Eldana saccharina (Lepidoptera: Pyralidae) Resistance in Sugarcane (Saccharum sp.): Effects of Fusarium spp., Stalk Rind, Fibre and Nitrogen Content

Sugarcane cultivar resistance to Eldana saccharina is the best strategy to control the stalk borer. The present study aimed to establish the influence of stalk rind hardness, fibre and nitrogen content, and the effect Fusarium species associated with E. saccharina infestation, on borer damage and performance in different sugarcane cultivars. In two glasshouse trials, larvae were inoculated into 7-month-old stalks of seven cultivars with different E. saccharina resistance ratings via wounds created in the rind. In one of the trials, E. saccharina-beneficial fungal strain Fusarium pseudonygamai SC17 and E. saccharina antagonistic F. sacchari PNG40 were inoculated into the stalk of N41 and NCo376 three weeks before larval inoculation. Rind hardness and fibre content were higher in resistant cultivars and mature stalk parts, whilst nitrogen content was lower in these genotypes and in older tissues. However, E. saccharina survival, damage and growth indicators were not entirely consistent with known resistance ratings of cultivars, possibly due to the absence of the rind effect owing to mechanical wounding and differential effects of fibre and nitrogen in the cultivars. The absence of rind protection did not affect resistance in N29 and N33 upper internodes. Fusarium infection was higher in the bottom of the stalk compared to the top in both N41 and NCo376. The least length bored was exhibited in the bottom internodes of NCo376 (3.3 cm) and N41 (1.7 cm) infected with PNG40, whilst SC17-colonized NCo376 stalks experienced the most damage (8.2 cm). The contribution of stalk rind hardness, fibre and nitrogen content to E. saccharina resistance in sugarcanemayvary in different cultivars and stalk parts, whilst biochemical defences possibly play a larger role in some genotypes. Infection by Fusarium species, especially in lower internodes,mayhave variable effects on resistance to the borer depending on the fungal strain present.