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Intumescence is a physiological disorder in tomato and other plant species that encompasses callus formation on leaves and stems. Next to a genetic predisposition, it has also been shown to be influenced by environmental factors like light spectrum. We grew tomato plants of four different recombinant inbred line (RIL) populations under high‐pressure sodium (HPS) and red/blue LED supplemental lighting in a greenhouse and determined the severity of intumescence on 4‐week‐old plants, in three subsequent replicates. The intumescence severity was scored on a scale from 0 to 3. The severity of intumescence was highly genotype dependent in three out of the four tested tomato populations, with the heritability ranging from 54% to 83%. In those three populations, two to eight QTL for intumescence were identified. One major effect quantitative trait locus (QTL) on the top of chromosome 1 was at a similar position in two genetically different RIL populations. The amount of genetic variation explained for these QTL ranged from 30% to 70% depending on the population. Next to chromosomal influences, we also identified differences in effects from maternal plastids on intumescence, by using reciprocal crosses. The cultivation of the tomato plants under HPS lamps or under red/blue LED supplemental lighting had no significant influence on intumescence score. All major QTLs appeared to be reproducible among the three replicates and among the two light conditions. Significant, though, low negative correlations were identified between the intumescence score and the area of leaves, chlorophyll content index, photosynthesis efficiency and fresh weight to dry weight ratio, which can reflect possible effects of the disorder on multiple aspects of plant performance. [ABSTRACT FROM AUTHOR]

Differences in growth have been reported for tomato under LED compared to HPS light, however, it is not clear if breeding specific for LED supplemental light is worthwhile. Therefore, we derived four recombinant inbred line (RIL) tomato populations from parents with contrasting growth responses to different light spectra. These RIL populations were grown for four weeks under supplemental HPS or 95% red and 5% blue LED light in the greenhouse. For one population we also studied fruit production. Plant height and size of the side shoots of the young plants were strongly reduced under LED supplemental lighting compared to HPS in all populations. The adult plants showed shorter internode lengths, less trusses, less fruits, and lower yield of ripe fruits per plant under LED. However, when the unripe fruits at the last harvest day were included, the difference in yield between HPS and LED disappeared, indicating that the plants under LED light were compacter and slower in development, but in the end produced similar yield. We found numerous QTL, but hardly any of these QTL appeared to be significantly LED-specific. Also, we found very significant genetic effects of maternally inherited plastids and mitochondria, showing the importance of using a parental genotype as mother or as father. However, these effects were very similar between the two light conditions. We conclude that our study does not justify tomato breeding programs that are specifically targeted at 95% red and 5% blue LED supplemental lighting. [ABSTRACT FROM AUTHOR]

LED lighting has emerged as alternative to the current HPS standard in greenhouse production. However little is known about the impact on fruit quality under the different light spectra. We grew a biparental tomato RIL population between September 2019 and January 2020 under two commercial greenhouse supplemental lighting conditions, i.e. HPS, and 95% red/5% blue- LED, of about 220 µmol m−2 s−1 at maximum canopy height for 16 h per day. Differences in Brix and blossom-end rot (BER) between the two light conditions were observed and we studied the genetic influences on those traits, separating genetics located on chromosomes from genetics located in plastids. The Brix value was on average 11% lower under LED than under HPS supplemental lighting. A LED-light specific QTL for Brix was identified on chromosome 6. This QTL can be of interest for breeding for tomato varieties cultivated under LED supplemental lighting. A Brix-QTL on chromosome 2 was found for both light conditions. In our study fewer plants developed BER under LED supplemental lighting than under HPS. We identified a novel genetic locus on chromosome 11 for the incidence of BER that lead to a difference in about 20% of fruits with BER. This genetic component was independent of the light. [ABSTRACT FROM AUTHOR]

High market price and low availability of local winter and spring production has stimulated production of blackberries in glasshouses at northern latitudes. For this production, light is the main limiting factor. We investigated the potential of intercanopy lighting (ICL) using light emitting diodes (LEDs) to improve blackberry fruit yield in a crop with a spring and an autumn production cycle. During the spring production cycle three light treatments were applied: only natural light (no ICL), 93 or 185 μmol m–2 s–1 ICL In summer the lateral shoots were cut back and 93 μmol m–2 s–1 ICL was applied to all plants after cutting back, investigating a possible carryover effect of supplemental light in spring on autumn production. Fresh fruit yield in spring increased by 79 and 122% with 93 and 185 μmol m–2 s–1 ICL, respectively, compared to no ICL. This represents 3.6 and 2.8% increase in harvestable product for every additional 1% of light. A yield component analysis and leaf photosynthesis measurements were conducted. Maximum photosynthetic capacity (A max) for leaves at 185 μmol m–2 s–1 ICL was about 50% higher, and LAI was 41% higher compared to no ICL. ICL increased the number of fruiting laterals per cane, and this explained 75% of the increase in yield. ICL at 185 μmol m–2 s–1 resulted in a higher yield compared to no ICL, primarily as a result of higher total dry matter production. Furthermore, a higher fraction of dry matter partitioned to the fruits (0.59 compared to 0.52) contributed to yield increase, whereas fruit dry matter content and fruit quality (sugar and acid content) was not affected by ICL. Averaged over the three light treatments autumn yield was 47% lower than spring yield. Autumn yield was 10% higher for plants at ICL 93 μmol m–2 s–1 in spring and 36% higher for plants at 185 μmol m–2 s–1 in spring compared to no ICL in spring. This increased autumn yield was caused by more fruiting laterals (less necrotic buds). It is concluded that management practices in spring can have a carryover effect on the autumn production. This is the first scientific paper on the potential for applying LED ICL in blackberries. Further research should focus on optimal intensity of ICL, positioning of supplementary lighting and economic feasibility. [ABSTRACT FROM AUTHOR]

The recent development of light-emitting diodes (LEDs) and their application in modern horticulture stimulated studies demonstrating that additional far-red (FR) radiation (700–800 nm) increases plant dry mass. This effect of FR has been explained by improved photosynthesis and/or plant architecture. However, the genotypic variation in this response is largely unknown. Here, we aim to explore and explain the genotypic variation in growth responses to additional FR. We expected the genotypic variation in the responses of plant dry mass to additional FR. Further, we hypothesized that a significant improvement of both net assimilation rate (NAR) and leaf area ratio (LAR) is responsible for a strong dry mass increase under additional FR, while some genotypes respond only marginally or even negatively in NAR or LAR under FR, thus resulting in a weak FR effect on plant dry mass. To test these hypotheses, we grew 33 different tomato genotypes for 21 days with 0, 25, or 100 μmol m–2 s–1 of FR added to a common white + red LED background lighting of 150 μmol m–2 s–1. Genotypes responded similarly with respect to plant height, stem dry mass, and shoot:root ratio; i.e., they all increased with increasing FR. However, the response of total plant dry mass varied among genotypes. We categorized the genotypes into three groups (strongly, moderately, and weakly responding groups) based on their relative response in total plant dry mass to FR. Growth component analysis revealed that the strongly responding genotypes increased strongly in NAR rather than LAR. The weakly responding genotypes, however, showed a substantial increase in LAR but not NAR. The increase in LAR was due to the increase in specific leaf area. Leaf mass fraction, which is the other component of LAR, decreased with FR and did not differ between groups. In conclusion, tomato genotypes that increased strongly in NAR in response to FR were able to achieve a more substantial increase in dry mass than did other genotypes. This is the first study to explain the differences in growth responses of a large number of tomato genotypes toward FR in their light environment. [ABSTRACT FROM AUTHOR]

Summary: Far‐red (FR) light promotes fruit growth by increasing dry mass partitioning to fruits, but the mechanism behind this is unknown. We hypothesise that it is due to an increased fruit sink strength as FR radiation enhances sugar transportation and metabolism.Tomato plants were grown with or without 50–80 μmol m−2 s−1 of FR radiation added to a common background 150–170 μmol m−2 s−1 red + blue light‐emitting diode lighting. Potential fruit growth, achieved by pruning each truss to one remaining fruit, was measured to quantify fruit sink strength. Model simulation was conducted to test whether the measured fruit sink strength quantitatively explained the FR effect on dry mass partitioning. Starch, sucrose, fructose and glucose content were measured. Expression levels of key genes involved in sugar transportation and metabolism were determined.FR radiation increased fruit sink strength by 38%, which, in model simulation, led to an increased dry mass partitioned to fruits that quantitatively agreed very well with measured partitioning. FR radiation increased fruit sugar concentration and upregulated the expression of genes associated with both sugar transportation and metabolism.This is the first study to demonstrate that FR radiation stimulates dry mass partitioning to fruits mainly by increasing fruit sink strength via simultaneous upregulation of sugar transportation and metabolism. [ABSTRACT FROM AUTHOR]

Vertical farming (VF) is a novel plant production system that allows local production of high-quality fruits and vegetables for rapidly growing cities. VF offers a myriad of opportunities to move from genetic to environmental modification and to produce crops of guaranteed quality and quantity independent of weather, soil conditions, or climate change. [ABSTRACT FROM AUTHOR]

• Adding far-red to red:blue or sole red promoted rooting in one of two experiments. • Adding far-red only in the initial stage improved rooting without stem elongation. • The presence or absence of blue did not significantly affect rooting. • IAA and carbohydrate concentrations did not correlate with rooting. Stem cuttings are used in the commercial cultivation of many crops, including medicinal cannabis, to produce large numbers of uniform and genetically identical plants. Light is an important environmental factor determining the success of the rooting of stem cuttings. The aim of this study was to investigate the influence of different fractions of far-red and blue during the adventitious rooting phase of medicinal cannabis stem cuttings on rooting and whether these effects are related to changes in endogenous auxin and/or carbohydrates. Two experiments were conducted in climate chambers with sole LED lighting (blue, red, far-red) using two cannabis cultivars. In Experiment 1, four light treatments were applied: 100 µmol m−2s−1 red:blue (88:12) with additional 0, 50 or 100 µmol m−2s−1 far-red and a fourth treatment with 100 µmol m−2s−1 sole red with additional 50 µmol m−2s−1 far-red. In Experiment 2, the following four light treatments were applied: 90 µmol m−2s−1 red:blue (45:45) with additional 0 or 45 µmol m−2s−1 far-red, a third treatment with 45 µmol m−2s−1 sole red with additional 45 µmol m−2s−1 far-red, and a fourth dynamic treatment which was 45 µmol m−2s−1 sole red with additional 45 µmol m−2s−1 far-red for 7 days followed by 90 µmol m−2s−1 red:blue (45:45) for 14 days. The effects on rooting in both experiments were measured after 21 days of light treatments. In Experiment 2, periodic measurements of auxin and carbohydrates were performed. Far-red improved adventitious rooting only in Experiment 2, where both cultivars responded similarly. Adding far-red only during the initial stage (7 days) of rooting was sufficient to improve rooting, while it did not result in excessive stem elongation. The presence or absence of blue did not significantly affect rooting. Although the positive effects of far-red on auxin and carbohydrate concentrations in stem cuttings are a likely explanation for the observed effects of far-red on rooting, we did not find a correlation between auxin or carbohydrates and rooting. [ABSTRACT FROM AUTHOR]