A Robust Disease Scoring Method to ScreenEucalyptusfor Resistance Against the Aggressive Leaf PathogenTeratosphaeria destructans

Abstract

Shoot and leaf blight caused by Teratosphaeria destructans is one of the most devastating foliar diseases of Eucalyptus. Therefore, breeding for resistance to this disease is considered urgent. Differences in susceptibility to T. destructans have been observed in the field, but a robust inoculation protocol has, until recently, been unavailable and a disease scoring method for precise phenotyping has not been established. A first objective of this study was to determine the optimal conidial concentration for T. destructans inoculations on a susceptible Eucalyptus host. This concentration was then used to determine differences in susceptibility of six genotypes of Eucalyptus grandis x Eucalyptus urophylla to the pathogen by assessing the percentage of infected stomata using electron microscopy and the percentage of leaf area covered by lesions (PLACL) using image processing. In addition, we developed a disease susceptibility index (SI) of six categories ranging from highly resistant (SI= 0), to highly susceptible (SI= 1.5-2). The more resistant genotypes were moderately resistant with an SI value of 0.49 - 0.54 and a PLACL of 6.5 – 9%. In contrast, the more susceptible genotype scored an SI of 1.52 and PLACL of 48%. Host susceptibility was also assessed relative to the sporulation of the pathogen. This showed that the percentage of sporulation did significantly correlate with host resistance. Overall, the results provide the basis for rigorous screening and selection of resistant genotypes to the disease caused by T. destructans using artificial inoculation.

Wide Distribution of Teratosphaeria epicoccoides and T. destructans Associated with Diseased Eucalyptus Leaves in Plantations in Southern China

“…During the sampling process in the current study, we found that the severity caused by each species of T. epicoccoides and T. destructans on different genotypes of E. urophylla × E. grandis were different. Research results showed that significant differences in resistance exist among the six tested E. grandis × E. urophylla genotypes to the inoculated T. destructans [ 71 ]. It is suggested that breeding and selection of Eucalyptus tolerant/resistant species, hybrids and clones are needed for the future management of leaf diseases caused by Teratosphaeria species [ 41 ].…”