Detection of downy mildew [Peronosclerospora philippinensis (W. Weston) C.G. Shaw] resistance in sugarcane (Saccharum officinarum L.) based on chlorophyll content and biomass
Peronosclerospora philippinensis (Weston) C.G. Shaw is the most virulent downy mildew in the Philippines and one of the major diseases that reduce the yield of sugarcane. Sixty sugarcane genotypes consisting of 49 hybrids and 11 varieties were screened in the greenhouse for downy mildew resistance. Chlorophyll reading and visual rating of the incidence of disease were performed for ten weeks, commencing one month after planting. T10-535 showed the lowest disease incidence among the hybrids and VMC-87599 showed the lowest disease incidence among the varieties. Other hybrids which showed the lowest disease incidence were E5-531 F, A50-530 M, and 150-530. Results of chlorophyll reading shows that VMC-87599 had the highest soil-plant analysis development (SPAD) value over the ten-week period. There was a significant correlation between disease rating and disease incidence, and a moderate correlation between chlorophyll content and disease incidence. No correlation was observed between disease incidence and roots, stalk and leaf biomass. The correlation in disease incidence and severity to roots, stalk and leaf biomass could be further checked throughout the growth phase of sugarcane to evaluate physiological parameters such as chlorophyll content and biomass partitioning.