High-resolution disease phenotyping reveals distinct resistance strategies of wild tomato crop wild relatives against Sclerotinia sclerotiorum

Besides the well-understood qualitative disease resistance, plants possess a more complex quantitative form of resistance: quantitative disease resistance (QDR). QDR is commonly defined as a partial but more durable form of resistance and, therefore, might display a valuable target for resistance breeding. The characterization of QDR phenotypes, especially of wild crop relatives, displays a major bottleneck in deciphering QDRs genomic and regulatory background. Moreover, the relationship between QDR parameters, such as infection frequency, lag phase duration, and lesion growth rate, remains elusive. High hurdles for applying modern phenotyping technology, such as the low availability of phenotyping facilities or complex data analysis, further dampen progress in understanding QDR. Here, we applied a low-cost phenotyping system to measure lesion growth dynamics of wild tomato species (e.g., S. pennellii or S. pimpinellifolium). We provide insight into QDR diversity of wild populations and derive specific QDR strategies and their crosstalk. We show how temporally continuous observations are required to dissect end-point severity into functional resistance strategies. The results of our study show how QDR can be maintained by facilitating different defense strategies during host-parasite interaction and that the capacity of the QDR toolbox highly depends on the hosts genetic context. We anticipate that the present findings display a valuable resource for more targeted functional characterization of the processes involved in QDR. Moreover, we show how modest phenotyping technology can be leveraged to help answer highly relevant biological questions.