A Rapid Seedling Assay for Determining Sweetpotato Resistance to Fusarium Wilt

Abstract

Fusarium wilt, caused by Fusarium oxysporum f. sp. batatas (Woolenw.) W. C. Snyder & H. N. Hansen (abbreviated as “Fob”), is a devastating disease that can cause sweetpotato [Ipomoea batatas (L) Lam.] yield losses of up to 50%. A rapid and efficient assay can expedite the selection of Fusarium wilt‐resistant cultivars. A rapid seedling assay was developed to evaluate sweetpotato resistance to Fusarium wilt. Seedlings of three cultivars—JinShan 57 (highly resistant), JinShan 696 (moderately resistant), and XinZhongHua (highly susceptible)—were grown in suspensions containing different conidial concentrations of Fob. Inoculation with a Fob conidial suspension of 1 × 105 conidia mL−1, incubation of inoculated plants at 28°C, and assessment of disease development 12 d after inoculation provided optimal results. Resistance of 28 sweetpotato advanced breeding selections was evaluated in 2014 and 2015 using the rapid method and a conventional field test. These tests confirmed the reliability of the rapid method. This study demonstrates that the new assay is rapid, efficient, and can facilitate screening of large numbers of sweetpotato cultivars and selections for Fob resistance.

Occurrence of Sweetpotato (Ipomoea batatas) Wilt and Surface Rot Disease and Determining Resistance of Selected Varieties to the Pathogen in Korea

“…Besides this, resistance variety selection has been done to avoid surface rot disease. Similar observations were recorded in Bangladesh [36], China [20], India [37], Peru [38], and the USA [35]. In Korea, severe surface rot disease was observed in the Yesumi variety, Yulmi showed resistance to the disease, and the other varieties were resistant to moderately susceptible to the disease.…”

“…Fusarium wilt and surface rot diseases of sweetpotato and their causal organism were investigated in the present study, which applied an established rapid screening method [20] with minor modifications for resistant variety selection. We followed their optimized conditions of temperature, relative humidity, and concentration of spore suspensions, but each seedling was immersed in spore suspensions separately in a 50 mL falcon tube ( Figure 5), while the previous report [20] explained that they immersed all the seedlings in the same bottle. Our explanation is that separate immersion could reduce the risk of contamination if there are any contaminated seedlings.…”

“…153909), which replaced the most serious disease with a less significant disease [17]. Screening has been conducted in different countries on sweetpotato and other plant species using conventional field trials or lab tests, which require significant time and space [18][19][20]. In Argentina, three cultivars collected from Argentina (Tucumana lisa), Brazil (Brasilera blanca) and the USA (Goldrush) were found resistant to the disease in sweetpotato [21].…”

“…Recently, a rapid seedling assay was conducted in sweetpotato in China by Yang et al [20] to test the resistance of Fusarium wilt, and factors involving the resistant test were optimized, including conidial suspensions, incubation time, and temperatures. An improved method was described long ago by Hanna et al in 1961 [16].…”

“…[23]. The effectiveness and the degree of resistance and susceptibility may vary among years or soil type and also can be affected by other soil microbes [20,24]. Fusarium surface rot resistance was tested in some countries at a low scale, and it was observed that the small number of roots or cultivars or varieties are moderately resistant to this disease.…”