Modified Scale for Evaluating Sugarcane Clones for Fusarium wilt Resistance with Plug Method of Inoculation

Abstract

Wilt of sugarcane caused by Fusarium sacchari is a serious disease affecting cane stalks in the crop. The disease affects the plant during any period of the crop cycle, decreasing agricultural and industrial production. Managing the disease through resistant varieties is considered as the most sustainable and economically viable approach. However, there is a lack of a versatile disease rating system for F. sacchari resistance in sugarcane. To address the issue, we developed a mean wilt severity index on a 0–9 rating scale. In the revised wilt severity system, essential criteria governing wilt were taken into account to develop 0–9 rating scale as resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible corresponding to 0–2.0, 2.1–4.0, 4.1–6.0, 6.1–8.0 and 8.1–9.0 scores, respectively, based on overall wilt expression in sugarcane. This new scale clearly discerns the varietal reactions based on internal symptoms, especially pith region cavities, cane and spindle leaf phenotype and disease progress through nodes and roots. This system of grading based on 0–9 scale was found better than the previous numeric index system which grouped clones into 4 grades, ignoring the relative importance of nodal transgression and pith cavity development. This new scale is applicable to grade sugarcane genotypes after plug method of inoculation or disease development screening through soil application of F. sacchari inoculum.