Comparison of the rooting ability of virus infected and virus-free cuttings of sweet potatoes (Ipomoea batatas Poir.) and an anatomical comparison of the roots

Summary

The rooting abilities of the filamentous virus infected and the virus-free cuttings of sweet potato (Ipomoea batatas Poir.) were compared, with an anatomical comparison of the root. The diameters of the pith and the vascular bundle cylinder at the node of the virus-free cutting were larger than in those of virus infected ones. Thicker and more vigorous roots were initiated in the virus-free cutting. The diameter of the central cylinder and the thickness of the cortical layer of the root were larger in the virus-free cutting than in the virus infected one. Larger and more numerous vessels developed, and larger and more distinct meristematic tissues surrounding the protophloem poles also developed in a fan form in the root of the virus-free cutting. The weight of the leaf and stem of the plant 80.d after planting in the field were larger in the virus-free cutting than in the virus infected cutting. From these results, the following assumptions on roots in the virus-free cutting can be made. Thicker roots with larger vessels and thicker meristematic tissues develop in the virus-free cutting because the meristematic activity is high in the tissues in the vicinity of the vascular bundle cylinder at the node, due to the recovery of normal physiological function by removal of the virus. There are fewer roots in the virus-free cutting because the smaller total area of the root is sufficient to absorb the nutrient elements owing to superior development of the vessels and meristematic tissues in the root. In the field, the larger weight of the leaf and stem in the virus-free cutting is caused by the high absorption ability of nutrient elements from the root.