Root plate growth in sunflower and its relevance to sclerotinia basal stalk rot

Authors: MISAR, CHRISTOPHER - Former ARS Employee

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sclerotinia basal stalk rot disease is a common fungal disease of sunflower, caused by infection of the root. However, effective methods for evaluating disease resistance of sunflowers in the field have been lacking. The author found that later growth stages are associated with higher rates of disease and increased statistical differentiation of susceptible and resistant sunflower lines. The author found that root plate diameter, or the width of the thick mat of roots near the soil surface in sunflower plants, is considerably larger in reproductive stage plants. Previous recommendations for mechanical inoculation of plots in the field included vegetative stage deposition of disease inoculum at a distance from the plant that was greater than the reach of the root plate, resulting in low disease in both susceptible and resistant sunflowers. A new recommendation of reproductive stage inoculation, closer to the plant, under high soil moisture conditions, is recommended so that inoculum is deposited at the known site of infection under a conducive soil environment.

Technical Abstract: Sclerotinia basal stalk rot (BSR) of sunflower (Helianthus annuus L.) is a fungal disease of the roots that causes symptoms of wilt and a basal stem lesion. Evaluating root plate growth could improve our understanding of BSR. Separate studies were conducted to determine the effect of sunflower growth stage or genotype on root plate diameter in North American environments. Root plate diameter of cultivated hybrids at reproductive growth stages was 3 to 4 times larger than vegetative stages. Cultivated hybrids had larger root plate diameter than interspecific lines. These results have implications for artificial inoculation methods that evaluate genotypes for BSR resistance in the field or greenhouse. Disease escapes can occur if field-grown plants are inoculated too far from the root plate and/or too early at vegetative growth stages. Side-dressing mycelium-infested cereal grain closer (i.e., 10 cm) to plants at reproductive growth stages (i.e., R1 - R4) can increase disease pressure and reduce disease escapes. These guidelines for the field can be used to validate results from artificial inoculations in the greenhouse.