Some morpho-anatomical characteristics of cotton (Gossypium hirsutum L.)in relation to resistance to cotton leaf curl virus (CLCuV)

摘要

Cotton leaf curl virus (CLCuV), transmitted by whitefly Bemisia tabaci, causes one of the most devastating diseases of cotton. The first disease symptom appearing on the leaves of susceptible plants is thickening of mid ribs and veins. To examine whether leaf morphology plays any role in avoiding or restricting the insect-vector, epicuticular wax content and hairiness of leaves were determined in three cultivars of cotton differing in resistance to CLCuV(i.e., S-12, CLCuV-susceptible; NIAB-Kirishma, moderately resistant; CIM-448, CLCuV-resistant). ClM-448 had considerably greater epicuticular wax on its leaf compared with the other two, but relatively very low leaf hair density as found in S-12. The diseased leaves of cvs S-12 and NIAB-Krishma had significantly greater epicuticular wax than on their healthy leaves. Hairiness was greatest in NIAB-Krishma. While probing the effects of disease on vein thickening, electron micrographs of the mid ribs of the three cultivars showed remarkable differences. In the mid rib of the diseased leaf of S-12, the xylem and phloem elements were partially or completely collapsed, whereas no such effect of the disease was observed in NIAB-Krishma or CIM-448. The vascular elements of the veins of S-12 were severely affected, and those of NIAB-Krishma slightly affected, thus clearly reflecting their differential degree of resistance to CLCuV. Thickening of mid ribs and veins in diseased leaves seemed to be mainly due to proliferation of parenchymatous tissues in these leaf parts.