Genetic components of variance and the role of pollen traits in sorghum ergot resistance

Ergot (caused predominantly by Claviceps africana Freder., Mantle & De Milliano) is a disease of sorghum (Sorghum bicolor L. Moench), with pollen traits reported to be associated with resistance. This study investigated the genetic architecture and the role of pollen quantity (PQ) and pollen viability (PV) in ergot resistance in an F5 recombinant inbred line (RIL) sorghum population developed from the cross between an elite germplasm line, 31945-2-2 from Australia, and a recently reported putatively resistance source line, IS8525. Percentage ergot infection (PCERGOT) in IS8525 was very low, while in contrast, 31945-2-2 was heavily infected at all inoculation dates of the two field trials conducted under artificial epiphytotic conditions during 2001 and 2002. The distribution of the predicted means for PCERGOT, PQ, and PV was normal, suggesting that the traits are polygenic in nature. Genetic correlations between the two pollen traits and PCERGOT were moderately negative, indicating that there might be some common genetic factors controlling these traits. However, low R-2 values of PQ (11%) and PV (9%) suggest that only a small part of the total variability in ergot resistance in this population was due to the variability in PQ and PV Correlations between ergot scores for different sampling dates (SDATEs) and years were moderate to high, indicating relatively low levels of genotype x environment interaction. Genetic variance and broad sense heritability were also high, indicating that ergot resistance is likely to respond well to conventional selection.