Potentiality of Inducer Resistance Chemicals and Bioagents in Managing Lettuce Downy Mildew

Khairy Abdel-Maksoud Abada

doi:10.11648/j.ajbio.20170501.12

Abstract

The tested inducer resistance chemicals (IRCs) bion (BTH), chitosan and salicylic acid as well as the bacterial bioagents Bacillus pumilus B. subtilis, B. thuringiensis and Pseudomonas fluorescens and the fungal bioagents Trichoderma album, T. harzianum and T. viride resulted in significant reduction to the germinated sporangia (conidia) of the fungus like Bremia lactucae Regel, the causal of lettuce downy mildew. This reduction was gradually increased by increasing the used concentration. The role of the tested IRCs and bioagents on management of the disease under greenhouse was evaluated. Under greenhouse conditions, spraying of lettuce plants artificially inoculted with the causal fungus like resulted in significant reduction to the severity of the disease compared with control treatment. Moreover, the IRC bion as well as P. fluorescens and T. harzianum were the most efficient treatments in this regard. Two field experiments were carried out during 2016/ 2017 growing season under natural infection by the disease to evaluate the efficacy of spraying of lettuce plants with any of the IRC bion and the bioagents P. fluorescens and T. harzianum on plants previously soaked or not in bion just before transplanting on the severity of the disease and weight of the grown plants. Data revealed that there was significant reduction to the severity of the disease with considerable increase to the average weight of each plant compared with control treatment due to sprying of these treatments. However, the fungicide Ridomil Gold MZ was the superior treatment in reducing the disease and increasing the weight of the foliage growth of lettuce plants. In addition, spraying of the IRC bion on plants soaked in bion just before transplanting ranked the second in this regarad followed by spraying of any of the two bioagents. Considerable increase in the activity of the oxidative reductive enzymes, i.e phenylalanine ammonia lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO), due to spraying of lettuce plants with bion, the bioagents P. fluorescens and T. harzianum as well as the fungicide Ridomil Gold MZ compared with unsprayed plants (control).

Highlights

Lettuce (Lactuca sativa L.) has become an increasingly important leafy vegetable crop in many parts of the world including Egypt
The fungicide Ridomil Gold MZ was the superior treatment in both experiments, being 0.3 and 1.2% disease severity, respectively followed by spraying of the Inducer Resistance Chemicals (IRCs) bion (1.3 and 3.6% disease severity, respectively) spraying of P. fluorescens (3.5 and 3.9% disease severity, respectively) and T. harzianum (4.8 and 5,1% disease severity, respectively)
Results shown in Table (5) show that the reduction in the severity of lettuce downy mildew was significantly reflected on the weight of the grown plants

Summary

Introduction

Lettuce (Lactuca sativa L.) has become an increasingly important leafy vegetable crop in many parts of the world including Egypt. Yield losses in the field at harvest may be substantial, downy mildew's impact is often accentuated by significant postharvest losses that occur during transit or storage. This pathogen requires cool, wet conditions for infection and disease development. The disease causes light green to yellow angular spots on the upper surfaces of leaves. White fluffy growth of the pathogen develops on the lower sides of these spots. With time these lesions turn brown and dry up.

Objectives

Methods

Results

Conclusion