Efficient Vineyard in the News:
How Sensors, Robotics And Artificial Intelligence Will Transform Agriculture
…”FarmView is also working with Cornell and the University of California Davis (UCD) on a project to increase efficiency and quality in grape production by actively managing vine balance…”
Concord Flowering and Fruit Set in the Lake Erie Region
This season, the staff at CLEREL recorded trace bloom in the standard phenology vines on 6/11/2017 and official bloom (50% cap fall) on 6/12/2017. The Concord flower cluster in this image is at over 90% full bloom on June 14th.
Most of the wild grapes you see on the roadside or in the woods have either all male or all female flowers. However, most of the cultivated grape varieties we grow have “perfect” or “hermaphrodite” flowers. Interestingly, cultivated grapes are also highly self-pollinated because the pollen will go from the anther to the stigma before the cap pops off.
The anthers typically release pollen prior to cap fall so pollination likely started on Monday (6/12) when we recorded trace bloom. To catch and rehydrate the pollen, the stigma produces a sap (seen at the tip of the stigma arrow in the picture). Rehydration of pollen takes about 30 minutes and then the pollen uses stored starch in the pollen grain to grow down the style. The speed of pollen tube growth and the time it takes to reach the ovule is related to temperature (roughly 48 hours at 60 degrees F, 24 hours at 70 degrees, and 12 hours at 18 degrees). The colder it is, the slower the pollen tubes grow. Since the ovules are only receptive for a short time, cool weather during bloom can cause the pollen to miss the window and lead to poor fruit set. Fortunately for 2017, it has been sunny and warm (between 60-80) for the past three days so Concord fruit set in the Lake Erie Region should be in decent shape.
Just after flowering, the pollinated pistils on the grape clusters will start do develop but not all of the ovaries will successfully develop into fruit. This Concord cluster has about 100 developing ovaries but will only retain and develop 25-30 fruit, on average. Expanding pollen must first fertilize at least one of four ovules while they are receptive. Successful fertilization induces the production of certain plant growth hormones for cell division (auxin) and cell expansion (gibberellin) in different tissue layers. The balance of these hormones is important for the successful retention of the developing ovary. Percent total fruit set is influenced by cultivar and certain management practices, such as pruning level. A variety of environmental stresses (light, temperature, carbohydrate, nutrient, and water stress) can also reduce fruit set. Many of our management recommendations, such as for weed control and mineral nutrition, aim to eliminate any vine stress during the fruit set and berry cell division phase in the 3-4 weeks after bloom. Unfertilized or stressed ovaries will eventually abscise or “shatter.”
Just one week after the start of bloom, Concord clusters are setting fertilized berries and dropping others. This cluster has dropped about 40% of the pistils which were originally pollinated but not successfully fertilized. A corky abscission scar can be seen where the pedicel of aborted flowers have separated from the rachis (cluster stem).
Why is it important to track fruit set?
Current research objectives aim to improve mid-season crop estimation. Grape yield is a function of shoots/vine, clusters/shoot, berries/cluster, and final berry weight. These “yield components” can be influenced by biological factors such as vine size and vine water status, management factors such as pruning level, or environmental factors such as temperature during fruit set. Spatial data from the Efficient Vineyard project illustrate how yield components can vary from vineyard to vineyard as well as within a vineyard. We are testing the use of the Carnegie Mellon Image sensor to directly detect and count certain yield components – such as shoot number and berry number across a vineyard. We are also combining this information with other spatial data to direct vineyard sampling during the middle of the growing season to predict final crop size across whole vineyard blocks.
One-Month Post-Bloom in Concord Vineyards
After bloom and fruit set, Concord berries enter a growth phase of both cell division and cell expansion. At 4-weeks post-bloom, Concord berries will reach approximately 50% of their final fresh weight but will still be in the middle of the rapid fruit growth (stage I). Berry size and weight in a cluster, vine, or vineyard varies at both 30 days after bloom and at harvest (as seen in the photo). Variation in berry growth is a function of both cell number (through cell division) and cell size (through cell expansion) – and these are controlled by both biological and environmental factors. The developing seeds produce auxin, cytokinin, and gibberellin and it is the balance of these hormones which influences the amount of cell division and expansion in the fruit. A berry with more seeds will tend to be larger than one with fewer seeds because of the seeds’ influence on cell division and expansion. While all parts of the fruit are developing during stage I, it is the division and expansion of the mesocarp (flesh or pulp) that makes up most of the berry volume. Environmental factors, such as water availability, will also influence berry weight at 30 days after bloom by influencing cell expansion – again primarily in the mesocarp tissue.
Concord Fresh Berry Weight Curve:
Concord berry growth is currently in stage I of rapid cell division and expansion. In general, the 2017 season can be characterized by having favorable weather conditions during bloom and set, possibly leading to average to above average seed number (unless vines were severely water stressed in 2016). In addition, 2017 has had above average precipitation in area vineyards. Taken together, we are measuring above average fresh berry weight in Concord at 30 days post-bloom. The 2017 berry curve is currently tracking like 2015 and we should expect above average berry weight at harvest. In contrast, 2005 and 2016 were seasons that were warm and dry early which led to lower than average final berry weight. This information can be used for vineyard crop estimation procedures.
A cross-section of a Concord berry at 30 days post-bloom. In addition to seed development, the cell division and expansion of the mesocarp tissue has a considerable influence on fresh berry weight. Cell number will double two times during stage I through cell division. In addition, cell volume will increase through cell wall loosening and the expansion of cell vacuole volume. Presumably, the cell division hormone, cytokinin, diminishes through stage I, which slows cell division as the berries enter the lag phase of berry growth (stage II).
70 Days Post-Bloom in Concord Vineyards
Concord Fresh Berry Weight Development: Beginning of Stage III. During stage III, the cells walls of the mesocarp change physically and chemically to soften and accumulate water and sugar. The seeds turn brown from tannin accumulation and harden through desiccation and become ready for dispersal. Veraison also triggers the accumulation of anthocyanins (purple pigments) in the grape skins (exocarp).
In Stage III of berry development from veraison to harvest, the seeds finish maturing and the fruit ripens to attract animal feeding for seed dispersal. Just before veraison, the berries are hard and green with relatively high organic acid (30 g/L) and low sugar concentrations (7.5 oBrix). Over a four to five week period from veraison to harvest, Concord fruit will become soft and dark purple with relatively low organic acid (10 g/L) and high sugar concentrations (16 oBrix). In Lake Erie Concord, veraison occurs 69 days after bloom, on average. Veraison may start a few days earlier in warm, dry years with moderate vine water stress and lower berry weight and it may be delayed in cool, wet seasons with high vine water status and larger berries. Veraison marks a physiological change in the fruit characterized by a rapid increase in water and sugar accumulation in the mesocarp (flesh) and anthocyanin accumulation in the exocarp (skin). There is also a degradation of organic acids and chlorophyll and the fruit will become soft as the cells walls of the mesocarp change and weaken.
Concord fresh berry weight curve indicating the percent of final weight (left). At veraison, Concord berries reach approximately 80% of their final weight. Much of the weight gain after veraison is a function of water and sugar influx to the berry from the phloem. The 2017 berry curve (right) is still running above the long term mean but has tapered through lag phase because of the dry weather conditions and large crop size.
Typical ripening concentration curves of juice soluble solids (left) and juice titratable acidity (right) in Lake Erie Concord. Desired fruit chemistry for producing single strength juice is 16 oBrix (+/- 0.5) and 1.0-1.1% titratable acidity at approximately 30-40 days post-veraison. Environmental conditions (precipitation, sunlight, temperature) as well as viticulture management (crop load) can influence berry weight and the rate of sugar accumulation.