Tolerance and compensatory response of rice to sugarcane borer (Lepidoptera: Crambidae) injury

A 3-yr field experiment was conducted to evaluate the tolerance and compensatory response of rice (Oryza sativa L.) to injury caused by sugarcane borer, Diatraea saccharalis (F.), as affected by cultivar (Cocodrie, Francis, and Jefferson), stage of crop growth during which the injury occurred (third tiller stage, panicle differentiation stage, and heading stage), and sugarcane borer density. The proportion of rice tillers with sugarcane borer injury (leaf and leaf sheath injury and/or stem injury) was lower when injury occurred at the third tiller stage (0.05) than at panicle differentiation (0.19) and heading (0.18). When injury occurred at the two latter stages, both the proportion of tillers with injury and the proportion of tillers with stem injury were negatively correlated with rainfall. Rainfall resulted in dislodgement and mortality of sugarcane borer eggs and larvae before the larvae entered the stems. Rice plant density in this study (111.1 plants/m2) was higher than recorded for previous research on rice compensation using potted rice or conducted in low-density hill production systems (26.7-51.3 plants/m2). Two mechanisms of within-plant tolerance/compensation were observed. Stem injured plants produced approximately 0.69 more tillers than uninjured plants, whereas tillers with leaf and leaf sheath injury produced larger panicles, up to 39.5 and 21.0% heavier than uninjured tillers, when injury occurred at third tiller stage and at panicle differentiation, respectively. Rice yield was not reduced with up to 23% injured tiller and up to 10% injured stems at the third tiller stage, 42% injured tillers and 17% injured stems at panicle differentiation, and 28% injured tillers and 14% injured stems at heading. Significant between-plant compensation was not detected, suggesting competition between adjacent plants is not significantly reduced by injury. Our results suggest that rice can tolerate and/or compensate for a level of stem borer injury previously considered to be economically damaging.