A Review on the Role of Silicon Treatment in Biotic Stress Mitigation and Citrus Production

This paper reviews the threat of citrus pathogens during citrus production, with a focus on two pre-harvest diseases, citrus leaf spot, caused by Alternaria alternata (Fr.) Keissl. (1912) and brown rot, caused by Phytophthora citrophthora (R.E. Sm. and E.H. Sm.) Leonian, (1906) as well as green and blue mold post-harvest disease, caused by Penicillium digitatum (Pers.) Sacc. and P. italicum Wehmer, (1894), respectively. Furthermore, it reviews the role of soluble silicon, Si nutrition in biotic stress mitigation and potential mitigation mechanisms. Previous studies on the use of Si fertilizers have focused on high accumulator Si crops. These have demonstrated the potential of Si to reduce the occurrence of biotic stresses, which takes place through both physical and biochemical mechanisms. However, few studies have demonstrated the potential of Si to mitigate biotic stress in citrus, or the mechanisms involved. There is a clear need for studies on the impact of Si on various stress biochemical pathways in plants generally, and specifically for citrus due to the huge loss caused by pre- and post-harvest pathogens. This will assist in deepening our understanding of the pathophysiology which is essential to develop resistant cultivars.

Bee-Vectored Aureobasidium pullulans for Biocontrol of Grey Mould in Strawberry

Grey mould caused by Botrytis cinerea is a common post-harvest disease in strawberries, reducing shelf life considerably. We investigated the potential of the yeast-like biocontrol fungus Aureobasidium pullulans (AP-SLU6) vectored by bumblebees (Bombus terrestris) in the Flying Doctors® system to inhibit the pathogen and increase the shelf life of harvested strawberries (cv. Sonata). Using bumblebees as vectors of various biocontrol agents is becoming increasingly popular, but any potentially negative effects on bee performance have been under-studied. Our results show that over the 4-week period of the trial the performance and activity of the bees were not negatively affected by A. pullulans. The bees successfully picked up the powder formulation, carried and deposited it on the flowers. The vectoring of the biocontrol agent significantly reduced grey mould development on the harvested fruits by 45 % and increased shelf life by 100 % in comparison to control treatments. This suggests that the biocontrol fungus applied during flowering successfully reduced Botrytis infection and thus effectively protected the fruits from grey mould. In addition, the bee-vectored application of the biocontrol agent was found to be significantly more effective than spray application, since the latter may temporarily increase humidity around the flower, thereby creating a suitable environment for the pathogen to thrive. In summary, our study demonstrates that A. pullulans vectored by bumblebees can decrease grey mould infection and improve the shelf life of strawberries without adversely affecting the bees, thus providing a basis for the sustainable and efficient control of grey mould on strawberry.

The Efficacy of Nature-Friendly Chemicals Eugenol and Sodium Bicarbonate against Post-Harvest Botrytis cinerea in Two Pepper Cultivars

Grey mold, caused by Botrytis cinerea, is the most important pre-harvest and post-harvest disease of pepper. The disease leads to huge losses in quality and yield of pepper. Synthetic fungicides should not be used because of their harmful residues in the fruits postharvest. Hence, alternative chemicals have gained more importance for human health now-a-days. In this study, the postharvest effectiveness of eugenol and sodium bicarbonate (NaHCO3) to B. cinerea was determined on two pepper varieties, ‘Demre’ and ‘Charleston’ obtained from pepper fields in Çanakkale. In essay the Eugenol was used at dosages of 0.75 and 1.5%, while sodium bicarbonate was used at dosages of 0.5 and 1.0%. Pepper varieties ‘Demre’ and ‘Charleston’ showed significantly different sensitivities against grey mold disease (P < 0.01), and this case reflected also to the efficacies of alternative chemicals. During eight days of storage, Charleston was more sensitive to B. cinerea than ‘Demre’ peppers. NaHCO3 at high dosage (1.0%) completely inhibited the disease on ‘Charleston’ and ‘Demre’ peppers. The lower dose of NaHCO3 (i.e., 0.5%) was also highly effective in ‘Demre’ (providing 95% reduction in the disease) but its efficacy was a little lower for ‘Charleston’ variety (84%). Efficacy (83.7%) of eugenol at dosage of 1.5% to B. cinerea on 'Demre' was found to be like NaHCO3 at dosage 0.5% on ‘Charleston’ peppers. Alternative chemicals had no adverse effects on pepper varieties. It is concluded that both tested nature-friendly chemicals (Eugenol and sodium bicarbonate) could be used (postharvest) against to B. cinerea on peppers. © 2021 Friends Science Publishers

Evaluation of the Efficacy of Different Fungicides against Fusarium musae, a Fruit Rot Disease of Banana

Fruit rot disease caused by Fusarium musae is one of the post-harvest disease of banana and is adversely affecting the fruit quality and the market value In vitro evaluation of different fungicides, against F. musae. Amongst, fungicides viz., mancozeb 75 WP at 2500 ppm, azoxystrobin (20%) + difenoconazole (12.5%) at 1000 ppm and propiconazole (25 EC) at 500 ppm and 1000 ppm were found cent per cent inhibition of mycelial growth of F. musae. Whereas, in vivo evaluation were lowest fusarium fruit rot severity was observed in propiconazole (25 EC) at 1000 ppm in pre (6.61%) and post- inoculation (6.70%) treatments at 8 days after inoculation.

Peeling the onion: towards a better understanding of Botrytis diseases of onion

Onion is cultivated worldwide for its bulbs, but production is threatened by pathogens and pests. Three distinct diseases of onion are caused by species that belong to the fungal genus Botrytis. Leaf blight is a well-known foliar disease caused by B. squamosa that can cause serious yield losses. Neck rot is a post-harvest disease that manifests in bulbs after storage and to which three species are associated with; B. aclada, B. allii and B. byssoidea. The symptomless infection of onion plants in the field make it difficult to predict the incidence of neck rot in storage although progression on the detection of latent infection has been made. In onion cultivation for seed production, blighting of the inflorescence is caused by all four onion-specific Botrytis species plus the broad host range pathogen B. cinerea. Flower blight can lead to heavily reduced seed yield and contaminated seed. In this review, the long history of Botrytis diseases of onion is discussed, as well as recent and future approaches to acquire a better understanding of the biology and ecology of Botrytis spp. pathogenic on onion. New fundamental insights in the genetic, biochemical and physiological aspects of Botrytis-onion interactions are essential to improve the breeding of Botrytis-resistant onion cultivars.

Biological Control of Citrus Postharvest Phytopathogens

Citrus are vulnerable to the postharvest decay caused by Penicillium digitatum, Penicillium italicum, and Geotrichum citri-aurantii, which are responsible for the green mold, blue mold, and sour rot post-harvest disease, respectively. The widespread economic losses in citriculture caused by these phytopathogens are minimized with the use of synthetic fungicides such as imazalil, thiabendazole, pyrimethanil, and fludioxonil, which are mainly employed as control agents and may have harmful effects on human health and environment. To date, numerous non-chemical postharvest treatments have been investigated for the control of these pathogens. Several studies demonstrated that biological control using microbial antagonists and natural products can be effective in controlling postharvest diseases in citrus, as well as the most used commercial fungicides. Therefore, microbial agents represent a considerably safer and low toxicity alternative to synthetic fungicides. In the present review, these biological control strategies as alternative to the chemical fungicides are summarized here and new challenges regarding the development of shelf-stable formulated biocontrol products are also discussed.

Mycoflora associated with post-harvest disease of papaya (Carica papaya L.) and their pathogenic potentiality

Nineteen species of fungi namely, Alternaria alternata (Fr.) Keissler, Aspergillus flavus Link, A. fumigatus Fresineus, A. niger Van. Tieghhm, Colletotrichum dematium (Pers.) ex. Fr., C. gloeosporioides (Penz.) Sacc., Corynespora citricola M.B. Ellis, Curvularia lunata Wakker, Fusarium flocciferum Corda, F. nivale (Fr.) Ces., Fusarium Link, Lasiodiplodia theobromae (Pat.) Griff & Moubl, Monilia Pers., Mucor Fresen, Penicillium Link, Pestalotiopsis guepinii (Desm.) Stay., Rhizoctonia solani J.G. Kuhn, Rhizopus stolonifer Bull. and Syncephalastrum Schroet were found to be associated with the diseased fruits of Carica papaya L. Among the isolated fungi C. gloeosporioides, F. nivale and Fusarium sp. were found to be pathogenic for both red and yellow cultivar Shahi papaya. Association of C. lunata, F. nivale, P. guepinii and Syncephalastrum sp. with papaya is a new record. The present report is the first record of Corynespora citricola and Fusarium flocciferum from Bangladesh.