Increasing the performance of Passion fruit (Passiflora edulis) seedlings by LED light regimes.

Due to progress in the industrial development of light-emitting diodes (LEDs), much work has been dedicated to understanding the reaction of plants to these light sources in recent years. In this study, the effect of different LED-based light regimes on growth and performance of passion fruit (Passiflora edulis) seedlings was investigated. Combinations of different light irradiances (50, 100, and 200 µmol m-2 s-1), quality (red, green, and blue light-emitting LEDs), and photoperiods (10 h/14 h, 12 h/12 h and 14 h/10 h light/dark cycles) were used to investigate the photosynthetic pigment contents, antioxidants and growth traits of passion fruit seedlings in comparison to the same treatment white fluorescent light. Light irradiance of 100 µmol m-2 s-1 of a 30% red/70% blue LED light combination and 12 h/12 h light/dark cycles showed the best results for plant height, stem diameter, number of leaves, internode distance, and fresh/dry shoot/root weights. 14 h/10 h light/dark cycles with the same LED light combination promoted antioxidant enzyme activities and the accumulation of phenols and flavonoids. In contrast, lower light irradiance (50 µmol m-2 s-1) had negative effects on most of the parameters. We conclude that passion fruit seedlings' optimal performance and biomass production requires long and high light irradiances with a high blue light portion.

Light quality and quantity affect graft union formation of tomato plants.

It is already known that there are many factors responsible for the successful formation of a graft union. However, the role of light has been little studied. In an anatomical study, Scanning Electronic Microscope (SEM) was used to explore the effects of different light-emitting diodes (LEDs) on graft union formation in grafted tomato. In addition, the expression genes related to Auxin hormone signaling pathway (SAUR67, AUX1, ARF30, and LAX3) was investigated. The obtained results showed that the concrescence process occurred faster under R7:B3 light conditions, as compared to blue (B) and white fluorescent (WFL) lights. Red light application caused a delay in the vascular tissue differentiation, which may lead to callus development on both sides, causing junctional failure and resulting in ineffective graft junctional arrangement. The expression of genes related to Auxin hormone significantly increased by R7:B3 application. We suggest that LED spectra affects the graft development of tomato plants and can improve the performance of grafted tomato seedlings.

The effect of the root-colonizing Piriformospora indica on passion fruit (Passiflora edulis) development: Initial defense shifts to fitness benefits and higher fruit quality.

Passion fruit (Passiflora edulis) has an important economic value as exotic ingredient in juice blends. We inoculated the passion fruit cultivar Passiflora edulis Sims f. edulis's roots with the beneficial root-colonizing fungus Piriformospora indica under greenhouse conditions. The experiments were performed at three different locations and times (between 2017 and 2019). After transient initial growth retardation associated with a mild salicylic-acid (SA)-dependent defense activation and reduced sucrose metabolism, plant performance and growth are promoted during later stages. The elevated SA level in the aerial parts stimulates the plant immune system and promotes pathogen resistance in the adult plants and the fruit peels. P. indica stimulates the fruit size and fruit quality, and the higher amounts of defense-related secondary metabolites in the peels restrict growth of herbivorous insect larvae fed with peel extracts. We conclude that application of P. indica to passion fruits stimulates the plants' immune system and improves the fruits' quality.