Plant pathogenicity and associated/related detection systems. A review

Highlights

• A review of the recent advances (2012–2022) in plant pathogen detection systems.

• Limitations of the gold standard techniques have led to emerging recent advances for on-field plant disease detection.

• Recent advances have been categorized into direct and indirect methods.

• Advancements in various types of biosensors– electrochemical, optical, and mass-based biosensors for plant disease detection.

• Future challenges and prospects of biosensors for on-site detection of plant diseases are proposed.

Abstract

There is an increasing demand for the development of various tools for diagnosis and control of plant infections. The early diagnosis of plant disease serves as a vital element to improve crop productivity and meet demands of the ever-growing world population. The traditional methods of plant disease detection are time consuming, laborious and require 3–5 days to estimate the disease incidence. In this review, we focus on the advances in the detection techniques, mainly the miniaturized systems that has developed in the last decade. The analytical techniques for plant pathogen detection have been classified as direct and indirect detection methods. The direct methods involving laboratory techniques such as polymerase chain reaction, enzyme-linked immune-sorbent assays, and immunofluorescence and their recent advances have been discussed. Similarly, indirect methods which rely on sensing the plant stress indicators to detect plant diseases have been categorized and reviewed. In the last decade, various detection platforms with high sensitivity and selectivity have been developed and commercialized into handheld devices and products for on-field plant disease detection. This review focusses on the transition from the gold standard techniques to the advanced on-field biosensors to detect plant diseases with higher accuracy, cost-effective and making timely diagnosis possible. A growing trend for pathogen detection based on biosensors has been highlighted and further categorized into electrochemical, optical, and mass-based sensors. These innovative advancements in plant pathogen detection systems help to make the agricultural sector more safe, reliable, and sustainable for the ever-growing population.

Introduction

Pathogens are microorganisms (bacteria, fungus, viruses, etc.) that cause diseases. Pathogens in the agricultural sector have a negative effect on food quality and safety. The yield loss range at a global level for five major crops are: wheat 10.1–28.1%, rice 24.6–40.9%, maize 19.5–41.1%, potato 8.1–21.0% and soybean 11.0–32.4% ranges that crop pathogens and pests reduce the yield and quality of agricultural production [1]. The various plant pathogens arising from different sources along with types of infection caused by them have been listed in Table 1. The pathogens listed in the table are examples of most prevalent disease-causing causing microbes which are categorized based on their source of infection into soil, airborne air borne. Soil serves as an important habitat for the growth of soil borne pathogens wherein extrinsic as well as intrinsic parameters play an important role such as soil pH, soil biota, temperature, moisture, and organic contaminants. Most soil borne pathogens rot the underground tissues and vascular wilts and a few of them are also known to cause foliar diseases. For example, Lettuce anthracnose infects the lettuce leaves as the fungus travels up to the leaves in the plant [2]. Water-borne pathogens are the disease causing agents which are being introduced into the agricultural lands by irrigation. Air-borne pathogens travel through air. In particular, the diseases which have attacked the leaves of plants spread by wind or droplets of rain or during irrigation [3]. More information on various sources of pathogens can be found in the literature [4,5]. There are different screening techniques have been developed over the years for various diseases caused by pathogens. From the simplest detection of symptoms appearing on leaves to more microscopic observation, the nucleic acid detection techniques as illustrated in Fig. 1.

The standard analytical techniques for detection of plant pathogens have been categorized into two types: The direct and the indirect methods of detection. The direct methods include: Polymerase chain reaction [6], immuno-assays (JR. 1995) and the culture colony counting. The indirect methods include thermography [7], hyper spectral imaging, gas chromatography and fluorescence imaging. To maximize productivity and minimize the agricultural losses due to pathogens, advanced plant disease detection and early screening serves to be an important aspect of plant sciences. There are various modes of infection spread which occur in agricultural lands. The different modes are through insects, wind, and water-soil transmissions as illustrated in Fig. 2. In last decade, various types of biosensors were reported for detecting plant diseases properties of those biosensors include their ease of use, high specificity, sensitivity, lower limits of detection, and multi-array capability. In this review, we present a thorough review covering the various types of plant pathogens, its sampling procedures and a detailed discussion on types of biosensors used for the detection of diseases on field.