Agronomic Comparison, Heterosis and Hydrocyanic Acid Potential (HCN-p) of Sudangrass-Sorghum and Sudangrass-Sudangrass Hybrids and Their Parents

Abstract

Cytoplasmic male-sterile sudangrass, A Rhodesian (Sorghum arundinaceum), was crossed with two sudangrasses (Sweet Sudan and Piper) and six forage sorghums (Sugar Drip, Brawley, Roma, Collier, Sumac and Meridian 55- 1). The eight F₁ hybrids and their male parents were compared for yield of green forage (GF), dry forage (DF), and crude protein (CP); dry matter (DM) and CP contents; plant height, leaf area, number of tillers, leaf/stem ratio and hydrocyanic acid potential (HCN-p). The first cutting was made 60 days after planting and the two subsequent cuttings at a 60-day interval. The second harvest had the greatest DF yields but a lower CP content when compared to the first harvest. The  F₁ hybrids were significantly superior than male parents for all traits except HCN-p at 45 and 60 days, leaf/stem ratio and DM and CP contents at each of the three harvests. Combined data for the three cuttings show that the  F₁'s of A Rhodesian x Sumac and A Rhodesian x Roma produced the greatest DF yields among hybrids. The DF yields of Sugar Drip were the highest among male parents. The average DF yield for  F₁ hybrids was 19% more than for the male parents. The DF yields of about 19 t/ha of the best hybrids compared favorably with other high yielding forage sorghums. Heterosis was observed for the most important traits,  F₁ hybrid A Rhodesian x Piper exhibiting the greatest value, 60 and 97% more DF than the midparent and high parent, respectively. The excellent DF yields, relatively low HCN-p values and high protein content of hybrids when A Rhodesian sudangrass was the female parent, make them potentially valuable genotypes for utilization in an intensive management program in the tropics. As in a previous study. A Rhodesian sudangrass proved to be a potentially useful male-sterile line in the development of superior F₁ forage sorghum hybrids in Puerto Rico.