Genetic variation for resistance to Sclerotinia head rot in sunflower inbred lines

Sclerotinia sclerotiorum is one of the most devastating pathogens of sunflower (Helianthus annuus), causing substantial yield losses. This study was conducted to screen sunflower lines for their reaction to S. sclerotiorum using artificial inoculation of sunflower heads. A set of 15 maintainer and 30 restorer lines was screened in four years by inoculating the heads with mycelium grown on millet seed. Susceptibility was assessed by measuring the lesion length of the head and scoring the part of the head that was rotted. With the exception in 1999, with no results owing to an infection rate less than 50%, the test proved to be effective and practicable. Significant genotypic variances among lines and moderate heritabilities were observed for the resistance traits. No differences between the means of maintainer and restorer lines were found. While lesion length of the head showed no differences between branched and unbranched restorer lines, significantly higher means for head rot were observed for branched lines. Both scoring traits were moderately correlated and showed a weak correlation to stem lesion length after leaf inoculation. Inbreds with high resistance were identified that can be used as parents in resistance breeding programs. (C) 2002 Elsevier Science B.V. All rights reserved.