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Sorghum improvement for energy production
Biomass 6 (1984) 145-153
Sorghum Improvement for Energy Production R. L. Monk, F. R. Miller and G. G. McBee Texas Agricultural Experiment Station and Department of Soil & Crop Sciences, Texas A&M University, College Station, Texas 77843, USA
(Received: 11 June, 1984) A BS TRA CT Sorghum (Sorghum bicolor (L. ) Moench ) has emerged as a leading candidate for biomass utilization among energy crops due to high yield potential, ease o f culture and wide adaptibility. Previously, enormous diversity present in the germplasm has been manipulated by sorghum breeding programs primarily to produce grain, syrup or forage. Development of sorghums for energy utilization will require a similar effort but should be more rapid based on current knowledge of the genetics of desirable characteristics. Results from yield trials of sweet, grain and grain x sweet sorghum hybrids demonstrate that partitioning carbohydrate into both grain and stalks can increase the suitability o f the crop for energy. Fresh weight biomass yields in excess of 60 Mg ha-1 and ethanol yields in excess o f 5000 litres ha-~ are possible from the use of improved cultivars. Key words: biomass production, sorghum, ethanol, agronomic characteris-
tics, dry weight partitioning
INTRODUCTION From the search among cultivated crops for high biomass production, sorghum ( S o r g h u m bicolor (L.) Moench) has emerged as a leading candidate.l, 2 Attainment of this position is due in part to the enormous diversity and varied growth habits within the genus and the knowledge of cultural and genetic factors affecting yields gleaned from over 30 years o f experience with hybrid sorghum production. The crop is produced on more than 49 million ha in the world annually and ranks fifth 145 Biomass 0144-4565/84/$03.30-© Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
146
R. L. Monk, F. R. Miller, G. G. McBee
among grain crops produced. Uses of sorghum include feed, food, syrup and forage) Some advantages for using sorghum as an energy resource include farmer expertise in managing the crop, rapid production to meet short-term demands and productivity over a wide range of environments. Sorghums can be classified into sweet, grain and forage types, but the categories are not completely distinct because hybrids are viable among most types. Among sorghums, the sweet type has received the most attention in the US as a biomass c r o p 4-6 due to high stalk and sugar yields. Syrup cultivars generally are highest for tonnage, while sugar cultivars have greater purity. Although their potential is recognized, sweet sorghums may have disadvantages for economical large-scale production. They are maintained and produced as pure lines with concomitant seed production problems of purity, availability and low vigor. High energy sorghums (HES), hybrids that combine characteristics of both sweet and grain sorghums, have been proposed as a logical way to increase production potential s' 7 by utilizing heterosis for vegetative and phenological development. By manipulating dwarfing genes in the parental lines, it is possible to produce hybrid seed on short-statured females that will grow tall plants of high vigor, when the hybrid seed are planted. Use of hybrids also simplifies incorporating disease and insect resistances. Once the correct ideotype for energy conversion is formulated, numerous characteristics are available to alter sorghum by directed breeding programs. Kresovich 8 found maturity to be a significant constraint when sorghums were planted in Ohio where the cultivars failed to mature before frost. Schaffert and Gourley 9 also noted that photoperiod sensitivity was a problem in Brazilian breeding programs aimed at extending the milling season to produce sugar for conversion into alcohol. Genes for stem sweetness, 1° low lignin content, 11 height, 11 and nonsenescence ~2 have been identified in existing germplasm and can be incorporated as needed. The impact of these characteristics on energy conversion schemes, however, has not been fully explored. Additionally, the influence of the environment on productivity is known to be significant, but the resulting changes in physiological and agronomic characteristics of individual cultivars are not clearly understood. Seasonal and diurnal patterns of carbohydrate accumulations for selected cultivars have been studied) 3' ~4 Objectives of the sorghum improvement program in relation to energy production include increasing the biomass yields, improving the product and limiting inputs into the crop. Specifically, this paper will
Sorghum improvement for energy production
147
address the types of sorghum that appear to be most productive and agronomic traits associated with maximum production that will allow plant breeders to optimize selection procedures.
MATERIALS AND METHODS In order to examine productivity of sorghum types, an array of sweet, grain and HES sorghums was grown at the Brazos Valley Experimental Laboratory near College Station, Texas, during 1981-83. Plants were established in two-row plots on rows spaced 75 cm apart, and fertilizer, irrigation water and insect control were applied as required for maximum production. Soil type at the experimental site is a Ships clay (very fine, mixed, thermic Udic Chromusterts) and the previous crop was sorghum. The experimental design included randomized complete blocks with three replications. Plots were harvested once each year at approximately three weeks past physiological maturity of most of the plants. Data collected included: (1) Plant maturity - the number of days from planting until 50% of the plants within the plot were at anthesis. (2) Plant height - height (cm) from the ground to panicle tip. (3) Y i e l d - total fresh weight (Mg ha-1) calculated from weighing biomass from 2 m of row. (4) B r i x % - measurement of % soluble carbohydrates in juice obtained from a hand-pressed stalk section taken from the fourth internode below the panicle. Additional measurements recorded in 1983 included dry weights of leaves, stalks and panicles. These data were obtained from five plants per plot dried for 144 h at 55°C in a forced draft oven. Statistical analyses were performed using analysis of variance and correlation techniques.
RESULTS AND DISCUSSION During the period of study a total of 45 different cultivars was evaluated. Fresh weight yields for 10 cultivars common to all three years are
R. L. Monk, F. R. Miller, G. G. McBee
148
TABLE 1 Fresh Weight Yields (Mg ha-1) of 10 Sorghum Cultivars During 3 Years at College Station
Designation
1981
1982
1983
Sweet sorghums Rio Brandes
68.5 85.3
51.2 68.0
60.0 115.5
59.9 89.6
Grain sorghums AT x 623 × RT x 430 APur 1 × RT x 432 AT x 623 x RT x 432
39.8 37.8 34.3
45-5 32.6 33-3
34.3 40.2 30-5
39.9 36.0 32.7
High energy sorghums AT x 623 x Wray AT × 623 × Rio AAtlas x RT x 430 AAtlas x P-3 AAtlas x RT × 432
83.8 64.l 60.4 48.8 41.8
64.5 47.0 51.1 30.7 50.3
58.0 51-8 46.4 41.5 36.0
69.1 54.3 52-6 40.3 43.0
LSD (0-05)
13.3
21.8
18.9
shown in Table 1. A maximum fresh weight yield o f 1 15 Mg ha -x was produced by the cultivar Brandes during 1983. Total fresh weight was highest for the sweet sorghums, intermediate for the HES types and lowest for the grain types. These results confirm previous experiments showing a yield advantage for the syrup type (Brandes) when compared to the sugar type (Rio). Significant differences occurred among cultivars and years. A significant year X cultivar interaction occurred in these tests for yield, which may complicate the breeding procedures required because regional adaptation o f hybrids must be considered. Selected agronomic data presented in Table 2 show that further differences exist in the growth and development of sorghum cultivars. Days to anthesis is a measurement of maturity and the data indicate sweet sorghum to be later in maturity than the other types. In areas where only one crop can be grown, late maturity may be advantageous, but late-maturing varieties are a greater risk over much o f the current sorghum belt. Grain producers have always realized the advantage o f
149
Sorghum improvement for energy production TABLE 2
Agronomic Data for Sorghum Cultivars Grown at College Station in 1983
Designation
Maturity (days)
Height (cm)
Brix (%)
Rate of growth (g day -1)
108 130
307 233
19.6 17.1
1.194 1.414
80 82 86
159 167 163
10.2 12.1 12-2
1.056 1.265 0-871
92 85 81 81 82
279 290 226 210 224
12-9 14.2 12-5 13.0 10.3
1.554 1.253 1-027 0-897 0-764
Sweet sorghums Rio Brandes
Grain sorghums AT × 623 x RT x 430 APur 1 x RT × 432 AT × 623 × RT x 432
High energy sorghums AT x 623 x Wray AT x 623 x Rio AAtlas x RT x 430 AAtlas x P-3 AAtlas x RT x 432 LSD (0.05)
1.3
21-2
4-8
long-season crops, but a rather narrow range of maturity is required in much of Texas to escape insect and drought pressures. Maturity is known to be primarily controlled by four genes and thus can be manipulated within limits to achieve regional a d a p t a t i o n ) 2 Use of the ratooning capability of sorghum to produce a second crop from one planting would also require earlier genotypes. Significant positive correlation for height of sorghum with total biomass production occurred (r = 0.53); however, there are limits to o p t i m u m heights. Lodging can become a serious problem in many areas where thunderstorms accompanied by high winds are commonplace during the production season. Extremely tall crops are difficult to harvest and often contain large variations in height down the row thus complicating harvesting schemes aimed at removing the panicles. Height is an especially important part of the breeding program for the HES types because grain production greatly exceeds that of sweet types and
150
R. L. Monk, F. R. Miller, G. G. McBee
the added weight of the grain can result in significant stalk breakage and root lodging. A three-point break test and penetrometer measurements have been used to screen materials for lodging, as The Brix measurement is an indication of the soluble carbohydrate content in the stalk and, as expected, the sweet sorghums were the highest (Table 2). A severe limitation currently exists in the germplasm base in that few sweet short females are available for hybrid combinations. Since sweetness is reportedly a recessive characteristic controlled by two genes, it is needed on both sides of the cross. Clark, 16 however, found the inheritance of fermentable carbohydrates to be considerably more complex than two genes. He also found a positive correlation between grain yield and stalk carbohydrate level which indicates that breeders can potentially increase both without exhausting photosynthetic capabilities of the plant. Percent dry matter varies among the types, being lowest for sweet types and highest for the grain types. Some of the HES hybrids partitioned approximately equal amounts of dry weight into stalks and grain with sweet sorghum partitioning up to 70% into stalks (Table 3). The partitioning of HES hybrids allows an efficient dual-purpose crop since the grain can be marketed in one channel while the stalks can be utilized in energy conversion schemes. A genetic trait useful in this regard is nonsenescence which contributes to maintenance of carbohydrates in the stalks and leaves after grain maturity. ~7 On the other hand, with sweet or grain sorghums, the partitioning is directed towards a single commodity only. Using the dry weights of plants harvested and the length of the growing season required, a rate of weight accumulation was calculated. A fixed length of 35 days was added to each anthesis date to allow comparison of season-long production. The comparison indicates HES hybrids produce at a rate near equal or greater than the other types. Yield advantages of the sweet sorghums appear to be primarily a function of maturity and thus greater yields can be produced by HES hybrids simply by increasing the length of season. The data presented above indicate that significant diversity exists among sorghum genotypes for a number of characteristics that impact on sorghum improvement for energy production. Increases in rate of weight accumulation and total biomass production plus changes in partitioning of carbohydrate will allow a farmer to produce a crop possessing several marketing options. The extent to which such changes
Sorghum improvement for energy production
151
TABLE 3 Partitioning of Dry Weight into Plant Parts
Designation
% of total dry weight Leaf blades
Stalks
Panicles
16.8 21.7
66.8 73.4
16.4 4.9
Grain sorghums AT x 623 x RT x 430 APur 1 × RT x 432 AT x 623 x RT × 432
13.7 16.6 13.3
25.3 27.9 30.4
61.0 55.4 56.3
High energy sorghums AT × 623 x Wray AT x 623 x Rio AAtlas × RT × 430 AAtlas x P-3 AAtlas × RT × 432
15-2 13.8 12.8 12.8 11.2
39.5 40.5 35.7 35.3 37.3
45.3 45.8 51.4 51-9 51.5
Sweet sorghums Rio Brandes
in genetics could affect one pr oduc t , ethanol, were summarized by Miller and Creelman. 7 Their data indicated that low grain yielding sweet sorghums were not competitive with high yielding grain types or HES hybrids when b o t h grain and stalk c arbohydrat es were included. E t h a n o l estimates based on b o t h grain and stalk c o m p o n e n t s were over 5000 l i t r e s h a -1 for the HES hybrids whereas sweet and grain types averaged 3 0 0 0 - 4 0 0 0 litres ha -a. Their evaluation did not include the use o f cellulose or hemicellulose components. If there were economical ways to convert these structural c a r b o h y d r a t e fractions into fermentable forms, the yields o f ethanol would be even greater. Schaffert and G o u r ley 9 also r e p o r t e d yields exceeding 50001itres ha -1 o f ethanol from sorghums in Brazil. F r o m the above summary o f results, it was concluded that breeding sorghum specifically for energy will greatly increase yield potentials. Existing sweet or grain sorghum cultivars do not appear to be the o p t i m u m materials when c om par e d on a rate or multiple use basis.
152
R. L. Monk, F. R. Miller, G. G. McBee
F u r t h e r increases in biomass p r o d u c t i o n will necessitate the utilization o f h y b r i d vigor and the i n c o r p o r a t i o n o f a n u m b e r o f specific genetic traits to increase the quality o f specific end products.
REFERENCES 1. Lipinsky, E. S.. Kresovich, S., McClure, T. A., Jackson, D. R., Lawhon, W. T., Kalyoncu, A. A. & Daniels, E. L. (1978). Sugar crops as a source o f fuels. I. Agricultural research, DOE Contract No. W-7405 eng 92. 2. Nathan, R. A. (1978). Fuels from sugar crops, San Mateo, Solar Energy Information Services. 3. MacKey, J. (1981). Cereal production. In: Cereals: a renewable resource, eds Y. Pomeranz and L. Munck, St Paul, Am. Assoc. of Cereal Chemists. 4. Kresovich, S. (1981). Sweet sorghum. In: CRC handbook o f bisolar resources, eds T. A. McClure and E. S. Lipinsky, Boca Raton, CRC Press, Inc. 5. Creelman, R. A., Rooney, L. W. & Miller, F. R. (1981). Sorghum. In: Cereals: a renewable resource, eds Y. Pomeranz and L. Munck, St Paul, Am. Assoc. of Cereal Chemists. 6. Elawad, S. H., Gascho, G. J. & Shih, S. F. (1980). The energy potential of sugarcane and sweet sorghum. In: Energy from biomass and wastes IV, ed. D. L. Klass, Chr. Symposium, 21-25 January, Lake Buena Vista. 7. Miller, F. R. & Creelman, R. A. (1980). Sorghum - a new fuel. In: Proc. 35th Ann. Corn & Sorghum Research Conf. Am. Seed Trade Assoc. , Washington, DC. 8. Kresovich, S. (1982). The potential of sorghum as a raw material for ethanol production in midwestern cropping systems. PhD Thesis, Ohio State University, Columbus. 9. Schaffert, R. E. & Gourley, L. M. (1982). Sorghum as an energy source. In: Sorghum in the eighties: proceedings o f the international symposium on sorghum, Pantancheru, A.P., ICRISAT. 10. Ayyangar, G. N. R., Ayyar, M. A. S., Rao, V. P. & Nambiar, A. K. (1936). Mendelian segregations for juiciness and sweetness in sorghum stalks. Madras Agric. J., 24, 247-8. 11. Porter, K. S. Axtell, J. D., Lechtenberg, V. L. & Colenbrander, V. F. (1978). Phenotype, fiber composition and in vitro dry matter disappearance of chemically induced brown midrib mutants of sorghum. Crop Sci., 18, 205-8. 12. Quinby, J. R. (1974). Sorghum improvement and the genetics o f growth, College Station, Texas A&M University Press. 13. McBee, G. G. & Miller, F. R. (1982). Carbohydrates in sorghum culms as influenced by cultivars, spacing and maturity over a diurnal period. Crop Sci., 22, 381-5.
Sorghum improvement for energy production
153
14. McBee, G. G., Waskom, R. M. III, Miller, F. R. & Creelman, R. A. (1983). Effect of senescence and nonsenescence on carbohydrates in sorghum during late kernel maturity states. Crop. Sci., 23,372-6. 15. Creelman, R. A., Miller, F. R. & Monk, R. L. (1982). Lodging resistance in high energy sorghum. Sorg. Newsl., 25-31. 16. Clark, J. W. (1981). The inheritance of fermentable carbohydrates in stems of Sorghum bicolor (L.) Moench. PhD Thesis, College Station, Texas A&M University. 17. Duncan, R. R., Bockholt, A. J. & Miller, F. R. (1981). Descriptive comparison of senescent and nonsenescent sorghum genotypes. Agron. J., 73,849-53.
Sorghum Improvement for Energy Production R. L. Monk, F. R. Miller and G. G. McBee Texas Agricultural Experiment Station and Department of Soil & Crop Sciences, Texas A&M University, College Station, Texas 77843, USA
(Received: 11 June, 1984) A BS TRA CT Sorghum (Sorghum bicolor (L. ) Moench ) has emerged as a leading candidate for biomass utilization among energy crops due to high yield potential, ease o f culture and wide adaptibility. Previously, enormous diversity present in the germplasm has been manipulated by sorghum breeding programs primarily to produce grain, syrup or forage. Development of sorghums for energy utilization will require a similar effort but should be more rapid based on current knowledge of the genetics of desirable characteristics. Results from yield trials of sweet, grain and grain x sweet sorghum hybrids demonstrate that partitioning carbohydrate into both grain and stalks can increase the suitability o f the crop for energy. Fresh weight biomass yields in excess of 60 Mg ha-1 and ethanol yields in excess o f 5000 litres ha-~ are possible from the use of improved cultivars. Key words: biomass production, sorghum, ethanol, agronomic characteris-
tics, dry weight partitioning
INTRODUCTION From the search among cultivated crops for high biomass production, sorghum ( S o r g h u m bicolor (L.) Moench) has emerged as a leading candidate.l, 2 Attainment of this position is due in part to the enormous diversity and varied growth habits within the genus and the knowledge of cultural and genetic factors affecting yields gleaned from over 30 years o f experience with hybrid sorghum production. The crop is produced on more than 49 million ha in the world annually and ranks fifth 145 Biomass 0144-4565/84/$03.30-© Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
146
R. L. Monk, F. R. Miller, G. G. McBee
among grain crops produced. Uses of sorghum include feed, food, syrup and forage) Some advantages for using sorghum as an energy resource include farmer expertise in managing the crop, rapid production to meet short-term demands and productivity over a wide range of environments. Sorghums can be classified into sweet, grain and forage types, but the categories are not completely distinct because hybrids are viable among most types. Among sorghums, the sweet type has received the most attention in the US as a biomass c r o p 4-6 due to high stalk and sugar yields. Syrup cultivars generally are highest for tonnage, while sugar cultivars have greater purity. Although their potential is recognized, sweet sorghums may have disadvantages for economical large-scale production. They are maintained and produced as pure lines with concomitant seed production problems of purity, availability and low vigor. High energy sorghums (HES), hybrids that combine characteristics of both sweet and grain sorghums, have been proposed as a logical way to increase production potential s' 7 by utilizing heterosis for vegetative and phenological development. By manipulating dwarfing genes in the parental lines, it is possible to produce hybrid seed on short-statured females that will grow tall plants of high vigor, when the hybrid seed are planted. Use of hybrids also simplifies incorporating disease and insect resistances. Once the correct ideotype for energy conversion is formulated, numerous characteristics are available to alter sorghum by directed breeding programs. Kresovich 8 found maturity to be a significant constraint when sorghums were planted in Ohio where the cultivars failed to mature before frost. Schaffert and Gourley 9 also noted that photoperiod sensitivity was a problem in Brazilian breeding programs aimed at extending the milling season to produce sugar for conversion into alcohol. Genes for stem sweetness, 1° low lignin content, 11 height, 11 and nonsenescence ~2 have been identified in existing germplasm and can be incorporated as needed. The impact of these characteristics on energy conversion schemes, however, has not been fully explored. Additionally, the influence of the environment on productivity is known to be significant, but the resulting changes in physiological and agronomic characteristics of individual cultivars are not clearly understood. Seasonal and diurnal patterns of carbohydrate accumulations for selected cultivars have been studied) 3' ~4 Objectives of the sorghum improvement program in relation to energy production include increasing the biomass yields, improving the product and limiting inputs into the crop. Specifically, this paper will
Sorghum improvement for energy production
147
address the types of sorghum that appear to be most productive and agronomic traits associated with maximum production that will allow plant breeders to optimize selection procedures.
MATERIALS AND METHODS In order to examine productivity of sorghum types, an array of sweet, grain and HES sorghums was grown at the Brazos Valley Experimental Laboratory near College Station, Texas, during 1981-83. Plants were established in two-row plots on rows spaced 75 cm apart, and fertilizer, irrigation water and insect control were applied as required for maximum production. Soil type at the experimental site is a Ships clay (very fine, mixed, thermic Udic Chromusterts) and the previous crop was sorghum. The experimental design included randomized complete blocks with three replications. Plots were harvested once each year at approximately three weeks past physiological maturity of most of the plants. Data collected included: (1) Plant maturity - the number of days from planting until 50% of the plants within the plot were at anthesis. (2) Plant height - height (cm) from the ground to panicle tip. (3) Y i e l d - total fresh weight (Mg ha-1) calculated from weighing biomass from 2 m of row. (4) B r i x % - measurement of % soluble carbohydrates in juice obtained from a hand-pressed stalk section taken from the fourth internode below the panicle. Additional measurements recorded in 1983 included dry weights of leaves, stalks and panicles. These data were obtained from five plants per plot dried for 144 h at 55°C in a forced draft oven. Statistical analyses were performed using analysis of variance and correlation techniques.
RESULTS AND DISCUSSION During the period of study a total of 45 different cultivars was evaluated. Fresh weight yields for 10 cultivars common to all three years are
R. L. Monk, F. R. Miller, G. G. McBee
148
TABLE 1 Fresh Weight Yields (Mg ha-1) of 10 Sorghum Cultivars During 3 Years at College Station
Designation
1981
1982
1983
Sweet sorghums Rio Brandes
68.5 85.3
51.2 68.0
60.0 115.5
59.9 89.6
Grain sorghums AT x 623 × RT x 430 APur 1 × RT x 432 AT x 623 x RT x 432
39.8 37.8 34.3
45-5 32.6 33-3
34.3 40.2 30-5
39.9 36.0 32.7
High energy sorghums AT x 623 x Wray AT × 623 × Rio AAtlas x RT x 430 AAtlas x P-3 AAtlas x RT × 432
83.8 64.l 60.4 48.8 41.8
64.5 47.0 51.1 30.7 50.3
58.0 51-8 46.4 41.5 36.0
69.1 54.3 52-6 40.3 43.0
LSD (0-05)
13.3
21.8
18.9
shown in Table 1. A maximum fresh weight yield o f 1 15 Mg ha -x was produced by the cultivar Brandes during 1983. Total fresh weight was highest for the sweet sorghums, intermediate for the HES types and lowest for the grain types. These results confirm previous experiments showing a yield advantage for the syrup type (Brandes) when compared to the sugar type (Rio). Significant differences occurred among cultivars and years. A significant year X cultivar interaction occurred in these tests for yield, which may complicate the breeding procedures required because regional adaptation o f hybrids must be considered. Selected agronomic data presented in Table 2 show that further differences exist in the growth and development of sorghum cultivars. Days to anthesis is a measurement of maturity and the data indicate sweet sorghum to be later in maturity than the other types. In areas where only one crop can be grown, late maturity may be advantageous, but late-maturing varieties are a greater risk over much o f the current sorghum belt. Grain producers have always realized the advantage o f
149
Sorghum improvement for energy production TABLE 2
Agronomic Data for Sorghum Cultivars Grown at College Station in 1983
Designation
Maturity (days)
Height (cm)
Brix (%)
Rate of growth (g day -1)
108 130
307 233
19.6 17.1
1.194 1.414
80 82 86
159 167 163
10.2 12.1 12-2
1.056 1.265 0-871
92 85 81 81 82
279 290 226 210 224
12-9 14.2 12-5 13.0 10.3
1.554 1.253 1-027 0-897 0-764
Sweet sorghums Rio Brandes
Grain sorghums AT × 623 x RT x 430 APur 1 x RT × 432 AT × 623 × RT x 432
High energy sorghums AT x 623 x Wray AT x 623 x Rio AAtlas x RT x 430 AAtlas x P-3 AAtlas x RT x 432 LSD (0.05)
1.3
21-2
4-8
long-season crops, but a rather narrow range of maturity is required in much of Texas to escape insect and drought pressures. Maturity is known to be primarily controlled by four genes and thus can be manipulated within limits to achieve regional a d a p t a t i o n ) 2 Use of the ratooning capability of sorghum to produce a second crop from one planting would also require earlier genotypes. Significant positive correlation for height of sorghum with total biomass production occurred (r = 0.53); however, there are limits to o p t i m u m heights. Lodging can become a serious problem in many areas where thunderstorms accompanied by high winds are commonplace during the production season. Extremely tall crops are difficult to harvest and often contain large variations in height down the row thus complicating harvesting schemes aimed at removing the panicles. Height is an especially important part of the breeding program for the HES types because grain production greatly exceeds that of sweet types and
150
R. L. Monk, F. R. Miller, G. G. McBee
the added weight of the grain can result in significant stalk breakage and root lodging. A three-point break test and penetrometer measurements have been used to screen materials for lodging, as The Brix measurement is an indication of the soluble carbohydrate content in the stalk and, as expected, the sweet sorghums were the highest (Table 2). A severe limitation currently exists in the germplasm base in that few sweet short females are available for hybrid combinations. Since sweetness is reportedly a recessive characteristic controlled by two genes, it is needed on both sides of the cross. Clark, 16 however, found the inheritance of fermentable carbohydrates to be considerably more complex than two genes. He also found a positive correlation between grain yield and stalk carbohydrate level which indicates that breeders can potentially increase both without exhausting photosynthetic capabilities of the plant. Percent dry matter varies among the types, being lowest for sweet types and highest for the grain types. Some of the HES hybrids partitioned approximately equal amounts of dry weight into stalks and grain with sweet sorghum partitioning up to 70% into stalks (Table 3). The partitioning of HES hybrids allows an efficient dual-purpose crop since the grain can be marketed in one channel while the stalks can be utilized in energy conversion schemes. A genetic trait useful in this regard is nonsenescence which contributes to maintenance of carbohydrates in the stalks and leaves after grain maturity. ~7 On the other hand, with sweet or grain sorghums, the partitioning is directed towards a single commodity only. Using the dry weights of plants harvested and the length of the growing season required, a rate of weight accumulation was calculated. A fixed length of 35 days was added to each anthesis date to allow comparison of season-long production. The comparison indicates HES hybrids produce at a rate near equal or greater than the other types. Yield advantages of the sweet sorghums appear to be primarily a function of maturity and thus greater yields can be produced by HES hybrids simply by increasing the length of season. The data presented above indicate that significant diversity exists among sorghum genotypes for a number of characteristics that impact on sorghum improvement for energy production. Increases in rate of weight accumulation and total biomass production plus changes in partitioning of carbohydrate will allow a farmer to produce a crop possessing several marketing options. The extent to which such changes
Sorghum improvement for energy production
151
TABLE 3 Partitioning of Dry Weight into Plant Parts
Designation
% of total dry weight Leaf blades
Stalks
Panicles
16.8 21.7
66.8 73.4
16.4 4.9
Grain sorghums AT x 623 x RT x 430 APur 1 × RT x 432 AT x 623 x RT × 432
13.7 16.6 13.3
25.3 27.9 30.4
61.0 55.4 56.3
High energy sorghums AT × 623 x Wray AT x 623 x Rio AAtlas × RT × 430 AAtlas x P-3 AAtlas × RT × 432
15-2 13.8 12.8 12.8 11.2
39.5 40.5 35.7 35.3 37.3
45.3 45.8 51.4 51-9 51.5
Sweet sorghums Rio Brandes
in genetics could affect one pr oduc t , ethanol, were summarized by Miller and Creelman. 7 Their data indicated that low grain yielding sweet sorghums were not competitive with high yielding grain types or HES hybrids when b o t h grain and stalk c arbohydrat es were included. E t h a n o l estimates based on b o t h grain and stalk c o m p o n e n t s were over 5000 l i t r e s h a -1 for the HES hybrids whereas sweet and grain types averaged 3 0 0 0 - 4 0 0 0 litres ha -a. Their evaluation did not include the use o f cellulose or hemicellulose components. If there were economical ways to convert these structural c a r b o h y d r a t e fractions into fermentable forms, the yields o f ethanol would be even greater. Schaffert and G o u r ley 9 also r e p o r t e d yields exceeding 50001itres ha -1 o f ethanol from sorghums in Brazil. F r o m the above summary o f results, it was concluded that breeding sorghum specifically for energy will greatly increase yield potentials. Existing sweet or grain sorghum cultivars do not appear to be the o p t i m u m materials when c om par e d on a rate or multiple use basis.
152
R. L. Monk, F. R. Miller, G. G. McBee
F u r t h e r increases in biomass p r o d u c t i o n will necessitate the utilization o f h y b r i d vigor and the i n c o r p o r a t i o n o f a n u m b e r o f specific genetic traits to increase the quality o f specific end products.
REFERENCES 1. Lipinsky, E. S.. Kresovich, S., McClure, T. A., Jackson, D. R., Lawhon, W. T., Kalyoncu, A. A. & Daniels, E. L. (1978). Sugar crops as a source o f fuels. I. Agricultural research, DOE Contract No. W-7405 eng 92. 2. Nathan, R. A. (1978). Fuels from sugar crops, San Mateo, Solar Energy Information Services. 3. MacKey, J. (1981). Cereal production. In: Cereals: a renewable resource, eds Y. Pomeranz and L. Munck, St Paul, Am. Assoc. of Cereal Chemists. 4. Kresovich, S. (1981). Sweet sorghum. In: CRC handbook o f bisolar resources, eds T. A. McClure and E. S. Lipinsky, Boca Raton, CRC Press, Inc. 5. Creelman, R. A., Rooney, L. W. & Miller, F. R. (1981). Sorghum. In: Cereals: a renewable resource, eds Y. Pomeranz and L. Munck, St Paul, Am. Assoc. of Cereal Chemists. 6. Elawad, S. H., Gascho, G. J. & Shih, S. F. (1980). The energy potential of sugarcane and sweet sorghum. In: Energy from biomass and wastes IV, ed. D. L. Klass, Chr. Symposium, 21-25 January, Lake Buena Vista. 7. Miller, F. R. & Creelman, R. A. (1980). Sorghum - a new fuel. In: Proc. 35th Ann. Corn & Sorghum Research Conf. Am. Seed Trade Assoc. , Washington, DC. 8. Kresovich, S. (1982). The potential of sorghum as a raw material for ethanol production in midwestern cropping systems. PhD Thesis, Ohio State University, Columbus. 9. Schaffert, R. E. & Gourley, L. M. (1982). Sorghum as an energy source. In: Sorghum in the eighties: proceedings o f the international symposium on sorghum, Pantancheru, A.P., ICRISAT. 10. Ayyangar, G. N. R., Ayyar, M. A. S., Rao, V. P. & Nambiar, A. K. (1936). Mendelian segregations for juiciness and sweetness in sorghum stalks. Madras Agric. J., 24, 247-8. 11. Porter, K. S. Axtell, J. D., Lechtenberg, V. L. & Colenbrander, V. F. (1978). Phenotype, fiber composition and in vitro dry matter disappearance of chemically induced brown midrib mutants of sorghum. Crop Sci., 18, 205-8. 12. Quinby, J. R. (1974). Sorghum improvement and the genetics o f growth, College Station, Texas A&M University Press. 13. McBee, G. G. & Miller, F. R. (1982). Carbohydrates in sorghum culms as influenced by cultivars, spacing and maturity over a diurnal period. Crop Sci., 22, 381-5.
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14. McBee, G. G., Waskom, R. M. III, Miller, F. R. & Creelman, R. A. (1983). Effect of senescence and nonsenescence on carbohydrates in sorghum during late kernel maturity states. Crop. Sci., 23,372-6. 15. Creelman, R. A., Miller, F. R. & Monk, R. L. (1982). Lodging resistance in high energy sorghum. Sorg. Newsl., 25-31. 16. Clark, J. W. (1981). The inheritance of fermentable carbohydrates in stems of Sorghum bicolor (L.) Moench. PhD Thesis, College Station, Texas A&M University. 17. Duncan, R. R., Bockholt, A. J. & Miller, F. R. (1981). Descriptive comparison of senescent and nonsenescent sorghum genotypes. Agron. J., 73,849-53.