Abstract
The global spinach (
Spinacia oleracea
) seed trade has contributed to the spread of plant pathogens such as
Verticillium dahliae
and
Peronospora effusa
.
Verticillium dahliae
causes Verticillium wilt in a broad range of crops, including lettuce (
Lactuca sativa
) and strawberry (
Fragaria
×
ananassa
). Verticillium wilt occurs only in spinach seed production fields and is not observed in spinach production fields as the crop is harvested well before symptom manifestation. In contrast,
P
.
effusa
exclusively infects spinach in production fields causing the destructive downy mildew. Managing these pathogens is challenging. Both pathogens survive in seeds, so efforts to minimize seed infestations are an important component of management. In this study, we examined nitrogen dioxide (NO
2
) and sulfur dioxide (SO
2
) treatments against
V
.
dahliae
and
P
.
effusa
in spinach seeds. Compared with untreated infested control seeds, treatments with 3% NO
2
for 3 days significantly reduced viable seedborne
V
.
dahliae
infestation by 60.7% as observed in grow-outs from whole seeds and reduced viable
V
.
dahliae
colonies by 91.0% when seeds were ground and plated on the semiselective NP-10 medium following seed treatment. The 3% NO
2
treatment eliminated the transmission of downy mildew from oospore-infested spinach seeds. Notably, NO
2
treatment also significantly enhanced seed germination. In contrast, SO
2
treatments (0.25 to 0.5% for 1 h) only reduced the viability of seedborne
V
.
dahliae
by 19.5 to 24.7% but reduced seed germination by 7.0 to 16.4%. These findings suggest that NO
2
treatment has potential as an effective treatment for controlling
V
.
dahliae
and
P
.
effusa
in spinach seeds and for managing seedborne pathogens in other crops.