Physical-mechanical berry skin traits as additional indicators of resistance to botrytis bunch rot and grape sunburn

Abstract

Climate change increasingly leads to altered growing conditions in viticulture, such as heat stress, drought or high infection pressure favoring pathogen infection. However, for one of the major diseases, Botrytis bunch rot (BBR), no resistance genes have yet been described in grapevine. Physical-mechanical traits like loose bunch structure and thick, impermeable berry cuticles, phenotyped with high-throughput sensors, have been shown to be effective parameters to prevent BBR infections. Further, berry skin traits like berry impedance (indicator for cuticle thickness), seems to be correlated with sensitivity of berries towards induced heat stress (HS), an indicator for grape sunburn susceptibility. Within the collaborative project WiVitis these traits will be objectively investigated by sensors (physical), microscopic (visible) and metabolomic studies (analytical) in order to characterize and compare PIWIs, traditional varieties and elite breeding lines. This spatial and temporal high-resolution dataset of promising characteristics will be used to unravel the complex trait of BBR resilience and to check the transferability of gained knowledge to grape sunburn. Therefore, selected varieties were phenotyped by measuring berry impedance and berry texture (indicator for berry skin resistance) twice during berry ripening. Further, their sensitivity to induced HS and BBR was investigated under controlled lab conditions. Hereby, most of the investigated PIWI varieties and breeding lines showed resilience to both, HS and BBR as well as high values for the physical berry traits. As berry skin traits seems to be variety-specific, Quantitative Trait Locus (QTL) mapping was done aiming at the development of molecular markers. Therefore, 364 genotypes (F1 progeny of ‘Dakapo’ (VIVC 14728) x ‘Cabernet Sauvignon’ (VIVC 1929)) were phenotyped at harvest maturity in three consecutive years. The genetic map was constructed based on 737 genotypes and 322 SSR (Simple Sequence Repeats) markers mapped on 19 linkage groups. QTLs for berry impedance and berry texture were identified on chromosome 2, 6, 11, 15, 16 and 17. The identified QTLs were narrowed down by the newly developed SSRs resulting in an enhancement of LOD values. All of these findings will provide new options to characterize grapevine varieties objectively and will develop new molecular markers for more efficient and targeted breeding of resistant, climate change-adapted grape varieties for sustainable viticulture.