African Journal of Range & Forage Science 2010, 27(1): xx–xxPrinted in South Africa — All rights reserved

Copyright © NISC (Pty) LtdAFRICAN JOURNAL OF

RANGE & FORAGE SCIENCEISSN 1022–0119 EISSN 1727–9380

doi: 10.2989/10220111003703518

African Journal of Range & Forage Science is co-published by NISC (Pty) Ltd and Taylor & Francis

Research Note

New Sudangrass forage cultivars selected from the original population (Sorghum bicolor ‘Garawi’, syn. S. sudanense)

Maarouf I Mohammed

Forage Research Program, Agricultural Research Corporation, PO Box 30, Khartoum North, SudanE-mail: ibrahimarof@yahoo.com

Received 19 August 2009, accepted 18 January 2010

The study represents the first efforts since 1909 to develop improved Sudangrass (Sorghum bicolor (L.) Moench, syn. S. sudanense (Piper) Stapf) cultivars from the original genetic stock existing in the Sudan. Seven Sudangrass genotypes generated by individual plant selection within the land race ‘Garawi’ were evaluated across seven environments in Khartoum State in 2003–2006. Selection criteria were based on forage as well as seed-setting attributes. The objectives were to develop improved and reproducible cultivars from the parent population Garawi. The results indicated that two genotypes, S.(32-2)A and S.51, were superior to the parent population in forage yield, protein content, average stability of yield superiority and reproducibility. The increment in yield was attained without significant delay in flowering duration. Both genotypes were recommended for forage production under the traditional green chopping system. S.(32-2)A was officially released under the name Sudan-1 by the Variety Release Committee in February 2009. The newly developed genotypes will contribute to widening the currently narrow genetic base of Sudangrass cultivars. Seed of the newly developed genotypes can be provided in small amounts for research purposes upon written request to the author.

Keywords: forage sorghum, green chopping, Islang, neutral detergent fibre, Shambat

The currently available Sudangrass (Sorghum bicolor (L.) Moench, syn. S. sudanense (Piper) Stapf) cultivars share a very limited genetic background. Their genetic pool is confined to the few grams of seeds introduced to the USA from Sudan in 1909 by CV Piper (Maunder 1983). No attempts have been made, since then, to generate new lines from the land race ‘Garawi’, the mother population of Sudangrass existing in the country of origin, Sudan. The seeming variability among present Sudangrass cultivars is largely attributable to crosses between ‘Redlan’ and ‘Greenleaf’ (Harvey 1977). Garawi represents a highly mixed and genetically variable population with unpredict-able performance for forage and seed attributes, a situation that poses practical limitations on maintaining the required features of a cultivar. Selection for high seed set in Sudangrass has been rarely practiced (Kalton 1988). In 2001 a selection program within Garawi was initiated. This paper highlights the salient features and findings of a research program undertaken to develop improved and reproducible forms of Sudangrass from its original source population.

Seven Sudangrass genotypes were developed by individual plant selection during 2000–2003, namely S.10-1, S.50, S.34, S.18, S.32-1, S.(32-2)A and S.51. Table 1 shows the procedure used to generate these genotypes. The lines S.10-1, S.50 and S.34 were characterised by high tillering capacity and thin stems. The line S.(32-2)A was selected for earliness and vigour in growth. The lines S.(32-2)A, S.18 and S.32-1 showed good tillering capacity and medium stem

thickness. The line S.51 showed poor tillering and thick stems. It resembles grain sorghum in some morphological features, such as the ear shape and seed colour.

The selected lines were tested against three checks across seven environments in Khartoum State (an unbalanced combination of years and locations). The years extended from 2003 to 2006. The locations were Kuku (15°39′ N, 32°36′ E), Islang (15°53′ N, 32°32′ E) and Shambat (15°39′ N, 32°31′ E). Rainfall, temperature and relative humidity prevailing in Khartoum State during the years 2003 through 2006 and the long-term averages are shown in Table 2. Generally, the climate is hot and dry. The rainy season is short extending from July to September with scant and fluctuating precipitation.

The checks comprised the traditional Sudangrass land race Garawi, the traditional Abu Sab’in and Kambal (recommended Abu Sab’in). Abu Sab’in, a dual grain/forage variety, is the most widely grown forage sorghum cultivar in the country. Kambal is an improved version of Abu Sab’in released in 2004. Sowing dates covered most months of the year. Sowing was done manually by placing the seeds in furrows or holes opened on both sides of the ridges. Nitrogen fertiliser was added at a rate of 55 kg N ha−1. The experimental plots were hand-weeded twice and irrigated at intervals of 7–15 d. Chemical control of pests was not practiced in any of the experiments.

The first cut was taken at the dough stage. The dry matter yield (DMY) was estimated from a random sample

Mohammed2

of 0.5 kg taken from the harvested plot and air-dried to a constant weight. The second cut was evaluated from the experiments conducted at Shambat during the winter seasons of 2003/04 and 2005/06. Days to flower, plant height, stem diameter, tillering capacity, regrowth and leaf:stem ratio were studied. Regrowth was evaluated 15 d after cutting from three-metre-long rows randomly chosen from each plot. The newly emerging shoots were harvested and the average dry weight per metre row was determined. Proximate analyses for neutral detergent fibre (NDF), acid detergent fibre (ADF) and crude protein (CP) were performed on a dry matter basis following the standard procedure of the AOAC (1980).

A randomised complete block design was used. Combined analysis of variance (ANOVA) was performed using balanced data sets obtained for dry matter yield (DMY) in two environments (Kuku and Islang, 2003/04) and four environments (Kuku 2004, and Shambat 2005, 2005/06 and 2006). Stability analysis following Lin and Binns (1988) was performed. The residual maximum likelihood (REML)

method (Patterson 1997) was used to combine the data obtained for agronomic yield-related traits in different environments. The statistical package GenStat version 9.1.0.174 (VSN International, Hemel Hempstead) was used to perform ANOVA and REML analyses, whereas stability analysis was carried out using AGROBASE Generation II® version 14.4.1 (Agronomix Software, Winnipeg).

The performance of genotypes for DMY of the first cut is shown in Tables 3 and 4. The genotypes differed signifi-cantly (p < 0.01) in DMY in most of the separate environ-ments and in the combined analysis as well. The interaction of genotype with environment (Table 4) was highly signif-icant, implying the need to investigate the stability of genotypes across environments. The line S.(32-2)A had the highest yield in most environments, averaging 5.36 t ha−1 over the two environments at Kuku and Islang in 2003/04, and 5.16 t ha−1 across the four environments at Kuku in 2004, and Shambat in 2005, 2005/06 and 2006. Its DMY combined over Kuku and Islang 2003/04 (Table 3) exceeded that of the checks Kambal (3.09 t ha−1) and

Activity Population size Selection criteria No. of selected genotypesSource population (2001/02) Approximately 5 000 plants Individual plant selection for vigour

of growth, juiciness (green mid-rib), leafiness, healthiness, plant height, flowering time, tillering

220

Laboratory inspection (2002) 220 panicles Panicles with <75% seed set were discarded

56

Replicated nursery (July 2002) 56 lines Forage and seed attributes, uniformity 21

PYT 1 (January 2003) 21 genotypes Forage yield and related traits, uniformity 10

PYT 2 (July 2003) 10 genotypes Forage yield and uniformity 7

Table 1: Procedure used to develop seven Sudangrass genotypes by selection within the land race cultivar Garawi at Shambat in 2000–2003). PYT = preliminary yield trial

Month

2003 2004 2005 2006 Long-term average

Temp.RH

Rain fall

Temp.RH

Rain fall

Temp.RH

Rain fall

Temp.RH

Rain fall

Temp. Rain fall

Days with rainMin. Max. Min. Max. Min. Max. Min. Max. Min. Max.

Jan. 14.2 31.7 27 0.0 17.9 31.9 24.2 0.0 12.1 29.3 25 0.0 15.6 33.6 28 0.0 15.6 30.8 0.0 0.0Feb. 15.5 33.5 16 0.0 18.1 32.6 20.4 0.0 17.4 37.0 24 0.0 16.1 35.6 19 0.0 17.0 33.0 0.0 0.0Mar. 18.6 35.8 15 0.0 21.5 37.3 14.4 0.0 18.6 37.3 17 0.0 17.2 36.0 23 0.0 20.5 36.8 0.0 0.1Apr. 21.3 40.6 16 0.0 27.0 41.4 17.7 trace 23.0 41.2 19 trace 19.2 38.6 19 0.0 23.6 40.1 0.4 0.1May 25.8 41.9 21 26.2 27.9 43.3 20.0 20.0 22.9 40.7 23 12.3 25.7 41.2 25 35.5 27.1 41.9 4.0 0.9Jun. 27.0 40.9 33 6.0 28.0 40.0 30.6 3.8 27.3 41.7 25 0.0 26.8 41.0 32 3.1 27.3 41.3 5.4 1.2Jul. 25.2 37.3 49 41.1 28.1 40.8 30.4 25.0 24.5 34.3 41 3.0 27.5 40.2 39 0.1 25.9 38.4 46.3 4.8Aug 25.3 35.8 58 74.0 27.1 38.5 45.9 45.0 26.2 37.1 53 56.3 27.0 36.6 56 0.9 25.3 37.3 75.2 4.8Sep. 25.2 38.4 45 12.9 27.6 39.8 40.5 14.5 25.7 38.7 47 16.6 24.4 37.4 55 2.5 26.0 39.1 25.4 3.2Oct. 23.9 39.9 31 3.4 23.9 39.5 36.0 2.1 23.8 39.8 29 trace 25.5 38.7 39 0.0 25.5 39.3 4.8 1.2Nov. 20.3 36.1 29 0.0 19.9 36.1 32.0 0.0 19.6 35.6 25 0.0 19.9 33.3 27 0.0 21.0 35.2 0.7 0.0Dec. 15.1 31.5 33 0.0 15.1 31.5 29.0 0.0 16.8 34.1 34 0.0 13.5 28.7 29 0.0 17.1 31.8 0.0 0.0

Table 2: Mean minimum and maximum temperature (Temp.; °C), relative humidity (RH; %) and total rainfall (mm) as recorded by the Shambat Meteorological Observatory for the years 2003–2006 and the long-term averages (30 years)

African Journal of Range & Forage Science 2010, 27(1): xx–xx 3

Abu Sab’in (2.46 t ha−1), whereas in the four environments (Table 4) its DMY significantly exceeded that of the check Garawi by 43%. On the other hand, the genotype S.51 showed the second-highest DMY among the selected lines (4.98 t ha–1) with a significant increase over Garawi amounting to 38% (Table 4). Its average performance over Kuku and Islang during 2003/04 (Table 3) was also better than that of the checks Kambal and Abu Sab’in. Cultivar superiority analysis (Table 4) revealed that the linesS.(32-2)A and S.51 displayed the lowest G×E statistic among the selected genotypes. They were both better than the checks Garawi and Kambal in average stability of yield superiority. In the second cut (Table 5) the line S.(32-2)A significantly (p < 0.05) out-yielded the checks and other selected lines in DMY averaging 1.63 and 2.54 t ha−1 during the winter seasons in 2003/04 and 2005/06, respectively. The respective DMY obtained by the check Garawi was 1.21 and 1.45 t ha−1.

Significant (p < 0.001) differences were found between genotypes for all agronomic yield-related traits (Table 6). Differences in days to flower between the selected lines S.(32-2)A, S.51, and the checks Garawi and Kambal were not significant with respective flowering periods of 62.9, 63.6, 62.2 and 61.9 d (Table 6). Plants of these lines were about 30 cm taller than the check Garawi. The lines S.50 and S.10-1 were the best in tillering capacity with 7.86 and 7.27 tillers per plant. The line S.50 also had the highest regrowth ability and leaf:stem ratio, whereas S.51 was among those with fewer tillers per plant. The line S.(32-2)A showed medium value for regrowth, whereas S.51 showed the lowest value among selected lines (Table 6).

The proximate analysis for quality traits (Table 6) showed that the line S.(32-2)A had the highest CP content in the whole material studied amounting to 7.88% followed by S.51 (7.0%). The check Garawi and S.18 had the lowest CP content and showed similar values (5.25%). The best NDF

GenotypeLocation

Shambat Islang Kuku Mean combined (Kuku, Islang)1

S.50 3.51 4.17 3.75 3.92S.10-1 3.22 4.44 4.76 4.63S.18 2.88 3.74 2.93 3.26S.(32-2)A 3.53 6.04 4.90 5.36S.51 4.22 5.83 3.31 4.32S.34 2.53 4.24 3.54 3.82S.32-1 3.53 5.63 4.61 5.02Kambal (check) 3.60 2.75 3.09Abu Sab’in (check) 2.95 2.13 2.46Garawi (check) 2.33Mean 3.22 4.52 3.63 3.99Significance ns * ** **SE 0.438 0.495 0.356 0.289LSD (0.5) – 1.614 1.068 0.843CV (%) 19.3 15.5 17.0 16.21 Mean squares: environment (E) = 11.4106ns, genotype (G) = 4.4928**, G×E = 0.6669ns, residual = 0.4171*,** Significant at 0.05 and 0.01 probability level, respectively; ns = non-significant at 0.05 probability level

Table 3: Dry matter yield (DMY; t ha−1) of seven Sudangrass genotypes and three check cultivars at Khartoum State in 2003/04

GenotypeKuku Shambat

Mean combined1 G×E statistic2004 2005 2005/06 2006

S.50 5.33 4.13 4.32 2.49 3.95 1.574S.10-1 5.26 4.99 4.23 2.78 4.23 1.272S.18 5.68 4.59 4.88 2.99 4.43 0.912S.(32-2)A 6.57 5.00 5.50 4.03 5.16 0.214S.51 6.69 4.52 5.53 3.73 4.98 0.379Garawi (check) 4.04 3.97 3.64 2.91 3.60 2.256Kambal (check) 5.10 5.28 3.98 5.30 4.90 0.618Mean 5.52 4.64 4.58 3.46 4.46Significance ** ns ** ** **SE 0.303 0.312 0.253 0.282 0.145LSD (0.5) 1.049 – 0.779 0.868 0.415CV (%) 7.8 11.6 9.6 14.1 10.81 Mean squares: environment (E) = 10.5603**, genotypes (G) = 3.6464** , G×E = 1.0695**, residual = 0.2325** Significant at 0.01 probability level, ns = non-significant at 0.05 probability level

Table 4: Dry matter yield (DMY; t ha−1) and cultivar superiority analysis (G×E statistic) of five Sudangrass genotypes and two checks grown in different environments in Khartoum State

Mohammed4

percentages were shown by S.18 (44.6%) and S.50 (49.0%.). These lines were better than S.(32-2)A and Garawi, which showed similar NDF values of 60.5%. With regard to ADF,S.(32-2)A was the best among the selected lines (36.7%) but not better than Garawi (33.8%).

The results from experiments in different environments demonstrate clearly that the lines S.(32-2)A and S.51 were superior in forage yield than the traditional checks Garawi and Abu Sab’in, with S.(32-2)A being particularly distinguished for its improved second cut. Both genotypes were comparable or sometimes better in dry matter yield than the recommended cultivar Kambal. High forage yields in sorghum are usually associated with prolonged flowering period (Ross et al. 1983, Ferraris and Edwards 1986). In this study, increment in yield was achieved without significant delay in flowering duration, as both genotypes were comparable to the check Garawi in days to flower. Therefore, S.(32-2)A and S.51 are well suited to the locally prevailing green chopping system that favours

high forage yields produced over a relatively short period of time. Cultivar superiority analysis indicated that both genotypes showed the lowest G×E values; therefore they are expected to keep their superiority in forage yield across a wide range of environments.

Proximate analysis for quality traits indicated thatS.(32-2)A and S.51 were superior to Garawi in protein content. Positive favorable association between yield and protein, though of rare occurrence, has sometimes been encountered (Vidal and Lazarte 1975, Muhammad 1990). This favorable association was not evident for NDF and ADF percentages. The NDF measures intake potential while ADF predicts digestibility; however, the results suggest that S.(32-2)A was not significantly inferior to Garawi in these attributes. On the other hand, S.(32-2)A and S.51 were juicier (having a green mid-rib) than the check Garawi (with a white mid-rib). Juiciness is a good indicator for palatability, especially under the prevailing green chopping system, where forages are essentially offered as green matter. Being a simply inherited character, juiciness was fixed in the early stages of the breeding program by selecting for the green mid-rib colour.

As pointed out earlier, the present Garawi population is highly mixed and genetically variable. This is due to the high out-crossing rate known to occur in Sudangrass (Pedersen et al. 1998). According to de Wet et al. (1970), S. sudanense is among four species developed by natural hybridisation between cultivated forms and members of the weedy series Spontanea. Such a high level of heteroge-neity poses practical limitations on maintaining the required features of a cultivar. Moreover, low seed set is one of the negative contributions of the weedy types to the genetic pool of Sudangrass populations. In this study, uniformity and high seed set were some of the selection criteria that have been considered in developing S.(32-2)A and S.51. Therefore, in addition to their improved agronomic and quality performance, S.(32-2)A and S.51 have improved reproducibility over the traditional Garawi.

The newly developed genotypes may contribute to diversification of the already depleted genetic variability of Sudangrass populations. The lines S.(32-2)A and S.51

GenotypeDMY (t ha–1)

2003/04 2005/06S. 50 1.19 1.48S.10-1 1.36 1.59S.18 0.99 1.55S.(32-2)A 1.63 2.54S.51 1.46 1.48S.34 1.29S.32-1 1.35Garawi (check) 1.21 1.45Kambal (check) 1.24Abu Sab’in (check) 0.68Mean 1.31 1.50Significance * **SE 0.078 0.142LSD (0.05) 0.260 0.474CV (%) 8.4 13.4*,** Significant at 0.05 and 0.01 probability level, respectively

Table 5: Dry matter yield (DMY) of the second cut obtained by different Sudangrass genotypes and the check cultivars grown at Shambat

Genotype Days to flower

Plant height (cm)

No. of tillers per plant

Regrowth (g m–1 row)

Stem diameter (cm)

Leaf:stemratio (%)

Proximate analysis CP (%) NDF (%) ADF (%)

S.50 66.771.365.062.963.663.260.562.261.957.7

179177193214202207189173194182

7.867.275.735.083.026.413.294.35

525232206302110332322

141121

0.750.760.910.920.960.920.970.871.131.22

42.036.737.337.633.433.935.537.633.7

6.136.575.257.887.00

5.25

49.0

44.660.6

60.5

39.7

53.736.7

33.8

S.10-1S.18S.(32-2)AS.51 S.34S.32-1Garawi (check)Kambal (check)Abu Sab’in (check)Mean 63.5 191 5.38 255 0.94 36.4 6.35 53.7 41.0χ2 probability <0.001 <0.001 <0.001 <0.001 <0.001 <0.001SED 1.744 10.08 0.6432 63.82 0.09048 1.295 0.757 4.66 4.15

Table 6: Yield-related traits and proximate analysis of some Sudangrass genotypes and check cultivars grown in Khartoum State in 2003–2006). ADF = acid detergent fibre, CP = crude protein, NDF = neutral detergent fibre

African Journal of Range & Forage Science 2010, 27(1): xx–xx 5

were improved over their original population (Garawi) in terms of forage yield, uniformity and seed-setting ability. The former line was officially released by the Variety Release Committee in February 2009. In addition to their improved per se performance, they may also serve as potential parents in hybrid combinations. Seed of the newly developed Sudangrass genotypes is maintained by the Forage and Range Research Program, Agricultural Research Corporation (ARC), Shambat Research Station. Limited amounts of seed may be provided for research purposes upon a written request to the author.

Acknowledgements — The author is grateful to MAM Khair, national coordinator for forage and range research, ARC, Wad Medani, Sudan, and AE Elasha, Editor-in-chief of the Sudan Journal of Agricultural Research, ARC, Wad Medani, Sudan, for reviewing the manuscript and for their valuable comments and suggestions.

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