Screening a variable germplasm collection of Cucumis melo L. for seedling resistance to Macrophomina phaseolina

Abstract

We evaluate the seedling resistance to charcoal rot caused by Macrophomina phaseolina in ninety-seven Cucumis melo accessions, from different geographical origins and five F1 generations, derived from crosses of five accessions selected for their resistance. Artificial inoculations with the toothpick method, previously reported to be useful for predicting shoot resistance, were performed, and plants were scored using a scale of disease severity. The average disease severity was calculated for each accession and was used to cluster the accession in five reaction classes. The screening revealed that sources of natural resistance to this fungus are limited. However, seedlings of seven accessions of different botanic groups displayed a resistant response to the stem inoculation, one cantaloup from Israel, one conomon accession from Korea, two wild agrestis and one acidulus from Africa, and two dudaim accessions from Middle East. The response of the F1 progenies varied from susceptibility to high resistance, the latter in progenies from the two agrestis wild types. These results suggest differences in the genetic basis of the resistance in the different selected sources. The resistant accessions are suggested to be screened under field conditions to confirm the level of resistance at adult plant stage and under stressful conditions.