Objective A method was developed to rapidly evaluate the resistance of an asparagus cultivar to stem blight.

Method Seven asparagus cultivars with varying degrees of resistance to stem blight were selected for the study. To artificially induce the disease, (1) the asparagus seeds and/or roots were soaked in an aqueous solution containing the mycotoxin produced by Phomopsis asparagi, (2) the asparagus seeds were submerged in P. asparagi spore suspension, or (3) the asparagus roots were irrigated with an aqueousP. asparagi spore suspension to compare with (4) the natural induction on asparagus plants in the field. Seed germination and seedling root growth were monitored to grade the disease resistance or susceptibility of each asparagus variety.

Result  After 24h soaking in an aqueous solution containing mycotoxin, the seeds of Grande, Jialu No. 1, Zaojia No. 1, Fengdao No. 1, Huamiao, TC and UC157F₂ displayed inhibited germination at the rates of 3.62%, 4.29%, 13.98%, 4.26%, 2.19%, 4.95% and 15.00%, respectively. Accordingly, UC157F₂ and Zaojia No. 1 were classified as the susceptible varieties and the remainders moderately resistant ones. As the root growth of Grande, Jialu No. 1, Zaojia No. 1, Fengdao No. 1, Huamiao, TC and UC157F₂ plants affected by an exposure to mycotoxin were inhibited at the rates of 80.94%, 73.72%, 82.29%, 71.77%, 65.86%, 69.39% and 82.35%, respectively, the asparagus cultivars UC157F₂, Zaojia No. 1 and Grande were grouped in the susceptible class, Jialu No. 1 and Fengdao No. 1 in the moderately susceptible class, and TC and Huamiao in the moderately resistant class. The significant inhibition on germination by soaking the seeds in suspension of 1.0×10⁵ P. asparagi spores·mL⁻¹ was at a rate of 43.88% on the Grande seeds, 40.97% on the Jialu No. 1 seeds, 41.67% on the Zaojia No. 1 seeds, 32.87% on the Fengdao No. 1 seeds, 29.59% on the Huamiao seeds, 28.52% on the TC seeds, and 61.23% on the UC157F₂ seeds. The results placed UC157F₂ in the susceptible, Grande, Zaojia No. 1 and Jialu No. 1 in the moderately susceptible, and Fengdao No. 1, Huamiao and TC in the moderately resistant classifications. When the plants were irrigated with the P. asparagi spore suspension, the disease incidence on all tested asparagus was greater than 80% and not adequate to differentiate the resistance grades. Finally, in comparison, the stem blight-induced UC157F₂ plants in the field was the susceptible cultivar, whereas Zaojia No. 1, Grande, Jialu No. 1 and Fengdao No. 1 were the moderately susceptible and Huamiao and TC the moderately resistant varieties.

Conclusion  Of the various methods for comparing resistance to stem blight of asparagus varieties, soaking the seeds in P. asparagi spore suspension rendered the classification closest to that obtained by the field induction (P＜0.01). Therefore, along with field observation, it could be reliably applied to quickly estimate the disease resistance of an asparagus cultivar.