Leaf anatomical basis of woolly aphid resistance in sugarcane.

摘要

An experiment was conducted on sugarcane clones (resistant - SNK 192 and SNK 754; susceptible - CoC 671 and Co 92920) to determine the possible mechanism and basis of resistance to the woolly aphid Ceratovacuna lanigera. The leaf thickness, measured as the distance between the lower and upper leaf epidermis, did not differ significantly between resistant and susceptible groups of clones. Similarly, the group mean distance between lower epidermis and phloem in resistant clones was more compared to susceptible clones, even though the group mean did not differ significantly. The distance between large and small, large and medium, and medium and small vascular bundles varied significantly between the resistant and susceptible clones. Further, phloem width was significantly more in resistant clones compared to susceptible clones. The resistant clones had significantly thicker phloem fibre compared to the susceptible clones. Based on the absorbance values of hydroxamic acid (Hx) content on the resistant clones and field observations, the resistance mechanism operating may be antibiosis or antixenosis (feeding deterrence or toxic effect) and basis of resistance may be biochemical, as Hx content was higher in resistant clones compared to susceptible clones. In a field study, released apterous nymphs could not colonize on resistant clones leading to complete mortality after 48-72 h of release, compared to susceptible clones, which colonized immediately after 24 h of release. Further, aphids released on resistant clones did not secrete honeydew, indicating lowered or no ingestion of sap from phloem.