease in number of kernels per lateral tiller panicle with increased intraplant competition is typical of responses shown by other grasses in stress situations (Puckridge, 1968; Fischer and Wilson, 1975; Jenner, 1979; Fischer and Stockman, 1980; Frank, 1980; Lawlor et al., 1981). Regardless of whether planting occurred in early May or mid-June, kernel weight of lateral tiller grain declined by approximately 32% as competiion from additional tillers increased (Fig. 2b). These responses re-emphasize the importance of competition and stress in the expression of yield components. The greater the environmental stress (later planting} the more pronounced was the effect on number of kernels per panicle or plant and kernel weight. Tiller removal Number of kernels. The effect of tiller removal on kernel development on main culms is evident in Fig. 3. If competition effects were restricted by removing all tillers (TR0), then early removal was important. For example, removal of all tillers at the 8-leaf stage of development resulted in significantly more kernels being produced than if removal was delayed until the flag leaf was visible in the whorl -- a 10% decline. Thereafter, delaying tiller removal further resulted in a small decrease in number of kernels produced. 4.5
4.5 --
Number
.........
Weight
--
TRO
gO
4.0
4.0
X
._J LU Z
TFt2
~o .J
ILl
z rr
rr" 3.5
TRC
ILl LL
O rr
3.5 ---> -
-
-
-
-
~
~
0 0
3.0
-3.0
nI L S Dffi0 15
UJ
TR0 • 2.5
~---EZ . . . .
- - -- ~ ,
U.
0
l-"r"
2.5 Z
UJ
W
TRC TR2
o1"
Y
8-ieaf
flag'leaf in whorl
1"o
5'0% anthe~is
STAGE OF DEVELOPMENT
Fig. 3. N u m b e r and w e i g h t o f kernels f r o m main c u l m panicles as a f f e c t e d b y time and degree o f tiller removal ( T R 0 = 0 tiller remaining; T R 1 = I tiller; T R 2 = 2 tillers; TRC = u n c h e c k e d tillering or c o n t r o l ) . Least significant d i f f e r e n c e ( L S D ) values were calculated for the time-of-tiller-removal × degree-of-tiller-removal interaction, thus t h e y apply t o all values w i t h i n each variable.
132
Looking at the other individual lines where tillers were removed at the three stages of development (TR1 and TR2), it is evident that time of removal had no significant effect on number of kernels produced. It is important to note that under the conditions of this experiment, development of one tiller was sufficient to preclude any advantage of early tiller removal. Considering the situation where a differing number of tillers remained at the 8-leaf stage, we found an average decline, from TR0, of 12% in number of kernels produced by main culms if one tiller was present (TR1), a 15% decline if two tillers were present (TR2), and a 25% decline if unchecked tillering was allowed (TRC). When tiller removal was delayed until the flag-leaf stage, presence of one or two tillers (TR1 and TR2) resulted in approximately 7.5% fewer kernels. Control plants (TRC), because of unrestricted competition from tillers, produced significantly fewer kernels on main culms than other treatments. This is in accordance with the sorghum work of Castleberry et al. {1972) and Fischer and Wilson (1975) and the wheat studies by Puckridge (1968), Jenner (1979) and Mohamed and Marshall (1979). The total number of kernels produced by lateral tillers was not influenced by the stage of development at which tiller were removed.
Kernel weight. Interaction of number of tillers remaining and time of tiller removal was significant for main culm grain weight (Fig. 3). As the stage of development at which tillers were removed was delayed, removing all tillers (TR0) resulted in a linear increase in kernel weight. Other treatments (TR1 and TR2), however, maintained relatively constant kernel weights over time regardless of the relationship between time of floret initiation, approximately the 8-leaf stage of development (Castleberry et al., 1972) and competition among tillers. If tillers were not removed at the 8-leaf stage, thus ustaining higher competition, fewer florest were initially set. In those treatment where all tillers were initially at the flag-leaf or 50% bloom stage, fewer kernels had access to more photosynthates, thus larger kernels developed. Castleberry et al. {1972) similarly reported that grain sorghum responded to reduced competition with a 17% increase in kernel weight. Kirby and Jones (1977) and Walpole and Morgan (1973) have salso shown that lessened competition will result in an increase in the size of kernels formed by barley and wheat, respectively. Weight of kernels from lateral tillers was not influenced by time of tiller removal. REFERENCES Bartel, A.T., Martin, J.H. and Hawkins, R.S., 1935. Effects of tillers on the development of grain sorghum. J. Am. Soc. Agron., 27: 707--714. Castleberry, R.M., Eastin, J.D. and Clegg, M.D., 1972. The effects of thinning at specific growth stages on yield and yield components of sorghum. In: The Physiology of Yield and Management of Sorghum in Relation to Genetic Improvement. Annu. Rep. 6, Agricultural Experiment Station, University of Nebraska, Lincoln, NE, pp. 23--39.
133
Cloninger, F.D., Horrocks, R.D. and Heatherly, L.G., 1972. Missouri Crop Performance, 1972. Part If, Grain Sorghum. Spec. Rep. 149, Agricultural Experiment Station, Uni-
versityof Missouri,Columbia,M0, pp. 52--64. Evans, L.T., Bingham, J. and Roskams, M.A., 1972. The pattern of grain set within ears of wheat. Aust. J. Biol. Sci.,25: 1--8. Fischer, R.A. and Stockman, Y.M., 1980. Kernel number per spike in wheat (Triticum aestivum L.) responses to preanthesis shading. Aust. J. Plant Phys., 7 : 169--180. Fischer, K.S. and Wilson, G.L., 1975. Studies of grain production in Sorghum bicolor (L. Moench). IV. Some effects of increasing and decreasing photosynthesis at different stages of the plant's development on the storage capacity of the inflorescence. Aust. J. Agric. Res., 26: 25--30. Frank, R., 1980. Grain yield and ear development of spring barley as influenced by environmental conditions during early stages of plant development. Biol. Plant. (Praha), 22: 274--281. Helwig, J.T. and Council, K.A. (Editors}, 1979. SAS user's guide. SAS Institute Inc., Cary, NC, 494 pp. Jenner, C.F., 1979. Grain-filling in wheat plants shaded for brief periods after anthesis. Aust. J. Plant Physiol., 6 : 629--641. Jones, H.G. and Kirby, E.J.M., 1977. Effects of manipulation of number of tillers and water supply on grain yield in barley. J. Agric. Sci. (Camb.), 88: 391--397. Karchi, Z. and Rudich, Y., 1966. Effects of row width and seeding spacing on yield and its components in grain sorghum grown under drylandconditions. Agron. J., 58: 602--604. Kirby, E.J.M. and Faris, D.J., 1972. The effect of plant density on tiller growth and morphology in barley. J. Agric. Sci. (Camb.), 88: 381--389. Kirby, E.J.M. and Jones, H.G., 1977. The relations between the main shoot and tillers in barley plants. J. Agric. Sci. (Camb.), 88 : 381--389. Lawlor, D.W., Day, W., Johnston, A.E., Legg, B.J. and Parkinson, K.J., 1981. Growth of spring barley under drought: crop development, photosynthesis, dry-matter accumulation and nutrient content. J. Agric. Sci. (Camb.), 96: 167--186. Mohamed, G.E.S. and Marshall, C., 1979. Physiological aspects of tiller removal in spring wheat. J. Agric. Sci. (Camb.), 93: 457--463. Puckridge, D.W., 1968. Competition for light and its effect on leaf spikelet development of wheat plants. Aust. J. Agric. Res., 19: 191--201. Scott, W.R., Dougherty, C.T. and Langer, R.H.M., 1977. Development and yield components of high-yielding wheat crops. N.Z.J. Agric. Res., 20: 205--212. Stickler, F.C. and Pauli, A.W., 1961. Leaf removal in grain sorghum. I. Effects of certain defoliation treatments on yield and components of yield. Agron. J., 53: 99--102. Stickler, F.C. and Wearden, S., 1965. Yield and yield components of grain sorghum as affected by row width and stand density. Agron. J., 47 : 564--567. Vanderlip, R.L. and Reeves, H.E., 1972. Growth stages of sorghum (Sorghum bicolor (L.) Moench). Agron. J., 64: 13--16. Walpole, P.R. and Morgan, D.G., 1973. The effects of floret sterilization on grain number and grain weight of wheat ears. Ann. Bot., 37 : 1041--1048.