Objectives This study investigated the growth responses and sensitive plant parts of sweet potato seedlings subjected to different micronutrient deficiencies, aiming to screen out diagnosis parts of nutrient deficiency in sweet potato.

Methods A hydroponic experiment was conducted using the sweet potato cultivar ‘Pushu 32’ as the experimental material. The experiment included seven treatments: complete nutrient solution (CK), iron deficiency (−Fe), manganese deficiency (−Mn), zinc deficiency (−Zn), copper deficiency (−Cu), boron deficiency (−B), and molybdenum deficiency (−Mo). The phenotypic traits of the plants were systematically observed, and parameters such as chlorophyll content, vine length, biomass, root morphology, and plant micronutrient concentrations were measured.

Results 1) Micronutrient deficiency treatments induced obvious symptoms in sweet potato seedlings. The −Fe treatment caused interveinal chlorosis, with chlorophyll a and b decreasing by 53.61%−98.05% and 48.75%−97.76%, respectively. The −Mn treatment resulted in dark green veins and mild interveinal chlorosis, with chlorophyll a reduced by 19.43%−49.21%. The −Zn treatment led to smaller and thicker leaves with chlorosis between mid-veins. The −Cu treatment produced dense yellow spots on middle and lower leaves, with chlorophyll a and b decreasing by 12.79%−35.56% and 18.51%−44.99%, respectively. The −B treatment caused shell-like notches on leaf margins, while the −Mo treatment induced chlorotic patches, with chlorophyll a and b in middle and lower leaves reduced by 16.03%−49.98% and 16.91%−48.85%, respectively. 2) Micronutrient deficiency treatments significantly inhibited sweet potato growth. The −Fe, −Mn, −Zn, and −Cu treatments reduced vine length by 42.62%−67.97%, and shoot and root biomass by 25.91%−65.94%. All deficiency treatments decreased root diameter by 22.63−54.82%. The −Zn and −Mo treatments significantly increased root length by 45.06% and 22.57%, respectively, while the −Fe, −Mn, −Zn, and −Cu treatments reduced root volume by 26.40%−61.83%. 3) The decreases in micronutrient concentrations varied greatly among the leaves at different positions. The −Zn and −B treatments led to declines in Zn and B concentrations in upper leaves by 72.37% and 45.06%, respectively, indicating that upper leaves are sensitive to Zn and B deficiency and could serve as diagnostic plant parts; the −Mn treatment reduced Mn concentration by 94.77%, while the −Cu and −Mo treatments decreased the concentrations of the corresponding elements by nearly 100% in middle leaves; therefore, middle leaves were suitable for diagnosing Mn, Cu, and Mo deficiencies; lower leaves were sensitive to Fe deficiency, with Fe concentration reduced by 58.00%. 4) Cluster analysis indicated that sweet potato was sensitive to stress imposed by −Fe, −Cu, and −Zn, with a sensitivity order of −Fe>−Cu>−Zn, whereas it showed greater tolerance to −Mo, −B, and −Mn.

Conclusions Sweet potato is sensitive to deficiencies of Fe, Cu, and Zn; the corresponding diagnostic parts are lower, middle, and upper leaves, respectively. Sweet potato is relatively tolerant to Mo, B and Mn deficiencies, with middle leaves serving as the diagnostic plant parts for Mo and Mn deficiencies and upper leaves for B deficiency.