Evaluation of yield and forage quality in main and ratoon crops of different sorghum lines

<p>Improving the yield and quality of sorghum (<em>Sorghum bicolor</em>) forage for livestock feeding is a major breeding objective, because of sorghum’s inherently high biomass accumulation, high productivity per unit water utilized and its ability to produce a ratoon crop after harvesting of the plant crop. Newly bred sorghum lines, including 36 lines falling in 5 different categories, i.e. 12 experimental dual-purpose lines, 6 germplasm accessions from the ICRISAT collection, 11 commercial varieties and hybrids, 6 forage varieties and 1 <em>bmr</em> mutant line, were evaluated in terms of fodder yield, quality and ratooning ability. The main crop produced more dry biomass (P&lt;0.05) at 80 days after planting (mean 22.87 t DM/ha; range 17.32‒33.82 t DM/ha) than the ratoon crop (mean 8.47 t DM/ha; range 3.2‒17.42 t DM/ha) after a further 80 days of growth. Mean nitrogen concentration in forage did not differ greatly between main and ratoon crops (2.56 vs. 2.40%, respectively) but there was wide variation between lines (2.06‒2.89%). The line N 610 recorded highest N percentage of 2.89%, followed by SSG 59 3 (2.86%) and SX 17 (2.81%). Highest acid detergent fiber % was recorded by ICSV 12008 (42.1%), closely followed by CO 31 and IS 34638 (40.0%). The least acid detergent lignin % was observed in MLSH-296 Gold (3.59%), ICSV 700 (3.75%) and ICSSH 28 (3.83%). Metabolizable energy concentration was highest in N 610, Phule Yashodha and SX 17 (mean 8.34 MJ/kgDM), while in vitro organic matter digestibility ranged from 52.5 to 62.6%. The main crop contained much higher mean concentrations of the cyanogenic glycoside, <em>dhurrin</em>, than the ratoon (639 vs. 233 ppm, respectively) with ranges of 38 to 2,298 ppm and 7 to 767 ppm, respectively. There was no significant correlation between <em>dhurrin</em> concentration and dry biomass yield so breeding and selection for low <em>dhurrin</em> concentrations should not jeopardize yields. Hence, breeding for sorghum can target simultaneously both quality and biomass improvement.</p> <p> </p> <p><strong>Keywords: </strong>Cyanogenic glycoside, digestibility, dry biomass production, fodder quality, tillering ability.</p>