The 2021 greenhouse season is progressing well, despite the cool and cloudy start. Overall, percent seed germination and uniformity of seedling stands in most greenhouses appear to be quite good. Based on the greenhouses that the CTRF has visited, seedlings between farms do vary in size depending on the type of production method being used and when seeding was started. In some greenhouses, clipping is started already. Only a few isolated problems have been reported to date with algae and chilling injury being the issues observed the most.
1-Algae
Blue-green algae are the most common algae that colonizes mostly float trays, however in a couple of cases, red-orange algae were also found to be present. Algae formations depend upon what types were in the substrate used to fill the trays or which types were present on trays from previous seasons or and in greenhouses. Blue-green algae are the most common algae in tobacco greenhouses and produce an oily-looking, blackish-green slimy layer on the tray surface. Red-orange algae are less frequent in tobacco greenhouses, however they can also be found colonizing water systems and seeding soil substrates, such as soilless medium or muck soil beds.
Unlike blue-green algae, the red algae lack motility structures, this probably being the main reason for the algae to be less spread in float trays or muck soil beds, in which we have seen and found these algae often imbibed in the vermiculite layers on the muck bed. In float trays, the red algae tended to be attached to the sides of the Styrofoam tray cell, often staining them red-orange (Fig. 1).
Fig. 1.- Blue-green algae (arrow) and red-orange algae (circle).
Note the red/orange-stained Styrofoam surfaces under the red algae.
This because algae cause oxygen levels in the media to fall, and or promote formation of nitrites in the tray media which inhibits root growth as well as competing with the plants for fertilizer.
Fig. 2. a) Tray cells and seed covered with blue green algae and b) poorly established seedling due to algae.
More information on algae can be found here.
2-Chilling Injury
Chilling injury was also of concern especially with some of the recent weather conditions. The initial symptoms of chilling injury are often a bright yellow color in the growing point of the seedling and upward cupping of the leaves, as shown in the image below (Fig. 3).
Fig. 3. Chilling injury
As the seedlings become larger and the leaves grow out, some leaves will be malformed, cupped, and have a distinct yellow/white discoloration. Seedlings do outgrow chilling injury without any ill effects on the seedlings when transplanted to the field.
Chilling injury is caused by exposure of the seedlings to a large variation in air temperature, such as when ventilation occurs on a very cool but sunny day or at night when the temperature outside is quite cold and the temperature drops significantly in the greenhouse because the heaters do not have enough capacity to maintain the set temperature. Also, some varieties are more susceptible than others to chilling injury. However, cold injury is not usually severe enough to be fatal to the seedlings, but it can delay growth and allow other problems, such as algae on trays, to be more damaging than they would otherwise be.
Clipping is underway in tray greenhouses. Bacterial Soft Rot (also known as Blackleg) is a common issue during this crop phase in the greenhouse.Bacterial Soft Rot is caused by several bacteria with Pectobacterium carotovorum (previously Erwinia carotovora) being the most important. As seedlings are clipped, leaf debris from the clipper fall back onto the seedlings foliage as shown in Figure 4, and when conditions are favorable, for example, high nitrogen levels, warmtemperatures, high humidity, long periods of leaf wetness, and plant injury (by stress or wounding), outbreaks of Bacterial Soft Rot will occur. Bacterial spread to healthy seedlings continues as more clipping is carried out, particularly when clipping is done on wet foliage.
Fig. 4. Leaf debris from clipper that has fallen back on to the seedlings.
Bacterial Soft Rot can become a serious seedling problem during extended periods of warm, wet, overcast weather conditions during the greenhouse season. The disease infects tobacco seedlings in both dry and float trays and has the potential to destroy large numbers of plants in a relatively short period of time. Initially, the bacteria colonize wounded tissues, organic matter, and debris in trays. Leaves touching the surface of a tray can become infected and the rot can spread through the petioles into the stem. Debris and leaves
Fig. 5. Seedlings in a tray infected with Bacterial Soft Rot
There are no control agents registered for control of Bacterial Soft Rot in tobacco greenhouses. Removal of trays with the diseased seedlings from the greenhouse and replacing them with blank trays is the best control in this situation. Other practices for control include trying to keep leaf debris from the clipper out of the beds, not clipping when the leaves are wet, not over-fertilizing, keeping the foliage of the seedlings as dry as possible, and ventilating the greenhouse adequately to keep the humidity level down.
Click here for more information on Bacterial Soft Rot
Post prepared and sent by Canadian Tobacco Research Foundation
Mailing Address: CTRF, P.O. Box 322, Tillsonburg, ON N4G 4H5
Telephone: 519-842-8997
Web Address: http://ctrf1.com