Effect of Leaf Age, Leaf Segments and Surface Treatments on Pathogenicity Levels of Colletotrichum sublineola in Sorghum and Johnson Grass

Ezekiel Ahn,Farrell Fan,Clint Magill

doi:10.3390/crops1030011

Abstract

Colletotrichum sublineola is a casual pathogen of sorghum anthracnose. Sorghum pathologists often need to conduct evaluations for anthracnose resistance in large scale which are expensive and labor intensive. As a solution, an excised-leaf assay has been used, but whether or not leaf age, position or region affects pathogenicity scores has not previously been evaluated. Essentially, in an excised-leaf assay, is response to C. sublineola over all or part of a leaf blade identical? To get an answer, three sorghum and one Johnson grass cultivars were tested. The top five leaves were inoculated at the apex, mid-leaf and base of each leaf blade. Results show nearly no effect of leaf age to pathogenicity level within the top five leaves. Furthermore, in order to evaluate any protective role of leaf wax to C. sublineola, the wax was disrupted by simply wiping the leaf surface by a thumb, or as an alternative method, leaf surface tension was reduced by submerging leaves into 2% TWEEN 20 before inoculation. Compared to control, wiped leaves increased pathogenicity scores on the leaf blade and midrib in two of three sorghum cultivars, but 2% TWEEN 20-treated leaves had only minimal changes in pathogenicity level compared to controls.

Highlights

Sorghum (Sorghum bicolor) is the fifth most important cereal grown worldwide [1]
The responses elicited were lower than median score 3 which based on failure to produce acervuli is the cut-off for host susceptibility, so the slight effects observed for leaf age or position would not change the ultimate disease response evaluations
This study revealed that there can be minor effects of leaf age to pathogenicity level in some sorghum and Johnson grass cultivars to C. sublineola

Summary

Introduction

Sorghum (Sorghum bicolor) is the fifth most important cereal grown worldwide [1]. It is a drought-resilient crop grown extensively in semiarid regions/areas of the world [2].Sorghum is consistently exposed to abiotic and biotic stresses. Sorghum (Sorghum bicolor) is the fifth most important cereal grown worldwide [1]. It is a drought-resilient crop grown extensively in semiarid regions/areas of the world [2]. An excised-leaf assay offers several advantages in screening sorghum for anthracnose resistance, including saving time, labor, space and expenses [4]. The first question to be addressed was whether leaf age, based on position on the plant, has an effect on disease severity level in response to C. sublineola. Physiological characteristics such as leaf age could affect the outcomes of an excised assay. In wheat (Triticum aestivum), younger plants had significantly greater disease severity than older plants against Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust, and this effect was greater on upper leaves [5]

Methods

Results

Conclusion