Inheritance of partial resistance to black stem (Phoma macdonaldii) in sunflower

Abstract

Two programmes to investigate the inheritance of resistance to black stem in sunflowers were undertaken in a controlled-environment growth chamber. In the first, an experiment was performed using a randomized complete block design with 24 lines, six male-sterile (A lines), six maintainers (B lines), six restorers (R lines) and their six F 1 hybrids in six replications. Each treatment consisted of 12 seedlings. Twelve-day-old seedlings were inoculated with a suspension of pycniospores, and 7 days later the two cotyledon petioles of each seedling were scored on a 1±9 scale for the percentage of necrotic area. Some alloplasmic lines (which have the same nucleus and different cytoplasms) gave a significant cytoplasmic effect for improved partial resistance to the disease. Deviation of F 1 hybrids from the mean of the parent values was significant for partial resistance to Phoma macdonaldii in three of the six F 1 hybrids. Two further experiments with eight lines (resistant and susceptible) at the fifth leaf-pair and flowering stages were carried out under the same conditions. At both growth stages the previous classification of lines at the seedling stage was confirmed. In the second programme, five male-sterile sunflower lines were crossed with five fertility-restorers in a factorial mating design. The 10 inbred lines and their 25 F 1 hybrids were studied in two successive experiments under the same conditions and with the same experimental design and isolate of Phoma as in the seedling-stage experiment in the first programme. Analysis of variance showed that male-sterile and restorer lines possessed general combining abilities, and also that specific combining abilities of F 1 hybrids were significant. The estimates of general combining ability for partial resistance were significant in AS617A, AS618A and AS614R inbred lines. These lines are available for developing F 1 hybrids with improved resistance to Phoma in sunflower-breeding programmes.

Genotype‐isolate interaction for resistance to black stem in sunflower (Helianthus annuus)

“…For this reason, the artificial inoculation method developed by Roustaee et al (2000a) was used in the present studies. The seedling petiole test used in this study allowed the inoculum load per plant to be controlled, thus minimizing the number of plants escaping infection and consequently reducing the potential for false negatives, as up to now reports on black stem resistance in sunflower indicate the lack of full resistance in cultivated sunflower (Roustaee et al, 2000a;Debaeke & Pérès, 2003). Moreover, all plantlets with no visible lesion on the petiole were defined as not infected, and excluded from the present experiments.…”

Comparative genetic analysis of quantitative traits in sunflower (Helianthus annuus L.)

“…Black stem can occur at any time during the growing season, but is most common after flowering and the disease is most severe when abundant moisture is available during and after flowering. No control measures are totally effective (Roustaee et al 2000). Some cultivars are more tolerant than others, but no hybrids have been identified as being immune to the disease.…”

Characterisation of sunflower root colonisation by Phoma macdonaldii

“…Previous work showed that partial resistance to black stem disease is conferred by more than one gene with additive effects (Roustaee et al 2000a). A more recent study with nine French isolates of P. macdonaldii and four sunflower genotypes suggested the presence of tissue-specific resistance genes (Abou Al Fadil 2006) Phoma macdonaldii penetrates into the plants either directly via enzymatic degradation of the plant cell wall or by mechanical pressure, or indirectly through wounds and natural openings such as lenticels and stomata (Isaac 1992, Roustaee et al 2000b).…”