Exogenous Calcium Delays Grape Berry Maturation in the White cv. Loureiro While Increasing Fruit Firmness and Flavonol Content

Vineyard calcium (Ca) sprays have been increasingly used by grape growers to improve fruit firmness and thus maintain quality, particularly in periods of heavy rains and hail. The observation that Ca visibly modified berry size, texture, and color in the most prominent white cultivar of the DOC region ‘Vinhos Verdes’, cultivar (cv.) Loureiro, led us to hypothesize that Ca induced metabolic rearrangements that resulted in a substantial delay in fruit maturation. Targeted metabolomics by ultra-performance liquid chromatography coupled to mass spectrometry and directed transcriptomics were thus combined to characterize the metabolic and transcriptional profiles of cv. Loureiro berries that, together with firmness, °Brix, and fruit weight measurements, allowed to obtain an integrated picture of the biochemical and structural effects of Ca in this cultivar. Results showed that exogenous Ca decreased amino acid levels in ripe berries while upregulating PAL1 expression, and stimulated the accumulation of caftaric, coutaric, and fertaric acids. An increase in the levels of specific stilbenoids, namely E-piceid and E-ω-viniferin, was observed, which correlated with the upregulation of STS expression. Trace amounts of anthocyanins were detected in berries of this white cultivar, but Ca treatment further inhibited their accumulation. The increased berry flavonol content upon Ca treatment confirmed that Ca delays the maturation process, which was further supported by an increase in fruit firmness and decrease in weight and °Brix at harvest. This newly reported effect may be specific to white cultivars, a topic that deserves further investigation.

A SmelAAT Acyltransferase Variant Causes a Major Difference in Eggplant (Solanum melongena L.) Peel Anthocyanin Composition

Eggplant berries are rich in anthocyanins like delphinidin-3-rutinoside (D3R) and nasunin (NAS), which are accumulated at high amounts in the peel. NAS is derived by D3R through acylation and glycosylation steps. The presence of D3R or NAS is usually associated with black-purple or lilac fruit coloration of the most cultivated varieties, respectively. Building on QTL mapping position, a candidate gene approach was used to investigate the involvement of a BAHD anthocyanin acyltransferase (SmelAAT) in determining anthocyanin type. The cDNA sequence comparison revealed the presence of a single-base deletion in D3R-type line ‘305E40’ (305E40_aat) with respect to the NAS-type reference line ‘67/3’. This is predicted to cause a frame shift mutation, leading to a loss of SmelAAT function and, thus, D3R retention. RT-qPCR analyses confirmed SmelAAT and 305E40_aat expression during berry maturation. In D3R-type lines, ‘305E40’ and ‘DR2’ overexpressing the functional SmelAAT allele from ‘67/3’, the transcript levels of the transgene, correlated with the accumulation of NAS in fruit peel. Furthermore, it was also found a higher expression of the transcript for glucosyltransferase Smel5GT1, putatively involved with SmelAAT in the last steps of anthocyanin decoration. Finally, an indel marker matching with anthocyanin type in the ‘305E40’ × ’67/3’ segregating population was developed and validated in a wide number of accessions, proving its usefulness for breeding purposes.

Drought Analysis During the Growth Stages of Grape in the Main Grape-Growing Regions in China

In China, grape is one of the top five fruit crops for both bearing acreage and production. Recently, national grape production has been stalling because of an increase in drought events. In order to combat the adverse effects of drought on grape production, it is imperative to understand the historical drought trend and frequency during the growing season. In this study, we focused on agricultural drought during the four growth periods of grape: bud break-flowering, flowering-veraison, veraison-berry maturation, and berry maturation-leaf fall. Based on the weather data from 429 meteorological stations, we computed the Crop Water Deficit Index (CWDI) in the five main grape-growing regions of China: Northeast China, North China, Northwest China, Southwest China, and Southeast China. Then we evaluated the CWDI-based drought distribution and trend in the study regions, as well as the frequency of different degrees of drought. The results showed that exceptional drought was occurring frequently in Xinjiang Uyghur Autonomous Region, northern Gansu province, and northern Ningxia Hui Autonomous Region. Among the four study growth periods of grape, exceptional drought was the most expansive during bud break-flowering. What’s more, exceptional drought coverage during bud break-flowering in the study regions was increasing from 1981 to 2016. Analysis of butterfly structure showed that the occurrence of drought was continuous and persistent in northern China. Our study results could serve as guideposts to highlight Chinese grape production industry’s vulnerability to agricultural drought against the background of climate change.

Grapevine Latent Bud Dormancy and Shoot Development

Grapevine development comprises different phenological stages from bud break to berry maturation which are mainly temperature and water dependent. Pre bud break, there is a crucial stage called dormancy which can be divided in two periods: endodormancy and ecodormancy. Climate change (increase in average temperatures and drought) may accelerate the onset of bud burst, however with greater heterogeneity, thus increasing the risk of shoot exposure to abiotic and biotic constraints. Obviously, this could lead to yield and quality issues. In this regard, the ability to assess when climatic conditions are suitable for dormancy release and to predict the date of bud break is important.

Bagging Affecting Sugar and Anthocyanin Metabolism in the Ripening Period of Grape Berries

Grapevine is one of the most important fruit-bearing plants worldwide, for which bagging treatments can effectively improve fruit quality. However, the low-light conditions caused by bagging can delay grape berry maturation. Here, we analyzed glucose, fructose, and anthocyanin contents and the expression of sugar and anthocyanin-metabolism pathway genes in the grape berries of two cultivars, ‘Shenhua’ and ‘Shenfeng’, under different bagging treatments. Color development was incomplete in bagged grape berries and their soluble sugar contents were lower than those detected in un-bagged fruits. However, fruit color and SSC could be rapidly restored to normal levels after removing bags. Light affects the accumulation of sugar in grape berries, especially near the maturation period, as well as the contents and compositions of anthocyanins in the skin of grape berries. Although light helps in the accumulation of anthocyanins, significant differences were detected in anthocyanin composition between the two grapevine varieties. In addition, the expressions of myofibroblastic regulatory genes in the anthocyanin pathway were affected by light, and the light-responsive elements elongated hypocotyl 5 and constitutive photomorphogenic 1 acted synergistically to control grape berry coloration. Overall, these results provide a theoretical basis for the maturation mechanism in grape berries. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********