Current projects in our lab

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Due to postharvest losses, more than 40% of harvested fruits will not reach the consumers’ plates. Fungal pathogens play a key role in those losses, as they can cause most of the fruit rots and customer complaints. The best means to control those pathogenic fungi are chemical fungicides that need to be replaced. In our lab, we are looking for green and safe solutions for controlling the pathogenic fungi and we are studying problems that arise from the field and trying to find applicative solutions for them.

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Green Alternatives To Chemical Fungicides

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1. Phenylalanine induces the fruit defense response

L-phenylalanine (Phe) is an amino acid that initiates the phenylpropanoid pathway and the biosynthesis of flavonoids, which are health-promoting compounds that have antioxidants and antifungal activity. We found that by preharvest or postharvest applications of Phe, the amino acid penetrates the fruit, and induces the fruit defense response and the phenylpropanoid pathway, which leads to increased resistance to postharvest rot and chilling. Additionally, Phe application combined with sunlight radiation could lead to the biosynthesis of anthocyanins and accumulation of red color in mango and apple fruit, while Phe application combined with wounding could lead to lignin accumulation in potato tubers and faster wound curing. Phe not only induced the fruit’s defense response but also increased the fruit's sweetness and aroma, which increased its acceptability by tasting panels. 

 

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Double-stranded RNA controls postharvest gray mold

 

Botrytis cinerea, a common postharvest pathogen, was shown to uptake small double-stranded RNA (dsRNA) from its environment. We show that a direct application of dsRNA targeting three essential genes in the ergosterol biosynthesis pathway could offer systemic protection against B. cinerea. To protect the relatively short lifetime of dsRNA we used clay sheets [layered double hydroxide (LDH)]. LDH-dsRNA complex maintains the dsRNA potency during extended storage, which reduces gray mold development better compared to naked dsRNA. Furthermore, we demonstrate how storage conditions, such as high humidity and CO2 can control the rate of dsRNA release by accelerating LDH degradation.

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       dsRNA penetration to the fungi

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Sunlight induces the fruit defense response 

 

Sunlight radiation in the orchard induces the fruit defense response and the phenylpropanoid pathway to activate flavonoids and anthocyanins, which is associated with fruit tolerance to postharvest fungal pathogens.

 

 

 

 

 

 

 

 

Studying host-pathogen interaction at a transcriptomic and genomic level

We study fruit interaction with fungal pathogens (Colletotrichum gloeosporioides, Lasiodiplodia theobromae, Botrytis cinerea, Penicillium expansum, and Alternaria alternata) during the latent or quiescent stage and necrotrophic stage.

Colletotrichum gloeosporioides infects close to 500 plants and is the main pathogen in mango and avocado fruit worldwide. C. gloeosporioides penetrates the unripe fruit in the orchard. After penetration, using an appressoria formation, the fungi will remain at a quiescent stage until fruit ripening, a point at which the fruit’s defense reduces and the fungus switches from the dormant state to the necrotrophic stage and causes anthracnose.

​Lasiodiplodia is a main stem-end rot (SER) causing pathogen. SER is caused by diverse pathogenic fungi that endophytically colonize the stem phloem and xylem during fruit development in the orchard and remain quiescent until fruit ripening. Then, the fungus switches to a necrotrophic lifestyle and causes SER. We characterized the genomes of pathogenic and less pathogenic L. theobromae and L. pseudotheobromae and their interaction with mango fruit during different lifestyle stages.

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From The Field And Packinghouse To The Lab And Back

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Botryosphaeria and stem end rot in mango and avocado

Botryosphaeria genus contains many pathogenic fungi that cause stem dieback, fruit detachment, and postharvest stem end rot (SER). The main pathogens that cause the mango and avocado disease in Israel relate to the Lasiodiplodia species. We characterized four genomes of Lasiodiplodia and their fruit transcriptome. We found that the fungi penetrate mostly during flowering and treatments with biological or chemical fungicides during flowering controlled fungal penetration and establishment and reduced the occurrence of pathogenic fungi in the fruit's stem-end. This treatment reduced inflorescence/stem dieback and fruit drop, which led to an increase in yield.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

We also found that harvest with short stems could reduce SER by reducing the wound response and maintaining natural antifungal compounds in the fruit stem.

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​Increasing chilling tolerance allow cold quarantine in mango and avocado

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Quarantine treatment enables fruit export to different parts of the world that enforce quarantine against specific insects. Cold quarantine against fruit flies leads to chilling injuries in the avocado fruit. By integrating several treatments such as low-temperature conditioning (LTC), modified or controlled atmosphere (MA), and methyl jasmonate (MJ) or phenylalanine that induces fruit resistance, we were able to develop a cold quarantine for avocado fruit while maintaining fruit quality and reducing decay.

Mango fruit is very susceptive to chilling. By reanalyzing our mango transcriptome data, we found that under sub-optimal temperature storage, the fruit increases its ethylene biosynthesis and osmolarity by activating sugar metabolism, thereby reducing its freezing point. Similarly, ripe fruit with higher sugar concentration is more resistant to cold. By combining the treatment of artificial ripening, modified or controlled atmosphere, and low-temperature conditioning, we reduced fruit chilling injuries. Thus, by reversing the supply chain and storing ripe and ready-to-eat fruit, cold quarantine was enabled for mangoes.