Abstract
Physiological tolerance in response to Yellow Sugarcane Aphid feeding remains an unexplored area in the sugar industry of Zimbabwe and elsewhere. A 7 × 2 factorial in a complete randomized block design (CRBD) replicated four times was used, with seven sugarcane varieties (00-1165, ZN 3L, ZN 8, ZN 9, 96-1107, N14 and ZN 10) under two treatments of aphid infestation (un-infested (control) and infested). Results indicated that there were highly significant differences (p< 0.001) amongst the sugarcane varieties on chlorophyll content and percentage chlorophyll loss in control (sprayed) and infested (unsprayed) plots. Summer results recorded a great increase in percentage chlorophyll loss (21.4%) margin scored on ZN 10. Findings of the regression analysis displayed a highly significant (p< 0.001) strong positive correlation (r= 0.85) between chlorophyll loss and aphid number. Summer results showed highly significant differences (p< 0.001) on gas exchange responses in control and infested plots. Nevertheless, in YSA infested plots, 00-1165 recorded the highest compensatory photosynthetic rate (32.52), transpiration rate (4.32), stomata conductance (218.2) when compared to the least obtained from ZN 10 and N14 at day 28. Obtained results of the regression analysis presented highly significant positive correlation between; chlorophyll loss and photosynthesis (r= 0.44), photosynthesis and aphid number (r= 0.57). Ranking of sugarcane varieties was done according to YSA susceptibility; less susceptible (00-1165), moderate susceptible (ZN 3L, ZN 8 and ZN 9) and highly susceptible (96-1107, N14 and ZN 10). Sugarcane growers should add 00-1165 sugarcane variety amongst the existing sugarcane varieties as it is highly tolerant to YSA damage as proven by physiological compensatory and maintaining behavior.