Synergism of citrus nematode (Tylenchulus semipenetrans Cobb.) and Colletotrichum gloeosporioides plays a major role in citrus dieback

Citrus is known as a major fruit due to its high nutritional value and adaptability in tropical and sub-tropical regions. Among diseases, citrus dieback is one of the most threatening diseases in which overall plant growth is reduced. Major causes are Colletotrichum gloeosporioides and citrus nematode (Tylenchulus semipenetrans) with 15-35% losses all over the world. Plant material was established adopting sanitary measures in earthen pots (12-inch diameter). Fresh culture of C. gloeosporioides and T. semipenetrans was prepared for the inoculation by following the standard procedures. In the first set, rootstocks were inoculated with 200mL of water having spore suspension of C. gloeosporioides while in in the second set, inoculation of T. semipenetrans was done by using 45 mL of water suspension having 2000 freshly hatched juveniles per pot, while at the rate of 1 × 107 spores/mL per plant. In the third set, the interaction of C. gloeosporioides and T. semipenetrans was studied by inoculating selected citrus rootstocks by both pathogens. After four months of inoculation, data were recorded on plant disease index (PDI) along with plant growth parameters (root weight, shoot weight, shoot weight, shoot length and number of leaves). Trifoliate orange and cox mandarin hybrid showed resistance against the development of T. semipenetrans while rough lemon, C-35 Citrange and sour orange were found susceptible. There was a significant difference in plant growth parameters between inoculated and healthy plants. Root weight and shoot weight decreased by 8.98g and 11.53g, while root length and shoot length decreased by 7.29cm and 13.5cm respectively as compared to control treatments in most susceptible rootstocks. Per cent Branch Infection (PBI) and per cent Disease Index (PDI) were maximum (71.52, 37) per cent on rough lemon respectively. Results regarding combined inoculation of C. gloeosporioides and T. semipenetrans showed that there was a significant difference in plant growth parameters between inoculated and healthy plants. In rough lemon, Root weight and shoot weight decreased by 13.86 and 20.57g respectively in diseased and healthy plants. Root length and shoot length decreased by 8.37 and 20.04cm respectively as compared to control treatments in most susceptible rootstocks. Overall results depicted that inoculation of both pathogens reduced plant growth more severely as compared to their individual application.

THE IMPACT OF ESSENTIAL OILS OF THE LAMIACEAE FAMILY AGAINST TYLENCHULUS SEMIPENETRANS USING MOLECULAR MODELING METHODS

Tylenchulus semipenetrans is an economically important plant-parasitic nematode occurring in all citrus-producing regions of the world and causing a disease called “slow decline”. Chemical nematicides commonly used in agriculture have ecotoxicological effects. As a control method, attention has been paid to bio-nematicides that do not exhibit harmful effects on the ecosystem. In this study we will carry out the in scilico experiments in order to find the most coherent Enzyme-Ligand complex to lead to the best inhibitors of Acetyl CoA Carboxylase in Citrus Tylenchulus semipenetrans nematode. “Acetyl CoA Carboxylase” enzyme responsible for fatty acid synthesis in Tylenchulus semipenetrans, its alteration disrupting the synthesis of the surface layer, this inhibitory action is based on essential oils of aromatic plants, taking as an example the Lamiaceae family, using natural compounds extract from essential oils of Salvia verbenaca, Lavandula stoechas, Rosmarinus officinalis, and Thymus ciliatus. This study revealed for the first time that ?-phellandrène from Salvia verbenaca gives the best docking scores compared to Biotine, the co-crystallized inhibitor of the Acetyl CoA Carboxylase, to spirotetramat as chemical insecticide already used against citrus nematode, and to the other complexes. After that, the Molecular Dynamics Simulation study showed a good result for the ?-phellandrène- Acetyl CoA Carboxylase docked complex, for that we can consider that ?-phellandrène extracted from Salvia verbenaca’s essential oil as a functional inhibitor of Acetyl CoA Carboxylase activities and it can be used as good bio-nematicides against Tylenchulus semipenetrans.

Cocktail Therapy of Fosthiazate and Cupric-Ammoniun Complex for Citrus Huanglongbing

Huanglongbing (HLB) is a destructive citrus bacterial disease caused by Candidatus Liberibacter asiaticus (Ca.Las) and cannot be cured by current pesticides. Root lesion and Tylenchulus semipenetrans juveniles were observed in HLB-affected citrus tree roots. We hypothesize that root treatment with fosthiazate (FOS) and Cupric-Ammonium Complex (CAC) will improve the root growth and inhibit HLB. CAC is a broad spectrum fungicide and can promote growth of crops. FOS kills Tylenchulus semipenetrans and protects roots from damage by harmful bacteria such as Ca.Las. After 90 days of combination treatment of FOS and CAC through root drenches, the citrus grew new roots and its leaves changed their color to green. The inhibition rate of Ca.Las reached more than 90%. During treatment process, the chlorophyll content and the root vitality increased 396 and 151%, respectively, and starch accumulation decreased by 88%. Transmission electron microscopy (TEM) and plant tissue dyeing experiments showed that more irregular swollen starch granules existed in the chloroplast thylakoid system of the HLB-infected leaves. This is due to the blocking of their secretory tissue by starch. TEM and flow cytometry experiments in vitro showed the synergistic effects of FOS and CAC. A transcriptome analysis revealed that the treatment induced the differential expression of the genes which involved 103 metabolic pathways. These results suggested that the cocktail treatment of FOS and CAC may effectively kill various pathogens including Ca.Las on citrus root and thus effectively control HLB.

Pre-planting solutions for the slow decline of citrus caused by Tylenchulus semipenetrans.

The citrus nematode, Tylenchulus semipenetrans, is the causal agent of the slow decline of citrus. The nematode is well adapted to reproduce on citrus and very high densities are required to damage the trees and reduce yield. This chapter discusses the economic importance, geographical distribution, host range, damage symptoms, biology and life cycle, interactions with other pathogens, recommended integrated management, and management optimization of T. semipenetrans. Future research requirements and future developments are also mentioned.