Histology of resistant and susceptible pigeonpea infected with Fusarium udum

Abstract

Fusarium wilt caused by Fusarium udum Butler, is an economically important disease of pigeon pea (Cajanus cajan (L.) Mill). Information on the mechanisms of resistance to this disease in pigeonpea is limited. To study the role of vascular occlusion in wilt resistance, isolates of F. udum were inoculated onto resistant and susceptible varieties of pigeon pea and observed under light and transmission electron microscopes. The presence ofF. uduni in wilt susceptible plants was characterized by mycelia and conidia in the xylem vessels, plugging in some vessels, dlsintegration of xylem parenchyma cells in the infected areas, and the formation of cavities due to heavy colonization in the pith cortex vascular bundle. Resistance to F. udum in the roots and stems of wilt resistant plants was associated with low fungal colonisation and high occlusion due to tyloses and gels in the xylem vessels. There were significantdiffcrences (P = et05) in the number of xylem vessels occluded by tyloses in resistant and susceptible plants with a maximum 01'22.5% and 8.0% occlusion, respectively. It is probable that tyloses and gels formed as a result of F. udum interaction in wilt resistant plants are part of a resistance mechanism