Evaluation of sorghum hybrids for resistance to the root rot complex

Abstract

Seventy-one sorghum hybrids were evaluated for root rot resistance at Bethlehem and Potchefstroom, South Africa, from 1995/96 to 1998/99. Mean root rot severity ranged from 30.3% in PAN8494 to 41.3% in PAN8061 and root rot severity of hybrids differed significantly. However, highly significant genotype × environment interactions were recorded. Similarly, a significant environment × hybrid interaction was recorded for recovered root volume which ranged from 24.9 ml in Buster to 35.3 ml in CRN7686. Additive main effects and multiplicative interaction analyses (AMMI) were used to identify those hybrids in which root rot and root volume were significantly influenced by environment. Root discolouration and root volume were not correlated with plant length at both localities during 1997/98 and 1998/99. An index to quantify effective root volume (E) based on root rot severity and root volume i.e. E = [({100 - root rot severity)/100} × root volume] was significantly related to plant length during the 1997/98 (R2= 0.68 and R2= 0.51) and 1998/99 (R2 = 0.36 and R2= 0.62) seasons at Bethlehem and Potchefstroom respectively. Similarly, a significant relationship was recorded between effective root volume and head volume during 1998/99 at both localities (R2= 0.46 and R2= 0.63 respectively) but not with head length. Although seasonal variation in effective root volume was recorded, relatively little variation in mean effective root volumes of hybrids over the entire evaluation period was recorded.