Phloem transport of carboxyfluorescein through tomato roots infected with Meloidogyne incognita

Abstract The fluorescent acidic dye, carboxyfluorescein (CF) was used to study phloem transport through M. incognita infected tomato roots. Following application to leaves, CF moved via the internal and external phloem of the stem towards the roots. In infected intact roots, dye accumulated inside galls. Movement to more apical root regions occurred via irregularly arranged phloem elements. At the infection sites, dye accumulated inside the nematode induced giant transfer cells. When CF was applied directly to the xylem vessels, the giant cells failed to accumulate dye. These observations suggest that a symplastic transport pathway exists between the phloem and giant cells. Continuous dye application over prolonged periods to triple-split, singly infected shoot-root systems, revealed a transport pathway for solutes from the giant cells, via the body of the nematode, out of the root. This pathway may contribute to the higher leakage of solutes known to occur from root-knot nematode infected roots.